Er:Yb:glass material limits in case of compact passively Q-switched nanosecond DPSS lasers

Erbium-Ytterbium co-doped glass is extensively utilized in the laser industry, particularly for 1.5μm, eye-safe lasers employed in lidar and range-finding applications. These applications necessitate high repetition rates and pulse energies in the millijoule range. However, the inherent properties of the material, including low thermal conductivity, pronounced thermal lensing, and depolarization, present significant challenges in laser design. This study conducts a comparative analysis of passively Q-switched diode-pumped solid-state (DPSS) lasers operating in both single pulse and burst regimes. A case study involving several sample lasers, with a resonator optimized for a 5-10Hz repetition rate across a temperature range of -20 to +60 degrees Celsius, demonstrates sustained operation at a 20Hz repetition rate in the single pulse regime (~2mJ) and 30 pulses per second in burst mode at room temperature. Examination of burst pulse sequences reveals that each subsequent pulse exhibits different transverse modes, resulting in energy variations of up to 40-50%. This phenomenon is attributed to the changing volumetric distribution of excited erbium and ytterbium ions within the pumped volume. Consequently, the applicability of lasers operating in burst regimes is limited to scenarios where laser mode variation is acceptable. This research aims to elucidate the operational constraints of the Er:Yb:glass active medium over a wide temperature range (-20 to +60 degrees Celsius) and to explore resonator design modifications by thermal modeling and experimentation to mitigate limiting factors such as low thermal conductivity and significant thermal lensing.