1. Photoacoustic Spectroscopy of the Oxygen A-band
PAS Signal (mV/W)
Wavenumber (cm-1)
Elizabeth M. Lunny1, Thinh Q. Bui1, Caitlin K. Bray2, Priyanka Milinda Rupasinghe1, Brian J. Drouin3, Mitchio Okumura1
1 Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA
2 Department of Chemistry, Wesleyan University, Middletown, CT
3 Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA

2. OCO-2
GOAL: to understand the nature, geographic distribution and temporal variability of CO2 sources and sinks through space-based remote sensing of atmospheric CO2
Equipped with 3 spectrometers to simultaneously measure reflected sunlight at:
0.76 μm-O2 A-band
1.61 μm-CO2 weak band
2.06 μm-CO2 strong band
Measures CO2/O2 ratio to retrieve column integrated CO2 dry air mole fraction, χCO2
GOAL: 0.25% (1 ppm) precision in χCO2
----- Meeting Notes (6/4/15 10:23) -----
line mixing, real oco spectrum,

3. Oxygen A-band Advantages Uniform, well-known mixing ratio
Spectral isolation
Triply forbidden by electric dipole
selection rules
Magnetic Dipole Allowed
ΔJ=0,±1
b1Σg+
X3Σg-
PAS Signal (mV/W)
Wavenumber (cm-1)

4. OCO-2 Spectra O2 A-band (0.76 μm) CO2 weak band (1.61 μm)
CO2 strong band
(2.06 μm)
Crisp, OCO-2’s first light spectra (2014)

5. A-band Residuals ABSCO telecon Sept 22, 2014
slide with fs-crds, FTS, lots of previous works, motivate pas with separate slide, line shapes, show single line-thinh's stuff pressure dependence
ABSCO telecon Sept 22, 2014

6. A-band Residuals
slide with fs-crds, FTS, lots of previous works, motivate pas with separate slide, line shapes, show single line-thinh's stuff pressure dependence
Similarities in OCO-2 and GOSAT residuals suggest unsatisfactory spectroscopic model rather than instrumental errors
ABSCO telecon Sept 22, 2014

7. Line Mixing and Collision Induced Absorption
----- Meeting Notes (6/4/15 10:23) -----
slide with fs-crds, FTS, lots of previous works, motivate pas with separate slide, line shapes, show single line-thinh's stuff pressure dependence
Hartman, Boulet, Robert Collisional effects on molecular spectra (2008)

8. Line Mixing and Collision Induced Absorption
Results from a transient dipole induced during collisions at sufficiently high gas densities
broad weak absorption underlying the entire band
----- Meeting Notes (6/4/15 10:23) -----
slide with fs-crds, FTS, lots of previous works, motivate pas with separate slide, line shapes, show single line-thinh's stuff pressure dependence
Hartman, Boulet, Robert Collisional effects on molecular spectra (2008)
Long and Hodges, J. Geophys. Res., 111, D12309 (2012)

9. Multispectrum Fitting Approach
Advantages
Disadvantages
FTS
Capable of high pressures
Relatively fast acquisition time
Instrumental background
PAS
Large dynamic range
Zero-background
Difficulty in quantifying intensity axis
Long acquisition times
FS-CRDS
Long optical pathlength
Precise frequency axis
Absolute intensities
Limited dynamic range
Increasing S/N
----- Meeting Notes (6/4/15 10:23) -----
add another figure to explain more, pressure wave ect., but bottom stuff on separate slide, intermediate region, add designed for gillis, havey hodges

10. Multispectrum Fitting Approach
Advantages
Disadvantages
FTS
Capable of high pressures
Relatively fast acquisition time
Instrumental background
PAS
Large dynamic range
Zero-background
Difficulty in quantifying intensity axis
Long acquisition times
FS-CRDS
Long optical pathlength
Precise frequency axis
Absolute intensities
Limited dynamic range
Increasing S/N
----- Meeting Notes (6/4/15 10:23) -----
add another figure to explain more, pressure wave ect., but bottom stuff on separate slide, intermediate region, add designed for gillis, havey hodges
Brian Drouin RF02

11. Photoacoustic Spectrometer
----- Meeting Notes (6/4/15 10:23) -----
add another figure to explain more, pressure wave ect., but bottom stuff on separate slide, intermediate region, add designed for gillis, havey hodges
Gillis, Havey, Hodges, Rev. Sci. Instrum. 81, (2010)

12. Photoacoustic Spectrometer
----- Meeting Notes (6/4/15 10:23) -----
add another figure to explain more, pressure wave ect., but bottom stuff on separate slide, intermediate region, add designed for gillis, havey hodges
1% to wavemeter, 99% to tapered amplifier
Gillis, Havey, Hodges, Rev. Sci. Instrum. 81, (2010)

13. Photoacoustic Spectrometer
----- Meeting Notes (6/4/15 10:23) -----
add another figure to explain more, pressure wave ect., but bottom stuff on separate slide, intermediate region, add designed for gillis, havey hodges
AOM for intensity modulation at acoustic frequency of the resonator
Gillis, Havey, Hodges, Rev. Sci. Instrum. 81, (2010)

14. Photoacoustic Spectrometer
----- Meeting Notes (6/4/15 10:23) -----
add another figure to explain more, pressure wave ect., but bottom stuff on separate slide, intermediate region, add designed for gillis, havey hodges
AOM for intensity modulation at acoustic frequency of the resonator
Gillis, Havey, Hodges, Rev. Sci. Instrum. 81, (2010)

15. Photoacoustic Spectrometer
----- Meeting Notes (6/4/15 10:23) -----
add another figure to explain more, pressure wave ect., but bottom stuff on separate slide, intermediate region, add designed for gillis, havey hodges
Gillis, Havey, Hodges, Rev. Sci. Instrum. 81, (2010)

16. Photoacoustic Spectrometer
----- Meeting Notes (6/4/15 10:23) -----
add another figure to explain more, pressure wave ect., but bottom stuff on separate slide, intermediate region, add designed for gillis, havey hodges
Non-radiative
de-excitation
Energy is released in translational modes
Heat dissipation creates pressure wave
Optical
Excitation
Gillis, Havey, Hodges, Rev. Sci. Instrum. 81, (2010)

17. Photoacoustic Spectrometer
----- Meeting Notes (6/4/15 10:23) -----
add another figure to explain more, pressure wave ect., but bottom stuff on separate slide, intermediate region, add designed for gillis, havey hodges
Non-radiative
de-excitation
Energy is released in translational modes
Heat dissipation creates pressure wave
Optical
Excitation
Gillis, Havey, Hodges, Rev. Sci. Instrum. 81, (2010)

18. Photoacoustic Spectrometer
----- Meeting Notes (6/4/15 10:23) -----
add another figure to explain more, pressure wave ect., but bottom stuff on separate slide, intermediate region, add designed for gillis, havey hodges
Microphone signal is detected by lock-in and normalized to transmitted power measurement
Gillis, Havey, Hodges, Rev. Sci. Instrum. 81, (2010)

19. PAS A-band spectra

20. PAS A-band spectra

21. PAS A-band spectra

22. PAS A-band spectra
mention dicke narrowing ect. elaborate more on basics

23. Multispectrum Fits

24. Multispectrum Fits

25. Multispectrum Fits

26. Multispectrum Fits
Line mixing

27. Multispectrum Fits

28. Multispectrum Fits
Line mixing

29. Multispectrum Fits

30. Multispectrum Fits
First order, nearest neighbor line mixing is not sufficient

31. Acknowledgements