www.inp-greifswald.de
On Recent Progress in Diagnostics of Molecular Plasmas using Mid
Infrared Diode Lasers
Jürgen Röpcke
Utilasation des Diodes Laser
WS2005
March 17th, 2005
Col de Porte France
Vor_Grenoble1_publ.ppt
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2Outline
Introduction and Motivation
TDLAS in Molecular Plasmas Containing Hydrogen
IRMA: Transportable Infrared TDLAS System
Plasmas Containing Boron in Research and Industry
QCLAS for Plasma and Trace Gas Monitoring and Control in Industry
“Q-MACS”- A New Compact QCL System for Plasma and Gas Analysis
Summary
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3Orientation
Orientation in Europe's
Plasma and Diagnostics Community
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4Orientation
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5Greifswald – Old Town at the Baltic Sea
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6INP Greifswald
1999: new building
3700 sqm floor space
110 working places
26 laboratories, clean room, chemical laboratory
15 complete devices for plasma research
mobile measuring and diagnostics equipment
laboratories for applications
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7TDLAS
Tunable Diode Laser Absorption Spectroscopy
for Plasma Diagnostics and Trace Gas Measurements
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8IR Spectroscopy
Why absorption spectroscopyin the mid infrared region,
3 – 20 µm
and NOT in the visible 0.3 – 0.8 µm
or near infrared region ?0.8 – 3 µm
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9IR Absorption Spectroscopy
Species Ratio of Absorption Coefficients αMIR/ αNIR
H2O 5CH4 18NH3 132HBr 2820CO 18400CO2 52500
Many others (e.g. H2S, N2O, NO, HCN) – only absorptions in MIR !
It is the sensitivity !
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10
IR Absorption Spectroscopy with Tunable Diode Lasers (TDLAS)
Detection of Stable and Transient Molecular SpeciesGround State Concentrations
High Sensitivity and Selectivity (∆ν ~ 10-4 cm-1, (I0-I)/I0 ~ 10-4...10-5)
Time Resolution (s ... ms ... µs … ns)
Cooling necessary: Laser Diodes 20-100 K, Detectors 80 K !!Low power: < 1 mW
Alternative:Quantum Cascade Lasers: QCLAS☺ Room Temperature Operation☺ Short Pulses (ns), Power > 10 mW
Plasma Diagnostics by IR Absorption Spectroscopy
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11TDLAS
distance
inte
nsityI0 I
plasma
ν
exponentialdecay
I (ν) = I0 (ν) exp (-k(ν) l n)
Infrared Tunable Diode Laser Absorption Spectroscopy (TDLAS)stable and transient molecular species
ground state information - species concentration
high selectivity and sensitivity (∆ν ~ 10-4 cm-1, (I0-I)/I0 ~ 10-4...10-5)
spatial and temporal resolution (s ... ms ... µs)
Lambert-Beer absorption law
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12TDLAS
+
-
p region
n regionp-n junction
metal contact
metal contact
insulator
resonator front facet
active zone
© U. Haeder
Infrared Diode Laser
U Schießl et al. Booklet of Laser Components 1998
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13Plasma Chemistry and Reaction KineticsPlanar Microwave Plasma Reactor
with optical multi pass set-up (White cell)
Principle of a White cellca. 30 passes possible
improved sensitivity fordetection of transient species
HgCdTedetector
HgCdTedetector
HgCdTedetector
TDL system
monochromator
microwave window
microwave appliancemodule (2.45 GHz)
Discharge vessel with long path cell
planar microwave plasma reactor
plasma regionobjectivemirror box
field mirror box
beam splitter
etalon
reference gas cell
He closed cyclerefigerator
F Hempel, P B Davies, D Loffhagen, L Mechold and J Röpcke 2003 Plasma Sources Sci. Technol. 12 S98
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14Plasma Chemistry and Reaction KineticsPlanar Microwave Plasma Reactor
A Ohl 1998 J. Phys. IV France 8 Pr7-82, U Haeder INP-Greifswald 2000
basic research of non-stationary excitation - relaxationphenomena and of plasma chemistry
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15Plasma Chemistry and Reaction Kinetics
plasma region below the microwave window
A Ohl 1998 J. Phys. IV France 8 Pr7-82, U Haeder INP-Greifswald 2000
Sideview of a Double Microwave Plasma Source
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16Plasma Chemistry and Reaction Kinetics
606.0 606.1 606.2 606.30.0
0.2
0.4
0.6
0.8
1.0
wavenumber [cm-1]
inte
nsity
[a.u
.]
