Time-resolved Fourier Transform Infrared Emission Spectroscopy: Application to Pulsed Discharges and Laser Ablation

Abstract

1.1 Time-resolved Fourier transform infrared spectroscopy Time-resolved spectroscopy (TRS) is a wide-spectrum technique used for studying the dynamics of chemical reactions, or the dynamic properties of molecules, radicals and ions in liquid, gas and solid states. In the infrared spectral range it can be achieved by using lasers (Smith & Palmer, 2002), grating spectrometers (Rodig & Siebert, 2002) or by interferometers (Masutani, 2002). The presented report is focused on the development and application of a time resolved system based on commercially available continuously scanning high resolution interferometer and its modification for time resolved Fourier transform spectroscopy (TR-FTS) (Kawaguchi et al., 2003). The main advantage of TR-FTS lies in obtaining spectra in wide wavenumber intervals. The speed of data acquisition is limited by the duration of the acquisition process and by the band width of the used detector. There are basically two ways of obtaining the time-resolved spectra: the continuous scan and the non-continuous, step scan (Masutani, 2002; Rodig & Siebert, 2002; Smith & Palmer, 2002). The continuous scan is best used when the duration of the observed phenomenon is longer than the time needed for carrying out one scan, i. e. for obtaining an interferogram up to the maximum trajectory difference (Rapid and ultrarapid scanning FT). Time-shifted individual scans provide a sequence of interferograms from which a conventional spectrum can be calculated. When using the rapid scanning and short distance mirror traversing, a time resolution from 1000 s to 1 ms can be reached. A special approach to the time-resolved spectra of phenomena lasting from milliseconds to microseconds is the synchronous scanning FT technique (Kawaguchi et al., 2005). This method, as well as the methods mentioned below, requires the possibility of initiating the reaction in a pulse mode, e. g. using a laser, electric discharge, electron bombardment, a UV discharge lamp, etc. (Civis et al., 2006). The apparatus carries out a continuous scan and, during the pulse, it reads the signal from the detector corresponding to the position