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