Study On Ultrashort Laser Pulse Shaping In Time-domain And Modulation Algorithm

In recent years, with the rapid development of the picosecond, femtosecond ultrashortlaser pulses, and its potential applications become more apparent. people always wanta shorter pulse, but by compression of ultrashort pulses tend to have very widebase,and in practical application, not only the need for a ultrashort pulse but also the pulseshape of the specific requirements of ultrashort laser.So ultrashort pulse shapingtechnology also will be rapidly developed. Ultrashort laser pulse shaping technologycan be widely used in fiber optics, biology, and phase control of femtosecond amplifi-er, band-pass filtering, quantum coherent control and nonlinear optics and other fields,so the technology has been paid more and more attention.In all of ultrashort laser pulse shaping method, the Fourier transform pulse shapingmethod is the most common method, its basic idea is derived from the lineartime-invariant filtering theory, the basic experimental setup is the4-f system.4-f sys-tem is composed of a pair of diffraction grating and lens, and a pulse shaping mask.By diffraction gratings and prisms, the input pulse from the time domain to frequencydomain, pulse shaping was happened in the frequency domain, and then transformback to time domain, at last we can acquire the output pulse after shaping. Ultrashortpulse shapers can be operated either under open loop control or in closed-loop controlconfiguration. For open-loop control strategy, the most important thing is the designof the mask function. In this article the design of the mask function is given by nu-merical simulation. And we also simulated the process of pulse shaping in open-loopcontrol strategy, For the closed-loop control strategy, we need to use a programmablepulse shaper and write the control algorithm of the pulse shaper. Commonly used con-trol algorithms are simulated annealing algorithm and genetic algorithm, these twokinds of control algorithms has been well applied in the theoretical simulation andexperimental. In this article, a genetic algorithm was used to simulate the dispersioncompensation. At the same time, we write another kind of control algorithm-particleswarm optimization, and also use this algorithm to simulate the dispersion compensa-tion experiment, the dispersion of the pulse width is compressed to near the Fouriertransform limit. Therefore, the particle swarm algorithm can be used as the controlalgorithm of the ultrashort laser pulse shaping experiments in the closed-loop controlstrategy for dispersion compensation.