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 Einstein s coefficients Relation between Einstein s coefficients Condition for lasing Basic working of laser Components of laser Types of laser Laser system Applications
The acronym LASER stands Light Amplification by Stimulated Emission of Radiation
Characteristics of LASERs Monochromatic Coherent Directional Highly intense beam
E 2 E 2 E 2 hu hu hu In hu Out hu E 1 E 1 E 1 (a) Absorption (b) Spontaneous emission (c) Stimulated emission Absorption, spontaneous (random photon) emission and stimulated emission. E1 - Lower energy state E2- Higher energy state
Einstein s coefficient A 21 = "coefficient of spontaneous emission" A 21 Spontaneous emission = n 2 A 21 B 12 = "coefficient of absorption" Adsorption = n 1 B 12 J ν0 B 12 B 21 = "coefficient of induced emissions" B 21 Stimulated emission = n 2 B 21 J ν0
Relation between Einstein s coefficient J v0 = 2ħv0 3 c 3 e ( hv0 kt ) 1 By comparing equations
Population Inversion When no. of atoms per unit volume in higher energy state becomes greater than that of no. of atoms per unit volume in lower energy state, this condition is called Population inversion. This sets stimulated emission and emits identical photons as of incident photon. Threshold Condition For Lasing
Basic working of LASERs
Components of LASER
Types of LASER On the basis of medium there are different types of Lasers: Solid Lasers Liquid Lasers Gases Lasers Semiconductor Lasers.
Beam Generation Unit
Beam delivering unit Mirrors Beam splitters Focusing lens Fiber optic coupling
Applications:
Ruby Laser
Nd:YAG Laser
He-Ne Laser
Semiconductor laser-construction Active Medium: Heavily doped Semiconductor material such as GaAs, InP, etc. Optical Resonator: By cleaving two ends (110) optical resonator is obtained Due to refractive indices difference between material and air ideally R=33%. It is increased by coating both end with suitable materials such as Al2O3, TiO2 etc. Excitation Source : Current is pumping source.
Working When p-n junction is forward bias, depletion region is reduced and hence causing diffusion of electrons and holes further and recombination of these majority carrier takes place which leads to emission of light. E c p + Inversion region n + E c E F C E g ev E F V V
Optical fiber
What are Fiber Optics? Optical fibers are long, thin strands of pure glass or plastic about the diameter of a human hair. They are designed to transmit light signals over long distances with less signal loss. Based on total internal reflection.
Structure of Optical fiber Core Quartz Region through which light passes. Cladding Coaxial middle region surrounding the core. Provide confinement of light within the core. n cladding < n core Jacket Outer most region made with polymer. Protects core and cladding from abrasions, contamination, moisture. Provide mechanical strength.
Types of Optical Fibre 7.51
Losses Losses due to material defects Surface scattering Bending loss Splice
Merits of Fiber Optics
Demerits/limitations of Fiber Optics Costly maintenance and installation. Splicing and connecting is more delicate: Optical fiber can not be join together as easily as copper cable. It requires training and expensive splicing and measurement equipment.
Fiber optic splicing and connectors A splice is a permanent connection A connector is removable
Optical Couplers and Switches Power splitters - categorized : As star couples with multiple inputs and outputs As tees, which have one input and two outputs
Optical fiber sensors A fiber optic sensor is a sensing device that uses fiber optic technology for measuring physical quantities such as temperature, pressure, strain, voltages and acceleration. In particular, it uses an optical fiber as the sensing element, called an intrinsic sensor, or uses it to transport signals from the remote sensor to the signal processing module (extrinsic sensor). It can do sensing by measuring : Wavelength shift Time delay
Applications of optical fibers Communication - Telephone transmission method uses fibre-optic cables. Optical fibres transmit energy in the form of light pulses. Medical uses - Optical fibres are well suited for medical use. They can be made in extremely thin, flexible strands for insertion into the blood vessels, lungs, and other hollow parts of the body. Optical fibres are used in a number of instruments that enable doctors to view internal body parts without having to perform surgery. Simple uses - The simplest application of optical fibres is the transmission of light to locations otherwise hard to reach. Military Weight of aircraft are reduced.
In Industry Drilling Holes Welding Cutting (i) (ii) (iii)
In Every Day Life Bar Code Reader Hologram
In medicine Dental Treatment Treatment Of Kidney Stones Treatment Of Cancers etc