Active imaging with a mercury-cadmium-telluride avalanche photodiode versus a commercial-off-the-shelf camera at 1.645 μm

Active imaging techniques can provide an increased signal-to-noise ratio over passive imaging approaches, particularly in the reflective infrared bands (NIR, SWIR, and eSWIR) where passive solar illumination is reduced relative to the visible band, and cloud cover and time of day can further reduce available illumination. However, providing sufficient illuminator power at long range can introduce severe size, weight, and power trade-offs for system designers, as the strength of the illumination scales proportionally to the inverse square of the illuminator-to-target distance (for a resolved laser spot). Active systems must therefore use illuminator photons efficiently. Avalanche photodiodes (APDs) offer high gain in the electron domain, allowing the detection of a small number of photons by boosting the signal above the floor imposed by read noise. Using both experimental data and modeling, we compare the contrast-to-noise ratio performance of a mercury-cadmium-telluride APD camera and a commercial-off-the-shelf InGaAs SWIR camera with an illuminator at 1.645 μm as a function of illuminator power. Radiometric NVIPM modeling of the sensors is presented and compared to the measured data.