Background suppression for CARS thermometry in highly luminous flames using an electro-optical shutter

An electro-optical shutter (EOS), comprising a Pockels cell located between crossed-axis polarizers, is integrated into a nanosecond coherent anti-Stokes Raman scattering (CARS) system. The use of the EOS enables thermometry measurements in high-luminosity flames through significant reduction of the background resulting from broadband flame emission. A temporal gating ≤100 ns along with an extinction ratio >10,000:1 are achieved using the EOS. Integration of the EOS enables the use of an unintensified CCD camera for signal detection, improving upon the signal-to-noise ratio achievable with inherently noisy microchannel plate intensification processes previously employed for short temporal gating. The reduction in background luminescence afforded by the EOS in these measurements allows the camera sensor to capture CARS spectra at a broad range of signal intensities and corresponding temperatures, without saturation of the sensor, thus enhancing the dynamic range of these measurements.