New Enhanced Sensitivity Infrared Laser Spectroscopy Techniques Applied to Reactive Plasmas and Trace Gas Detection

New Enhanced Sensitivity Infrared Laser Spectroscopy Techniques Applied to Reactive Plasmas and Trace Gas Detection
Author :
Publisher : Logos Verlag Berlin GmbH
Total Pages : 198
Release :
ISBN-10 : 9783832523459
ISBN-13 : 3832523456
Rating : 4/5 (456 Downloads)

Book Synopsis New Enhanced Sensitivity Infrared Laser Spectroscopy Techniques Applied to Reactive Plasmas and Trace Gas Detection by : Stefan Welzel

Download or read book New Enhanced Sensitivity Infrared Laser Spectroscopy Techniques Applied to Reactive Plasmas and Trace Gas Detection written by Stefan Welzel and published by Logos Verlag Berlin GmbH. This book was released on 2009 with total page 198 pages. Available in PDF, EPUB and Kindle. Book excerpt: Infrared laser absorption spectroscopy (IRLAS) employing both tuneable diode and quantum cascade lasers (TDLs, QCLs) has been applied with both high sensitivity and high time resolution to plasma diagnostics and trace gas measurements. TDLAS combined with a conventional White type multiple pass cell was used to detect up to 13 constituent molecular species in low pressure Ar/H2/N2/O2 and Ar/CH4/N2/O2 microwave discharges, among them the main products such as H2O, NH3, NO and CO, HCN respectively. The hydroxyl radical has been measured in the mid infrared (MIR) spectral range in-situ in both plasmas yielding number densities of between 1011 ... 1012 cm-3. Strong indications of surface dominated formation of either NH3 or N2O and NO were found in the H2-N2-O2 system. In methane containing plasmas a transition between deposition and etching conditions and generally an incomplete oxidation of the precursor were observed. The application of QCLs for IRLAS under low pressure conditions employing the most common tuning approaches has been investigated in detail. A new method of analysing absorption features quantitatively when the rapid passage effect is present is proposed. If power saturation is negligible, integrating the undisturbed half of the line profile yields accurate number densities without calibrating the system. By means of a time resolved analysis of individual chirped QCL pulses the main reasons for increased effective laser line widths could be identified. Apart from the well-known frequency down chirp non-linear absorption phenomena and bandwidth limitations of the detection system may significantly degrade the performance and accuracy of inter pulse spectrometers. The minimum analogue bandwidth of the entire system should normally not fall below 250 MHz. QCLAS using pulsed lasers has been used for highly time resolved measurements in reactive plasmas for the first time enabling a time resolution down to about 100 ns to be achieved. A temperature increase of typically less than 50 K has been established for pulsed DC discharges containing Ar/N2 and traces of NO. The main NO production and depletion reactions have been identified from a comparison of model calculations and time resolved measurements in plasma pulses of up to 100 ms. Considerable NO struction is observed after 5 ... 10 ms due to the impact of N atoms. Finally, thermoelectrically cooled pulsed and continuous wave (cw) QCLs have been employed for high finesse cavity absorption spectroscopy in the MIR. Cavity ring down spectroscopy (CRDS) has been performed with pulsed QCLs and was found to be limited by the intrinsic frequency chirp of the laser suppressing an efficient intensity build-up inside the cavity. Consequently the accuracy and advantage of an absolute internal absorption calibration is not achievable. A room temperature cw QCL was used in a complementary cavity enhanced absorption spectroscopy (CEAS) configuration which was equipped with different cavities of up to 1.3 m length. This spectrometer yielded path lengths of up to 4 km and a noise equivalent absorption down to 4 x 10-8 cm-1Hz-1/2. The corresponding molecular concentration detection limit (e.g. for CH4, N2O and C2H2 at 1303 cm-1/7.66 Aem) was generally below 1 x 1010 cm-3 for 1 s integration times and one order of magnitude less for 30 s integration times. The main limiting factor for achieving even higher sensitivity is the residual mode noise of the cavity. Employing a 0.5 m long cavity the achieved sensitivity was good enough for the selective measurement of trace atmospheric constituents at 2.2 mbar.


New Enhanced Sensitivity Infrared Laser Spectroscopy Techniques Applied to Reactive Plasmas and Trace Gas Detection Related Books

New Enhanced Sensitivity Infrared Laser Spectroscopy Techniques Applied to Reactive Plasmas and Trace Gas Detection
Language: en
Pages: 198
Authors: Stefan Welzel
Categories: Science
Type: BOOK - Published: 2009 - Publisher: Logos Verlag Berlin GmbH

GET EBOOK

Infrared laser absorption spectroscopy (IRLAS) employing both tuneable diode and quantum cascade lasers (TDLs, QCLs) has been applied with both high sensitivity
Advances in Spectroscopy: Molecules to Materials
Language: en
Pages: 454
Authors: Dheeraj Kumar Singh
Categories: Science
Type: BOOK - Published: 2019-10-24 - Publisher: Springer Nature

GET EBOOK

This book presents and discusses recent developments in the broad field of spectroscopy, providing the reader with an updated overview. The main objective is to
Molecular and Laser Spectroscopy
Language: en
Pages: 706
Authors: V.P. Gupta
Categories: Science
Type: BOOK - Published: 2020-07-10 - Publisher: Elsevier

GET EBOOK

Molecular and Laser Spectroscopy, Advances and Applications: Volume 2 gives students and researchers an up-to-date understanding of the fast-developing area of
Cavity-Enhanced Spectroscopy and Sensing
Language: en
Pages: 537
Authors: Gianluca Gagliardi
Categories: Science
Type: BOOK - Published: 2013-10-19 - Publisher: Springer

GET EBOOK

The book reviews the dramatic recent advances in the use of optical resonators for high sensitivity and high resolution molecular spectroscopy as well as for ch
Laser Spectroscopy for Sensing
Language: en
Pages: 601
Authors: Matthieu Baudelet
Categories: Technology & Engineering
Type: BOOK - Published: 2014-02-15 - Publisher: Elsevier

GET EBOOK

Laser spectroscopy is a valuable tool for sensing and chemical analysis. Developments in lasers, detectors and mathematical analytical tools have led to improve