Picosecond hybrid laser based on semiconductor laser, fibre and Nd : YVO4 amplifiers. Investigation of effects limiting the peak power

Based on a distributed-feedback (DFB) semiconductor laser, an ytterbium fibre amplifier, an Nd : YVO₄ amplifier, and a frequency converter, we designed a hybrid picosecond laser for satellite laser ranging. A gain exceeding 10⁸ is achieved while maintaining the temporal shape and spectrum of the pulses, with a low noise level and a divergence close to the diffraction limit. The pulse energy after conversion to the second harmonic at λ = 532 nm is 2.2 mJ with a duration of 27 ps and a repetition rate of 1 kHz. It is shown that the main effects limiting the peak power are spectrum broadening due to self-phase modulation in a fibre amplifier and large-scale self-focusing in the Nd : YVO₄ amplifier. Optimisation of the amplifier geometry and the use of a uniform profile of the pump radiation intensity make it possible to reduce the effect of self-focusing and increase the energy efficiency of the amplifier.