Lasers. Optical Fibres

Size: px
Start display at page:

Download "Lasers. Optical Fibres"

Transcription

1 Lasers & Optical Fibres

2 P a g e 2 Contents LASER 1) Coherence 3 2) Interaction of radiation with matter 4 3) Laser fundamentals 5 4) Laser system 5 5) Ruby Laser 6 6) He-Ne Gas Laser 7 7) Semiconductor Laser 8 8) Properties of Lasers 9 9) Application of Lasers 9 10) Differences 10 OPTICAL FIBRE 1) Basic structure of optical fibre 11 2) Acceptance angle 12 3) Numerical Aperture 12 4) Classification of optical fibres 13 5) Differences 15 6) Attenuation in optical fibres 15 7) Applications of optical fibres 17 8) Advantages of optical fibres 19

3 P a g e 3 LASER LASER is the acronym for Light Amplification by Stimulated Emission of Radiation. Coherence Two light sources which vibrate with a fixed phase difference between them are said to be coherent. Coherence can be classified into two types: i) Temporal Coherence ii) Spatial Coherence Temporal Coherence: If the phase difference between any two points at an instant of time lying in the direction of propagation of the electromagnetic (light) wave is independent of time, the coherence is said to be temporal coherence. Spatial Coherence: If the phase difference between any two points at an instant of time lying in the plane perpendicular to the direction of propagation is time independent, the coherence is said to be spatial coherence. Let and be the phase angles at points P and Q at time t. Phase difference = Let and be the phase angles at points P and Q at time Phase difference = Then, spatial coherence is given by: Coherence Length & Coherence Time: Coherence is conveniently measured by the path difference between two rays of the same source having constant or zero phase difference. The length of the electromagnetic wave over which the spatial coherence is maintained is called as the coherence length and the corresponding time over which this coherence is maintained is called the coherent time. The relationship between coherence length and coherence time is given by: Where, L is the coherence length, c is the speed of light & τ is the coherence time If Δν is the spread in frequency of light then τ = 1/Δν and hence coherence length is given as i.e. more the spread in the frequency of the light signal, less is the coherent length. So, less the monochromaticity, less the coherence.

4 P a g e 4 Where, Q = is called the Quality factor. It indicates the sharpness of the signal. Greater the value of Q, lesser the beam spreading and more the coherence. Interaction of Radiation with Matter Any material medium is composed of identical atoms or molecules each of which is characterized by a set of discrete energy states. An atom can move from one energy state to another when it receives or release an amount of energy equal to the energy difference between these two states. Similarly energy will be emitted in the form of radiation if an atom jumps from a higher energy level to a lower one. The energy of the photon will be equal to the energy difference between the two levels. In equilibrium state, lower energy level density is densely populated (more in number) than in the upper levels. If by some means the atom is made to absorb energy equal to the difference of the energy levels of the two states, it jumps to the higher state. This condition is called as the non-equilibrium condition. The atom can remain in the equilibrium condition for unlimited time but an atom can remain in the excited state for limited time only. This limited time is called as lifetime of the state. After this the atom deexcites to the lower state and gives out a photon equal to the difference between the two energy levels. The interaction can occur in the following three ways: i) Absorption: A photon excites the atom from lower energy level E 1 to a higher energy level E 2. It absorbs energy equal to E 2 E 1 and stays at the higher energy level E 2. ii) Spontaneous Emission: In case of Spontaneous emission, after the lifetime of the state the atom in the excited state de-excites and comes back to the ground state on its own accord after emitting a photon of energy hν = E 2 E 1. It s not coherent and is randomly directed. It s a random mixture of quanta having different wavelengths and phases. Hence it gives rise to a broad spectrum. iii) Stimulated Emission: When the atom is excited to level E 2, an external photon having energy equal to E 2 E 1 is made incident on the atomic system and the atom de-excites from energy level E 2 to E 1 giving out a photon equal to energy difference E 2 E 1. This type of emission is called as stimulated emission.

5 P a g e 5 The emitted photon is of the same energy and has same phase, polarization, direction and frequency as that of the incident photon. This process can be controlled from outside and leads to amplification of light. LASER Fundamentals Metastable State: Lifetime of the excited state is of the order of 10-8 seconds. However some of the states have greater lifetime of the order of 10-3 seconds. These states are called metastable states and they play an important role in lasing action. Population Inversion: All the atoms of an element have their own characteristic system of energy levels. The number of atoms per unit volume occupying a certain state is called population. The population N of an energy level E depends upon the absolute temperature T of the system and is given by In a material, atoms tend to achieve the lowest possible energy level which may or may not be the ground state of the given configuration. For all laser operations, stimulated emission is required. For a high percentage of stimulated emission, a majority of atoms should be at higher energy levels than the lower energy level. For increasing the number of atoms in a higher state an artificial situation is created. This situation is known as population inversion. If N 1 and N 2 are the population of lower and higher energy levels, then their population ratio is given as At thermal equilibrium, there are more number of atoms in the lower state than in the higher state. Hence, a non-equilibrium position is created artificially in which population of higher level exceeds the population of the lower level. This is known as population inversion. This can be achieved only by applying a negative temperature. Hence, these states are also called as negative temperature states. Pumping: The process by which atoms are raised from the lower energy level E 1 to the higher energy level E 2 is called as pumping. It is of two types: i) Optical Pumping ii) Electrical Pumping Optical Pumping: A discharge tube is used to excite atoms from the ground state. The excited atom from the uppermost level goes to metastable state to create a state of population inversion. The frequency of pumping photons must be higher than emitted photons so that the atoms can be sent above the upper level from the lower level. Light sources emitting a range of wavelengths are used to excite the atoms. Ruby Laser uses this principle. Electrical Pumping: Electric current is used to excite atoms from lower to higher levels. Two types of electrical pumping are given below: a) Gas is ionized by electrical discharge to excite the atoms to the uppermost level and then stimulated emission is caused by light to cause lasing action. He-Ne Laser uses this principle. b) In case of a semiconductor Laser, charge carriers are excited and population inversion is created in the junction region which produces Laser light from the junction region. LASER System Laser system comprises of three components: i) Active Medium ii) Pumping Source iii) Optical Resonator

6 P a g e 6 Active Medium: Active medium consists of a collection of atoms, molecules or ions which are capable of amplifying light waves. In order to have optical amplification, the medium has to be kept in a state of population inversion i.e. a state in which the number of atoms in the upper energy level is greater than that in the lower energy level. Pumping Medium: The pumping mechanism provides for obtaining a state of population inversion between a pair of energy levels of the atomic system and when we have a state of population inversion, the input light beam can get amplified by stimulated emission. Optical Resonator: A medium with population inversion is capable of amplification. However in order that it acts as an oscillator, a part of the output energy must be fed back into the system. Such a feedback is brought about by placing the active medium in a resonator. We need to use highly reflective mirrors having a considerable space in between them. The stimulated emission also depends on a high population density of atoms in the metastable state within the cavity. If both these conditions are satisfied, the buildup of photons surging back and forth through the cavity can be self-sustaining and the system will oscillate spontaneously. Either both the mirrors or one of them is made partially transmitting which allows the Laser light out of the system. If a sufficient population inversion exists in the active medium, Laser oscillations buildup and become established as a standing wave in the cavity. The output is a powerful, highly directional, monochromatic and coherent beam of light. Few cavities are as shown below: Ruby Laser (Solid State Laser) (Pulse Laser) Ruby Laser is a 3-level Laser developed by Maiman in The active medium comprises of a Ruby rod. The optical pumping is given by a Xenon flash lamp. Ruby comprises of a host Al 2 O 3 crystal in which 0.05% atoms of Aluminum (Al) are replaced by Chromium (Cr) atoms. The lasing action takes place in the Cr 3+ atoms. The crystal is in the form of a cylindrical rod which is 2 to 20 cm in length and 0.1 to 2cm in diameter. Xenon photo flash lamp provides the optical pumping to raise the Chromium atoms to the higher energy level. Most of the heat given by the lamp is converted into heat while only a small part of energy is used by Chromium atoms to get excited. Hence a coolant (liquid N 2 ) is used to reduce thermal vibrations. A Ruby Laser and its energy diagram are shown in the figure.

