Harmonic Beam Coaxial Combination Delivering 132.5 W Picosecond Green Laser

A high power high beam quality picosecond green laser was demonstrated by using a beam combination technology named harmonic beam coaxial combination (HBCC). Each green laser was obtained based on extra-cavity frequency doubling of a picosecond 1064 nm Nd:YVO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> master oscillator power amplifier (MOPA) laser in a LiB<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub>O<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> (LBO) nonlinear crystal, delivering an average power of ~66 W at the 400 kHz pulse repetition rate (PRR) with diffraction limited beam quality. In the HBCC process, a dichroic mirror (DM) was used to deliver the second-harmonic (SH) beam of the first branch into the second LBO. The pulse sequence from two green beams was manipulated based on the delay technique of pulses. Consequently, a combined ~6.8 ps SH power of ~132.5 W at a doubled PRR of 800 kHz was obtained with a high combining efficiency of up to 99.9% and a linear polarization ratio >140:1. The combined beam quality factor was measured to be <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M_x</i><sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>=1.27 in the x direction and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M_y</i><sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>=1.25 in the y direction, respectively. The approach is inherently scalable: in the future work, we can combine many more picosecond beams using the same procedure to further scale SH power without sacrificing efficiency or beam quality, while retaining low implementation complexity, low cost, and high beam-combining efficiency.