1

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

IntraCavity Laser Absorption Spectroscopy

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

I I l

I I l

lI

I

( ) ( ).exp[ ( ) ]

( ) ( )[ ( ) ]

( )min

min

0

0

0

1

1

3

absorber

l

v

Principles of Intracavity Laser Absorption SpectroscopyPrinciples of Intracavity Laser Absorption Spectroscopy

emission spectrum

I

laser cavity L

mirrormirror

Є

laser gain

with c: speed of light , tg: generation time

Leq= c tg l/L

4

Principles of Intracavity Laser Absorption SpectroscopyPrinciples of Intracavity Laser Absorption Spectroscopy

qqq

qqqqqq

MBN

Pdt

dN

MBcMMdt

dM

)1(

Absorption Line

Losses

Cavity Modes

Detector

Amplification Medium

Absorption Cell

Spectrograph

5

1200012020

12040

12060

12080

12100 50

100

150

200

Spectral dynamics of ICLASSpectral dynamics of ICLAS

I (v, tg) = e- Leq

300 µs 90 km

min ~ 10-9 cm-1

Leq= c tg l/L

g

g ГtГtJ

2

00 exp

6

10640 10660 10680 10700 10720 10740 107600.010

0.015

0.020

1068

8

C2H

2

FTS-(ULB)l=40 metersP=75 Torrs

Tra

nsm

ittan

ce

Wavenumber

7

ICLAS spectrum of 12C2H2 presenting the Q branch of the - band at

10689.62 cm-1. P= 15 Torr (20 hPa) and leq= 8.6 km.

3711151921232527

12345

10675 10680 10685 10690

ICLAS

**

0.5

1.0

Q(J)

P(J)

Tra

nsm

ittan

ce

Wavenumber (cm-1)

8

ICLAS

set up

ICLAS

set up

L

Cold Cell

Grating Spectrograph

Absorption Cell

Reactor

SupersonicSlit Jet

Plasma,Diamond deposition...

Photodiodearray

Pump laser

Ti:Sapphireor Dye

AcoustoOptic

AO orchopper

Gener ation Time : 10 s < t g < 1 ms

Equivalent Path Length : L c teq g L

CavityLength

Timing : Pump Laser / Spectrograph Sampling

Vacuumpump

9

I(tg)

I(tg)

I(tg+ t

g )

I(tg+ t

g)

Inte

nsity

Laser generation

tg+ t

gtg

400s

~ 3x10-9 / cm

Wavelength

Two times ICLAS (A. Kachanov, D. Romanini, A. Charvat, and B. Abel (1998)

4000 spectral elements recorded within 0.5ms!!!

Two times ICLAS (A. Kachanov, D. Romanini, A. Charvat, and B. Abel (1998)

4000 spectral elements recorded within 0.5ms!!!

10

Correction of the Atmospheric Absorption Background

10732 10734 10736 107380

(c)

Wavenumber (cm-1)

0

(b)

0

(a)

Ratio

Intensity

(au)

12CO2

H2O + 12CO

2

H2O

Intensity

(au)

11

Detection and measurement of low

concentrated species

Detection of forbiddentransitions

Line profile analysis

(k

12

+

(b) Simulated

Wavenumber (cm-1)

0

1

2

3

(600

) 5 15

-414

(014

) 2 11

-312

(014

) 6 42

-643 (0

14)

4 41-4

40

(142

) 2 02

-303

(014

) 2 12

-313

(014

) 2 02

-303

(0 1

2 0)

211

-312

(142

) 3 03

-404

(014

) 2 21

-322

(014

) 2 20

-321

(0 1

2 0)

313

-404

(014

) 3 13

-414

(014

) 3 03

-404

++

+ ++

+

+

Inte

nsity

(au

)In

tens

ity (

au)

Abs

orba

nce

(l)

HDO

(a)ICLAS

15100 15110 15120 15130

(c) Partridge and Schwenke

ICLAS-dye of HDO

13

ICLAS- VECSEL of H2O Comparison with current databases

ICLAS- VECSEL of H2O Comparison with current databases

14

ICLAS is a quantitative method ICLAS is a quantitative method

Comparison ICLAS-FTS (Kalmar and O’Brien 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)

12473.6165 6.9 6.89 6.93

12474.6841 16.4 17.5 17.1

12475.037 3.55 3.81 3.55

12475.6919 15.9 16.2 16.0

12476.3955 46.4 49.4 50.6

12661.1102 60.8 62.4 59.3

0 10 20 30 40

0

10

20

30

40

50

Stoeckel et al, JQRST 33(1985)337 band of O

2

PQ13

PP13kN

l eq

generation time (tg) (s)

(or equivalent path length (km))

1511275 11280 11285 11290 11295 11300

0.4

0.6

0.8

1.0

R0 86420246810

P0

jet ICLAS

T r

a n

s m

i t t

a n

c e

Wavenumber (cm-1)

