Linewidth measurement method for fiber-solid-state hybrid high-energy single-frequency laser

In a fiber-solid-state hybrid high-energy single-frequency laser, a continuous-wave single-frequency fiber laser is employed as the seed source, by which pulsed laser is formed through electro-optic modulation, and the seed laser is amplified by multi-stage solid-state amplifiers, so that high-energy single-frequency pulsed laser output is achieved. Therefore, laser linewidth is regarded as one of the important indicators for evaluating the performance of this type of laser, and synchronous measurement of the linewidths of the seed laser and the amplified pulsed laser is considered to be of great significance for laser performance evaluation. A synchronous linewidth measurement method for fiber-solid-state hybrid high-energy single-frequency lasers based on optical heterodyne detection was proposed in this paper. For the continuous-wave single-frequency fiber laser seed source, its linewidth was measured by a short-fiber delayed self-heterodyne method; for the amplified single-frequency pulsed laser, the seed laser was served as the local oscillator, optical heterodyne detection was adopted for measurement, and the pulsed laser linewidth was extracted by combining with fast Fourier transform; meanwhile, the two measurement modes were switched by an optical switch, by which synchronous measurement of the seed laser and pulsed laser linewidths was realized. In this paper, a linewidth measurement model for single-frequency continuous-wave/pulsed lasers based on optical heterodyne detection was first established, the design parameters of the linewidth measurement system were formed, and the corresponding measurement system was constructed. Meanwhile, a fiber-solid-state hybrid high-energy single-frequency laser was built, and the linewidths of the laser seed and the amplified pulsed laser were tested by using this measurement system. A seed laser linewidth of 2.198 kHz was measured, and a pulsed laser linewidth of 0.706 MHz was obtained after solid-state amplification, which represents a broadening of approximately 321 times relative to the seed laser. It is demonstrated by the results that the linewidths of the seed laser and the amplified pulsed laser can be effectively measured by this method, and the linewidth broadening during the multi-stage amplification process is revealed, by which a supporting means is provided for the development of fiber-solid-state hybrid high-energy single-frequency lasers.