Light makes a double pass through the interferometer in the white light velocimeter.
Noncontact remote measurement of velocity has important applications in industry, medicine, science, and law enforcement. Most velocimetry techniques measure the Doppler frequency shift that target motion imparts to reflected light. Because the velocities being measured are much smaller than the speed of light, the Doppler shifts are extremely slight. To detect such small shifts, velocimeters require highly coherent lasers to produce light with high spectral purity. To analyze the reflected light, these techniques use an interferometer that is extremely vibration-sensitive and difficult to align and requires heavy, expensive optical mounts and a sturdy platform.