0.0

0.2

0.4

0.6

0.8

1.0

1.211275 11280 11285 11290 11295 11300

NO2

ICLAS Ti:Sapphireroom temperature P = 6 Torr l

eq = 9km

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

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

16

Plasma Diagnostics:Absolute Density and Temperature measurements of N2(A3u

+) in a microwave discharge

17

17270 17280 17290

Medium Resolution

High resolution

Cooled cell (77K)

Tra

nsm

issi

on

-1)

17265 17270 17275 17280 17285

Abs

orba

nce

O2

*

***

295K

Nombre d'onde ( cm-1 )

223K

145K

112K

H2O

Wavenumber (cm

Supersonic expansion

80K

(O2)2

Cell cooled down to 77K

First observation of the (O2)2 dimer of oxygen

(1-0) band at 598 nm First observation of the (O2)2 dimer of oxygen

(1-0) band at 598 nm [O2(1g)(v=0)+ O2(1g)(v=1)][O2(3g)(v=0)] 2

Cooled cell

18

15808 15810 15812 15814 15816 15818

0

5

10

15

x 108

/cm

ln (

I 0 /I)

/ (

l/L c

t g)

1 /(

l/L

c )

1 /cln (I0 /I) / (ctg )

ICLAS

Wavenumber (cm-1)

0

5

10

CRDS

0,0

2,5

5,0

0,0

0,5

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 (O2)2Comparison: ICLAS and CRDS of the (0-0) band of (O2)2[O2(1g)(v=0)+ O2(1g)(v=0)][O2(3g)(v=0)] 2

19

Spectral regions accessible for ICLASSpectral regions accessible for ICLAS

Ti:Sa

Nd:glass

VECSEL

cm-1

dyes

0 5000 10000 15000 20000 VCH 1 2 3 4 5 6 7VSiH 1 2 3 4 5 6 7 8

20

VeCSEL - Vertical External Cavity

Surface Emitting LaserVeCSEL - Vertical External Cavity

Surface Emitting Laser

9600 9800 10000 10200 10400

T = 0°C T= 60°C

wavenumber (cm-1)

Photoluminescence

of a VeCSEL sample

~ few

Substrate

QWs

HRAR

Output coupler

VeCSEL laser structure

21

ICLAS + VeCSELICLAS + VeCSEL

AOM

CM

DiodeLaser

OC

CCD

Spectrograph

MInj

MQWs

PD

Oscilloscope

tg tg

Peltier

Intracavity

Cell

22

Head of VeCSELHead of VeCSELMQWs

SDL - diodepumping laser

Intracavity cell

Concave mirrorCooling Peltier element

Towards the outputmirror and spectrometer

23

8975 8980 8985

0 5 10 15 20

38424446485052545659

N2O

R(J)

(16 0 7)

Abs

orba

nce

Wavenumber (cm-1)

ICLAS + VeCSEL at 1.1mICLAS + VeCSEL at 1.1m

24

ICLAS_VECSEL of H2S in the region of the (40±, 0) transitionICLAS_VECSEL of H2S in the region of the (40±, 0) transition

0.95

1.00

9785 9790 9795 9800

Wavenumber (cm-1)

N

eper

ian

Abs

orba

nce

Inte

nsity

(cm

-2/a

tm)

Tra

nsm

ittan

ce

(a) FTS l=100m (Hefei)

0

1

(30+ ,2

)[32

1]-[

330]

(40- ,0

)[53

2]-[

643]

(30+ ,2

)[31

2]-[

321]

(40- ,0

)[10

28]

-[10

47]

(40- ,0

)[62

4]-[

725]

(40- ,0

)[10

1 9

]-[1

0 3

8]

(40- ,0

)[63

3]-[

734]

9785 9790 9795 98000

2x10-6

4x10-6 (c) Simulated

ICLAS-VECSEL

P=27 Torr

leq=30km

259652 9654 9656 9658 9660 96620

1x105

P=1 torr

wavenumber (cm-1)

2.0x105

P=1.3 torr

1x106

P=2.2 torr

4.0x105

P=3.8 torr

Specific laser dynamics of a VECSEL: spectral condensationSpecific laser dynamics of a VECSEL: spectral condensation

Spectral condensation increases with:

Gas pressure

Line intensity

Pumping rate

Generation time

Dependence on the gas pressure

26

Advantages of ICLASQuantitative accuracy similar to classical absorptionNot fluorescing transitionsLimited quantity of gas required (typically 1mmol)Possible association with slit jet or reactorMULTIPLEX ADVANTAGENear infrared and visible accessible

Drawbacks of ICLASNeed for a reference for wavenumber calibrationSpectral resolution limited by the spectrograph Baseline uncertainty in the case of broad unresolved spectrumUV not accessible

SummarySummary