Chinese Journal of Lasers,2017,Vol 44,No. 04
【Abstract】 The output laser pulse cannot sustain a flat-top temporal profile owing to the time domain distortion caused by gain saturation effect in laser amplifiers during the transmission and the amplification of high-energy pump laser pulse. Therefore, the pump laser pulse needs to be pre-shaped to compensate the gain saturation in the amplifier. A temporal shaping technology based on optical-optical synchronization amplification is proposed to compensate the time domain distortion caused by gain saturation. The proposed technology is based on the conventional amplification model, and it is not restricted to the width of laser pulse. The proposed technology is simple to operate and costs low. Theoretical simulation results indicate that the effective temporal shaping for the input pulse of laser system can be achieved and the gain saturation can be compensated by the proposed technology, and the output pulse with flat-top shape in time domain can be obtained.
Acta Optica Sinica,2019,Vol 39,No. 03
【Abstract】 An improved Gerchberg-Saxton (G-S) algorithm is proposed to realize the accurate design of the diffractive optical elements based on annular beams. This algorithm ensures a small sampling interval in the output plane and suppresses speckles. Compared with the design results of the conventional improved G-S algorithm without speckle suppression, a uniform spot with better performance is obtained by the proposed algorithm. The simulated results are in agreement with the experimental results.
Chinese Journal of Lasers,2019,Vol 46,No. 03
【Abstract】 The Gaussian laser beam is shaped into a flattop laser beam with uniform energy distribution by a diffractive optical element. The Cu plasma characteristics induced by two laser beams are compared, and the improvement of the beam shape modification on the stability of laser-induced breakdown spectrum is studied. The research results show that the uniformity of beam energy distribution causes the difference in the morphology of the ablation crater and single-shot ablation amount. The relative standard deviations of the Gaussian laser and the flattop laser induced spectra intensity, plasma temperature and electron density are 12.33% and 6.37%, 2.10% and 1.32%, 5.31% and 0.65%, respectively. The stability of the laser-induced breakdown spectrum after beam shape modification is significantly improved, and the two laser-induced plasmas are both in the local thermodynamic equilibrium state.