On Recent Progress in Diagnostics of Molecular On Recent Progress in Diagnostics of Molecular Plasmas

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    On Recent Progress in Diagnostics of Molecular Plasmas using Mid

    Infrared Diode Lasers

    Jürgen Röpcke

    Utilasation des Diodes Laser

    WS 2005

    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 spectroscopy in 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 5 CH4 18 NH3 132 HBr 2820 CO 18400 CO2 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 Species Ground 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

    in te

    ns ityI0 I

    plasma

    ν

    exponential decay

    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 region p-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 Kinetics Planar Microwave Plasma Reactor

    with optical multi pass set-up (White cell)

    Principle of a White cell ca. 30 passes possible

    improved sensitivity for detection of transient species

    HgCdTe detector

    HgCdTe detector

    HgCdTe detector

    TDL system

    monochromator

    microwave window

    microwave appliance module (2.45 GHz)

    Discharge vessel with long path cell

    planar microwave plasma reactor

    plasma region objective mirror box

    field mirror box

    beam splitter

    etalon

    reference gas cell

    He closed cycle refigerator

    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 Kinetics Planar Microwave Plasma Reactor

    A Ohl 1998 J. Phys. IV France 8 Pr7-82, U Haeder INP-Greifswald 2000

    basic research of non-stationary excitation - relaxation phenomena 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

    606.0 606.1 606.2 606.3 0.0

    0.2

    0.4

    0.6

    0.8

    1.0

    wavenumber [cm-1]

    in te

    ns ity

    [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 Radical measured with optical multi pass cell

    H2-Ar-N2-CH3OH p= 1.5 mbar

    P= 1.5 kW pulsed 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 Kinetics Molecular 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

    0 100 200 300 400 1E11

    1E12

    1E13

    1E14

    1E15

    1E16

    CH3OH NH

    3 HCN CH3

    CH 3 OH addedCH

    3 OH added

    N2 [sccm]

    co nc

    en tra

    tio n

    [m ol

    ec ul

    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 used 100 150 200

    1E-16

    1E-15

    1E-14

    1E-13

    1E-12

    1E-11

    1E-10

    H2 N2 CH CH2 CH3 CH4

    E0/N [Td]

    k d is [

    cm 3 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 Kinetics Comparison 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, [