High Brightness 556 nm Laser by Frequency Doubling of a 1112 nm Nd:YAG Laser

We demonstrate an efficient high power and high brightness yellow-green 556-nm laser generated from second harmonic generation (SHG) of a master oscillator power amplifier (MOPA) laser system at 1112 nm. The oscillator was a pulsed laser diode (LD) pumped and Q-switched Nd:YAG laser at 1112 nm operated at TEM₀₀ mode with an average output power of 35 W, providing 200-μs long macropulses and constituting 700-ns micropulses. The seed laser was amplified by two LD side-pumped Nd:YAG amplifiers and the MOPA system delivered a maximum output power of 78 W. Using a type-I phase-matching lithium triborate nonlinear crystal, the SHG maximum output power of 48 W was obtained at 556 nm with a conversion efficiency as high as 61.5%. The beam quality factor was measured to be M² = 1.53 and the corresponding brightness was as high as 6.63 × 10⁹ W/cm²·sr.