diode- and difference-frequency laser studies of atmospheric molecules in the near- and...

DIODE- AND DIFFERENCE-FREQUENCY LASER DIODE- AND DIFFERENCE-FREQUENCY LASER STUDIES OF ATMOSPHERIC MOLECULES IN THE STUDIES OF ATMOSPHERIC MOLECULES IN THE

NEAR- AND MID-INFRARED: HNEAR- AND MID-INFRARED: H22O, NHO, NH33, and NO, and NO22

Johannes ORPHAL, Pascale CHELIN,

Nofal IBRAHIM, and Pierre-Marie FLAUD

Laboratoire Interuniversitaire des Systèmes Atmosphériques

Université de Paris-12, Créteil, France

Quantitative Spectroscopy Using DioQuantitative Spectroscopy Using Diode- and DFG Lasers in the IRde- and DFG Lasers in the IR

9th International HITRAN Conference, Cambridge, 9th International HITRAN Conference, Cambridge, June 26, 2006June 26, 2006

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Tunable diode-lasers are available in the near-infrared region: 0.7 – 2.0 m (optical telecommunication)

Extremely useful for quantitative spectroscopy of atmospheric molecules (many studies in the last 5 years) Very high-resolution (less than 0.0001 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 m)

This talk: applications to HThis talk: applications to H22O, NHO, NH33, NO, NO22

Quantitative Spectroscopy Using IR LasersQuantitative Spectroscopy Using IR Lasers Quantitative Spectroscopy Using IR LasersQuantitative Spectroscopy Using IR Lasers



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Toptica DL-100 (“Littrow” configuration)

External Cavity Diode-LasersExternal Cavity Diode-Lasers External Cavity Diode-LasersExternal Cavity Diode-Lasers

• grating forms part of the cavity

• linewidth 1 MHz (0.00003 cm-1)

• output power up to 30 mW

• spectral range: 810 – 880 nm (11360 – 12350 cm-1) 1535 – 1565 nm (6390 – 6515 cm-1)

• tunable range (single mode) at least 20-30 GHz (0.6-1.0 cm-1)

• relatively small beam divergence



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H2O absorption line around 830 nm




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White-type absorption cellWhite-type absorption cellWhite-type absorption cellWhite-type absorption cell

L = 1 m, maximum path length 100 m, CaF2 windows

3 MKSBaratrons

Water sample

Thermometer



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The HThe H22O band around 822 nmO band around 822 nmThe HThe H22O band around 822 nmO band around 822 nm



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• R. A. Toth, J. Mol. Spectrosc., 166, 176-183 (1994)• J.-M. Flaud et al., J. Mol. Spectrosc., 185, 211-221 (1997)• P. L. Ponsardin et al., J. Mol. Spectrosc., 185, 58-70 (1997)• A. Lucchesini et al., Eur. Phys. J. D., 8, 223-226 (2000)• R. Schermaul et al, J. Mol. Spectrosc. 208, 32-42 (2001)• A. Ray et al., Appl. Phys. B, 79, 915-921(2004)

Previous measurements of HPrevious measurements of H22O around 822 nmO around 822 nmPrevious measurements of HPrevious measurements of H22O around 822 nmO around 822 nm

Example: line intensities (S1023/cm molecule-1)

position (cm-1) HITRAN04 Ponsardin Schermaul Ray

12014.1431 1.679 --- 1.960 1.504

12218.8248 1.865 2.185 2.290 1.888

12244.7233 3.236 3.81 5.080 ---

12244.7873 0.888 1.08 --- ---

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



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Experimental PrecautionsExperimental PrecautionsExperimental PrecautionsExperimental 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



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10

10

Results from LISAResults from LISAResults from LISAResults from LISA

Example 1: Self-broadening of the line at 12226.101 cm-1

High S/N ratio( >1000) Experimental lines well reproduced using Voigt profile Weak residuals due to Dicke narrowing



1010

10

10


Example 2: Air-broadening of the line at 12226.101 cm-1

Again: weak residuals due to Dicke narrowing (even at 200 Torr)



1111


Example 3: Self-broadening of 3 lines near 12259 cm-1

Note: the Dicke-narrowing also affects the baseline between the lines



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Line intensitiesLine intensitiesLine intensitiesLine intensities

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

FixedFree



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Self-broadeningSelf-broadeningSelf-broadeningSelf-broadening

Note:

• Straight line (1 %)

• BUT: 10 % lower than HITRAN2004



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Air-broadeningAir-broadeningAir-broadeningAir-broadening

Note:

• Straight line (< 1 %)

• Good agreement with HITRAN2004 (< 5 %)



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Conclusions for HConclusions for H22O around 822 nmO around 822 nmConclusions for HConclusions for H22O around 822 nmO 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



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• grating as part of the cavity

• linewidth 1 MHz (0.00003 cm-1)


• spectral range: 810 – 880 nm (11360 – 12350 cm-1) 1535 – 1565 nm (6390 – 6515 cm-1)

• tunable range (single mode) at least 20-30 GHz (0.6-1.0 cm-1)