16.502 16.500 16.498 16.496 16.494
CH3OH CH3
wavelength [µm]
F Hempel, L Mechold and J Röpcke 2001 XXV. ICPIG, Nagoya, Conf. Proc. 4 223
Example of Sensitive Detection of Methyl Radicalmeasured with optical multi pass cell
H2-Ar-N2-CH3OHp= 1.5 mbar
P= 1.5 kWpulsed diode laser
nCH3 ~ 1012 cm-3 (~ 20 % abs.)
detection of transient species
in a wider dynamic range possible
time resolved analysis for kinetic
studies
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17Plasma Chemistry and Reaction KineticsMolecular Concentrations as a Function of Various H2/N2 Ratios
in H2-N2-Ar-CH3OH Plasmas
microwave plasma, p=1.5 mbar, P=1.5 kW, flowing conditions
0 100 200 300 4001E11
1E12
1E13
1E14
1E15
1E16
CH3OH NH
3 HCN CH3
CH3OH addedCH
3OH added
N2 [sccm]
conc
entra
tion
[mol
ecul
es c
m-3] 400 300 200 100 0
H2 [sccm]
0 100 200 300 400
CH4 C2H2 C2H4 C2H6 CH2O
N2 [sccm]
400 300 200 100 0
1E11
1E12
1E13
1E14
1E15
1E16
H2 [sccm]
F Hempel, P B Davies, D Loffhagen, L Mechold and J Röpcke 2003 Plasma Sources Sci. Technol. 12 S98
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18Plasma Chemistry and Reaction Kinetics
Calculated Rate Coefficients for Electron Impact Dissociation
Kdis as a function of
reduced field strength E0/N
in H2-N2-Ar-CH4 plasmas
determined from
Boltzmann equation
for model: E0/N= 180 Td
was used100 150 200
1E-16
1E-15
1E-14
1E-13
1E-12
1E-11
1E-10
H2 N2 CH CH2 CH3 CH4
E0/N [Td]
k dis [c
m3 s-1
]
100 150 200
C2H C2H2 C2H3 C2H4 C2H5 C2H6
E0/N [Td]
F Hempel, P B Davies, D Loffhagen, L Mechold and J Röpcke 2003 Plasma Sources Sci. Technol. 12 S98
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19Plasma Chemistry and Reaction KineticsComparison of Experimental and Modelling Results
in H2-N2-Ar-CH4 Plasmas
prediction of further radicals: [NH] = 6 x 1012 cm-3,[NH2] = 3 x 1011 cm-3, [CH] = 8 x 1010 cm-3, [CH2] = 1 x 1012 cm-3,[C2H] = 7 x 106 cm-3, [C2H3] = 3 x 109 cm-3, and [C2H5] = 5 x 1010 cm-3
NH3 HCN CH3 CH4 C2H2 C2H4 C2H6
1E11
1E12
1E13
1E14
1E15co
ncen
tratio
n [m
olec
ules
cm
-3]
white – measured by TDLAS
grey – calculated
F Hempel, P B Davies, D Loffhagen, L Mechold and J Röpcke 2003 Plasma Sources Sci. Technol. 12 S98
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20Plasma Chemistry and Reaction KineticsMain Reaction Paths in H2-N2-Ar-CH4 Plasmas
F Hempel, P B Davies, D Loffhagen, L Mechold and J Röpcke 2003 Plasma Sources Sci. Technol. 12 S98
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21TDLAS Applications
Properties of Radicals
CN, CH3
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22TDLAS for Molecular SpectroscopyPlanar Microwave Plasma Reactor
with optical multi pass set-up (White cell)
Principle of a White cellca. 30 passes possible
improved sensitivity fordetection of transient species
HgCdTedetector
HgCdTedetector
HgCdTedetector
TDL system
monochromator
microwave window
microwave appliancemodule (2.45 GHz)
Discharge vessel with long path cell
planar microwave plasma reactor
plasma regionobjectivemirror box
field mirror box
beam splitter
etalon
reference gas cell
He closed cyclerefigerator
F Hempel, P B Davies, D Loffhagen, L Mechold and J Röpcke 2003 Plasma Sources Sci. Technol. 12 S98
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23
Detection of Four Isotopic Forms of the CN Radicalin Microwave Discharges
12C15N P(20) line with doublet
splitting at 1931.80 cm-1
1931.75 1931.80 1931.85 1920.20 1920.25
TDLAS for Basic Research
13C15N P(13) line with doublet
splitting at 1920.20 cm-1
2f modulation technique forground state detection (81 lines)
M. Hübner, M. Castillo, P. B. Davies, and J. Röpcke 2005 Spectrochim. Acta A 61 57.F. Hempel, J. Röpcke, A. Pipa and P. B. Davies 2003 Mol. Phys. 101 589
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24
12C14N and 13C14N (dotted) lines
1900 1950 2000 2050 21000
5
10
15
20
inte
nsity
[a.u
.]
