Efficient 640  nm actively Q-switched Pr:YLF laser.

An electro-optical (EO) Q-switched laser at 640 nm in Pr3+:LiYF4 (Pr:YLF) is achieved in a compact plane-parallel cavity design. An intracavity lens enables a tightly focused mode within the praseodymium-doped crystal while maintaining a collimated beam in the EO modulator. This configuration is expected to reduce astigmatism and depolarization losses. Under Q-switching laser operation, the system delivers a single-pulse energy of 28.9 µJ with a pulse duration of 47.5 ns at a repetition rate of 5 kHz. When operated at 20 kHz, the laser produces an average power of 380 mW, corresponding to a slope efficiency of 21.2%, demonstrating efficient energy extraction from the Pr:YLF gain medium under EO modulation. To the best of our knowledge, this result represents the highest slope efficiency reported for an EO Q-switched visible Pr:YLF laser.