Continuous-wave and pulsed operation of Ho:YLF laser end-pumped by Tm:fiber laser

Abstract

Continuous-wave and pulsed operation of a Ho:YLF laser was demonstrated. A Tm:fiber laser with 70 W output power was used for the pump source. In this experimental setup, the end-pumped gain medium with 0.5% and 1% Ho concentration in the optical resonators were used. In the continuous-wave regime, 14.2 and 12.8 W linearly polarized power with a concave-concave resonator for 1.0% and 0.5% Ho dopes were extracted, respectively. These amounts correspond to slope efficiencies of 51.9% and 71.3% and optical-to-optical efficiencies of 39.4% and 54.7% for absorbed pump power, respectively. To avoid optical damage, a U-shaped concave-concave resonator was installed, and the resulting spot size in the resonator was about 1.31 mm. The spot size changes about 10% along the total physical length of the resonator. In the pulsed operation regime, for 0.5% Ho concentration with 20 ms pump pulse duration and 10 Hz repetition rates, the free-running output energy was 172 mJ with 16 ms pulse duration. In addition, the absorbed pump energy was about 485 mJ, corresponding to the slope and the optical-to-optical efficiencies of 14.8% and 12.3%, respectively. Also, 27 mJ pulse energy with 29.7 ns duration was achieved for Q-switched operation. Finally, the angle of output beam divergence was measured at approximately 1.1 mrad, and the laser emission wavelength was 2.0568 µm with 0.0065 µm line width.

Influence of pump source beam quality and OPO cavity resonance regime on output characteristics of mid-infrared ZGP-OPO laser

“…In our previous works, the Q-switched Ho: YLF laser was developed. A 60 mJ at 2 µm wavelength with a pulse duration of 24.5 ns was recorded in the laser experimental setup [25]. In this research, the results of two Q-switched resonators for a 2-micron pump laser were investigated.…”

“…Furthermore, higher energy at 2-micron region with Ho:YLF crystal based on MOPA con guration was presented [13 and 24]. In our previous works, the results of simulations and experimental setup of the Ho:YLF oscillator at 2 microns have been presented [25][26]. In addition to the pump source in an OPO structure, the type of OPO cavity must also be considered.…”