Development and characterization of PILOT: a transportable instrument for laser-induced grating spectroscopy

Abstract

Laser-induced grating spectroscopy (LIGS) is an optical diagnostic technique for gas-phase thermometry in challenging environments where physical probes are undesirable. The Portable In-line LIGS for Optical Thermometry (PILOT) instrument is a novel self-contained, compact device capable of tracer-free LIGS measurements at 400 Hz. It can be mounted in any orientation and includes internal alignment capability, adjustable path length matching for the pump beams, and an energy/power attenuation mechanism for the pump/probe beams. Characterization of the instrument demonstrated that it can produce accurate (<0.37% in ambient air) and precise (±0.7% in ambient air) spatially- and temporally-resolved temperature measurements, and is now ready to be deployed in research facilities.

Spatial Temperature and Water Molar Concentration Measurements Using Thermal and Electrostrictive LIGS During Operation of a Swirl Burner at Pressure

“…A Verdi V-18 laser from Coherent was used as the probe laser, producing a probe beam at 532 nm with an adjustable power of up to 18 W. Figure 1 shows a schematic of the PILOT unit along with the HPOC and back-end collection optics. The design and characterisation of the unit has been previously discussed [31].…”

“…3. Peak frequencies in the power spectrum, Ŝ𝑖 ( 𝑓 ) between 20 to 90 MHz are expected as thermal and electrostrictive signal frequencies for the given beam crossing geometry [31]. The magnitude of these peaks were interpreted as the characteristic intensity of the signal in the analysis of dominant frequencies.…”

“…This would suggest that it would be possible for the hotter ORZ gases to leak out the slot windows in the tube, causing this result. The PILOT unit is estimated to have a spatial resolution of 6 mm × 0.3 mm × 0.3 mm [31]. Therefore, there is an uncertainty in the position of the measurement volume in the radial direction of the order of 6 mm, so the locations may reflect temperatures inside rather than outside the tube.…”

“…In this work, we applied the Portable In-line LIGS for Optical Thermometry (PILOT) unit [31] to obtain, for the first time, LIGS measurements in a high-pressure gas turbine research facility (the GTRC in Port Talbot, UK). The compact unit was mounted onto a motorised two axis translation stage for effective mapping of the radial (𝑟) and axial (𝑧) directions.…”