Efficient CW Nd:YLF laser in-band diode-pumped at 908 nm and its thermal lensing
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Date
2019
Authors
Sedaghati, Zohreh
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Abstract
Diode-pumped solid-state lasers are highly recommended for a variety of industrial and scientific applications as they can offer high efficiency and excellent beam quality. However, power scaling of these lasers is a challenging task. The main limitation in power scaling of famous neodymium doped lasers such as Nd:YVO4 is the thermal lensing effect. Thermal lensing degrades the output beam quality and in extreme cases can result in crystal fracture. One potential solution to this problem is to reduce the induced heat load inside the gain media by decreasing the quantum defect. This was demonstrated successfully for the Nd:YVO4 laser by pumping the laser at a long wavelength of 914 nm instead of the traditional pumping at 808 nm wavelength.
Among the Nd-doped crystals operating in the near infrared range, the crystal of yttrium lithium fluoride (Nd:YLF) is another interesting gain medium as it has the benefits of natural birefringence (can generate naturally polarized laser beam), negative dn/dT (reduces thermal effects) and long upper level lifetime (in favor of Q-switched operation).
In this work we used a long wavelength pumping approach and for the first time examined the performance of a continuous-wave Nd:YLF laser at 1047 nm under 908 nm diode pumping. This pumping wavelength reduced the quantum defect by 50% as compared to the conventional 808 nm pumping. The laser produced an output power of 850 mW at 1047 nm with excellent beam quality and 625 mW at 1053 nm. The slope efficiency was ~73.9% and 46% for 1047 and 1053 nm, respectively. Therefore, a considerable power scaling is possible for Nd:YLF crystals owing to the strongly reduced quantum defect and, hence, thermal lensing.
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Keywords
Diode-pumped lasers, Nd:YLF, Solid-state lasers