Application of quantum cascade lasers in studies of low-pressure plasmas: Characterization of rapid passage effects on density and temperature measurements

Helden, J. H. van; Horrocks, S. J.; Ritchie, Grant A. D.

doi:10.1063/1.2885725

Cited by 27 publications

(34 citation statements)

References 15 publications

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“…This is of particular importance at lower pressures, since under such conditions the effective laser line width of pulsed QCLs exceeds the typical Doppler line broadening. Non-linear effects also appeared more pronounced [26,78].…”

Section: General Spectroscopic Issuesmentioning

confidence: 88%

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Applying Quantum Cascade Laser Spectroscopy in Plasma Diagnostics

et al. 2016

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Abstract:The considerably higher power and wider frequency coverage available from quantum cascade lasers (QCLs) in comparison to lead salt diode lasers has led to substantial advances when QCLs are used in pure and applied infrared spectroscopy. Furthermore, they can be used in both pulsed and continuous wave (cw) operation, opening up new possibilities in quantitative time resolved applications in plasmas both in the laboratory and in industry as shown in this article. However, in order to determine absolute concentrations accurately using pulsed QCLs, careful attention has to be paid to features like power saturation phenomena. Hence, we begin with a discussion of the non-linear effects which must be considered when using short or long pulse mode operation. More recently, cw QCLs have been introduced which have the advantage of higher power, better spectral resolution and lower fluctuations in light intensity compared to pulsed devices. They have proved particularly useful in sensing applications in plasmas when very low concentrations have to be monitored. Finally, the use of cw external cavity QCLs (EC-QCLs) for multi species detection is described, using a diagnostics study of a methane/nitrogen plasma as an example. The wide frequency coverage of this type of QCL laser, which is significantly broader than from a distributed feedback QCL (DFB-QCL), is a substantial advantage for multi species detection. Therefore, cw EC-QCLs are state of the art devices and have enormous potential for future plasma diagnostic studies.

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Section: General Spectroscopic Issuesmentioning

confidence: 88%

“…In particular, under low pressure conditions, non-linear absorption effects may appear. As a consequence, correction or calibration procedures for measuring reliable concentration values have to be considered [24,26].…”

Section: General Spectroscopic Issuesmentioning

confidence: 99%

Applying Quantum Cascade Laser Spectroscopy in Plasma Diagnostics

et al. 2016

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“…detector, preamplifier, digitiser) may alter the observed absorbance. Nevertheless, the normalised values still enable quantitative results to be obtained [12] or may be transferred to other systems.…”

Section: Discussionmentioning

confidence: 99%

“…However, at low pressure conditions the measured absorption features are affected by an obstacle known as the "rapid passage effect" accompanied by potential power saturation effects [16,17]. Nevertheless, if a sensible normalisation [12] or calibration [9,11] is performed quantitative results can be obtained. This also addresses the required high resolution spectra of molecules with a complex structure which are typically absent or difficult to measure in jet cooled experiments.…”

Section: Introductionmentioning

confidence: 98%

“…QCLAS in the gas phase is now applied in various fields covering environmental trace gas detection [1][2][3], detection of toxic species or explosives [4,5], isotope ratio measurements [6], breath gas analysis [7,8] as well as industrial process monitoring [9] and plasma diagnostics [10][11][12]. The first demonstration of a QCL in 1994 [13], based on the idea of Kazarinov and Suris [14], and further development enable now pulsed or continuous wave, thermoelectrically (TE) cooled, single-mode distributed feedback (DFB-)QCLs to be used in spectrometers.…”

Section: Introductionmentioning

confidence: 99%

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Application of quantum cascade laser absorption spectroscopy to studies of fluorocarbon molecules

Welzel¹,

Степанов²,

Meichsner³

et al. 2009

J. Phys.: Conf. Ser.

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Abstract. The recent advent of quantum cascade lasers (QCLs) enables room-temperature mid-infrared spectrometer operation which is particularly favourable for industrial process monitoring and control, i.e. the detection of transient and stable molecular species. Conversely, fluorocarbon containing radio-frequency discharges are of special interest for plasma etching and deposition as well as for fundamental studies on gas phase and plasma surface reactions. The application of QCL absorption spectroscopy to such low pressure plasmas is typically hampered by non-linear effects connected with the pulsed mode of the lasers. Nevertheless, adequate calibration can eliminate such effects, especially in the case of complex spectra where single line parameters are not available. In order to facilitate measurements in fluorocarbon plasmas, studies on complex spectra of CF 4 and C 3 F 8 at 7.86 µm (1269 -1275 cm -1 ) under low pressure conditions have been performed. The intra-pulse mode, i.e. pulses of up to 300 ns, was applied yielding highly resolved spectral scans of ~ 1 cm -1 coverage. Effective absorption cross sections were determined and their temperature dependence was studied in the relevant range up to 400 K and found to be non-negligible.

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In Situ Monitoring Capabiities of Quantum Cascade Laser Absorption Spectroscopy in Industrial Plasma Processes

Lang

Macherius

Glitsch

et al. 2015

Contrib. Plasma Phys.

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Plasmas in interaction with surfaces are of key importance in a wide range of applications, which include materials technology, microelectronics, environmental issues, and biomedicine. The intense use of plasma technological processes demands proper plasma diagnostic techniques for monitoring, controlling and optimization purposes in industrial environments. In particular, for the improvement of the efficiency of a production process, in situ diagnostic techniques with online capabilities are favorable. From the middle of the last decade a variety of phenomena in molecular non-equilibrium plasmas in which many short-lived and stable species are produced have been successfully studied with quantum cascade laser absorption spectroscopy (QCLAS) in the mid-infrared spectral range. It has been possible to determine absolute concentrations of species, temperatures, degrees of dissociation, dynamics of reaction processes and phenomena involving plasma-surface interactions using spectroscopy, thereby providing a link with chemical and kinetic modelling of the plasma. Since quantum cascade lasers (QCLs) emit near room temperature, i.e., without the need of cryogenic cooling, very compact and robust spectroscopic instruments can be designed. This has stimulated the adaptation of infrared spectroscopic techniques to industrial requirements. Recent applications of infrared absorption spectroscopy using QCLs for in situ monitoring of plasma processes in industrial environments are reviewed. Examples which emphasize the capabilities of QCLAS as plasma diagnostic technique in industrial plasma processes will be given.

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Application of quantum cascade lasers in studies of low-pressure plasmas: Characterization of rapid passage effects on density and temperature measurements

Cited by 27 publications

References 15 publications

Applying Quantum Cascade Laser Spectroscopy in Plasma Diagnostics

Applying Quantum Cascade Laser Spectroscopy in Plasma Diagnostics

Application of quantum cascade laser absorption spectroscopy to studies of fluorocarbon molecules

In Situ Monitoring Capabiities of Quantum Cascade Laser Absorption Spectroscopy in Industrial Plasma Processes

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