OPAC 101 Introduction to Optics

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1 OPAC 101 Introduction to Optics Topic 2 Light Sources Department of Optical & Acustical Engineering Gaziantep University Sep 2017 Sayfa 1

2 Light Sources: maybe natural or artificial Sunlight, skylight Fire Incandecent sources Blackbody sources Tungsten flament Discharge lamps (Gas Filled Tubes) Monochromatic and spectral sources High-intensity sources Semiconductor light-emitting diodes (LEDs) Coherent source (laser) Sayfa 2

3 Day Light: combination of sunlight and skylight Sayfa 3

4 Sun Wavelength distribution measured in our laboratory Sayfa 4

5 Tungsten Bulb Tungsten Halogen Lamb is an incandescent (=akkor) lamp that has a small amount of a halogen such as iodine or bromine added. Sayfa 5

6 Tungsten Bulb Typical wavelength distribution as a function of temperature: Sayfa 6

7 Tungsten Bulb Wavelength distribution measured in our laboratory Sayfa 7

8 Flame Wavelength distribution measured in our laboratory Sayfa 8

9 Discharge Lamps(Gas Filled Tubes) Gas-discharge lamps are a family of artificial light sources that generate light by sending an electric discharge through an ionized gas, a plasma. Typically, such lamps use a noble gas (argon, neon, krypton, and xenon) or a mixture of these gases. Each gas, depending on its atomic structure, emits certain wavelengths. The emission spectrum determines the color of the light from the lamp. Sayfa 9

10 Discharge Lamps (Gas Filled Tubes) Sayfa 10

11 Some Wavelength distributions measured in our laboratory Sayfa 11

12 LED A light-emitting diode (LED) is a semiconductor light source. Circuit Symbol: A LED can produce the visible, ultraviolet and infrared wavelengths, with very high brightness. Sayfa 12

13 Wavelength distributions of some colored LEDs measured in our laboratory. Sayfa 13

14 Wavelength distribution of a white LED measured in our laboratory. Sayfa 14

LEDs in ILLUMINATION Admittedly, illumination is one of the main requirements of people.

15 LEDs in ILLUMINATION Admittedly, illumination is one of the main requirements of people. LED (Light Emitting Diode) is an energy-saving light source providing high light efficiency and long life time. Nowadays, many cities across North America, China and Europe start to prefer LED for internal/external/street illumination. In Türkiye, both government politics and companies working many years on the illumination sector foresee that all illumination systems are going to be based on LEDs in the near future. Long Distance Illumination LED Projector Sayfa 15

16 LASER Laser" stands for Light Amplification by Stimulated Emission of Radiation A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. A Laser is coherent, monochromatic and collimated light. A Laser light can be * visible * infrared * ultraviolet * X-ray Sayfa 16

17 Laser is highly collimated --> beam divergence ~ mrad (milli-radians) Properties of an example laser pointer (GLP-III-594) Sayfa 17

18 EXAMLPE Consider laser pointer whose aperture diameter is D = 1.5 mm and beam divergence is Δθ = 1.5 mrad (=0.086 o ). What is the diameter of the laser spot on a screen at a distance L = 100 m away from the pointer? SOLUTION Δθ/2 L D D From figure: tan( / 2) D' / 2 L D 2L tan( / 2) (2)(100 m) tan(0.086 o / 2) 0.15 m 15 cm Sayfa 18

19 LED vs Laser Comparison of Beam Divergence of LED and Laser Sayfa 19

20 LED vs Laser blue green red Spectral width of the laser is 10,000 times narrower than the spectral width of a light-emitting diode. LED Helium-Neon laser spectrum Sayfa 20

Unprotected Human Eye is extremely sensitive to laser radiation and

21 Laser Radiation Lasers can cause damage in biological tissues, both to the eye and to the skin. Unprotected Human Eye is extremely sensitive to laser radiation and can be permanently damaged from direct or reflected beams. High power lasers can also burn the skin. Sayfa 21

The red glow that you see consists of photons with energies in the visible red

22 Blackbody Radiation If you turn on an electric stove, the stove plate heats up until it becomes red or orange hot. The red glow that you see consists of photons with energies in the visible red range. When the stove plate was cold, it also emitted photons, but those were of too low energy to be seen by our eyes. Sayfa 22

23 All objects radiate energy continuously in the form of electromagnetic waves produced by thermal vibrations of the molecules. The characteristics of this radiation depend on the temperature and properties of the object s surface. Every second, approximately 1370 J of electromagnetic radiation from the Sun passes perpendicularly through each 1 m 2 at the top of the Earth s atmosphere. Sayfa 23

24 BlackBody: ideal absorber & ideal emitter Hot objects emits thermal radiation. From a classical viewpoint, thermal radiation originates from accelerated charged particles in the atoms near the surface of the object; Blackbody is an ideal system that absorbs all radiation incident on it. The electromagnetic radiation emitted by the black body is called blackbody radiation. Sayfa 24

25 Blackbody Spectrum When a black body heated a distribution of wavelength is observed. The distribution was perfectly explanined by M. Planck (1900). Sayfa 25

26 Blackbody Spectrum Intensity of blackbody radiation versus wavelength at three temperatures. The amount of radiation emitted (the area under a curve) increases with increasing temperature. Sayfa 26

27 BlackBody: spectrum Intensity of blackbody radiation versus wavelength and temperatures. max T m K λ max = peak position T = surface temperature Sayfa 27

28 BlackBody max T m K Sayfa 28

29 Example Can you estimate the surface temperature of Sun? (See distibution on page 3) max T m K Sayfa 29

What are the six common sources of light?

What are the six common sources of light? Common light sources include incandescent, fluorescent, laser, neon, tungsten-halogen, and sodium-vapor bulbs. Objects that give off their own light are luminous.