Abstract
The recent availability of thermoelectrically cooled pulsed and continuous wave quantum and inter-band cascade lasers in the mid-infrared spectral region has led to significant improvements and new developments in chemical sensing techniques using in-situ laser absorption spectroscopy for plasma diagnostic purposes. The aim of this article is therefore two-fold: (i) to summarize the challenges which arise in the application of quantum cascade lasers in such environments, and, (ii) to provide an overview of recent spectroscopic results (encompassing cavity enhanced methods) obtained in different kinds of plasma used in both research and industry.
Highlights
Over the past two decades chemical sensing using laser absorption spectroscopy (LAS) in the molecular fingerprint region from 3 to 20 μm has been established as a powerful in-situ diagnostic tool for molecular plasmas [1,2,3,4,5,6]
These are detailed : Potential non-linear absorption effects and their treatment are briefly discussed in Sections 2.2 and 2.3 Time resolution issues are concerned in Section 2.4 Recent examples of these aspects of p-QCLAS will be presented (Section 2.5)
quantum cascade lasers (QCLs) have been available for more than a decade and in the interim have been extensively used for highly sensitive trace gas sensing spectrometers
Summary
Over the past two decades chemical sensing using laser absorption spectroscopy (LAS) in the molecular fingerprint region from 3 to 20 μm has been established as a powerful in-situ diagnostic tool for molecular plasmas [1,2,3,4,5,6]. In contrast to non-linear frequency conversion, which typically covers only the 3 to 5 μm range and requires optical pumping and an additional (near-IR) light source [8], direct stimulated emission from 3 to 30 μm is achieved across the band gap in tuneable diode lasers (TDLs) composed of lead salts. Another quantity, namely the noise equivalent absorption, NEA, is used to estimate the detection limit: NEA ~ ∆kf −1 / 2 ,.
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