7 P a g e 7 Photons from the Xenon flash lamp excite atoms from ground state E 1 to excited state E 3. State E 3 has a lifetime of about 10-9 to 10-8 seconds. The atoms de-excites from this energy level to the metastable state E 2. Population inversion occurs at this energy level. Another photon from the Xenon flash lamp falls on an atom in the state E 2 and stimulates the atom to make a transition to the ground state E 1. During this transition, the atom emits a photon along with the incident photon. These photons travelling along the axis trigger many excited Chromium atoms in E 2 level to emit photons by resonance action. Multiple reflections occur between the end faces of the rod. The stimulated radiation dominates multiple reflections at the two end faces of the rod. The output beam has space, time and directional coherence. Ruby Laser emits light of wavelength 6943 A 0. In a very short time the operation of flash lamp consumes several thousand joules of energy in which major part of energy is simply converted into heat. Hence to reduce thermal vibrations or to compensate the produced heat, cooling arrangement has to be made. As the flash lamp stops operating, population of upper level decreases rapidly and laser action stops. It again begins when the flash lamp starts. As the flash lamp is operated with flashes having small intervals of time, the laser also has pulsed type output depending on the pulses of the flash lamp. Hence, this laser is also called as the Pulsed type Laser. Advantages of the coolant i) It results in lower thermal vibrations in the Ruby crystal so that more atoms are in the ground state prior to optical pumping. ii) Excited atoms continue in the excited state for a longer time. iii) Noise level is reduced. He-Ne Gas Laser Ali Javan, W. R. Bennett, Jr. and D. R. Herriott developed the He-Ne gas Laser in It s easy to construct, relatively inexpensive and fairly reliable. Pumping is actually accomplished by electrical discharge. Free electrons and ions are accelerated by an applied field and as a result of collisions cause further ionization and excitation of the gaseous medium. It comprises of a fused quartz tube of 10 to 100 cm in length and 2 to 8 mm in diameter. The tube contains 85% Helium (He) gas at a pressure of 1mm of Hg and 15% Neon (Ne) gas at a pressure of 0.1mm of Hg. A high voltage radio frequency source is used to provide the electric discharge to the mixture of gases. He-Ne Laser is as shown in figure. Actual lasing action occurs due to the Ne atoms while He is used just for selective pumping of the upper laser levels of Ne. High voltage discharge produces ions and electrons. Electrons collide with Helium (He) and Neon (Ne) atoms and excite them to high energy levels. He atoms are more readily excitable than neon as they are lighter. Lifetime of energy levels F 2 and F 3 of He is more (10-4 secs and 10-6 secs) therefore these levels of Helium become densely populated. E 4 and E 6 energy levels of Neon are close to the energy levels F 2 and F 3 of Helium. Energy is transferred by inelastic collision to the E 4 and E 6 energy levels of Neon. These states are metastable states and lead to subsequent emissions of photons due to stimulated emissions. The dominant laser transitions

8 P a g e 8 correspond to 6328 A 0 (E 6 E 3 ), 3.39 μm (E 6 E 5 ) and 1.15 μm (E 4 E 3 ). The energy band diagram of He-Ne laser is as shown below: He-Ne lasers are low power lasers having power output of 1mW to 5mW. Advantages of He-Ne Laser over Ruby Laser i) He-Ne Laser has continuous output as compared to pulsed output of Ruby laser. ii) It has large output per unit bandwidth. iii) It has comparatively high spectral purity. iv) It has narrow spectral width. v) It s highly monochromatic. vi) It s highly unidirectional. vii) It doesn t need a coolant as it doesn t dissipate heat as comparable to Ruby Laser. Semiconductor Laser A semiconductor diode laser is a specially designed P-N junction diode which emits coherent radiation when forward biased. If a transition of electron occurs from conduction band to valence band so that the electron recombines with the hole in the valence band, the energy (E C - E V ) is given out in the form of a photon. A schematic diagram of a semiconductor laser is as shown in figure. The diode is extremely small in size with sides of the order of 1mm. The junction lies in a horizontal plane through the centre while the top and bottom faces are given ohmic contacts. The front and rear faces are polished parallel to each other and perpendicular to the plane of the junction. These polished faces constitute the resonating cavity. The other two opposite faces are roughened so as to prevent the laser output in that direction. Because of heavy doping, the donor levels as well as portion of conduction band are occupied by electrons. Hence, the Fermi level lies within the conduction band. Similarly, holes exists in valence band and acceptor levels are unoccupied so that the Fermi level lies within the valence band as shown in figure below:

9 P a g e 9 When the junction is forward biased, the energy levels shift. Due to the injection of electrons and holes into the depletion region, its width reduces. At low forward current, the electron-hole recombinations result in spontaneous emissions of photons and the junction acts as a LED. With the increase in current, the intensity of light increases and for a certain threshold current, the carrier concentration in the depletion region reaches very high values. The region now contains a large concentration of electrons in the conduction band and a large concentration of holes in the valence band as shown in figure above. Now the upper energy levels in the depletion region have a high population density of electrons while the lower energy levels are vacant. Thus the necessary population inversion has been achieved. The narrow region is called the active region or the inversion region. Forward biasing the junction plays the role of pumping agent. Because of the stimulated electron-hole recombinations, coherent radiation of very narrow bandwidth is emitted. GaAs laser gives light of wavelength 9000A 0 in the infrared region while GaAsP laser gives light of wavelength 6500 A 0 in the visible red region. Properties of Lasers i) Coherence: Lasers are highly coherent in nature. Emitted photons are exactly in phase with the incident photons. ii) Monochromaticity: Lasers are highly monochromatic. iii) Unidirectionality; Lasers emit light only in one direction. The width of the beam is extremely narrow and hence can travel long directions without spreading. They can be brought to an extremely sharp focus. iv) Brightness: Lasers are much brighter than any conventional source. v) Power Output: Lasers have power range from few milliwatts to several kilowatts. The low power lasers are used for surgical purposes while the high power ones are used for welding, cutting and fusion purposes. vi) Temperature: Temperatures of the order of 10 4 Celsius are obtained at the point of focus. Applications i) Laser beams are useful for precision spot welding. It involves no physical contacts with the material to be welded. ii) Laser can be used to cut metals and drill holes in diamond. iii) Laser radiations are highly unidirectional and have narrow angular spread and hence are used in fibre optics communications. iv) Due to its intensity and directionality, laser is used in surveying. During the construction of a tunnel, engineers use the laser beam as a reference to check the construction along a straight line.

10 P a g e 10 v) Laser beams are used in holography i.e. storage of three dimensional image on two dimensional photographic plate. vi) Laser beam can be used as a war weapon as attacking missiles could be destroyed. vii) Laser radars are used for safe checking of space vehicles. viii) Laser beam can be used to remove coronary artery blockage. ix) Bloodless cancer surgery can be performed with lasers. x) Lasers can be used for reconstructive surgery. Differences i) Spontaneous and Stimulated Emission Spontaneous Emission It does not require external triggering. Time duration of excited state is of the order of 10-9 seconds. It occurs under natural conditions. It is a random phenomenon. The resulting radiation is polychromatic, incoherent, non-directional and weak. Stimulated Emission It requires external triggering. Time duration of metastable state is of the order of 10-4 seconds. It requires artificial condition of population inversion. It is a planned phenomenon. The resulting radiation is highly monochromatic, coherent, directional and intense. ii) Laser and Ordinary light Laser The light originates due to process of stimulated emission. It requires non-equilibrium condition of population inversion of atoms. The light is highly monochromatic. The light is highly directional. The light is highly intense. The light is highly coherent. Ordinary Light The light originates due to process of spontaneous emission. It takes place under the condition of thermal equilibrium condition of population of atoms. The light is polychromatic. The light is non directional. The light is less intense. The light is less coherent. iii) Three level and Four level lasers Three level lasers It involves three distinct energy levels. Population inversion condition occurs between metastable and usually ground state. It is difficult to maintain population inversion condition between metastable and ground state since ground state is stable state. It is not efficient. Four level lasers It involves four distinct energy levels. Population inversion condition occurs between metastable and lower excited state. It is easy to maintain population inversion condition between metastable and lower energy state since lower energy state is unstable state. It is more efficient.

