Spatial and electrical characteristics of a Doppler velocimeter

Consistent application of the Huygens–Fresnel principle is used to obtain general relationships for the calculation of the signal/noise ratio of a Doppler photoheterodyne velocimeter. Possible angular and linear mismatch in the optical receiving and transmitting channel is allowed for. Analytic expressions are obtained for the case of unrestricted Gaussian beams. It is shown that the velocimeter is more sensitive to an angular mismatch of the optic axes of the receiver and transmitter. The expressions obtained can be used to estimate the potential usefulness of a velocimeter and to specify the tolerances in the fabrication of the receiving and transmitting optics.