DIODE- AND DIFFERENCE-FREQUENCY LASER STUDIES OF ATMOSPHERIC MOLECULES IN THE NEAR- AND MID-INFRARED: H2O, NH3, and NO2

Transcription

1 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 IR Lasers Tunable diode-lasers are available in the near-infrared region: 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 2

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: nm ( cm-1) nm ( cm-1) tunable range (single mode) at least GHz ( cm-1) relatively small beam divergence 3

4 External Cavity Diode-Lasers H2O absorption line around 830 nm 4

5 White-type absorption cell 3 MKS Baratrons Water sample Thermometer L = 1 m, maximum path length 100 m, CaF2 windows 5

6 The H2O band around 822 nm 6

7 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 ! Differences between different authors exceed stated accuracy (up to 30%) need for more measurements 7

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 8

9 Results from LISA Example 1: Self-broadening of the line at cm High S/N ratio( >1000) Experimental lines well reproduced using Voigt profile Weak residuals due to Dicke narrowing 9

10 Results from LISA Example 2: Air-broadening of the line at cm Again: weak residuals due to Dicke narrowing (even at 200 Torr) 10

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 11

12 Line intensities Note: Fixed Free 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 12

13 Self-broadening Note: Straight line (1 %) BUT: 10 % lower than HITRAN

14 Air-broadening Note: Straight line (< 1 %) Good agreement with HITRAN2004 (< 5 %) 14

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 15

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: nm ( cm-1) nm ( cm-1) tunable range (single mode) at least GHz ( cm-1) relatively low beam divergence 16

17 External Cavity Diode-Lasers Toptica DL-100 ( Littrow configuration) output power up to 30 mw Photo-acoustic spectroscopy (PAS) 17

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 18

19 Photoacoustic Spectroscopy of NH3 around 1.5 mm Simultaneous direct absorption measurements using a White-type multiple-pass cell 19

20 Photoacoustic Spectroscopy of NH3 around 1.5 mm Simultaneous direct absorption measurements using a White-type multiple-pass cell 20

21 Photoacoustic Spectroscopy of NH3 around 1.5 mm Spectral calibration using the FTS line positions of Lundsberg-Nielsen et al. (1993) 21

22 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 22

23 Absorption Spectroscopy of NH3 around 1.5 mm Spectral calibration using the FTS line positions of Lundsberg-Nielsen et al. (1993) 23

24 Absorption Spectroscopy of NH3 around 1.5 mm 24

25 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 % The fitted Doppler widths are not equal! of the line No. 1 Spectral calibration using the FTS line positions of Lundsberg-Nielsen et al. (1993) 25

26 00 Absorption Spectroscopy of NH3 around 1.5 mm wavenumber in cm New absorption spectra using FTS: Bruker IFS 120 HR Fourier spectrometer (Orsay) Absorption cell 25 cm, CaF2 windows NH3 pressure 30 mbar Spectral range cm-1 Spectral resolution 0.02 cm-1 26

27 Absorption Spectroscopy of NH3 around 1.5 mm 14NH 3 15NH 3 27

28 Absorption Spectroscopy of NH3 around 1.5 mm Comparison of the NH3 line positions (example) 14NH 3 Line No. Lundsberg-Nielsen et al. JMS 162 (1993) This work (FTS) (*) Difference in cm NH (*) 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. 28

29 Mid-IR NO2 line intensities using a DFG laser DFG (Difference Frequency Generation) Laser) ECDL: 30 mw nm Linewidth 1 MHz Chopper DFG 3-5 µm Linewidth 1MHz Wavemeter Mid IR Lock-in detection LabView acquisition S/N>1000 Measurement time: few minutes 29

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 30

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 31

32 II.1. Caractérisation instrumentale: spectroscopie de N2O. Mid-IR NO2 linedeintensities using a avec DFG laser Interféromètre Fabry Pérot, Validation N O. 2 Validation of the DFG using N2O, CH4 and HI PN2O = mbar 32

33 II.1. Caractérisation instrumentale: spectroscopie de N2O. Mid-IR NO2 linedeintensities using a avec DFG laser Interféromètre Fabry Pérot, Validation N O. 2 Validation of the DFG using N2O, CH4 and HI -2 P-1 RMS deviation cm N2O = 7,5.10 mbar 33

34 II.1. Caractérisation instrumentale: spectroscopie de N2O. Mid-IR NO2 linedeintensities using a avec DFG laser Interféromètre Fabry Pérot, Validation N O. 2 Validation of the DFG using N2O, CH4 and HI RMS deviation 0.7 % 34

35 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) 35

36 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 36

37 II.2. Intensités de raies de NO2. Mid-IR NO2 line intensities Motivationsusing a DFG laser NO2 concentrations determined using the VIS 37

38 II.2. Intensités de raies de NO2. Mid-IR NO2 line intensities Motivationsusing a DFG laser NO2 concentrations determined using the VIS 38

39 II.2. Intensités de raies de NO2. Mid-IR NO2 line intensities Motivationsusing a DFG laser NO2 concentrations determined using the VIS 39

40 II.2. Intensités de raies de NO2. Mid-IR NO2 line intensities Motivationsusing a DFG laser Typical mid-ir spectrum and fit (residuals 25) (υ1+ υ2+ υ3)- υ2 résidu x 25 υ1+ υ3 PNO2 = 2 mbar 40

41 II.2. Intensités de raies de NO2. Mid-IR NO2 line intensities Motivationsusing a DFG laser 41

42 II.2. Intensités de raies de NO2. Mid-IR NO2 line intensities Motivationsusing a DFG laser Results for the cold band n1+n3 Results for the hot band (n1+n2+n3) - n2 27 lines measured Mean deviation wrt. HITRAN2004: % ± 1.2 % 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) 42

43 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 midinfrared (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 43

44 Acknowledgements Pierre-Marie Flaud (PhD, ) Nofal Ibrahim (PhD, ) CNRS Department Sciences Physique et Mathématiques University of Paris-12 Créteil 44