11 P a g e 11 Optical Fibre Optical fibre is a transparent thin glass or plastic fibre used as a transmitting medium for light i.e. optical signal. It works on the principle of total internal reflection. Refraction: The bending of light ray when it travels from a rarer to a denser medium or vice-versa is called as refraction. If a light ray in medium I (having refractive index n 1 ) is incident at an angle i at the interface between medium I and medium II (having refractive index n 2 ), the light ray is refracted at an angle r to the normal to the interface and travels in medium II. This is given by Snell s law. Total Internal Reflection: If the light ray is incident from a denser medium to a rarer medium at an angle greater than the critical angle, it doesn t get refracted but comes back into the medium itself. This bouncing back of light into the incident medium is called as total internal reflection. Critical Angle: The angle of incidence at which the angle of refraction is 90 0 i.e. the refracted ray moves along the boundary is called the critical angle (i c ). The angle is given as Basic Structure of Optical Fibre The basic structure of an optical fibre consists of three parts; core, cladding and jacket or sheath. The basic structure is as shown below: Core: The core is a cylindrical solid rod generally made up of glass. Light propagates mainly along the core of the fibre. The refractive index of the core is more than that of the cladding. Light is made incident at an angle greater than the critical angle so that the light propagates along the core by the process of total internal reflection. Its diameter is of the order of few tens of micrometres. Cladding: The core is surrounded by a layer of material called as cladding. It has refractive index less than that of the core. It provides mechanical strength to the fibre and aids in total reflection of light signal in the core. It also reduces loss of light into the surroundings. It is made of either glass or plastic. It has diameter of the order of few hundred micrometers. Jacket (Sheath): For extra protection, the cladding is enclosed in an additional layer called the jacket or sheath or buffer. It is a layer of material used to protect an optical fibre from physical damage. The jacket is made of plastic and prevents abrasions.

12 P a g e 12 Acceptance Angle It is defined as the maximum angle that a light ray can have with the axis of the fibre so that light remains confined in the fibre suffering total internal reflection at the core-cladding interface. Let us denote it by θ 0. Rays entering within a cone having angle 2θ 0 are accepted by the fibre. This is called as the acceptance cone as shown in figure below: Let θ C be the critical angle for the core-cladding interface. As long as θ>θ C, light undergoes multiple internal reflections and remains confined into the fibre. Thus the light ray gets propagated along the core. Let n 0, n 1 and n 2 be the refractive indices of the launching medium, core and cladding respectively. At the launching medium-core interface, Also, If = 1, This is the expression for acceptance angle. Numerical Aperture Numerical aperture (N.A.) is the measure of the light gathering capability for optical fibres. It is defined as the sine of the acceptance angle. Fractional Refractive Index (Δ) Fractional refractive index is defined as the ratio of the difference in refractive indices of core and cladding to the refractive index of the core.

13 P a g e 13 Also, Normalized Frequency or V-Number The V-number is the parameter associated with optical fibre which decides the number of modes that can be supported by an optical fibre. It is given by Where, a is the radius of the core. Let N m denote the maximum number of nodes that an optical fibre can support. It is given by If, V < 2.405, the optical fibre supports only one mode of propagation. This type of a fibre is called as Single mode fibre. Otherwise it supports more than more than one mode and is called as multimode fibre. Classification of Optical Fibres Optical fibres can be classified according to i) Refractive index profile ii) Number of modes supported iii) Material used i) Refractive Index Profile On the basis of variation of the refractive index profile of core and cladding, optical fibre can be classified as a) Step Index Fibre b) Graded Index Fibre a) Step Index Fibre: Step index fibres have a uniform core with one index of refraction (n 1 ) and a uniform cladding with a smaller index of refraction (n 2 ). The refractive index changes abruptly at the core-cladding boundary i.e. the refractive index profile of the fibre makes a step change at the core-cladding interface. The variation in the refractive index with respect to the r is given as ( Where, a is the radius of the core. The situation is as shown below:

14 P a g e 14 b) Graded Index Fibre: Graded index fibre is the type of optical fibre where the refractive index of the core is non-uniform. Refractive index gradually decreases from centre of the core towards the core-cladding boundary. Variations in the composition of the glass in the core are used to create the decreasing refractive index profile. The cladding in general has a uniform refractive index. The situation is as shown below: ii) Number of Modes Supported Light rays can travel through the fibre in one or more paths. These paths are called modes of propagation. On the basis of the number of modes supported, optical fibre can be classified as a) Single mode fibre b) Multimode fibre a) Single Mode Fibre: In a single mode fibre only one mode of propagation exists. Only step index fibre can be used as a single mode fibre. The diameter of the core is relatively smaller as compared to the cladding. The core has a diameter of about 8 to 10 μm and the cladding has a diameter of about 100 to 125 μm. The signal travels as a single ray down the fibre. The situation is as shown below: b) Multimode Fibre: The diameter of the core of the multimode step index fibre is larger than in case of single mode fibre. When light enters the fibre, it naturally scatters and the multiple modes travel simultaneously along the path. The diameter of the core is about 50 μm. In case of a graded index fibre, only multimode propagation is supported. Both the situations are as shown below: Multimode Step Index Fibre Multimode Graded Index Fibre iii) Material Used Optical fibres can be classified on the basis of the material used for core and cladding as: a) All Glass Fibre: Both the core and cladding are made up of glass. b) All Plastic Fibre: Both the core and cladding are made up of plastic. c) Glass and Plastic Fibre: If the core is made up of glass, cladding is made up of plastic and vice versa.

15 P a g e 15 Differences i) Step Index Fibre and Graded Index Fibre Step Index Fibre The refractive index of the core to cladding changes abruptly at the core-cladding boundary. In step index fibre, core and cladding material have uniform refractive index profile respectively. The light rays moves along a zigzag path and crosses the axis each time when it is internally reflected at the core-cladding boundary. These rays are called as meridional rays. Step index fibre can support both single mode and multimode propagation. Graded Index Fibre The refractive index of the core to cladding changes gradually. In graded index fibre, core consists of layers of materials of refractive indices in decreasing order from core to cladding. The light rays move around the axis in a helical path and do not cross the axis. These rays are called as skew rays. Graded index fibre can support only multimode propagation of light. ii) Single Mode Fibre and Multimode Fibre Single Mode Fibre Multimode Fibre Light propagates as a single ray through the fibre. Light ray propagates following more than one path through the fibre. The diameter of the core is about 10 μm. The diameter of the core is about 50 to 200 μm. Single mode fibres have a lower signal loss. Multimode fibres have more signal loss. Laser diodes are used as optical sources. LEDs are used as optical sources. Core to core coupling between two fibres is Core to core coupling between two fibres is not critical. so critical. Attenuation The reduction of signal strength or loss of optical power over the length of the optical fibre as the signal travels through it is called as attenuation. It is defined as the ratio of the optical input power (P i ) to the optical output power (P o ). It is given as Where, L is the length of the optical fibre. It is measured in decibel/kilometre (db/km). The three main causes of attenuation are absorption, scattering and dispersion of the optical signal in the fibre. i) Intrinsic Losses: These losses are inherent and cannot be avoided. They arise due to the natural processes that occur when the radiation is incident on a material. Hence, they are present in all optical fibres. Two main mechanisms are: a) Absorption: A certain amount of light is absorbed by the core and cladding material when the optical signal passes through it. This amounts as the major reason for loss of the optical signal. b) Rayleigh scattering: Whenever radiation is incident on the material, it gets scattered. This arises generally due to variation of density of the material of core and cladding.

16 P a g e 16 ii) Extrinsic Losses: These losses arise due to many external reasons such as variation in diameter of fibre, mode coupling and misalignment in coupling two fibres. They are as chronicled below: a) Bending Losses: Light cannot be propagated over entire length of the fibre if it has bends. The bend may be a micro or a macro bend. The bends occur during the manufacturing of the optical fibre. b) Waveguide Losses: These losses occur due to non-uniformity of the material used. c) Mode Coupling Losses: Each optical fibre supports only a few particular modes of propagation. Mode coupling losses occur if the fibre supporting a certain number of modes is coupled with another fibre having a different number of modes. d) Misalignment in coupling of fibres: If the coupling between the fibres is not perfect, optical signal is lost in transition. Misalignment is of three types: Longitudinal Misalignment: If a small gap remains between the two fibres, signals leak through the gap and does not get coupled to the other fibre. Lateral or Axial Misalignment: If the fibres do not get aligned along the axis perfectly, signal cannot be coupled to the other fibre. Angular Misalignment: It occurs when the axes of the two fibres are not parallel but are inclined with respect to each other. All the three situations are as shown below: Longitudinal Misalignment Lateral Misalignment Angular Misalignment iii) Dispersion Losses: In optical fibres, signals of different wavelengths travel with different speeds and hence they reach at different times at the exit end. This results in overlapping of pulses and broadening of the output pulse due to which information is lost. This broadening of pulse is known as dispersion. The various dispersion losses are: a) Modal Dispersion: In a multimode fibre if different modes arrive at different instances at the exit end, the pulse broadens due to overlapping of the signals. This type of dispersion is called as modal dispersion. b) Material Dispersion: It s a fact that light of different wavelengths travel with different velocities in a given medium. Hence, in an optical fibre light of different wavelengths arrive at the exit end at different times and thus resulting in broadening of the pulse. This type of dispersion is called as material dispersion. c) Waveguide Dispersion: This type of dispersion occurs mainly in single mode fibres. The light travels faster in the cladding than in the core as its refractive index is less. Thus, the light from the

