Improvement of beam quality for fiber-coupled diode-side-pumped Nd:YAG rod lasers by an apertured resonator

Abstract

This paper demonstrates a method for improving the beam quality of the fiber-coupled diode-side-pumped Nd:YAG rod lasers. Because the beam quality of a rod laser varies with the pump and output power, to obtain high coupling efficiency, the parameters of the energy-transmitting fiber is commonly selected based on the worst scenario that occurs in the middle power range, at which the beam quality is much poorer than that at the rated power. To solve the problem, the beam quality in the middle power should be improved in a way that it does not affect the rated power. A simulation shows that the apertures matched with the spot size at the rated output can be inserted into the resonator to meet the requirements that the beam quality can be well controlled so that the laser can be coupled efficiently into the fiber, whose parameters are selected in accordance with the beam quality at the rated power, throughout the entire power range. Experimentally, with such a design, a ∼95% coupling efficiency from the laser output into a fiber with core diameter of 200μm, NA of 0.22 can be obtained over the full power range.