Professor Paul Ewart

Abstract:

Thermometry using Laser Induced Grating Spectroscopy (LIGS) is reported using a high– repetition rate laser system, extending the technique to allow time–resolved measurements of gas dynamics. LIGS signals were generated using the second harmonic output at 532 nm of a commercially available high– repetition rate Nd:YAG laser with nitrogen dioxide as molecular seed. Measurements at rates up to 10 kHz were demonstrated under static cell conditions. Transient temperature changes of the same gas contained in a cell subjected to rapid compression by injection of gas were recorded at 1 kHz to derive the temperature evolution of the compressed gas showing temperature changes of 50 K on a time scale of 0.1 s with a measurement precision of 1.4 %. The data showed good agreement with an analytical thermodynamic model of the compression process.

Abstract:

Detection of multiple transitions in NO and H2O using multi-mode absorption spectroscopy, MUMAS, with a quantum cascade laser, QCL, operating at 5.3 m at scan rates up to 10 kHz is reported. The linewidth of longitudinal modes of the QCL are derived from pressure-dependent fits to experimental MUMAS data. Variations in the spectral structure of the broadband, multi-mode, output of the commercially available QCL employed are analysed to provide accurate fits of modelled MUMAS signatures to the experimental data.