Power and energy scaling of a diode-end-pumped Nd:YLF laser through gain optimization

Abstract

An end-pumped Nd:YLF laser was demonstrated, which delivered 60.3 W continuous-wave and more than 52 W Q-switched average power for all repetition rates from 5 to 30 kHz. To achieve this, an analytical solution to estimate and optimize the unsaturated gain in an end-pumped laser gain medium was derived. The approach presented here should open up the route for scaling end-pumped lasers to even higher power and energy levels.

Thermal analysis and experimental study of end-pumped Nd: YLF laser at 1053 nm

“…The temperature dependence of the heat conductivity was taken into account. An additional concern in reducing pump intensity while maintaining diffraction limited fundamental mode oscillation was that the Nd: YLF radius was much larger ( 3 times [16][17]) than the pump radius. The Nd: YLF parameters used in the model were given in Table 1.…”

High average power Q-switched 1314 nm two-crystal Nd:YLF laser

“…The upper-laser-level ( 4 F3/2) lifetime of τ ~ 520 µs for Nd:YLF is longer compared to ~ 250 µs for Nd:YAG and ~ 100 µs for Nd:YVO4 [7,8]. The resulting high energy storage capability makes Nd:YLF suitable for generating high pulse energies during Q-switched operation [7][8][9][10]. The emission cross section (σem) at 1.3 µm for Nd:YLF is ~2 -2.5 × 10 -20 cm 2 (for both polarizations).…”

“…The σem and τ values of Nd:YLF necessitates a careful design of the pump beam radius in pulsed lasers where a trade-off has to be made between a reasonably low threshold and the risks of optical damage and thermal fracture [9]. Thermal effects are especially problematic under 1.3 µm operation (compared to 1.0 µm) due to the larger quantum defect.…”

“…Thermal effects are especially problematic under 1.3 µm operation (compared to 1.0 µm) due to the larger quantum defect. By using a relatively low Nd doping one can reduce upconversion and spread out the thermal load longitudinally in the crystal, which increases the thermal fracture pump limit [9,11,12]. Furthermore, Nd:YLF crystals grown by the Czochralski method have a longitudinal gradient in doping resulting from the physical crystal growth process.…”

“…The pump beam was focused to a waist radius of ~ 500 µm in the center of the gain medium with a roughly top-hat shaped energy distribution at that position. This waist radius was determined through a gain optimization method similar to the one described in [9] since both the pump and laser beam radii have a strong influence on the gain as well as on the thermal load. The CW incident optical-to-optical slope efficiency of the oscillator is shown in Fig.…”