17 P a g e 17 cladding arrives at the exit end before the light ray from the core thus broadening the signal. This type of dispersion is called as the waveguide dispersion. All the three situations are as shown below: Applications i) As Waveguide in Communications: Optical fibre used as the light transmitting medium between the optical source and the detector in optical communication systems. The system comprises of an optical transmitter, fibre as the communication medium and an optical receiver. LEDs or Lasers are used as optical sources while photo detectors such as photodiodes and PIN diodes act as the optical receivers. One such system is as shown below: ii) In Medical Diagnostics: Optical fibre acts as efficient transportation medium since it is very compact, flexible conduit for light or data delivery in surgical and instrumentation applications. Two diagnostics where it is used are: a) Eye Diagnostics: The optical fibre probe is used to study different parts of the eye. The probe positioned in front of the eye delivers a low power light from a laser into the eye and guides the light which is scattered back from different parts of the eye. The scattered ray is received by a photo detector. b) Endoscopy: It is the process where an optical instrument is introduced into the body cavities so that the organs of the body may be directly inspected. An endoscope consists of a light delivery system to illuminate the organ under inspection via an optical fibre system. A lens system transmits the image to the viewer via the fiberscope. An additional channel allows the entry of medical instruments. This can also be coupled with laser beam to carry out laser surgery. c) Missile Guiding: A guided missile is an unmanned vehicle that travels above the earth s surface. It carries an explosive war head or other payload and it contains some means for controlling its own trajectory. Hence it is called a guided missile. The sensors mounted on the missile transmit signals to the ground control and guidance van through optical fibre. The control system keeps the missile in stable flight and it translates the commands of the guidance system into motion of the missile. d) Optical Sensors: Optical fibre sensors are used to sense physical quantities like temperature, liquid level, pressure, vibrations, rotations, etc. The light beam may be altered in five of its optical

18 P a g e 18 properties namely intensity, phase, polarization, wavelength and spectral distribution. The principle of operation is that the light beam is changed by the measuring physical phenomenon and then the changed light is detected. The change in the property of the light beam is proportional to the measurable quantity. Three of them are as follows: Temperature Sensor: This sensor is an intensity modulated sensor. A thin layer of silicon is used as a sensor to detect the temperature. Intensity of light is modified when it gets reflected from the layer of silicon placed in contact with the target material. The sensor is as shown below: The light from a source is introduced into the fibre from one of the ends. The light is made incident on the silicon layer which is kept in contact with the object whose temperature is to be measured. The silicon layer absorbs part of the incident light depending on the temperature of the object. The light after passing through the silicon layer gets reflected from the reflecting mirror and passes through the other branch of the fibre. This reflected light is then detected by the photo detector which detects the change in the intensity due to absorption. This sensor uses multimode fibre and has a sensitivity of C. Liquid Level Indicator: It works on the principle of total internal reflection. A notch is cut at one end of the fibre. A source is placed at one end of the notch and a detector at other end. The fibre chosen has refractive index less than that of the liquid whose level is to be measured. One such sensor is as shown below: The optical fibre is placed at the desired level in the vessel. Light from the source is incident on one side of the notch from where it is reflected through an angle of If the liquid level is below the end of optical fibre, the ray gets reflected at the fibre-air interface. From there it gets incident on opposite face of the optical face of the optical fibre and is turned by 90 0 so that it is received by the detector. If the liquid touches the fibre, the ray is refracted into the liquid and hence the detector does not receive any signal. Thus a liquid level indicator works.

19 P a g e 19 Pressure Sensor: A change of shape of the fibre also alters the intensity of light transmitted through it. Pressure sensor works on the same principle. One such sensor is as shown below: A fibre is placed between two plates. A source of light is placed on one side of the plates and a detector on the other side of plates. The pressure is exerted on the top plate. Due to this pressure, the shape of the optical fibre is altered thus changing the intensity of the light passing through it. This change is detected by the detector. Advantages The advantages of optical fibres over other technologies are: i) Extreme high carrier frequencies (10 14 to Hz) provide large bandwidth. ii) They do not generate or receive any electromagnetic and Radio frequency interferences. iii) Provides low signal loss as compared to electrical cables. iv) Signals can be transmitted over longer distances without needing to be strengthened. Thus, less repeaters are needed. v) They are not affected by moisture or corrosion. vi) They operate at high speeds- up into gigabits. vii) They can be operated over high temperature range. viii) They are light and occupy less space. ix) No permanent damage takes place due to nuclear radiation. x) They have multiplexing capabilities i.e. multiple sensors in a single fibre line can be illuminated with a single optical source. Bibliography: 1) A Textbook of Engineering Physics M. N. Avadhanalu 2) Optics Eugene Hecht 3) Concepts of Physics Part 1 H. C. Verma 4) Fundamentals of Physics Halliday, Resnick, Walker 5)

PHYSICS. The Probability of Occurrence of Absorption from state 1 to state 2 is proportional to the energy density u(v)..

PHYSICS. The Probability of Occurrence of Absorption from state 1 to state 2 is proportional to the energy density u(v).. ABSORPTION of RADIATION : PHYSICS The Probability of Occurrence of Absorption from state 1 to state 2 is proportional to the energy density u(v).. of the radiation > P12 = B12 u(v) hv E2 E1 Where as, the

More information

Unit-2 LASER. Syllabus: Properties of lasers, types of lasers, derivation of Einstein A & B Coefficients, Working He-Ne and Ruby lasers.

Unit-2 LASER. Syllabus: Properties of lasers, types of lasers, derivation of Einstein A & B Coefficients, Working He-Ne and Ruby lasers. Unit-2 LASER Syllabus: Properties of lasers, types of lasers, derivation of Einstein A & B Coefficients, Working He-Ne and Ruby lasers. Page 1 LASER: The word LASER is acronym for light amplification by

More information

LASERS. Dr D. Arun Kumar Assistant Professor Department of Physical Sciences Bannari Amman Institute of Technology Sathyamangalam

LASERS. Dr D. Arun Kumar Assistant Professor Department of Physical Sciences Bannari Amman Institute of Technology Sathyamangalam LASERS Dr D. Arun Kumar Assistant Professor Department of Physical Sciences Bannari Amman Institute of Technology Sathyamangalam General Objective To understand the principle, characteristics and types

More information

Ms. Monika Srivastava Doctoral Scholar, AMR Group of Dr. Anurag Srivastava ABV-IIITM, Gwalior

Ms. Monika Srivastava Doctoral Scholar, AMR Group of Dr. Anurag Srivastava ABV-IIITM, Gwalior By Ms. Monika Srivastava Doctoral Scholar, AMR Group of Dr. Anurag Srivastava ABV-IIITM, Gwalior Unit 2 Laser acronym Laser Vs ordinary light Characteristics of lasers Different processes involved in lasers

More information

Unit I LASER Engineering Physics

Unit I LASER Engineering Physics Introduction LASER stands for light Amplification by Stimulated Emission of Radiation. The theoretical basis for the development of laser was provided by Albert Einstein in 1917. In 1960, the first laser

More information

QUESTION BANK IN PHYSICS

QUESTION BANK IN PHYSICS QUESTION BANK IN PHYSICS LASERS. Name some properties, which make laser light different from ordinary light. () {JUN 5. The output power of a given laser is mw and the emitted wavelength is 630nm. Calculate

More information

Chapter 24 Photonics Question 1 Question 2 Question 3 Question 4 Question 5

Chapter 24 Photonics Question 1 Question 2 Question 3 Question 4 Question 5 Chapter 24 Photonics Data throughout this chapter: e = 1.6 10 19 C; h = 6.63 10 34 Js (or 4.14 10 15 ev s); m e = 9.1 10 31 kg; c = 3.0 10 8 m s 1 Question 1 Visible light has a range of photons with wavelengths

More information

Laserphysik. Prof. Yong Lei & Dr. Yang Xu. Fachgebiet Angewandte Nanophysik, Institut für Physik

Laserphysik. Prof. Yong Lei & Dr. Yang Xu. Fachgebiet Angewandte Nanophysik, Institut für Physik Laserphysik Prof. Yong Lei & Dr. Yang Xu Fachgebiet Angewandte Nanophysik, Institut für Physik Contact: yong.lei@tu-ilmenau.de; yang.xu@tu-ilmenau.de Office: Heisenbergbau V 202, Unterpörlitzer Straße

More information

PHYSICS nd TERM Outline Notes (continued)

