Nd3+-doped phosphate fiber lasers with high peak power under direct pumping

In this paper, a directly pumped passively Q-switched Nd³⁺ -doped phosphate fiber laser using Cr⁴⁺:YAG as a saturable absorber is reported. The Nd³⁺ -doped phosphate fiber preform with minimal internal defects were prepared by the double-peeled isolation extrusion method and drawn into optical fibers. The core-clad size of the fiber was 234/356 μm, with a transmission loss of 1.1 dB/m at 1053 nm. Subsequently, a passively Q-switched fiber laser was constructed based on the homemade Nd³⁺ -doped phosphate fiber, and the effects of parameters such as the reflectivity of the output coupler mirror, the transmittance of the saturable absorber, the length of the fiber, and the pumping power on the characteristics of the output laser pulse were investigated. After optimizing the key parameters, the laser achieved a peak pulse energy of 388 μJ and a maximum peak power of 21.8 kW. The results provide fundamental theoretical and experimental guidance for the development of passively Q-switched fiber lasers with high peak power, demonstrating significant practical value and theoretical significance.