Analysis of laser thermal effect of funnel-shape beam generated by spherical lens pump system

Abstract

The uniformity of temperature distribution of an end-pumped laser can be improved simply and effectively by introducing the correct amount of spherical aberration into the pump system. An iterative model of optical-thermal coupling is proposed to calculate the temperature distribution of the end-pumped laser amplifier. The results showed that, the thermal effect of the laser gain medium in the coupling system composed of spherical lenses decreased significantly compared with the coupling system composed of aspherical lenses. This is proved by a neodymium-doped yttrium orthovanadate (Nd:YVO4) amplification experimental system, which was end-pumped by a fiber-coupled laser diode (LD) with the optimized wavelength of 878 nm. A comparative study of the two pump systems showed that the decrease in the gain medium thermal wavefront peak-to-valley (PV), the thermal lens effect, and an improvement in beam quality are still observed in the pump amplification experiment with spherical aberration. At last, the relationship between the spherical aberration and the output brightness of the amplifier was established, which provides guidance for further optimization of the spherical aberration of coupling pump systems and improving the beam quality.