Acousto-optic rf spectrum analyzer for plasma diagnostics

An acousto-optic rf spectrometer (AOS) has been designed and constructed for use on the Constance B and TARA mirror experiments at Massachusetts Institute of Technology (MIT). The AOS is, in essence, a preprocessor of data that can come from a variety of sources including rf probes and microwave/laser scattering experiments. The output of the AOS is the Fourier transform amplitude of the input in a parallel format suitable for computer acquisition. The spectrometer, having a bandwidth of 500 MHz, together with its receiver, is capable of looking at fluctuations anywhere in the frequency range of a few MHz up to 4 GHz. Power levels of a few nanowatts can be detected. Complete 500-MHz-wide spectrums can be processed and acquired at the rate of 1 every 10 ..mu..s. The optical components, receiver, and data-acquisition interface will be discussed and initial data taken on the Constance B experiment will be shown.