1. Johannes ORPHAL, Pascale CHELIN, Nofal IBRAHIM, and Pierre-Marie FLAUD
DIODE- AND DIFFERENCE-FREQUENCY LASER STUDIES OF ATMOSPHERIC MOLECULES IN THE NEAR- AND MID-INFRARED: H2O, NH3, and NO2
Johannes ORPHAL, Pascale CHELIN, Nofal IBRAHIM, and Pierre-Marie FLAUD
Laboratoire Interuniversitaire des Systèmes Atmosphériques Université de Paris-12, Créteil, France

2. Quantitative Spectroscopy Using IR Lasers
Tunable diode-lasers are available in the near-infrared region: 0.7 – 2.0 mm (optical telecommunication)
Extremely useful for quantitative spectroscopy of atmospheric molecules (many studies in the last 5 years)
Very high-resolution (less than cm-1) with external cavities
Many photons (at least a few mW) on output
High signal/noise ratio (a few 1000) in short measurement time
Single wavelength, tunable over several 10 nms (a few 100 cm-1)
A laser based on difference-frequency generation can “transport” these properties into the mid-infrared (3 – 5 mm)
This talk: applications to H2O, NH3, NO2
Quantitative Spectroscopy Using Diode- and DFG Lasers in the IR
9th International HITRAN Conference, Cambridge, June 26, 2006

3. External Cavity Diode-Lasers
Toptica DL-100 (“Littrow” configuration)
grating forms part of the cavity
linewidth 1 MHz ( cm-1)
output power up to 30 mW
spectral range: 810 – 880 nm (11360 – cm-1) – 1565 nm (6390 – 6515 cm-1)
tunable range (single mode) at least GHz ( cm-1)
relatively small beam divergence
Quantitative Spectroscopy Using Diode- and DFG Lasers in the IR
9th International HITRAN Conference, Cambridge, June 26, 2006

4. External Cavity Diode-Lasers
H2O absorption line around 830 nm
Quantitative Spectroscopy Using Diode- and DFG Lasers in the IR
9th International HITRAN Conference, Cambridge, June 26, 2006

5. White-type absorption cell
L = 1 m, maximum path length 100 m, CaF2 windows
3 MKS Baratrons
Water sample
Thermometer
Quantitative Spectroscopy Using Diode- and DFG Lasers in the IR
9th International HITRAN Conference, Cambridge, June 26, 2006

6. 9th International HITRAN Conference, Cambridge, June 26, 2006
The H2O band around 822 nm
Quantitative Spectroscopy Using Diode- and DFG Lasers in the IR
9th International HITRAN Conference, Cambridge, June 26, 2006

7. Example: line intensities (S1023/cm molecule-1)
Previous measurements of H2O around 822 nm
R. A. Toth, J. Mol. Spectrosc., 166, (1994)
J.-M. Flaud et al., J. Mol. Spectrosc., 185, (1997)
P. L. Ponsardin et al., J. Mol. Spectrosc., 185, (1997)
A. Lucchesini et al., Eur. Phys. J. D., 8, (2000)
R. Schermaul et al, J. Mol. Spectrosc. 208, (2001)
A. Ray et al., Appl. Phys. B, 79, (2004)
Example: line intensities (S1023/cm molecule-1)
position (cm-1)
HITRAN04
Ponsardin
Schermaul
Ray
1.679
---
1.960
1.504
1.865
2.185
2.290
1.888
3.236
3.81
5.080
0.888
1.08
! Differences between different authors exceed stated accuracy (up to 30%)
 need for more measurements
Quantitative Spectroscopy Using Diode- and DFG Lasers in the IR
9th International HITRAN Conference, Cambridge, June 26, 2006