wavenumber [cm-1]1900 1950 2000 2050 2100
0
5
10
15
inte
nsity
[a.u
.]
wavenumber [cm-1]
M. Hübner, M. Castillo, P. B. Davies, and J. Röpcke 2004 Spectrochim. Acta A Mol. Spectrosc. A 61 57.F. Hempel, J. Röpcke, A. Pipa and P. B. Davies 2003 Mol. Phys. 101 589
TDLAS for Basic Research
Stick Diagrams of CN Absorption Lines from the Fundamental Band
determination of molecular parameters and constants:- band origins, Bv, Dv, re - values
12C15N and 13C15N (dotted) lines
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25TDLAS for Basic Research at Radicals
The CH3 Radical
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26
5 µmWhy CHWhy CH33 ??
- Important growth species growth species for diamond anddiamond-like carbon films
- Key role in the complex chemical scheme ofcarbon-containing species discharges
- Important in interstellar chemistry
Why ν2 Band?
- The strongest band of CH3 - IR at 16.5 µm
- Successfully used for [CH3] by IR-TDLAS
- ν2 band pattern detected on the upperatmosphere of Neptune
TDLAS for Basic Research at Radicals
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27
microwavegenerator
optical unit
IRMA system
control unit
discharge vessel with mutiple pass optics
planar microwave plasma reactor
microwave appliancemodule ( 2.45 Ghz )
IR detectormicrowave window
objective mirror box
functiongenerator
Experimental set-up: Pulsed microwave plasma with optical multiple pass IR-TDLAS arrangement
Characteristics:
- f = 2.45 GHz;- fpulse = 50 mHz;- P = 1.5 kW;- p = 1 mbar;- precursor:
[(CH3)3CO]2diluted in Ar 20 sccm
IRMA +TDL Wintel Software
- integral of absorption
coefficient
- ms – time resolution
TDLAS for Basic Research at Radicals
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28
Decay method for CH3 Concentration- during the plasma off phase – decaymeasurements of the ∫ k(ν)dν
- the main loss channel of CH3:
CH3 + CH3 + M K1 C2H6 + M
- time dependency of the concentration:
0 5 10 15 20 250.0
0.2
0.4
0.6
0.8
1.0N(t)/N0=K2/[(K2+2N0K1)exp(K2t)-2K1N0]
N(t)/N0=1/(1+2N0K1t)
N(t)/N0=exp(-K2t)
N(t)
/N0
time [ms]
0 5 10 15 20 250
6
12
18 N0/N(t)=1+2K1N0t
N0/N
(t)
time [ms]
The recombination into C2H6 - the mainloss channel.
NKNKdtdN
22
12 −−=
The concentration is obtained from theslope of:
N0/N(t)=1+2K1N0t
K1 - the recombination rate constant
K2 - other loss channels
Based on the new data of K1 the total [CH3] was determined.
TDLAS for Basic Research at Radicals
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29
Temperature dependence of the line strength
200 400 600 800 1000 1200 1400 16001E-22
1E-21
1E-20
1E-19
1E-18
S [c
m m
olec
ule-1
]
temperature [K]
Q(3,3) Q(6,6) Q(12,12)
Region IIIRegion IIRegion I
- for practical purpose - line strength values are more convenient
- three temperature regions where Q(3,3), Q(6,6) or Q(12,12) is recommended
- changes about two orders of magnitude of line strengths in 1000 K temperature range
Region I:
- astrophysics
Region II:
- moderate temperature
plasmas
Region III:
- diamond processplasmas
TDLAS for Basic Research at Radicals
G. D. Stancu, P. B. Davies, and J. Röpcke 2005 J. Chem. Phys. 122 014306.
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30
Transition dipole moment of the ν2 fundamental band
The present value 0.22±0.02 D leads to two times higher concentrations!
