Passively Q-switched sub-100 ps Yb3+:YAG/Cr4+:YAG microchip laser: experimental results and numerical analysis

We demonstrate sub-100 ps pulses with a Yb³⁺:YAG microchip laser passively Q-switched by a Cr⁴⁺:YAG saturable absorber. By introducing a subcavity, the laser threshold and the saturation energy are decreased which helps to prevent damage and to vary the effective emission and absorption cross sections. Pulse widths of 84 ps, repetition rates of 3.3 kHz and pulse energies of 32 μJ are achieved. This allows direct micromaterial processing e.g. for ophthalmic surgeries. To the best of our knowledge, this is the first sub-100 ps Yb³⁺:YAG/Cr⁴⁺:YAG microchip laser. A new approximation is used to calculate the rate equations for multiple longitudinal modes and to determine the threshold for single-longitudinal-mode operation.