8. Experimental Precautions
H2O samples: distilled, cleaned by ultrasonic procedure
Calibrating the MKS Baratron heads
Validation of detector linearity using neutral density filters
Linearization of the wavenumber axis: FP etalon (1 MHz)
Simultaneous recording of HDO lines (in the mid-IR using a DFG laser) to validate H2O pressure values (assumption: natural HDO abundance); result: less than 2 % deviations
Background emission of the ECDL  narrow spectral filter
Validate analysis software with synthetic lines
Quantitative Spectroscopy Using Diode- and DFG Lasers in the IR
9th International HITRAN Conference, Cambridge, June 26, 2006

9. Results from LISA
Example 1: Self-broadening of the line at cm-1
10
10
High S/N ratio( >1000)
Experimental lines well reproduced using Voigt profile
Weak residuals due to Dicke narrowing
Quantitative Spectroscopy Using Diode- and DFG Lasers in the IR
9th International HITRAN Conference, Cambridge, June 26, 2006

10. Results from LISA
Example 2: Air-broadening of the line at cm-1
10
 10
Again: weak residuals due to Dicke narrowing (even at 200 Torr)
Quantitative Spectroscopy Using Diode- and DFG Lasers in the IR
9th International HITRAN Conference, Cambridge, June 26, 2006

11. Results from LISA
Example 3: Self-broadening of 3 lines near cm-1
Note: the Dicke-narrowing also affects the baseline between the lines
Quantitative Spectroscopy Using Diode- and DFG Lasers in the IR
9th International HITRAN Conference, Cambridge, June 26, 2006

12. 9th International HITRAN Conference, Cambridge, June 26, 2006
Line intensities
Fixed Free
Note:
Straight lines (1-2 %)
Up to 10 % difference between fixed and free D in the Voigt profile
MEAN value (!) 15 % above HITRAN2004
Good agreement (5 %) with Ponsardin and Browell, JMS 1997
Difference can not be explained by line profile
Quantitative Spectroscopy Using Diode- and DFG Lasers in the IR
9th International HITRAN Conference, Cambridge, June 26, 2006

13. 9th International HITRAN Conference, Cambridge, June 26, 2006
Self-broadening
Note:
Straight line (1 %)
BUT: 10 % lower than HITRAN2004
Quantitative Spectroscopy Using Diode- and DFG Lasers in the IR
9th International HITRAN Conference, Cambridge, June 26, 2006

14. 9th International HITRAN Conference, Cambridge, June 26, 2006
Air-broadening
Note:
Straight line (< 1 %)
Good agreement with HITRAN2004 (< 5 %)
Quantitative Spectroscopy Using Diode- and DFG Lasers in the IR
9th International HITRAN Conference, Cambridge, June 26, 2006

15. Conclusions for H2O around 822 nm
40 different H2O lines measured between 815 and 835 nm.
Intensities in the 830 nm band 15% higher than HITRAN2004.
Self-broadening coefficients 10% lower than HITRAN2004.
Air-broadening coefficients in good agreement (< 5%) with HITRAN2004.
Dicke-narrowing  although weak, check impact on line intensities using other profiles (Galatry, Rautian,…)
Perform new, independent experiments (FTS?)
Strategies for H2O broadening in HITRAN
Quantitative Spectroscopy Using Diode- and DFG Lasers in the IR
9th International HITRAN Conference, Cambridge, June 26, 2006

16. External Cavity Diode-Lasers
Toptica DL-100 (“Littrow” configuration)
grating as part of the cavity
linewidth 1 MHz ( cm-1)
output power up to 30 mW
spectral range: 810 – 880 nm (11360 – cm-1) – 1565 nm (6390 – 6515 cm-1)
tunable range (single mode) at least GHz ( cm-1)
relatively low beam divergence
Quantitative Spectroscopy Using Diode- and DFG Lasers in the IR
9th International HITRAN Conference, Cambridge, June 26, 2006

17. External Cavity Diode-Lasers
Toptica DL-100 (“Littrow” configuration)
output power up to 30 mW
Photo-acoustic spectroscopy (PAS)
Quantitative Spectroscopy Using Diode- and DFG Lasers in the IR
9th International HITRAN Conference, Cambridge, June 26, 2006