• relatively low beam divergence



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Photo-acoustic spectroscopy (PAS)



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Reminder: How works PAS

Thanks to Prof. Th. Huet, University of Lille, France

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

Photoacoustic Spectroscopy of NHPhotoacoustic Spectroscopy of NH33 around 1.5 around 1.5 mm Photoacoustic Spectroscopy of NHPhotoacoustic Spectroscopy of NH33 around 1.5 around 1.5 mm



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Simultaneous direct absorption measurements using a White-type multiple-pass cell




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Simultaneous direct absorption measurements using a White-type multiple-pass cell




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Spectral calibration using the FTS line positions of Lundsberg-Nielsen et al. (1993)



2222

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


1 2 3



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1 2 3

Absorption Spectroscopy of NHAbsorption Spectroscopy of NH33 around 1.5 around 1.5 mm Absorption Spectroscopy of NHAbsorption Spectroscopy of NH33 around 1.5 around 1.5 mm




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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 !





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6300 6400 6500 6600 6700 6800 6900 7000 7100 7200 7300 7400 75000.0

1.0

2.0

wavenumber in cm-1

inte

nsi

ty in

a.u

.

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




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14NH3

15NH3




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14NH3

15NH3

Line No.Lundsberg-Nielsen

et al.JMS 162 (1993)

This work (FTS) (*)

Difference in cm-1

1 6528.764 6528.7585 0.0055

2 6528.894 6528.8828 0.0112

3 6529.184 6529.1766 0.0074

(*) calibrated using the IUPAC recommended standard: H2O lines of Toth, accuracy (RMS) 0.0005 cm-1

The new NH3 linelist is available in digital format upon request to the authors.


Comparison of the NH3 line positions (example)



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Chopper

Wavemeter

DFGDFG (Difference Frequency Generation) Laser)

Mid-IR NOMid-IR NO22 line intensities using a DFG laser line intensities using a DFG laserMid-IR NOMid-IR NO22 line intensities using a DFG laser line intensities using a DFG laser

Mid IR

ECDL: • 30 mW• 810 - 880 nm• Linewidth 1 MHz

DFG• 3 - 5 µm• Linewidth 1MHz

• Lock-in detection• LabView acquisition• S/N>1000 • Measurement time: few minutes



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3131








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PN2O = 0.075 mbar

II.1. Caractérisation instrumentale: spectroscopie de N2O.

Interféromètre de Fabry Pérot, Validation avec N2O.

Validation of the DFG using NValidation of the DFG using N22O, CHO, CH44 and HI and HI




3333

PN2O = 7,5.10-2 mbar





RMS deviation 0.00006 cm-1



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RMS deviation 0.7 %



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Spectre d’absorption de la bande fondamentale de HI.

Bande d’absorption υ1



R(0)



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Spectre d’absorption de la bande fondamentale de HI.

Bande d’absorption υ1





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II.2. Intensités de raies de NO2.

Motivations

NONO22 concentrations determined using the VIS concentrations determined using the VIS




3838


Motivations





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Motivations





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Motivations

Typical mid-IR spectrum and fit (residuals × 25)Typical mid-IR spectrum and fit (residuals × 25)


rési

du x

25

υ1+ υ3 (υ1+ υ2+ υ3)- υ2

PNO2 = 2 mbar



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MotivationsMid-IR NOMid-IR NO22 line intensities using a DFG laser line intensities using a DFG laserMid-IR NOMid-IR NO22 line intensities using a DFG laser line intensities using a DFG laser



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Motivations

Results for the “cold” band Results for the “cold” band 11++33 27 lines measured27 lines measured Mean deviation wrt. HITRAN2004: - 4.9 % ± 1.2 %Mean deviation wrt. HITRAN2004: - 4.9 % ± 1.2 %

Results for the “hot” band (Results for the “hot” band (11++22++33) - ) - 22 8 lines measured (many lines are blended)8 lines measured (many lines are blended) Mean deviation wrt. HITRAN2004: - 2.3 % ± 1.2 %Mean deviation wrt. HITRAN2004: - 2.3 % ± 1.2 %

Line positions of the “hot” band (Line positions of the “hot” band (11++22++33) - ) - 2 2

slightly shifted (see also Perrin et al., 1997)slightly shifted (see also Perrin et al., 1997)




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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 m) and possibly at longer wavelengths

HH22O: line intensities of the 822 nm band 15 % too lowO: line intensities of the 822 nm band 15 % too low

NHNH33: new NIR line list recorded using FTS : new NIR line list recorded using FTS

NONO22: very good agreement between UV and IR at 3 : very good agreement between UV and IR at 3 mm

Further studies: HFurther studies: H22CO, OCO, O33, HO, HO22 … …

ConclusionsConclusions ConclusionsConclusions



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Pierre-Marie Flaud (PhD, 2003-2005) Nofal Ibrahim (PhD, 2003-2006)

AcknowledgementsAcknowledgements AcknowledgementsAcknowledgements

CNRS Department “Sciences Physique et Mathématiques” University of Paris-12 Créteil

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