PHYSICS nd TERM Outline Notes (continued) PHYSICS 2800 2 nd TERM Outline Notes (continued) Section 6. Optical Properties (see also textbook, chapter 15) This section will be concerned with how electromagnetic radiation (visible light, in particular)

More information

Lasers E 6 E 4 E 3 E 2 E 1

Lasers E 6 E 4 E 3 E 2 E 1 Lasers Laser is an acronym for light amplification by stimulated emission of radiation. Here the process of stimulated emission is used to amplify light radiation. Spontaneous emission: When energy is

More information

Chapter 5. Semiconductor Laser

Chapter 5. Semiconductor Laser Chapter 5 Semiconductor Laser 5.0 Introduction Laser is an acronym for light amplification by stimulated emission of radiation. Albert Einstein in 1917 showed that the process of stimulated emission must

More information

Model Answer (Paper code: AR-7112) M. Sc. (Physics) IV Semester Paper I: Laser Physics and Spectroscopy

Model Answer (Paper code: AR-7112) M. Sc. (Physics) IV Semester Paper I: Laser Physics and Spectroscopy Model Answer (Paper code: AR-7112) M. Sc. (Physics) IV Semester Paper I: Laser Physics and Spectroscopy Section I Q1. Answer (i) (b) (ii) (d) (iii) (c) (iv) (c) (v) (a) (vi) (b) (vii) (b) (viii) (a) (ix)

More information

-I (PH 6151) UNIT-V PHOTONICS AND FIBRE OPTICS

-I (PH 6151) UNIT-V PHOTONICS AND FIBRE OPTICS Engineering Physics -I (PH 6151) UNIT-V PHOTONICS AND FIBRE OPTICS Syllabus: Lasers Spontaneous and stimulated emission Population Inversion -Einstein s co-efficient (Derivation)- types of lasers-nd-yag,co

More information

Dept. of Physics, MIT Manipal 1

Dept. of Physics, MIT Manipal 1 Chapter 1: Optics 1. In the phenomenon of interference, there is A Annihilation of light energy B Addition of energy C Redistribution energy D Creation of energy 2. Interference fringes are obtained using

More information

Laser Types Two main types depending on time operation Continuous Wave (CW) Pulsed operation Pulsed is easier, CW more useful

Laser Types Two main types depending on time operation Continuous Wave (CW) Pulsed operation Pulsed is easier, CW more useful What Makes a Laser Light Amplification by Stimulated Emission of Radiation Main Requirements of the Laser Laser Gain Medium (provides the light amplification) Optical Resonator Cavity (greatly increase

More information

Modern optics Lasers

Modern optics Lasers Chapter 13 Phys 322 Lecture 36 Modern optics Lasers Reminder: Please complete the online course evaluation Last lecture: Review discussion (no quiz) LASER = Light Amplification by Stimulated Emission of

More information

Laser Types Two main types depending on time operation Continuous Wave (CW) Pulsed operation Pulsed is easier, CW more useful

Laser Types Two main types depending on time operation Continuous Wave (CW) Pulsed operation Pulsed is easier, CW more useful Main Requirements of the Laser Optical Resonator Cavity Laser Gain Medium of 2, 3 or 4 level types in the Cavity Sufficient means of Excitation (called pumping) eg. light, current, chemical reaction Population

More information

FIBER OPTICS. Prof. R.K. Shevgaonkar. Department of Electrical Engineering. Indian Institute of Technology, Bombay. Lecture: 17.

FIBER OPTICS. Prof. R.K. Shevgaonkar. Department of Electrical Engineering. Indian Institute of Technology, Bombay. Lecture: 17. FIBER OPTICS Prof. R.K. Shevgaonkar Department of Electrical Engineering Indian Institute of Technology, Bombay Lecture: 17 Optical Sources- Introduction to LASER Fiber Optics, Prof. R.K. Shevgaonkar,

More information

BANNARI AMMAN INSTITUTE OF TECHNOLOGY SATHYAMANGALAM DEPARTMENT OF PHYSICAL SCIENCES. UNIT II Applied Optics

BANNARI AMMAN INSTITUTE OF TECHNOLOGY SATHYAMANGALAM DEPARTMENT OF PHYSICAL SCIENCES. UNIT II Applied Optics BANNAI AMMAN INSTITTE OF TECHNOLOGY SATHYAMANGALAM DEPATMENT OF PHYSICAL SCIENCES NIT II Applied Optics PAT A A1 The superimposition of one light wave over another is called as a) interference b) Diffraction

More information

What Makes a Laser Light Amplification by Stimulated Emission of Radiation Main Requirements of the Laser Laser Gain Medium (provides the light

What Makes a Laser Light Amplification by Stimulated Emission of Radiation Main Requirements of the Laser Laser Gain Medium (provides the light What Makes a Laser Light Amplification by Stimulated Emission of Radiation Main Requirements of the Laser Laser Gain Medium (provides the light amplification) Optical Resonator Cavity (greatly increase

More information

Experiment 3 1. The Michelson Interferometer and the He- Ne Laser Physics 2150 Experiment No. 3 University of Colorado

Experiment 3 1. The Michelson Interferometer and the He- Ne Laser Physics 2150 Experiment No. 3 University of Colorado Experiment 3 1 Introduction The Michelson Interferometer and the He- Ne Laser Physics 2150 Experiment No. 3 University of Colorado The Michelson interferometer is one example of an optical interferometer.

More information

Chapter-4 Stimulated emission devices LASERS

Chapter-4 Stimulated emission devices LASERS Semiconductor Laser Diodes Chapter-4 Stimulated emission devices LASERS The Road Ahead Lasers Basic Principles Applications Gas Lasers Semiconductor Lasers Semiconductor Lasers in Optical Networks Improvement

More information

UNIT- I: LASERS AND OPTICAL FIBRES

UNIT- I: LASERS AND OPTICAL FIBRES UNIT- I: LASERS AND OPTICAL FIBRES LASERS Introduction: LASER is an acronym for Light Amplification by Stimulated Emission of Radiation. Laser device produces a beam of coherent, monochromatic, intense

More information

LASER. Light Amplification by Stimulated Emission of Radiation

LASER. Light Amplification by Stimulated Emission of Radiation LASER Light Amplification by Stimulated Emission of Radiation Laser Fundamentals The light emitted from a laser is monochromatic, that is, it is of one color/wavelength. In contrast, ordinary white light

More information

B.Tech. First Semester Examination Physics-1 (PHY-101F)

B.Tech. First Semester Examination Physics-1 (PHY-101F) B.Tech. First Semester Examination Physics-1 (PHY-101F) Note : Attempt FIVE questions in all taking least two questions from each Part. All questions carry equal marks Part-A Q. 1. (a) What are Newton's

More information

Laser Basics. What happens when light (or photon) interact with a matter? Assume photon energy is compatible with energy transition levels.

Laser Basics. What happens when light (or photon) interact with a matter? Assume photon energy is compatible with energy transition levels. What happens when light (or photon) interact with a matter? Assume photon energy is compatible with energy transition levels. Electron energy levels in an hydrogen atom n=5 n=4 - + n=3 n=2 13.6 = [ev]

More information

Stimulated Emission Devices: LASERS

Stimulated Emission Devices: LASERS Stimulated Emission Devices: LASERS 1. Stimulated Emission and Photon Amplification E 2 E 2 E 2 hυ hυ hυ In hυ Out hυ E 1 E 1 E 1 (a) Absorption (b) Spontaneous emission (c) Stimulated emission The Principle

More information

Chemistry Instrumental Analysis Lecture 5. Chem 4631

Chemistry Instrumental Analysis Lecture 5. Chem 4631 Chemistry 4631 Instrumental Analysis Lecture 5 Light Amplification by Stimulated Emission of Radiation High Intensities Narrow Bandwidths Coherent Outputs Applications CD/DVD Readers Fiber Optics Spectroscopy

More information

DEPARTMENT OF PHYSICS RV COLLEGE OF ENGINEERING

DEPARTMENT OF PHYSICS RV COLLEGE OF ENGINEERING DEPARTMENT OF PHYSICS RV COLLEGE OF ENGINEERING ENGINEERING PHYSICS NOTES-07-8 COURSE CODE: 6PH/ Semester: I/II ENGINEERING PHYSICS( Theory and practice) Course Code: 6PH/6PH CIE Marks:00+5050 Hrs/Week:

More information

Lasers & Holography. Ulrich Heintz Brown University. 4/5/2016 Ulrich Heintz - PHYS 1560 Lecture 10 1

Lasers & Holography. Ulrich Heintz Brown University. 4/5/2016 Ulrich Heintz - PHYS 1560 Lecture 10 1 Lasers & Holography Ulrich Heintz Brown University 4/5/2016 Ulrich Heintz - PHYS 1560 Lecture 10 1 Lecture schedule Date Topic Thu, Jan 28 Introductory meeting Tue, Feb 2 Safety training Thu, Feb 4 Lab

More information

Lasers and Electro-optics

Lasers and Electro-optics Lasers and Electro-optics Second Edition CHRISTOPHER C. DAVIS University of Maryland III ^0 CAMBRIDGE UNIVERSITY PRESS Preface to the Second Edition page xv 1 Electromagnetic waves, light, and lasers 1

More information

Signal regeneration - optical amplifiers

Signal regeneration - optical amplifiers Signal regeneration - optical amplifiers In any atom or solid, the state of the electrons can change by: 1) Stimulated absorption - in the presence of a light wave, a photon is absorbed, the electron is

More information

The Electromagnetic Properties of Materials

The Electromagnetic Properties of Materials The Electromagnetic Properties of Materials Electrical conduction Metals Semiconductors Insulators (dielectrics) Superconductors Magnetic materials Ferromagnetic materials Others Photonic Materials (optical)

More information

What do we study and do?

