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Components of Optical Instruments

Chapter 7. Chapter 7. Chapter 7. Chapter 7. Chapter 7. Chapter 7. Chapter 7. Chapter 7. Chapter 7. Chapter 7. Chapter 7. Chapter 7. Chapter 7. Chapter 7. Chapter 7. Chapter 7. Chapter 7. Chapter 7. Chapter 7. Chapter 7. Chapter 7. Chapter 7. Chapter 7. Chapter 7. Chapter 7.

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Components of Optical Instruments

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  1. Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Components of Optical Instruments Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7 Chapter 7

  2. Optical Instruments اجزاء دستگاههای نوری six phenomena: 1-absorption 2-emission 3-fluorescence 4-phosphorescence 5-scattering 6-chemiluminescence Five components: 1-stable source 2-sample holder 3-wavelength selector 4-detector 5-signal processor and readout

  3. 8888 l Components of optical instruments 1. Absorption 2. Fluorescence and phosphorescence 3. Emission and chemiluminescence Source Wavelength Selector Sample Detector Readout Rgb back 146,184. 148

  4. Construction Materials for Spectroscopic Instruments Wavelength 100 180 380 850 20001800040000 Region VUV UVVisible Near IR IR Far IR LiF Fused silica or quartz Materials for cells, windows, lenses and prisms Corex glass Silica glass NaCl KBr TlBr or TlI ZnSe

  5. Sources for Spectroscopic Instruments Wavelength 100 180 380 850 2000 18000 40000 Region VAC UV Visible Near IR IRFar IR Ar lamp Sources Continous Line Xe lamp H2 or D2 lamp Tungtstan lamp Nernst glower ZnO2+Y2O3 Nichrome wire Glowbar SiC Hollow cathode lamp Lasers

  6. Wavelength Selectors for Spectroscopic Instruments Wavelength 100 180 380 850 20001800040000 Region VAC UVVisible Near IR IR Far IR Fluorite prism Wavelength selectors Continous Dis-continous Fused silica or quartz prism Glass prism NaCl prism KBr prism 3000 lines/mm Grating 50 lines/mm Interference wedge Interference filter Glass filter

  7. Detectors for Spectroscopic Instruments Wavelength 100 180 380 850 2000 18000 40000 Region VAC UV Visible Near IR IRFar IR Photographic plates Detectors Photo- electric Thermal Photomultiplier tube Photo tubes Photo cells Photo diodes Charge coupled devices Photo conductors Thermocouples or bolometers Golay pneumatic cell Pyroelectric cell

  8. Light Amplification by Stimulated Emission of RadiationLASER • Characteristics of a laser: • Spatially narrow and intense • Highly monochromatic • Coherence

  9. Schematic of a Laser Source Nonparallel radiation Active lasing medium Laser radiation Mirror Partially transmitting mirror Radiation Pumping source Power supply

  10. Laser 1-pumping 2-Spontaneous emission 3-Stimulated emission 4-Absorption

  11. Processes in Laser Action 1- Pumping Excitation by electrical, radiant or chemical energy 1- Pumping 2- Spontaneous emission 1- Pumping 2- Spontaneous emission 3-Stimulated emission 1- Pumping 2- Spontaneous emission 3- Stimulated emission 4-Absorption Ey’’’ Ey’’ Ey’ Ey Ex Metastable Excited state

  12. Processes in Laser Action 1- Pumping Excitation by electrical, radiant or chemical energy 1- Pumping 2- Spontaneous emission 1- Pumping 2- Spontaneous emission 3-Stimulated emission 1- Pumping 2- Spontaneous emission 3- Stimulated emission 4-Absorption Ey’’’ Ey’’ Ey’ Ey Ex Metastable Excited state

  13. Light attenuation by absorption Noninverted population Light amplification by stimulated emission Inverted population

  14. E1 E1 Ey Ey Ex E0 E0 Three level system Four level system

  15. 1-solid state laser 2-Gas laser -neutral atom laser -ion laser -molecular laser -excimer laser 3-Dye laser 4-Semiconductor diode laser

  16. Conduction band Conduction band Conduction band Valence band Valence band Valence band Conductor Semiconductor Insulator

  17. p-metal Emitted radiation 3mm strip width n- type GaAs substrate n-metal Fig. 7.9

  18. 974 nm laser 450 nm laser Nonlinear crystal Blue-green output Laser diode

  19. Wavelength Selectors • Filters • Interference • Absorption • Gratings • Prisms

  20. Effective Bandwidth of Filters 100 Interference Filter 80 60 Effective bandwidth=10nm Percent Transmittance 40 Absorption Filter Effective bandwidth= 50nm 20 0 40 450 500 550

  21. Coupling of Filters 100 Orange cut-off filter Green filter 50 Combination of two filters Percent Transmittance 0 400 500 600 700 Wavelength nm

  22. Interference Filters Glass plate Metal film Dielectric layer Metal film Glass plate

  23. Interference Filters q Metal film t Dielectric layer Metal film • Condition for reinforcement nl’ =2t/cos q • If q < 10onl’ =2t • = l’h l = 2th/n

  24. Wedge Type Interference Filters Glass plate Metal film Dielectric layer Metal film Glass plate l1 l2

  25. Interference wedge

  26. Transmission Characteristic of Interference Filters Effective bandwidth= 45 A 100 80 Effective bandwidth= 45 A 60 Effective bandwidth= 15 A Percent Transmittance Effective bandwidth 40 1/2 Peak height 20 0 5090 5110 6215 6225 6940 6960 Wavelength

  27. Dispersion by a Prism a r i Mirror r b Quartz cornu Littrow

  28. Bunsen Prism Monochromator Entrance slit Focal plane l1 Exit slit Collimating lens l2 Focusing lens Prism

  29. Czerny Turner Grating Monochromator Concave mirrors Reflection grating l1 l2 Entrance slit Focal plane Exit slit

  30. Detector Source Diffracted beams at refelected angle r Monochromatic beams at incident angle i d* sin i + d sin r = l r n=1 d*sin i i d*sin r d

  31. Detector Diffracted beams at refelected angle r Source d*sin r d*sin i d* sin i + d *sin r = 1.5 * l Monochromatic beams at incident angle i r d*sin i i d*sin r d

  32. Performance Characteristics of a Grating Monochromator l + l1 l Exit slit

  33. Dispersion of Monochromators 200 300 400 500 600 700 800 nm Grating 200 350 400 450 500 600 800 nm Glass prism 200 250 300 350 400 500 800 nm Quartz prism cm 0 5 10 15 20 25 Distance along focal plane

  34. Performance Characteristics of a Grating Monochromator

  35. Echelle Monochromator i r = i = b = 63o26’ r

  36. Wavelength, nm Diffraction order, n Echelle grating 30 Degree prism 260 240 220 108 300 280 260 98 340 320 300 280 Prism dispersion Diffraction order, n 88 400 380 360 340 320 78 500 480 420 460 440 68 620 600 580 560 540 520 500 58 48 760 720 680 800 740 700 660 640 480 Wavelength, nm Grating dispersion

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