Dual Bragg cell local oscillator generator for laser heterodyne radar systems

In a laser heterodyne radar system it is convenient to generate the necessary optical local oscillator beam by frequency translating a sample of the transmitter beam power. Of the several means for doing this, one that stands out for simplicity, stability, and efficiency is the Bragg cell. The Bragg cell generates an output beam at frequency f0 − f a from a transmitter beam at f0. Unfortunately, it also provides some weaker outputs at h0 + f a , f0, f0 − 2f a , etc. These first two weaker outputs can interfere with the acquisition of fine Doppler information in weak returns at zero range rate and at some other range rates.