18. Photoacoustic Spectroscopy of NH3 around 1.5 mm
Reminder: How works PAS
Photoacoustic effect: Collisional energy transfer
Laser tuned to a molecular transition:
 Excited molecules
 Partly, non radiative de-excitation
 Temperature changes
 Pressure changes
 Acoustic wave
 Detection by microphone
Thanks to Prof. Th. Huet, University of Lille, France
Quantitative Spectroscopy Using Diode- and DFG Lasers in the IR
9th International HITRAN Conference, Cambridge, June 26, 2006

19. Photoacoustic Spectroscopy of NH3 around 1.5 mm
Simultaneous direct absorption measurements using a White-type multiple-pass cell
Quantitative Spectroscopy Using Diode- and DFG Lasers in the IR
9th International HITRAN Conference, Cambridge, June 26, 2006

20. Photoacoustic Spectroscopy of NH3 around 1.5 mm
Simultaneous direct absorption measurements using a White-type multiple-pass cell
Quantitative Spectroscopy Using Diode- and DFG Lasers in the IR
9th International HITRAN Conference, Cambridge, June 26, 2006

21. Photoacoustic Spectroscopy of NH3 around 1.5 mm
Spectral calibration using the FTS line positions of Lundsberg-Nielsen et al. (1993)
Quantitative Spectroscopy Using Diode- and DFG Lasers in the IR
9th International HITRAN Conference, Cambridge, June 26, 2006

22. Check with direct absorption spectra
Photoacoustic Spectroscopy of NH3 around 1.5 mm
Problem:
The relative line intensities seem to be incorrect: Lines No. 2 and 3 should be very similar, about 60 % of the line No. 1
Check with direct absorption spectra
Quantitative Spectroscopy Using Diode- and DFG Lasers in the IR
9th International HITRAN Conference, Cambridge, June 26, 2006

23. Absorption Spectroscopy of NH3 around 1.5 mm
Spectral calibration using the FTS line positions of Lundsberg-Nielsen et al. (1993)
Quantitative Spectroscopy Using Diode- and DFG Lasers in the IR
9th International HITRAN Conference, Cambridge, June 26, 2006

24. Absorption Spectroscopy of NH3 around 1.5 mm
Quantitative Spectroscopy Using Diode- and DFG Lasers in the IR
9th International HITRAN Conference, Cambridge, June 26, 2006

25. The fitted Doppler widths are not equal !
Absorption Spectroscopy of NH3 around 1.5 mm
Problem:
The relative line intensities seem to be incorrect: Lines No. 2 and 3 should be very similar, about 60 % of the line No. 1
The fitted Doppler widths are not equal !
Spectral calibration using the FTS line positions of Lundsberg-Nielsen et al. (1993)
Quantitative Spectroscopy Using Diode- and DFG Lasers in the IR
9th International HITRAN Conference, Cambridge, June 26, 2006

26. Absorption Spectroscopy of NH3 around 1.5 mm
New absorption spectra using FTS:
Bruker IFS 120 HR Fourier spectrometer (Orsay)
Absorption cell 25 cm, CaF2 windows
NH3 pressure 30 mbar
Spectral range 5950 – 7850 cm-1
Spectral resolution 0.02 cm-1
Quantitative Spectroscopy Using Diode- and DFG Lasers in the IR
9th International HITRAN Conference, Cambridge, June 26, 2006

27. Absorption Spectroscopy of NH3 around 1.5 mm
Quantitative Spectroscopy Using Diode- and DFG Lasers in the IR
9th International HITRAN Conference, Cambridge, June 26, 2006