What do we study and do? What do we study and do? Light comes from electrons transitioning from higher energy to lower energy levels. Wave-particle nature of light Wave nature: refraction, diffraction, interference (labs) Particle

More information

ENGINEERING PHYSICS UNIT I - LASERS SV COLLEGE OF ENGINEERING, KADAPA

ENGINEERING PHYSICS UNIT I - LASERS SV COLLEGE OF ENGINEERING, KADAPA Syllabus:- Characteristics of laser spontaneous and stimulated emission of radiation Einstein s coefficients - population inversion excitation mechanism and optical resonator Nd:YAG laser He-Ne laser semiconductor

More information

Population inversion occurs when there are more atoms in the excited state than in the ground state. This is achieved through the following:

Population inversion occurs when there are more atoms in the excited state than in the ground state. This is achieved through the following: Lasers and SemiconductorsTutorial Lasers 1. Fill in the table the differences between spontaneous emission and stimulated emission in atoms: External stimulus Direction of emission Phase & coherence of

More information

LASERS. Amplifiers: Broad-band communications (avoid down-conversion)

LASERS. Amplifiers: Broad-band communications (avoid down-conversion) L- LASERS Representative applications: Amplifiers: Broad-band communications (avoid down-conversion) Oscillators: Blasting: Energy States: Hydrogen atom Frequency/distance reference, local oscillators,

More information

FIBER OPTICS. Prof. R.K. Shevgaonkar. Department of Electrical Engineering. Indian Institute of Technology, Bombay. Lecture: 15. Optical Sources-LASER

FIBER OPTICS. Prof. R.K. Shevgaonkar. Department of Electrical Engineering. Indian Institute of Technology, Bombay. Lecture: 15. Optical Sources-LASER FIBER OPTICS Prof. R.K. Shevgaonkar Department of Electrical Engineering Indian Institute of Technology, Bombay Lecture: 15 Optical Sources-LASER Fiber Optics, Prof. R.K. Shevgaonkar, Dept. of Electrical

More information

Materialwissenschaft und Nanotechnologie. Introduction to Lasers

Materialwissenschaft und Nanotechnologie. Introduction to Lasers Materialwissenschaft und Nanotechnologie Introduction to Lasers Dr. Andrés Lasagni Lehrstuhl für Funktionswerkstoffe Sommersemester 007 1-Introduction to LASER Contents: Light sources LASER definition

More information

OPTICAL GAIN AND LASERS

OPTICAL GAIN AND LASERS OPTICAL GAIN AND LASERS 01-02-1 BY DAVID ROCKWELL DIRECTOR, RESEARCH & DEVELOPMENT fsona COMMUNICATIONS MARCH 6, 2001 OUTLINE 01-02-2 I. DEFINITIONS, BASIC CONCEPTS II. III. IV. OPTICAL GAIN AND ABSORPTION

More information

External (differential) quantum efficiency Number of additional photons emitted / number of additional electrons injected

External (differential) quantum efficiency Number of additional photons emitted / number of additional electrons injected Semiconductor Lasers Comparison with LEDs The light emitted by a laser is generally more directional, more intense and has a narrower frequency distribution than light from an LED. The external efficiency

More information

Sunlight. 1 radiation.

Sunlight. 1 radiation. Sunlight The eye has evolved to see a narrow range of EM waves which we call 'visible light'. This visible range of frequency is due to the light comes from the Sun. The photosphere of the Sun is a blackbody

More information

Optical Fiber Signal Degradation

Optical Fiber Signal Degradation Optical Fiber Signal Degradation Effects Pulse Spreading Dispersion (Distortion) Causes the optical pulses to broaden as they travel along a fiber Overlap between neighboring pulses creates errors Resulting

More information

EE 6313 Homework Assignments

EE 6313 Homework Assignments EE 6313 Homework Assignments 1. Homework I: Chapter 1: 1.2, 1.5, 1.7, 1.10, 1.12 [Lattice constant only] (Due Sept. 1, 2009). 2. Homework II: Chapter 1, 2: 1.17, 2.1 (a, c) (k = π/a at zone edge), 2.3

More information

What can laser light do for (or to) me?

What can laser light do for (or to) me? What can laser light do for (or to) me? Phys 1020, Day 15: Questions? Refection, refraction LASERS: 14.3 Next Up: Finish lasers Cameras and optics 1 Eyes to web: Final Project Info Light travels more slowly

More information

Laser Physics OXFORD UNIVERSITY PRESS SIMON HOOKER COLIN WEBB. and. Department of Physics, University of Oxford

Laser Physics OXFORD UNIVERSITY PRESS SIMON HOOKER COLIN WEBB. and. Department of Physics, University of Oxford Laser Physics SIMON HOOKER and COLIN WEBB Department of Physics, University of Oxford OXFORD UNIVERSITY PRESS Contents 1 Introduction 1.1 The laser 1.2 Electromagnetic radiation in a closed cavity 1.2.1

More information

In a metal, how does the probability distribution of an electron look like at absolute zero?

In a metal, how does the probability distribution of an electron look like at absolute zero? 1 Lecture 6 Laser 2 In a metal, how does the probability distribution of an electron look like at absolute zero? 3 (Atom) Energy Levels For atoms, I draw a lower horizontal to indicate its lowest energy

More information

Advanced Optical Communications Prof. R. K. Shevgaonkar Department of Electrical Engineering Indian Institute of Technology, Bombay

Advanced Optical Communications Prof. R. K. Shevgaonkar Department of Electrical Engineering Indian Institute of Technology, Bombay Advanced Optical Communications Prof. R. K. Shevgaonkar Department of Electrical Engineering Indian Institute of Technology, Bombay Lecture No. # 15 Laser - I In the last lecture, we discussed various

More information

Modern Physics for Frommies IV The Universe - Small to Large Lecture 4

Modern Physics for Frommies IV The Universe - Small to Large Lecture 4 Fromm Institute for Lifelong Learning University of San Francisco Modern Physics for Frommies IV The Universe - Small to Large Lecture 4 3 February 06 Modern Physics IV Lecture 4 Agenda Administrative

More information

(b) Spontaneous emission. Absorption, spontaneous (random photon) emission and stimulated emission.

(b) Spontaneous emission. Absorption, spontaneous (random photon) emission and stimulated emission. Lecture 10 Stimulated Emission Devices Lasers Stimulated emission and light amplification Einstein coefficients Optical fiber amplifiers Gas laser and He-Ne Laser The output spectrum of a gas laser Laser

More information

LASER. Challenging MCQ questions by The Physics Cafe. Compiled and selected by The Physics Cafe

LASER. Challenging MCQ questions by The Physics Cafe. Compiled and selected by The Physics Cafe LSER hallenging MQ questions by The Physics afe ompiled and selected by The Physics afe www.thephysicsafe.com www.pmc.sg 1 laser point creates a spot on a screen as it reflects 70% of the light striking

More information

MODERN OPTICS. P47 Optics: Unit 9

MODERN OPTICS. P47 Optics: Unit 9 MODERN OPTICS P47 Optics: Unit 9 Course Outline Unit 1: Electromagnetic Waves Unit 2: Interaction with Matter Unit 3: Geometric Optics Unit 4: Superposition of Waves Unit 5: Polarization Unit 6: Interference

More information

1) Introduction 2) Photo electric effect 3) Dual nature of matter 4) Bohr s atom model 5) LASERS