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45
unknown third body
K1 - new dataJ.Pacansky,W.Koch and M.D. Millertheoretical calculations (1990)
present workmeasurement (2004)
J.Wormhoudt and K.E.McCurdymeasurement (1989)
P.Botshwina,J.Flesch and W.Meyerwavefunctions calculation (1983)
C.Yamada and E. Hirotameasurement (1983)
µ(v=1 0) [D]
C.Yamada,E.Hirota and K.Kawaguchiassumption (1981)
TDLAS for Basic Research at Radicals
G. D. Stancu, P. B. Davies, and J. Röpcke 2005 J. Chem. Phys. 122 014306.
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31Tunable Diode Laser Absorption Spectroscopy
Status:
Detection of Only One Molecule or Radical in Time
Time Resolution: Rather Slow and Difficult
Data Handling: Slow and Difficult
New Approach:
TDLAS System with 4 Diodes (T ≥ 30 K)
Time Resolution ~ 1 ms (Lifetime of Radicals, ...)
Simultaneous Detection of ~ 4 Species
Spatial Resolution Inside Plasma
Exhaust Gas Detection (Multi Path Cell)
System: Compact and Transportable !!
Objective: ☺ TDLAS for Plasma Process Control in Industry !!
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32IRMA System
J Röpcke, L Mechold, M Käning, J Anders, F G Wienhold, D Nelson, M Zahniser2000 Rev. Sci. Instrum. 71 3706
left: optical table
right: data acquisition
with controllers and PCs
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33Properties of Plasmas Containing Boron
J Röpcke, L Mechold, M Osiac, S Saß and A Liebetrau 2000 Zwischenbericht BMBF-Projekt, FKZ: 13N7451
Measurement Campaign in Cooperation with IndustryTDLAS and OES at industrial reactors
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34Properties of Plasmas Containing Boron
B P Lavrov, M Osiac, A V Pipa, J Röpcke 2003 Plasma Sources Sci. Technol. 12 576
64 % H2 + 33 % Ar + 3 % B2H6
p= 1.5 mbar, φtotal= 150 sccm
OES
Fragmentation of Diborane in Microwave Plasmasdepending on power and admixture
0.0 0.5 1.0 1.5 2.0 2.5
0.0
0.5
1.0
BH
BH3
B2H6
abso
rptio
n co
effic
ient
s [a.
u.]
P [kW]
TDLAS
H2 + Ar + B2H6
P= 2.5 kW, p= 2.5 mbar, φtotal= 150 sccm
0 1 2 3 4
0
1
2
3
4
[B] [
1011
ato
ms c
m-3]
B2H6 admixture [%]
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35
Measurement Campaign at Uni Erlangen 05/2004
TDLAS in Hot Filament Reactors
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36QCLAS
Quantum Cascade Laser Absorption Spectroscopy
(QCLAS)
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37Scheme of a DFB-QCL
Alpes Lasers, Neuchatel, Switzerland
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38Photo of a DFB-QCL
Product of Alpes Lasers, Neuchatel, Switzerland
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39Systems with DFB-QCL
Advantages:• Decreased Instrument Size and Weight
• Reduced Transport Logistics
• Unattended Remote Monitoring
• “Turn-Key” Operation
• Improved Safety
Disadvantages:• Increased Laser Line Width
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40Q-MACS-System
QCL-System „Q-MACS“
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41Q-MACS Idea
Problem: In-situ controlling of plasma processes and trace gas analysis in ppb range - on-line not available
Idea: Using of a new class of infrared laser: Quantum Cascade Lasers (QCL) – working without heavy cooling at room temperature
Result: Development of a new compact measuring system for industrial applications of QCLAS : Q-MACS
Q-MACS: Quantum Cascade Laser Measuring and Controlling System
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42Q-MACS-System
Working at room temperature: Q-MACS-Heads
recent development for industrial application of QCLAS
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43View Inside a DFB-QCL
Alp
es L
a ser
s, N
euch
a tel
, Sw
itzer
land
back- contact
top-contact
buried grating
active regions& injectors
InP substrate
high intensity (3-20 µm)short pulsestuneablesmall line width
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44Plasma – and Trace Gas Analysis with Q-MACS
Gas Molecules
Q-MACS
Principle: Absorption of the laser beam by gas / plasma molecules
Result: On-line concentration of molecules
Control Unit
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45Q-MACS System
Q-MACS Head with Control Unit
Prototype
