Formation of flat-top picosecond pump pulses for OPCPA systems by cascade second harmonic generation

Abstract

We report on the method for picosecond pulse envelope shaping that is based on pulse temporal profile transformations during the cascade second harmonic generation. It was demonstrated theoretically and experimentally that under a particular second harmonic generation condition, e. g. pump pulse intensity and crystal length, the 1064 nm pump pulses with a temporal profile close to the Gaussian one and pulse width of 75 ps at FWHM can be converted to pulses of fundamental and second harmonics with the super-Gaussian temporal profile having an intensity plateau region extending over a ~100 ps time interval when conversion efficiency in the first stage of the harmonic generator was around 45–50%. Our proposed shaping method is particularly suitable for the application in the multistage OPCPA pumped by the second harmonic of Nd:YAG laser radiation.