jats:titleAbstract</jats:title> jats:pLaser-Induced Grating Spectroscopy (LIGS) was applied in a high-pressure combustion facility. Instantaneous (sub-μs), spatially resolved (within 5 mm) measurements of temperature and molar fractions of water were obtained using thermal and electrostrictive LIGS signals. Temperatures up to 1800 K and water molar fractions between 0.01 and 0.12 were measured. A new analytic approach was developed to extract temperature from the frequencies of the measured signal within the flame brush region, where mixtures contain both burnt and unburnt gases. Mean product temperatures are shown to be 8% lower than the adiabatic temperatures for the nominal equivalence ratio, and 14% higher than measurements made with a thermocouple, uncorrected for radiation losses. This work represents the first application of LIGS to a high-pressure, turbulent swirling flame, opening up the potential for future uses in other real world applications. Challenges associated with the deployment of the technique are described, as are potential measures to overcome these difficulties.</jats:p>