1. 4-1 Chap. 7 (Optical Instruments), Chap. 8 (Optical Atomic Spectroscopy) General design of optical instruments Sources of radiation Selection of wavelength Sample containers Radiation Transducers Instruments Optical instruments fundamental methods §Absorption §Fluorescence §Phosphorescence §Scattering §Emission §Chemical Luminenscence

2. 4-2 Optical methods Similarities for differing methods over wavelength range §Stable source of radiation §Transparent sample holder §Isolation of region of interest §Radiation detector Transducer Signal processor Variations in setup depend upon detection of light §Linear for absorbance §90 degrees for fluorescence §Emission and chemiluminescence source and sample are same

3. 4-3 Apparatus

4. 4-4 Sources of radiation Materials §Transparent windows

5. 4-5 Sources of Radiation Continuum source §Emission over a large range §Intensity can vary with wavelength Line Source §Intense emission of discrete lines

6. 4-6 Light Sources

7. 4-7 Laser Sources Laser properties §light amplification by stimulated emission of radiation High intensity Narrow wavelength Coherent *Can very pulse energy, wavelength *Combined with laser system electronics for short lifetime measurements

8. 4-8 Laser Process

9. 4-9 Laser Process Pumping §Excitation of lasing material Crystal (ruby) Semiconducter (GaAs) Dye Gas (Ar) §Spontaneous Emission Emission of radiation in random direction §Stimulated Emission Excited laser species interact with emitted radiation *Deexcitation of excited species Photon emission energy same as spontaneous emitted photon Coherent emission

10. 4-10 Laser Dyes

11. 4-11 Population Inversion and Amplification Need to highly populate excited state

12. 4-12 Three and four level transitions Excitation to high state, transition to metastable state

13. 4-13 Absorption and fluorescence process of Cm 3 + Optical Spectra HGFHGF 7/2A Z Fluorescence Process Excitation Emissionless Relaxation Fluorescence Emission

14. 4-14

15. 4-15 Wavelength Selectors Quality of selected wavelength based on full with at half maximum

16. 4-16 Filters Absorption filter §Visible region §Colored glass or dye act as the filter

17. 4-17 Filters Interference filters §Combination of constructive and destructive interference §Filter wavelength based on properties of filter Dielectric layer determines wavelength

18. 4-18 Filters Constructive interference equations  n = 2dsin    90°, sin  1  n = 2d  air = glass ×    = refractive index  n is order of interference

19. 4-19 Monochromators Allow selection of specific wavelengths over a scanned range §IR, Visible, Ultraviolet Similar components §Entrance slit Rectangular optical image §Collimating lens Parallel beam of radiation §Prism or grating Selection of wavelength §Focus element Reforms image and places on focal plan §Exit slit Isolates desired wavelength

20. 4-20 Monochromators Grating are more common in modern equipment Linear dispersion= variation in along plane AB D=Fdr/d, F= focal length D -1 =d/nF=  [nm/mm]

21. 4-21 Monochromator Can calculate §i is incident §r is reflection i is known d is from grating in nm §i.e., 2000 lines/mm needs to be converted to nm/line n is generally 1 Angle r must be defined to find

22. 4-22 Monochromator Slit Parameter that can be set Controls light input Resolution can be affected by slit width §Wavelength to be examined is considered §Wider slits less resolution but may have better signal

23. 4-23 Monochromator Slit Can calculate slit width based on experimental consideration §Resolution difference of wavelength to be examined Theoretical calculation §Actually need narrower slit width due to imperfections

24. 4-24 Radiation Transducers Photon Transducers §Photovoltaic cells §Phototubes e - emission from phosphor §Photomultiplier Cascade of electrons §Photoconductors §Photodiodes §Charge-transfer Si crystal collects charge due to absorption

25. 4-25 Phototube and Photomultiplier 10 5 -10 7 electrons/photon

26. 4-26 Optical Atomic Spectroscopy Atomization Methods Sample Introduction Optical Spectroscopy §Elements converted to gaseous atoms or ions §Measurements of atomic species Fluorescence UV-Visible absorption Emission Calculations can be made based on electron energy diagrams §Transition between states

27. 4-27 Na and Mg energy levels

28. 4-28 Electronic Energy Symbols 2S+1 L J S is spin from unpaired e - §+ ½ §L is written as S, P, D §J=L+S Li= 1s 2 2s 1 §L=0, S =+ ½ § 2 S 1/2

29. 4-29 Atomic Emission Spectra Excitation of electrons §Short lived §Relaxation to ground state Emission of photon *Visible range *Possible multiple lines Absorption spectroscopy §Resonance due to transitions from ground to excited state Fluorescence can also occur

30. 4-30 Atomic Line Widths Broadening due to differing effects §Uncertainty  v  t Line width due to Hg with lifetime of 2E-8s at 253.7 nm

31. 4-31 Line Widths Doppler §Atom moves during radiation interaction

32. 4-32 Thermal effects Boltzmann equation Calculate Na atoms in 3p excited states to ground as 2500 K 3s to 3p transition is 3.37E-19J P based on quantum states §3s has 2, 3p has 6

33. 4-33

34. 4-34