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Photonics 2016, 3(3), 45; doi:10.3390/photonics3030045

Applying Quantum Cascade Laser Spectroscopy in Plasma Diagnostics

1
Leibniz Institute for Plasma Science and Technology (INP Greifswald), Felix-Hausdorff-Str. 2, 17489 Greifswald, Germany
2
Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, UK
*
Author to whom correspondence should be addressed.
Received: 22 June 2016 / Revised: 19 July 2016 / Accepted: 21 July 2016 / Published: 25 July 2016
(This article belongs to the Special Issue Quantum Cascade Lasers - Advances and New Applications)

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. View Full-Text
Keywords: plasma diagnostics; quantum cascade laser; infrared spectroscopy plasma diagnostics; quantum cascade laser; infrared spectroscopy
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Röpcke, J.; Davies, P.B.; Hamann, S.; Hannemann, M.; Lang, N.; van Helden, J.-P.H. Applying Quantum Cascade Laser Spectroscopy in Plasma Diagnostics. Photonics 2016, 3, 45.

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