RF-modulated optical pulses generated by non-resonant frequency-shifted feedback for Lidar-Radar velocimetry

Lidar-Radar detection is based on the use of an optically-carried radiofrequency (RF) signal in order to benefit from both the directivity of the optical beam (Lidar), and the accuracy of RF signal processing (Radar) [1]. For many applications, the use of modulated optical pulses becomes mandatory since the detection is quadratic and the optical power of cw lasers is relatively low. Meanwhile, the pulse-to-pulse coherence has to be preserved to efficiently measure the target velocity from the Doppler shift on the RF [2]. We report on the use of an external feedback cavity containing an acousto-optic modulator to generate a RF-modulated pulse train from any Q-switched laser without any electronics feedback loop. A demonstration of a Doppler velocimetry measurement is performed.