1 Alain.Campargue@ujf-grenoble.fr Laboratoire de Spectrométrie Physique (CNRS UMR C5588) Université Joseph Fourier de Grenoble (France) M. Chenevier, F

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1 Alain.Campargue@ujf-grenoble.fr Laboratoire de Spectromtrie Physique (CNRS UMR C5588) Universit Joseph Fourier de Grenoble (France) M. Chenevier, F. Stoeckel, A. Kachanov and D. Romanini IntraCavity Laser Absorption Spectroscopy Slide 2 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 Slide 3 3 absorber l v Principles of Intracavity Laser Absorption Spectroscopy emission spectrum I laser cavity L mirror laser gain with c: speed of light, t g : generation time L eq = c t g l / L Slide 4 4 Principles of Intracavity Laser Absorption Spectroscopy Slide 5 5 Spectral dynamics of ICLAS I (v, t g ) = e - L eq 300 s 90 km min ~ 10 -9 cm -1 L eq = c t g l / L Slide 6 6 Slide 7 7 ICLAS spectrum of 12 C 2 H 2 presenting the Q branch of the - band at 10689.62 cm -1. P= 15 Torr (20 hPa) and l eq = 8.6 km. Slide 8 8 ICLAS set up ICLAS set up Slide 9 9 Two times ICLAS (A. Kachanov, D. Romanini, A. Charvat, and B. Abel (1998) 4000 spectral elements recorded within 0.5ms!!! Slide 10 10 Correction of the Atmospheric Absorption Background Slide 11 11 Detection and measurement of low concentrated species Detection of forbidden transitions Line profile analysis ( k Slide 12 12 ICLAS-dye of HDO Slide 13 13 ICLAS- VECSEL of H2O Comparison with current databases Slide 14 14 ICLAS is a quantitative method Comparison ICLAS-FTS (Kalmar and OBrien JMS 192, 386-393 (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) 12473.61656.96.896.93 12474.684116.417.517.1 12475.0373.553.813.55 12475.691915.916.216.0 12476.395546.449.450.6 12661.110260.862.459.3 Slide 15 15 ICLAS of weak vibronic transition jet cooled NO 2 in the near infrared Slide 16 16 Plasma Diagnostics:Absolute Density and Temperature measurements of N 2 (A 3 u + ) in a microwave discharge Slide 17 17 172701728017290 Medium Resolution High resolution Cooled cell (77K) Transmission ) H2OH2O Wavenumber (cm Supersonic expansion (O 2 ) 2 Cell cooled down to 77K First observation of the (O 2 ) 2 dimer of oxygen (1-0) band at 598 nm First observation of the (O 2 ) 2 dimer of oxygen (1-0) band at 598 nm [O 2 ( 1 g ) (v=0)+ O 2 ( 1 g ) ( v=1 ) ][O 2 ( 3 g ) (v=0) ] 2 Cooled cell Slide 18 18 l/L~50% t=50 min l/L~5% t ~ 10 sec p = 2.7 bar (continuous expansion) p = 9 bar Comparison: ICLAS and CRDS of the (0-0) band of (O 2 ) 2 [O 2 ( 1 g ) (v=0)+ O 2 ( 1 g ) ( v=0 ) ][O 2 ( 3 g ) (v=0) ] 2 Slide 19 19 Spectral regions accessible for ICLAS Ti:Sa Nd:glass VECSEL cm -1 dyes 0 5000 10000 1500020000 V CH 1 2 3 4 5 6 7 V SiH 1 2 3 4 5 6 7 8 Slide 20 20 VeCSEL - Vertical External Cavity Surface Emitting Laser Photoluminescence of a VeCSEL sample VeCSEL laser structure Slide 21 21 ICLAS + VeCSEL AOM CM Diode Laser OC CCD Spectrograph M Inj MQW s PD Oscilloscope tgtg tgtg Peltier Intracavity Cell Slide 22 22 Head of VeCSEL MQWs SDL - diode pumping laser Intracavity cell Concave mirror Cooling Peltier element Towards the output mirror and spectrometer Slide 23 23 ICLAS + VeCSEL at 1.1 m Slide 24 24 ICLAS_VECSEL of H 2 S in the region of the (40 , 0) transition ICLAS-VECSEL P=27 Torr l eq =30km Slide 25 25 Specific laser dynamics of a VECSEL: spectral condensation Spectral condensation increases with: Gas pressure Line intensity Pumping rate Generation time Dependence on the gas pressure Slide 26 26 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 Summary