High-Beam-Quality Frequency-Doubled Laser with a Gradient-Doped Nd:YAG Crystal End-Pumped by an 808-nm LD

A novel frequency-doubled laser using an end-pumped gradient-doped Nd:YAG crystal with continuously increasing dopant concentration to lower the thermal effect of the gain medium is proposed. By controlling the beam waist size of the fundamental wave and optimizing both the length and temperature of KTP crystals to enhance second-harmonic generation efficiency, the maximum output power with high beam quality is achieved at 532 nm. The second-harmonic generation efficiency reaches 59.8%, with a shortest pulse duration of 6.5 ns and a corresponding peak power of 469 kW. The beam qualities are Mx2=1.32 and My2=1.36, and the power instability is 0.24% (RMS). To the best of our knowledge, this is the first systematic SHG study of a continuously graded-doped Nd:YAG end-pumped laser, achieving higher-efficiency green laser output under near-diffraction-limited beam quality. This development holds significant importance for advancing the progress of high-performance frequency-doubled lasers.