1) Introduction 2) Photo electric effect 3) Dual nature of matter 4) Bohr s atom model 5) LASERS 1) Introduction 2) Photo electric effect 3) Dual nature of matter 4) Bohr s atom model 5) LASERS 1. Introduction Types of electron emission, Dunnington s method, different types of spectra, Fraunhoffer

More information

Photonics and Optical Communication

Photonics and Optical Communication Photonics and Optical Communication (Course Number 300352) Spring 2007 Optical Source Dr. Dietmar Knipp Assistant Professor of Electrical Engineering http://www.faculty.iu-bremen.de/dknipp/ 1 Photonics

More information

ENGINEERING PHYSICS WAVES AND FIBER OPTICS

ENGINEERING PHYSICS WAVES AND FIBER OPTICS PH8151 ENGINEERING PHYSICS UNIT II WAVES AND FIBER OPTICS Oscillatory motion forced and damped oscillations: differential equation and its solution plane progressive waves wave equation. Lasers : population

More information

Light Emission. Today s Topics. Excitation/De-Excitation 10/26/2008. Excitation Emission Spectra Incandescence

Light Emission. Today s Topics. Excitation/De-Excitation 10/26/2008. Excitation Emission Spectra Incandescence Light Emission Excitation Emission Spectra Incandescence Absorption Spectra Today s Topics Excitation/De-Excitation Electron raised to higher energy level Electron emits photon when it drops back down

More information

Homework 1. Property LASER Incandescent Bulb

Homework 1. Property LASER Incandescent Bulb Homework 1 Solution: a) LASER light is spectrally pure, single wavelength, and they are coherent, i.e. all the photons are in phase. As a result, the beam of a laser light tends to stay as beam, and not

More information

Because light behaves like a wave, we can describe it in one of two ways by its wavelength or by its frequency.

Because light behaves like a wave, we can describe it in one of two ways by its wavelength or by its frequency. Light We can use different terms to describe light: Color Wavelength Frequency Light is composed of electromagnetic waves that travel through some medium. The properties of the medium determine how light

More information

Introduction Fundamentals of laser Types of lasers Semiconductor lasers

Introduction Fundamentals of laser Types of lasers Semiconductor lasers Introduction Fundamentals of laser Types of lasers Semiconductor lasers Is it Light Amplification and Stimulated Emission Radiation? No. So what if I know an acronym? What exactly is Light Amplification

More information

Saveetha Engineering College, Thandalam, Chennai. Department of Physics. First Semester. Ph6151 Engineering Physics I (NOV/DEC 2014)

Saveetha Engineering College, Thandalam, Chennai. Department of Physics. First Semester. Ph6151 Engineering Physics I (NOV/DEC 2014) Saveetha Engineering College, Thandalam, Chennai. Department of Physics First Semester Ph6151 Engineering Physics I (NOV/DEC 2014) Part A (Questions and Answers) 1. Distinguish between Crystalline and

More information

Phys 2310 Fri. Dec. 12, 2014 Today s Topics. Begin Chapter 13: Lasers Reading for Next Time

Phys 2310 Fri. Dec. 12, 2014 Today s Topics. Begin Chapter 13: Lasers Reading for Next Time Phys 2310 Fri. Dec. 12, 2014 Today s Topics Begin Chapter 13: Lasers Reading for Next Time 1 Reading this Week By Fri.: Ch. 13 (13.1, 13.3) Lasers, Holography 2 Homework this Week No Homework this chapter.

More information

Review of Optical Properties of Materials

Review of Optical Properties of Materials Review of Optical Properties of Materials Review of optics Absorption in semiconductors: qualitative discussion Derivation of Optical Absorption Coefficient in Direct Semiconductors Photons When dealing

More information

FIBER OPTICS. Prof. R.K. Shevgaonkar. Department of Electrical Engineering. Indian Institute of Technology, Bombay. Lecture: 14.

FIBER OPTICS. Prof. R.K. Shevgaonkar. Department of Electrical Engineering. Indian Institute of Technology, Bombay. Lecture: 14. FIBER OPTICS Prof. R.K. Shevgaonkar Department of Electrical Engineering Indian Institute of Technology, Bombay Lecture: 14 Optical Sources Fiber Optics, Prof. R.K. Shevgaonkar, Dept. of Electrical Engineering,

More information

Laser Fundamentals and its Applications. Photonic Network By Dr. M H Zaidi

Laser Fundamentals and its Applications. Photonic Network By Dr. M H Zaidi Laser Fundamentals and its Applications LASER LASER is acronym of Light Amplification by Stimulated Emission of Radiation. http://www.semicon.toshiba.co.jp Lasers Outline Introduction and Overview Theory

More information

Practical 1P4 Energy Levels and Band Gaps

Practical 1P4 Energy Levels and Band Gaps Practical 1P4 Energy Levels and Band Gaps What you should learn from this practical Science This practical illustrates some of the points from the lecture course on Elementary Quantum Mechanics and Bonding

More information

Practical 1P4 Energy Levels and Band Gaps

Practical 1P4 Energy Levels and Band Gaps Practical 1P4 Energy Levels and Band Gaps What you should learn from this practical Science This practical illustrates some of the points from the lecture course on Elementary Quantum Mechanics and Bonding

More information

Stimulated Emission. Electrons can absorb photons from medium. Accelerated electrons emit light to return their ground state

Stimulated Emission. Electrons can absorb photons from medium. Accelerated electrons emit light to return their ground state Lecture 15 Stimulated Emission Devices- Lasers Stimulated emission and light amplification Einstein coefficients Optical fiber amplifiers Gas laser and He-Ne Laser The output spectrum of a gas laser Laser

More information

ELECTRONIC DEVICES AND CIRCUITS SUMMARY

ELECTRONIC DEVICES AND CIRCUITS SUMMARY ELECTRONIC DEVICES AND CIRCUITS SUMMARY Classification of Materials: Insulator: An insulator is a material that offers a very low level (or negligible) of conductivity when voltage is applied. Eg: Paper,

More information

LASERS AGAIN? Phys 1020, Day 17: Questions? LASERS: Next Up: Cameras and optics Eyes to web: Final Project Info

LASERS AGAIN? Phys 1020, Day 17: Questions? LASERS: Next Up: Cameras and optics Eyes to web: Final Project Info LASERS AGAIN? Phys 1020, Day 17: Questions? LASERS: 14.3 Next Up: Cameras and optics Eyes to web: Final Project Info 1 Group Exercise Your pennies will simulate a two state atom; tails = ground state,

More information

Propagation losses in optical fibers

Propagation losses in optical fibers Chapter Dielectric Waveguides and Optical Fibers 1-Fev-017 Propagation losses in optical fibers Charles Kao, Nobel Laureate (009) Courtesy of the Chinese University of Hong Kong S.O. Kasap, Optoelectronics

More information

Photonics and Fibre optics

Photonics and Fibre optics Unit 5 Photonics and Fibre optics Learning objective 1. To learn basics of lasers viz., the fundamental theory, conditions of laser action, few types of lasers, laser application in industries and medicine.

More information

Optics, Optoelectronics and Photonics

Optics, Optoelectronics and Photonics Optics, Optoelectronics and Photonics Engineering Principles and Applications Alan Billings Emeritus Professor, University of Western Australia New York London Toronto Sydney Tokyo Singapore v Contents

More information

Optics in a Fish Tank Demonstrations for the Classroom

Optics in a Fish Tank Demonstrations for the Classroom Optics in a Fish Tank Demonstrations for the Classroom Introduction: This series of demonstrations will illustrate a number of optical phenomena. Using different light sources and a tank of water, you

More information

Energetic particles and their detection in situ (particle detectors) Part II. George Gloeckler

Energetic particles and their detection in situ (particle detectors) Part II. George Gloeckler Energetic particles and their detection in situ (particle detectors) Part II George Gloeckler University of Michigan, Ann Arbor, MI University of Maryland, College Park, MD Simple particle detectors Gas-filled

More information

Metal Vapour Lasers Use vapoured metal as a gain medium Developed by W. Silfvast (1966) Two types: Ionized Metal vapour (He-Cd) Neutral Metal vapour

Metal Vapour Lasers Use vapoured metal as a gain medium Developed by W. Silfvast (1966) Two types: Ionized Metal vapour (He-Cd) Neutral Metal vapour Metal Vapour Lasers Use vapoured metal as a gain medium Developed by W. Silfvast (1966) Two types: Ionized Metal vapour (He-Cd) Neutral Metal vapour (Cu) All operate by vaporizing metal in container Helium

More information

Chemistry Instrumental Analysis Lecture 8. Chem 4631

Chemistry Instrumental Analysis Lecture 8. Chem 4631 Chemistry 4631 Instrumental Analysis Lecture 8 UV to IR Components of Optical Basic components of spectroscopic instruments: stable source of radiant energy transparent container to hold sample device

More information

Phys 2310 Mon. Dec. 4, 2017 Today s Topics. Begin supplementary material: Lasers Reading for Next Time

Phys 2310 Mon. Dec. 4, 2017 Today s Topics. Begin supplementary material: Lasers Reading for Next Time Phys 2310 Mon. Dec. 4, 2017 Today s Topics Begin supplementary material: Lasers Reading for Next Time 1 By Wed.: Reading this Week Lasers, Holography 2 Homework this Week No Homework this chapter. Finish

More information

Radionuclide Imaging MII Detection of Nuclear Emission

Radionuclide Imaging MII Detection of Nuclear Emission Radionuclide Imaging MII 3073 Detection of Nuclear Emission Nuclear radiation detectors Detectors that are commonly used in nuclear medicine: 1. Gas-filled detectors 2. Scintillation detectors 3. Semiconductor

More information

A beam of coherent monochromatic light from a distant galaxy is used in an optics experiment on Earth.

