2-2. 2. Radiation source ( 광원 ) 1
a) Continuous wave(cw) sources ( 지속광원 : 띠파장 ) UV : D2 lamp, High pressure - Arc lamps (Ar, Xe, Hg) Vis : tungsten lamp (Halogen lamp) IR : Inert solid 1500~2000K eg.) Nernst glower, nichrome wire b) Line sources : nearly monochromatic light ( 선광원 : 선파장 ) eg.) Hollow Cathode lamp (for AA) Na-D line 589nm c) Lasers ( 레이져 ) 2
LASER (Light Amplification by Stimulated Emission of Radiation) high intensity, narrow band width, coherent nature, high resolution spectroscopy, life time (10-9, 10-12 ) Components of laser Lasing medium ( 레이저발생매체 ) Solid crystal (Ruby), Semiconductor (GaAs), Ar ion, Kr, He-Ne, CO 2, N 2 etc(gas), Organic Dye 3
Mechanism of Laser action a) pumping b) spontaneous emission (fluorescence) 4
c) stimulated emission d) absorption 5
Figure 7-6 6
Laser source - Semiconductor Diode Lasers conductor, semiconductor, insulator, LED(light emitting diodes) 7
- Solid State Lasers three level device : ruby crystal (Al 2 O 3 +0.05% Cr(Ⅲ) ) 694.3nm, 길이 4cm, 지름 0.5cm Nd YAG : neodymiunion yttrium aluminum garnet four level : population inversion이쉽다. 1064nm 532nm - Gas Laser : He-Ne ( 값이싸다, 632.8nm) ArF +, KrF +, XeF + (eximer laser) UV (193nm, 248nm, 351nm) CO 2 (900~1100cm -1 ) - IR, N 2 (337.1nm), Ar+, Kr+ (ion laser) - Vis( 선스펙트럼 ) (514.5nm, 488nm) - Dye Laser 20~50nm, solution of organic compounds (UV/Vis/IR), four-level systems 8
- Nonlinear optical effects with Lasers 9
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2-3. Wavelength Selectors 11
the sensitivity of absorbance A narrow bandwidth 파장의범위좁고연속적인복사선, 충분한세기 band : narrow, continuous, 파장선택기구단일파장 - 이상적 effective bandwidth : 파장이좁고넓음을측정하는척도 12
a) Filter - interference filter (Fabry-Perot filter) : UV, Vis, IR 13
interference filter 의이용 UV Vis IR 일반적인 effective bandwidth ( 유효띠나비 ) 14
- absorption filter less expensive, widely used in visible region colored glass : thermal stability dye suspended in gelatin and sandwiched between glass plates effective bandwidth : 30~250nm transmittance : 10% cut off filter - transmittance 100%, absorption 0% 15
b) Monochromators = scanning a spectrum slits, lenses, mirrors, window, prisms, grating, UV, Vis, IR ⑴ an entrance slit ⑵ a collimating lens or mirror ⑶ a prism or grating ⑷ a focusing element, focal plane ⑸ an exit slit - Grating Monochromators 16
concave grating : 에너지소비가적고빛살통과량이증가 holographic grating : 레이저로홈을판것, 6000선 /mm 별도의초점과렌즈가불필요, 완벽하게할수있다. echelle grating : 홈의밀도가낮다. 250/mm 17
- Prism Monochromators Monochromator Performance (quality factors) Spectral purity: contaminated ( 차폐장치, 검은색테이프, 먼지 증기방어 ) 18
Dispersion of grating 19
Resolving Power (for two lights) - 인접파장의상을분리하는능력 Light gathering power 20
Slits 일반적으로입구슬릿과출구슬릿은같다. 21
Effect of slit width on Resolution 22
2-4. Sample containers 23
cells, cuvettes Radiation을잘통과시켜야함 quartz or fused silica (H 2 SiO 3 ) 2 3-350nm 이하 ( 자외선영역 ) silicate glass - 350 ~ 2000 nm crystalline sodium chloride : IR Plastic : 가시선영역 24
2-5. Radiation detector 25
- Ideal detectors S = kp S : signal p : light power but most cases S = kp + k d k : Calibration const. k d : dark current sig - Types of radiation detectors a) photon detector (photoelectric detector, quantum detector) UV, Vis, near IR radiation photo conduction λ>3mm (dry ice or nitrogen으로냉각 ) b) thermal detector (heat detector) IR radiation ( 냉각 ) 26
Photon detector a) photovoltaic cell ( 광전압전지 ) b) vacuum phototube ( 진공광전관 ) c) photomultiplier tubes ( 광전증배관 ) d) photo conductivity detectors ( 광전도검출기 ) e) silicon photodiode ( 규소다이오드검출기 ) 27
- Photovoltaic cell ( 광전압전지 ) : visible region 550nm : maximum sensitivity 350~750nm : 10% of the maximum sensitivity 장점 : 단단하고값이싸다. 외부전원이필요하지않다. 단점 : 센복사선만을쉽게측정. 계속사용하면전류출력이감소하는피로현상을나타냄. 이용 : 가지고다닐수있는간단한기기에이용. 28
- Vacuum phototubes ( 진공광전관 ) 광전방출면에서방출하는전자수는표면에부딪히는복사선세기에정비례. 고감도용 (highly sensitive) : bialkali type (K, Cs, Sb) red sensitive ( 적색감응층 ) : multialkali type (Na/K/Cs/Sb) or Ag/O/Cs ultraviolet sensitive ( 자외선감응층 ) : 모든종류 flat response ( 평판 ) : Ga/As 29
- Photomultiplier tubes ( 광전증배관 ) : for low radiant power a) highly sensitive to ultraviolet and visible radiation b) extremely fast time responses dark current 에서제한, 약한복사선측정에이용 30
- Photo conductivity detectors ( 광전도검출기 ) 0.75~3 μm : 근적외선영역검출에가장예민복사선흡수 전기저항감소하는반도체를이용 FT-IR 에많이사용 ( 저온에서사용하면 noise 감소 ) PbS : 0.8~2 μm영역의복사선, 실온가능 ( 금속광자물 : Pb, Cd, In, Ga) - Silicon photodiode detectors : 190~1100nm 에사용 31
- Multichannel photo detectors : linear photodiode array - vidicon : image sensing vacuum tube 광전증배관의성능에못미침. 이를능가하는장점이있을경우를 제외하고는사용하지않는다. charge transfer device 32
Fourier transformation 33
Fourier transformation 34
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