Gain switched Ho:YAG lasers with 2-4ns pulse duration, and high energy per pulse

The 2 μm wavelength range provides a wide range of applications requiring short pulse durations, high peak power, and high atmospheric transmittance. Typically, Ho:YAG lasers are suitable for such applications due to their emission at 2.1 μm. Unfortunately, the existing literature reveals either short pulse durations with low energies using the cavity dumping method or high energies with longer pulse durations using the Q-switch method within this spectral range. Here, we present a novel approach that combines high energy per pulse and short pulse duration for a Ho:YAG laser, utilizing the Gain-switch method. The main advantage of the Gain- switch over Q-switch is the ability to design a short cavity, thereby achieving short pulse durations. Two different lengths of Ho:YAG crystals (20 mm or 7 mm) were tested using an actively (acousto optic modulator) or passively (Cr:ZnS) Q-switched Tm:YLF laser that was tuned to the Ho:YAG absorption peak, at 1879 nm, as a pump source. The Ho:YAG laser emitted at 2090 nm. Pulse durations of 3.35 ns with energies up to 0.7 mJ were obtained for the 20mm Ho:YAG crystal using the active or passive seed lasers. Shorter pulses of 2.3 ns with energies up to 0.35 mJ, were obtained for the 7mm Ho:YAG crystal using the passive seed laser. The reported results were limited by the output coupler's damage threshold level. These results represent the highest achievements in terms of pulse duration and energy per pulse using the Gain-switch method.