| सारांश: | <p>Laser-Induced Grating Spectroscopy (LIGS) is a non-intrusive optical diagnostic primarily used for temperature measurements in the gas phase. The technique boasts excellent accuracy and precision, achieved at relatively low cost and complexity, compared to similar diagnostics.</p>
<p>A drawback of the technique is its temporal resolution, which has generally been limited to 10 Hz without compromising the accessibility of the technique (through the use of toxic tracer species or expensive lasers). The discovery of a new LIGS tracer species, biacetyl, which enables the use of accessible high repetition rate lasers is presented. Temperature measurements, obtained at a rate of 1 kHz, and the application of the technique to study thermoacoustic instabilities, have been demonstrated.</p>
<p>A significant problem for LIGS is an inherently poor spatial resolution due to an elongated (in the axial direction) measurement region. A novel approach enabling simultaneous 1-D spatially-resolved LIGS measurements in the axial direction is presented. This capability can be incorporated into standard LIGS experiments with a negligible increase in cost or complexity, thus preserving the accessibility of the technique. A computational model for the approach was developed and validated. A preliminary experiment demonstrated a 93% improvement in axial spatial resolution, as well as a three-fold increase in the number of single-shot measurements obtained, when compared to a standard LIGS configuration.</p>
<p>To exploit the significant advantages of the technique by enhancing its accessibility, a unique transportable LIGS system (named PILOT) was designed, manufactured and characterised. The mobile, self-contained system is capable of collecting tracer-free LIGS measurements at a rate of 400 Hz. An accuracy of less than 0.37% and precision of +/-0.7% was demonstrated for temperature measurements in room air. Characterisation experiments showed that the use of an avalanche photodetector for signal detection would permit the use of the system in scattering environments. A novel systematic investigation of tracer-free LIGS in different gases highlighted the polarisability of a gas as a key indicator for performance of the technique. These findings will inform experimental design for future applications. Finally, the deployment of PILOT in a research facility was demonstrated.</p>
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