High-power slab-based Tm:YLF laser for in-band pumping of Ho:YAG

Abstract

Several remote sensing applications require pulsed sources in the mid-infrared spectral regime with high average powers and good beam quality. Ho:YAG lasers have a number of attractive features for high power generation at 2.1microns, either for direct applications or as a pump source for parametric conversion to longer infra-red wavelengths. Unfortunately, direct diode pumping of Ho:YAG is not practical, so a two-step process is generally employed in which one or more diode-pumped thulium-doped lasers are used to directly pump (in-band) the Ho:YAG laser. In response, we have investigated a slab-based architecture for scaling the output power of a Tm:YLF laser to the 100W power regime at 1.91microns, corresponding to a strong Ho:YAG absorption line. Multiple slab lasers with moderate beam quality in the plane of the slab can be combined to efficiently end-pump a low-doping concentration Ho:YAG rod in a pump-guided configuration. In a preliminary demonstration, two 2at.% doped Tm:YLF slab lasers with a spatially multiplexed output of 74W were employed to end-pump a 1.5mm diameter, 80mm long, 0.25at.% Ho:YAG barrel-polished rod. A twomirror plano-concave cavity, with 11% output coupling transmission, produced a CW output of 38W with a slope efficiency of 60% with respect to the incident power. Q-switched operation at a repetition rate of 20Hz with two intracavity Brewster plate polarizers and a 60% transmitting output coupler produced 14mJ pulses with a pulse duration (FWHM) of 18ns. This architecture offers an attractive route for future high-power 2micron lasers.

LD pumped high efficiency, high power Tm:YLF laser with adhesive-free bond laser composites

“…Besides the remote sensing and medical applications of 2-μm eye-safe lasers, the Tm:YLF laser is one of the ideal pump sources for Ho:YAG lasers due to the fact that the emission band of Tm:YLF is well overlapped with the strongest absorption peak of Ho:YAG [1][2][3]. In addition, Tm:YLF has a broad absorption band near 800 nm that can be directly pumped by commonly available high power diode lasers [4,5].…”

“…In addition, Tm:YLF has a relatively low thermal stress fracture limit. The doping concentration also needs to be balanced between the laser efficiency and maximum output power [3]. In this work, in order to resolve the conflicting doping requirement in the 2-μm thulium lasers, un-doped end-capped Tm:YLF and segmentally bonded Tm:YLF laser composites have been designed and prepared with adhesive-free bond (AFB) technology.…”

Thermal lensing effects in rod-based Tm3+: YLF amplifiers versus pump and cooling conditions

“…This implies a comprehensive study of their dependency with the actual pump and sizing conditions, regarding the rod itself and the cooling conditions. A series of experimental works have already been involved in the field [9][10][11][12], within the frame of more basic computational conditions [13,14] and without formal optimization [15]. Our study aims to complete these works, in terms of more generic trends for optimizing the laser design in connection with subsequent thermal-lensing phenomena.…”

Resonantly pumped high efficiency Ho:YAG laser

“…Recently, a Ho:YAG laser directly pumped by laser diode stack at 1.9 μm was demonstrated [9][10][11]. So et al reported a slope efficiency of 60% in a Ho:YAG laser pumped by Tm-slab lasers [12]. A slope efficiency of 81.2% has previously been reported in a Ho:YAG laser pumped by Tm-doped fiber laser [13]; however it is based on a four-pass end-pump design.…”