A dual-frequency continuous wave Doppler lidar for long-distance and high-precision velocity measurement is experimentally demonstrated in this article. The lidar system uses the optical heterodyne detection method to avoid complicated optical coherent configuration. All Phase Fast Fourier Transform and Chirp-Z Transform are used to obtain the Doppler frequency shift. The maximum of the calculated Doppler shift was 999.83 Hz with the frequency resolution of 0.54 Hz, and the corresponding theoretical velocity was determined to be 749.87 m/s. During the experiment, the speed of the car was successfully measured in the outdoor environment, the frequency and velocity resolutions were less than 0.5 Hz and AE 0.2 m/s, respectively, and the detection distance of moving and stationary targets reached 1100 m and 2300 m. The capability of the dual-frequency Doppler lidar system has been verified.

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This study presents a dual-frequency microchip laser with a thermo-optically and electro-optically tuned frequency difference. The dual-frequency microchip cavity is formed by bonding a Lithium tantalite (LiTaO3, LTO) crystal chip and a neodymium-doped yttrium aluminum garnet (Nd:YAG) crystal chip. A single longitudinal mode is generated by the Nd:YAG crystal and split into two frequencies with perpendicular polarizations due to birefringent effect in the LTO chip. Furthermore, continuous beat frequency tuning at different scales is realized by adjusting the temperature and voltage applied to the LTO crystal. A maximum beat frequency of up to 27 GHz is obtained, and the frequency difference lock-in phenomenon is observed below the frequency difference of 405 MHz.

A dual-polarization, dual-frequency and dual-transvers-mode laser beam is generated by a dual-medium microchip laser. The dual-transvers-mode includes a linearly polarized LG 01 mode and a perpendicular polarized TEM 00 mode, which have different optical frequencies. How is the beat frequency of the dual-mode influenced by the thermal factors, including cooling temperature of birefringent crystal and thermal effect of gain medium, is experimentally investigated and theoretically analyzed. These studies offer an extension and better understanding of the dual-medium based dual-frequency laser, which is of important applications in coherent Lidar detection and optical communications.

A coherent dual-frequency lidar architecture for long-distance high-precision ranging and velocity measurement is proposed, using the method of optical heterodyne detection, which can avoid complex optical coherence configurations. The system uses a dual-frequency laser with a beat frequency of 200MHz as the dual-frequency light source, and performs measurement through the principles of phase ranging and Doppler velocimetry. The experimental verification shows that the operating distance of the system reaches 3200m, the distance resolution is less than 0.5m, and the speed measurement accuracy range is ±0.25m/s. The results show that the system can realize long-distance high-precision single-point ranging and speed measurement.