Multichannel light detectors and their use for CARS spectroscopy

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Abstract
A broadband CARS system designed to measure flame temperature from hot nitrogen CARS spectra is described, and a source of temperature error is identified and attributed to nonlinear behavior of the optical multichannel diode array detector. Detector sensitivity, linearity, uniformity, and noise are discussed. Data are presented for the Tracor-Northern TN-1223-4GI and TN-6132 detectors. It is shown that the nonlinearity observed with CARS signals is a function of radiation density at the detector input plane. This nonlinearity is associated with saturation in the microchannel plate intensifier and should be observable with short duration high intensity light pulses other than CARS, and with intensified detectors (both diode array and vidicon) other than the Tracor-Northern. The nonlinearity observed with the TN-1223-4GI detector can be eliminated by reducing the radiation density. At maximum sensitivity the detector shot noise contributes a significant component to the shot-to-shot variation of the spectral profile of the CARS signal.