28. Absorption Spectroscopy of NH3 around 1.5 mm
Comparison of the NH3 line positions (example)
Line No.
Lundsberg-Nielsen et al.
JMS 162 (1993)
This work (FTS) (*)
Difference in cm-1 1
0.0055 2
0.0112 3
0.0074
14NH3
15NH3
(*) calibrated using the IUPAC recommended standard: H2O lines of Toth, accuracy (RMS) cm-1
The new NH3 linelist is available in digital format upon request to the authors.
Quantitative Spectroscopy Using Diode- and DFG Lasers in the IR
9th International HITRAN Conference, Cambridge, June 26, 2006

29. Mid-IR NO2 line intensities using a DFG laser
DFG (Difference Frequency Generation) Laser)
Chopper
Wavemeter
ECDL:
30 mW nm
Linewidth 1 MHz
DFG
3 - 5 µm
Linewidth 1MHz
Lock-in detection
LabView acquisition
S/N>1000
Measurement time: few minutes
Mid IR
Quantitative Spectroscopy Using Diode- and DFG Lasers in the IR
9th International HITRAN Conference, Cambridge, June 26, 2006

30. Mid-IR NO2 line intensities using a DFG laser
DFG (Difference Frequency Generation) Laser)
ECDL:
30 mW nm
Linewidth 1 MHz
DFG
3 - 5 µm
Linewidth 1MHz
Lock-in detection
LabView acquisition
S/N>1000
Measurement time: few minutes
Quantitative Spectroscopy Using Diode- and DFG Lasers in the IR
9th International HITRAN Conference, Cambridge, June 26, 2006

31. Mid-IR NO2 line intensities using a DFG laser
DFG (Difference Frequency Generation) Laser)
ECDL:
30 mW nm
Linewidth 1 MHz
DFG
3 - 5 µm
Linewidth 1MHz
Lock-in detection
LabView acquisition
S/N>1000
Measurement time: few minutes
Quantitative Spectroscopy Using Diode- and DFG Lasers in the IR
9th International HITRAN Conference, Cambridge, June 26, 2006

32. Mid-IR NO2 line intensities using a DFG laser
II.1. Caractérisation instrumentale: spectroscopie de N2O.
Mid-IR NO2 line intensities using a DFG laser
Interféromètre de Fabry Pérot, Validation avec N2O.
Validation of the DFG using N2O, CH4 and HI
PN2O = mbar
Quantitative Spectroscopy Using Diode- and DFG Lasers in the IR
9th International HITRAN Conference, Cambridge, June 26, 2006

33. Mid-IR NO2 line intensities using a DFG laser
II.1. Caractérisation instrumentale: spectroscopie de N2O.
Mid-IR NO2 line intensities using a DFG laser
Interféromètre de Fabry Pérot, Validation avec N2O.
Validation of the DFG using N2O, CH4 and HI
RMS deviation cm-1
PN2O = 7, mbar
Quantitative Spectroscopy Using Diode- and DFG Lasers in the IR
9th International HITRAN Conference, Cambridge, June 26, 2006

34. Mid-IR NO2 line intensities using a DFG laser
II.1. Caractérisation instrumentale: spectroscopie de N2O.
Mid-IR NO2 line intensities using a DFG laser
Interféromètre de Fabry Pérot, Validation avec N2O.
Validation of the DFG using N2O, CH4 and HI
RMS deviation 0.7 %
Quantitative Spectroscopy Using Diode- and DFG Lasers in the IR
9th International HITRAN Conference, Cambridge, June 26, 2006

35. Mid-IR NO2 line intensities using a DFG laser
Spectre d’absorption de la bande fondamentale de HI.
Mid-IR NO2 line intensities using a DFG laser
Bande d’absorption υ1
Validation of the DFG using N2O, CH4 and HI
R(0)
Quantitative Spectroscopy Using Diode- and DFG Lasers in the IR
9th International HITRAN Conference, Cambridge, June 26, 2006

