Theoretical analyses of a mid-infrared Ho:BYF laser with the small rod diameter side-pumped by LDs

A mid-infrared (MIR) Ho:BYF solid-state laser with the central wavelength of 3.9 μm can be realized by applying laser diodes (LDs) through the direct-pumping scheme, and it has such advantages as the simple mechanism, compact structure, and wide outputted spectrum. It holds significant application value in many fields of laser radar, atmospheric probing, and biomedicine, etc. However, due to the severe quantum defect of such a Ho:BYF laser directly-pumped by LDs by comparing with a conventional solid-state laser, serious thermal accumulation will occur when the high-powered pumping is adopted, which not only leads to the deterioration of the outputted beam quality but also causes the crystal damage and even crystal fracture. To overcome such problems, a protocol using side-pumped Ho:BYF crystal with the small diameter has been proposed in this paper. By increasing the specific surface area of laser crystal, the heat dissipation efficiency can be significantly enhanced, and the adverse thermal effects can also be effectively suppressed. A laser dynamics model for the side-pumped Ho:BYF laser has been established on the MATLAB platform. Such a model was used to systematically simulate and analyze the influence of the crystal geometry and pump structure on the laser output under the pulsed pumping regime. The study provides an important theoretical reference for the practical development of high-powered Ho:BYF lasers directly-pumped with LDs.