compact, exact, easy to usewww.q-macs.de
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46Q-MACS System
Applications: Insight into plasma chemical processes
Trace gas monitoring for environmental studies
High sensitive gas analysis in chemical industry
Advantages: Ground state concentrations of molecules
Monitoring and control of combustion and plasma processes
Temporal resolution of concentration measurements
Software for industrial requirementsFor improvements of process effectiveness, reliability and reproducibility
Disadvantage: Line-off-sight method: Difficult spatial resolution
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47Q-MACS System
Technical Features: Width of single pulses: 10 … 255 ns
Power: 10 – 30 - … mW
Pulse frequency: up to 1 MHz
Working regime: Single pulse
Ramp
Gate
Temperature range: - 30 … + 40 °CAdapted to TDLWintel (Aerodyne Research, USA)Adapted to QCLs from Alpes Lasers, CH
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48Wide Spread Applications
Exhaust Gas Treatment / Environmental Technology
Process Control in Deposition and Etching ReactorsSemiconductor IndustryCar IndustryMedicine TechniqueCombustion Fusion Devices...
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49Q-MACS-System
System Test
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50Q-MACS-SystemExample of a fast measurement
NH3 Spectrum with FitMeasured in a Single Pulse
100 ns
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51Q-MACS-System
Example of a slow measurement
NH3 Absorption Lines at 1614 cm-1 with FitMeasured with Current Ramp
1 ms
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52Q-MACS-System
Test at Aerodyne Research Inc., USA
In a QCLAS System for Air-born Measurements - May 2004
Q-MACS Head
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53Q-MACS-SystemQ-MACS Trace
1 channel system with56 m long path cell
Sensitivity: ppb(e.g. NH3, CH4)
Q-MACS Head
Control Unit
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54Q-MACS-System
Measurements at Industrial Plasma Reactors
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55Plasma Reactors of Eltro GmbH, Baesweiler
Open DC-Reaktorof Average Size
Working in Pulse Mode
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56Q-MACS-System
Measurements at DaimlerChrysler AG
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57Q-MACS-SystemMeasurements at DaimlerChrysler AG
View into the Plasma of the Pulsed Reactor
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58
Time Dependence of Diborane Concentration in DC-Reactor
B2H6 Spectrumwith Fit
[B2H6] = f(t)
t
C4%
0
cm-1
I
ca. 1618 cm-1
First QCLAS Measurements inIndustrial Plasma Reactors !!
Q-MACS-System
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59QCLAS at Industry
Related Problems of QCLAS at Industry
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60Measurement of Complex Spectra - TDLAS
BCl3-Absorption Spectra Measured with TDLAS and IRMA TDLWintel: Aerodyne Research Inc. USA
left: 963.4 – 963.8 cm-1, right: 964.3 – 964.6 cm-1
Software: In Co-operation with Dr. C. Harward, Nottaway, VA, USA
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61BCl3-Concentration - TDLAS
Monitoring of the BCl3-Concentration in a Plasma Reactorrel. Precision: ca. 0.1 %
t
C
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62Chemistry in CH4 Plasma - QCLAS
On-Line Measurement of CH4 Dissociation and C2H2 Productionat 1300 cm-1
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63Software for Industrial Applications
Time Dependence of [BCl3] in Plasma Reactor
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64SummaryApplication of TDLAS to study plasma chemistry and reaction kinetics
TDLAS Status: 16 stable and 10 transient molecules in 12 different
discharge configurations
Multiple on-line concentration measurement possible in ms
QCLs provide cryogen-free trace gas detection with both open and closed path sampling: sensitivity up to ppb level, temporal resolution: >20 ns
QCLAS - potential for compact instrumentation and remote operation
and industrial process monitoring and controlCH4, C2H2, C2H4, NH3, NO2, BCL3, B2H6 measured by QCLAS
QCL-System „Q-MACS“ – recent development for industrial application