36. Mid-IR NO2 line intensities using a DFG laser
Spectre d’absorption de la bande fondamentale de HI.
Mid-IR NO2 line intensities using a DFG laser
Bande d’absorption υ1
Validation of the DFG using N2O, CH4 and HI
Quantitative Spectroscopy Using Diode- and DFG Lasers in the IR
9th International HITRAN Conference, Cambridge, June 26, 2006

37. Mid-IR NO2 line intensities using a DFG laser
II.2. Intensités de raies de NO2.
Mid-IR NO2 line intensities using a DFG laser
Motivations
NO2 concentrations determined using the VIS
Quantitative Spectroscopy Using Diode- and DFG Lasers in the IR
9th International HITRAN Conference, Cambridge, June 26, 2006

38. Mid-IR NO2 line intensities using a DFG laser
II.2. Intensités de raies de NO2.
Mid-IR NO2 line intensities using a DFG laser
Motivations
NO2 concentrations determined using the VIS
Quantitative Spectroscopy Using Diode- and DFG Lasers in the IR
9th International HITRAN Conference, Cambridge, June 26, 2006

39. Mid-IR NO2 line intensities using a DFG laser
II.2. Intensités de raies de NO2.
Mid-IR NO2 line intensities using a DFG laser
Motivations
NO2 concentrations determined using the VIS
Quantitative Spectroscopy Using Diode- and DFG Lasers in the IR
9th International HITRAN Conference, Cambridge, June 26, 2006

40. Mid-IR NO2 line intensities using a DFG laser
II.2. Intensités de raies de NO2.
Mid-IR NO2 line intensities using a DFG laser
Motivations
Typical mid-IR spectrum and fit (residuals × 25)
résidu x 25
υ1+ υ3
(υ1+ υ2+ υ3)- υ2
PNO2 = 2 mbar
Quantitative Spectroscopy Using Diode- and DFG Lasers in the IR
9th International HITRAN Conference, Cambridge, June 26, 2006

41. Mid-IR NO2 line intensities using a DFG laser
II.2. Intensités de raies de NO2.
Mid-IR NO2 line intensities using a DFG laser
Motivations
Quantitative Spectroscopy Using Diode- and DFG Lasers in the IR
9th International HITRAN Conference, Cambridge, June 26, 2006

42. Mid-IR NO2 line intensities using a DFG laser
II.2. Intensités de raies de NO2.
Mid-IR NO2 line intensities using a DFG laser
Motivations
Results for the “cold” band n1+n3
27 lines measured
Mean deviation wrt. HITRAN2004: % ± 1.2 %
Results for the “hot” band (n1+n2+n3) - n2
8 lines measured (many lines are blended)
Mean deviation wrt. HITRAN2004: % ± 1.2 %
Line positions of the “hot” band (n1+n2+n3) - n2 slightly shifted (see also Perrin et al., 1997)
Quantitative Spectroscopy Using Diode- and DFG Lasers in the IR
9th International HITRAN Conference, Cambridge, June 26, 2006

43. 9th International HITRAN Conference, Cambridge, June 26, 2006
Conclusions
Using ECDL for studying line intensities and shapes in the near- and mid-IR, at very high S/N and spectral resolution
DFG lasers can “transport” these properties into the mid- infrared (3 – 5 mm) and possibly at longer wavelengths
H2O: line intensities of the 822 nm band 15 % too low
NH3: new NIR line list recorded using FTS
NO2: very good agreement between UV and IR at 3 mm
Further studies: H2CO, O3, HO2 …
Quantitative Spectroscopy Using Diode- and DFG Lasers in the IR
9th International HITRAN Conference, Cambridge, June 26, 2006

44. 9th International HITRAN Conference, Cambridge, June 26, 2006
Acknowledgements
Pierre-Marie Flaud (PhD, )
Nofal Ibrahim (PhD, )
CNRS Department “Sciences Physique et Mathématiques”
University of Paris-12 Créteil
Quantitative Spectroscopy Using Diode- and DFG Lasers in the IR
9th International HITRAN Conference, Cambridge, June 26, 2006