<title>Multichannel acousto-optic spectrometer</title>

Abstract

Radiometer spectrometers are used in millimeter-wave radio astronomy for the spectral measurement of molecular rotational transitions. The spectrum ofinterest spans 10's ofGHz and the measurement time is large in order to obtain useful signal-to-noise ratio. We describe here the design and performance of a multichannel acousto-optic spectrometer for radio astronomy spectroscopy applications. This instrument has 4 channels and can process signals from 4 separate sources simultaneously. The bandwidth ofeach channel is 1 GHz and the frequency resolution is 1 MHz, providing simultaneous processing over 4,000 1 MHz channels. The instrument's optical train includes a laser diode source integrated into one single path using an innovative polarization switching 4-channel self-collimating Gallium Phosphide Bragg cell with close channel packing. A two-dimensional photodetector array samples all 4 channels using a novel read-out scheme that allows a subset of the array to be read out and digitized to 12 bits while simultaneously integrating photo-charge for the next image. The instantaneous RF power spectral density measurement capability of this instrument also makes it useful for signal analysis (including electronic intelligence reception) and test and measurement equipment applications.