Laser Doppler velocimeter with a differential photodiode array.

A laser Doppler velocimeter is analyzed based on a Fourier optical model. A relation between power spectral density of output signal and structure of optical elements is derived. Based on the relation, a low-frequency disturbance, which appears in an ordinary LDV output, is shown to be canceled by using a differential detector. The output signal becomes a pure narrowband signal whose center frequency is proportional to the object velocity. A velocity measurement experiment result shows the usefulness of the differential detector method.