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IntraCavity Laser Absorption Spectroscopy

IntraCavity Laser Absorption Spectroscopy. Alain.Campargue@ujf-grenoble.fr Laboratoire de Spectrométrie Physique (CNRS UMR C5588) Université Joseph Fourier de Grenoble (France) M. Chenevier, F. Stoeckel, A. Kachanov and D. Romanini. Introduction: High Sensitive Absorption Techniques.

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IntraCavity Laser Absorption Spectroscopy

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  1. IntraCavity Laser Absorption Spectroscopy Alain.Campargue@ujf-grenoble.fr Laboratoire de Spectrométrie Physique (CNRS UMR C5588) Université Joseph Fourier de Grenoble (France) M. Chenevier, F. Stoeckel, A. Kachanov and D. Romanini

  2. Introduction: High Sensitive Absorption Techniques  increase of l : multipass cell, ICLAS, CRDS  decrease of the noise level : in particular FMDL and also CRDS, OA  measurement of the absorbed energy dark background methods: OA and OT NB. If the absorption linewidth is limited by the instrumental resolution, sensitivity  when the spectral resolution 

  3. emission spectrum laser gain mirror mirror absorber a Є I v n n l laser cavityL Leq= c tg l/L withc: speed of light , tg: generation time Principles of Intracavity Laser Absorption Spectroscopy

  4. Principles of Intracavity Laser Absorption Spectroscopy

  5. Spectral dynamics of ICLAS I (v, tg) = e-aLeq Leq= c tg l/L 300 µs  90 km amin ~ 10-9 cm-1

  6. ICLAS spectrum of 12C2H2 presenting the Q branch of the P-S band at 10689.62 cm-1. P= 15 Torr (20 hPa) and leq= 8.6 km.

  7. Timing : Pump Laser / Spectrograph Sampling m Gener ation Time : 10 s < t < 1 ms g L Equivalent Path Length : = ´ L c t eq g Cavity Length Photodiode array Grating Spectrograph Pump laser Acousto AO or Optic chopper Ti:Sapphire or Dye L Absorption Cell Supersonic Slit Jet Reactor Cold Cell Vacuum pump Plasma, Diamond deposition... ICLAS set up

  8. Two times ICLAS (A. Kachanov, D. Romanini, A. Charvat, and B. Abel (1998)4000 spectral elements recorded within 0.5ms!!!

  9. Correction of the Atmospheric Absorption Background

  10. a(s) = N ks F(s) Line profile analysis Detection and measurement of low concentrated species Detection of forbidden transitions

  11. ICLAS-dye of HDO

  12. ICLAS- VECSEL of H2O Comparison with current databases

  13. ICLAS is a quantitative method Comparison ICLAS-FTS (Kalmar and O’Brien JMS 192, 386-393 (1998)

  14. ICLAS of weak vibronic transition jet cooled NO2 in the near infrared

  15. Plasma Diagnostics:Absolute Density and Temperature measurements of N2(A3Su+) in a microwave discharge

  16. [O2(3Sg)(v=0)] 2 [O2(1Dg)(v=0)+ O2(1Dg)(v=1)] Cell cooled down to 77K Supersonic expansion (O2)2 Wavenumber (cm First observation of the (O2)2 dimer of oxygen (1-0) band at 598 nm Cooled cell H2O Cooled cell (77K) Transmission Medium Resolution High resolution 17270 17280 17290 -1 )

  17. [O2(3Sg)(v=0)] 2 [O2(1Dg)(v=0)+ O2(1Dg)(v=0)] Comparison: ICLAS and CRDS of the (0-0) band of (O2)2 p = 2.7 bar (continuous expansion) l/L~50% Dt=50 min p = 9 bar l/L~5% Dt ~ 10 sec

  18. Spectral regions accessible for ICLAS VECSEL Ti:Sa dyes Nd:glass 0 5000 10000 15000 20000 VCH 1 2 3 4 5 6 7 VSiH 1 2 3 4 5 6 7 8 cm-1

  19. VeCSEL - Vertical External Cavity Surface Emitting Laser Photoluminescenceof a VeCSEL sample VeCSEL laser structure

  20. CCD Spectrograph AOM MInj tg tg Oscilloscope PD ICLAS + VeCSEL MQWs IntracavityCell CM OC Peltier DiodeLaser

  21. MQWs SDL - diodepumping laser Intracavity cell Towards the outputmirror and spectrometer Concave mirror Head of VeCSEL Cooling Peltier element

  22. ICLAS + VeCSEL at 1.1mm

  23. ICLAS_VECSEL of H2S in the region of the (40±, 0) transition ICLAS-VECSEL P=27 Torr leq=30km

  24. Specific laser dynamics of a VECSEL: spectral condensation Dependence on the gas pressure • Spectral condensation increases with: • Gas pressure • Line intensity • Pumping rate • Generation time

  25. Summary Advantages of ICLAS Quantitative accuracy similar to classical absorption Not fluorescing transitions Limited quantity of gas required (typically 1mmol) Possible association with slit jet or reactor MULTIPLEX ADVANTAGE Near infrared and visible accessible Drawbacks of ICLAS Need for a reference for wavenumber calibration Spectral resolution limited by the spectrograph Baseline uncertainty in the case of broad unresolved spectrum UV not accessible

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