A beam of coherent monochromatic light from a distant galaxy is used in an optics experiment on Earth. Waves_P2 [152 marks] A beam of coherent monochromatic light from a distant galaxy is used in an optics experiment on Earth. The beam is incident normally on a double slit. The distance between the slits

More information

10.8 LASERS Principle of Laser Induced Absorption

10.8 LASERS Principle of Laser Induced Absorption 10.8 LASERS The word Laser stands for Light Amplification by Stimulated Emission of Radiations. Laser is biggest achieve of twentieth century in the field of research. The first laser was developed by

More information

δf / δx = σ F (N 2 -N 1 ) ΔF~N 2 -N 1

δf / δx = σ F (N 2 -N 1 ) ΔF~N 2 -N 1 LASER Light Amplification by Stimulated Emission of Radiation BASIC PROPERTIES O LASER RADIATION Spontaneous emission Incoherence in time Incoherence in space Polychromatic light Small energy density Non-polarized

More information

Name : Roll No. :.. Invigilator s Signature :.. CS/B.Tech/SEM-2/PH-201/2010 2010 ENGINEERING PHYSICS Time Allotted : 3 Hours Full Marks : 70 The figures in the margin indicate full marks. Candidates are

More information

Laser Optics-II. ME 677: Laser Material Processing Instructor: Ramesh Singh 1

Laser Optics-II. ME 677: Laser Material Processing Instructor: Ramesh Singh 1 Laser Optics-II 1 Outline Absorption Modes Irradiance Reflectivity/Absorption Absorption coefficient will vary with the same effects as the reflectivity For opaque materials: reflectivity = 1 - absorptivity

More information

Single Photon detectors

Single Photon detectors Single Photon detectors Outline Motivation for single photon detection Semiconductor; general knowledge and important background Photon detectors: internal and external photoeffect Properties of semiconductor

More information

Chapter 7: Optical Properties of Solids. Interaction of light with atoms. Insert Fig Allowed and forbidden electronic transitions

Chapter 7: Optical Properties of Solids. Interaction of light with atoms. Insert Fig Allowed and forbidden electronic transitions Chapter 7: Optical Properties of Solids Interaction of light with atoms Insert Fig. 8.1 Allowed and forbidden electronic transitions 1 Insert Fig. 8.3 or equivalent Ti 3+ absorption: e g t 2g 2 Ruby Laser

More information

Engineering Medical Optics BME136/251 Winter 2017

Engineering Medical Optics BME136/251 Winter 2017 Engineering Medical Optics BME136/251 Winter 2017 Monday/Wednesday 2:00-3:20 p.m. Beckman Laser Institute Library, MSTB 214 (lab) Teaching Assistants (Office hours: Every Tuesday at 2pm outside of the

More information

A system of two lenses is achromatic when the separation between them is

A system of two lenses is achromatic when the separation between them is L e c t u r e 1 5 1 Eyepieces Single eye lens in a telescope / microscope produces spherical and chromatic aberrations. The field of view is also narrow. The eye lens is replaced by a system of lenses

More information

FIBER OPTICS. Prof. R.K. Shevgaonkar. Department of Electrical Engineering. Indian Institute of Technology, Bombay. Lecture: 12.

FIBER OPTICS. Prof. R.K. Shevgaonkar. Department of Electrical Engineering. Indian Institute of Technology, Bombay. Lecture: 12. FIBER OPTICS Prof. R.K. Shevgaonkar Department of Electrical Engineering Indian Institute of Technology, Bombay Lecture: 12 Optical Sources Fiber Optics, Prof. R.K. Shevgaonkar, Dept. of Electrical Engineering,

More information

Characterisation of vibrational modes of adsorbed species

Characterisation of vibrational modes of adsorbed species 17.7.5 Characterisation of vibrational modes of adsorbed species Infrared spectroscopy (IR) See Ch.10. Infrared vibrational spectra originate in transitions between discrete vibrational energy levels of

More information

Laser Diodes. Revised: 3/14/14 14: , Henry Zmuda Set 6a Laser Diodes 1

Laser Diodes. Revised: 3/14/14 14: , Henry Zmuda Set 6a Laser Diodes 1 Laser Diodes Revised: 3/14/14 14:03 2014, Henry Zmuda Set 6a Laser Diodes 1 Semiconductor Lasers The simplest laser of all. 2014, Henry Zmuda Set 6a Laser Diodes 2 Semiconductor Lasers 1. Homojunction

More information

Other Devices from p-n junctions

Other Devices from p-n junctions Memory (5/7 -- Glenn Alers) Other Devices from p-n junctions Electron to Photon conversion devices LEDs and SSL (5/5) Lasers (5/5) Solid State Lighting (5/5) Photon to electron conversion devices Photodectors

More information

Electromagnetic spectra

Electromagnetic spectra Properties of Light Waves, particles and EM spectrum Interaction with matter Absorption Reflection, refraction and scattering Polarization and diffraction Reading foci: pp 175-185, 191-199 not responsible

More information

Chapter 21 魏茂國. Materials Science and Engineering

Chapter 21 魏茂國. Materials Science and Engineering Chapter 21 ntroduction Electromagnetic radiation Light interactions with solids Atomic and electronic interactions Refraction Reflection Absorption Transmission Color Opacity and translucency in insulators

More information

Polarization of Light and Birefringence of Materials

Polarization of Light and Birefringence of Materials Polarization of Light and Birefringence of Materials Ajit Balagopal (Team Members Karunanand Ogirala, Hui Shen) ECE 614- PHOTONIC INFORMATION PROCESSING LABORATORY Abstract-- In this project, we study

More information

Chapter 4 Scintillation Detectors

Chapter 4 Scintillation Detectors Med Phys 4RA3, 4RB3/6R03 Radioisotopes and Radiation Methodology 4-1 4.1. Basic principle of the scintillator Chapter 4 Scintillation Detectors Scintillator Light sensor Ionizing radiation Light (visible,

More information

Quantum Electronics Laser Physics PS Theory of the Laser Oscillation

Quantum Electronics Laser Physics PS Theory of the Laser Oscillation Quantum Electronics Laser Physics PS407 6. Theory of the Laser Oscillation 1 I. Laser oscillator: Overview Laser is an optical oscillator. Resonant optical amplifier whose output is fed back into its input

More information

OPAC 101 Introduction to Optics

OPAC 101 Introduction to Optics OPAC 101 Introduction to Optics Topic 2 Light Sources Department of http://www1.gantep.edu.tr/~bingul/opac101 Optical & Acustical Engineering Gaziantep University Sep 2017 Sayfa 1 Light Sources: maybe

More information

Optics, Light and Lasers

Optics, Light and Lasers Dieter Meschede Optics, Light and Lasers The Practical Approach to Modern Aspects of Photonics and Laser Physics Second, Revised and Enlarged Edition BICENTENNIAL.... n 4 '':- t' 1 8 0 7 $W1LEY 2007 tri

More information

The Michelson Interferometer and the He-Ne Laser Physics 2150 Experiment No. 3 University of Colorado

The Michelson Interferometer and the He-Ne Laser Physics 2150 Experiment No. 3 University of Colorado Experiment 3 1 Introduction The Michelson Interferometer and the He-Ne Laser Physics 2150 Experiment No. 3 University of Colorado In the experiment, two different types of measurements will be made with

More information

Michelson Interferometer

Michelson Interferometer Michelson Interferometer Objective Determination of the wave length of the light of the helium-neon laser by means of Michelson interferometer subsectionprinciple and Task Light is made to produce interference

More information