A two-grating method for combined beam splitting and frequency shifting in a two-component laser-Doppler velocimeter

The use of a rotating radial phase grating to carry out beam splitting and frequency shifting in a laser-Doppler velocimeter is briefly reviewed. This technique is not new. However, the present design adds a substantial new element by using two overlapping radial gratings to produce a two-channel system in which channel separation can be accomplished by electronic filtering of the signal from a single detector.