Single-frequency Q-switched Er:YAG laser with Herriott-type multi-pass cavity

We report a single-frequency Er:YAG Q-switched laser with Herriott-type multi-pass cavity (MPC). The use of the MPC increases the output pulse width from 189 ns to 445 ns. The single-frequency pulsed laser with the MPC delivers output at a repetition rate of 500 Hz and achieves a maximum single-pulse energy of 5.4 mJ. A monolithic Er:YAG non-planar ring oscillator (NPRO) serves as the seed laser, and single-frequency pulsed operation is realized through the Ramp-Fire injection-locking technique. The linewidth of the pulsed laser is measured to be 1.09 MHz, with a standard deviation of the central frequency of 0.97 MHz. The standard deviation of the energy fluctuation is 0.10 mJ. The M²factors are measured as 1.69 in the X direction and 1.70 in the Y direction. To the best of our knowledge, this is the first demonstration of a single-frequency pulsed injection-locked laser employing an MPC configuration.