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IntraCavity Laser Absorption Spectroscopy

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Presentation on theme: "IntraCavity Laser Absorption Spectroscopy"— Presentation transcript:

1 IntraCavity Laser Absorption Spectroscopy
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 with c: speed of light , tg: generation time
Principles of Intracavity Laser Absorption Spectroscopy emission spectrum I n laser cavity L mirror n Є laser gain absorber l a v with c: speed of light , tg: generation time Leq= c tg l/L

4 Principles of Intracavity Laser Absorption Spectroscopy

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


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

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

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

10 Correction of the Atmospheric Absorption Background

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

12 ICLAS-dye of HDO

13 ICLAS- VECSEL of H2O Comparison with current databases

14 ICLAS is a quantitative method
Comparison ICLAS-FTS (Kalmar and O’Brien JMS 192, (1998) Line Position (cm-1) Intensity in units of 10-6 cm-2/atm at 300K Absorbance vs Generation Time Absorbance vs Pressure FTS and Multipass (Toth et al) 6.9 6.89 6.93 16.4 17.5 17.1 3.55 3.81 15.9 16.2 16.0 46.4 49.4 50.6 60.8 62.4 59.3

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

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

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

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

19 Spectral regions accessible for ICLAS
VECSEL Ti:Sa dyes Nd:glass VCH VSiH cm-1

20 VeCSEL - Vertical External Cavity Surface Emitting Laser
Photoluminescence of a VeCSEL sample VeCSEL laser structure

21 ICLAS + VeCSEL Intracavity Cell tg AOM MQWs MInj CM OC PD Peltier CCD
Spectrograph MInj MQWs AOM Intracavity Cell PD Oscilloscope CM OC Peltier Diode Laser tg

22 Head of VeCSEL MQWs Intracavity cell SDL - diode pumping laser
Towards the output mirror and spectrometer Concave mirror Cooling Peltier element

23 ICLAS + VeCSEL at 1.1mm

24 ICLAS_VECSEL of H2S in the region of the (40±, 0) transition
P=27 Torr leq=30km

25 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

26 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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