Coherent Control Via Adaptive Pulse Shaping

Coherent control based on femtosecond pulse shaping is one of the hot and developing fields, and it has been widely applied on controlling chemical reaction, high intense laser ionization, high harmonic generation, attosecond pulse generation, coherent control transfer, and future on the process and storage of quantum information. In this thesis, we focus on investigating the coherent control of two-photon transitions, second harmonic generation and stimulated Raman scattering based on adaptive pulse shaping technique.(1) The basic theory for Fourier transformed pulse shaping technique and development of the pulse shaping and measurement technique are systematically reviewed, and femtosecond adaptive pulse shaping based on spatial light modulator (SLM) and genetic algorithm are successfully achieved.(2) The two-photon transition probability in Coumarin 515 can be effectively controlled by modulating the spectral phase with periodic square distribution (including of the modulation depth, period and phase), and the two-photon fluorescence signal can be efficiently enhanced by adaptive feedback control, and second harmonic generation frequency-resolved optical gating (SHG-FROG) traces indicate that the optimized laser pulses are positive chirp, which are in favor of the effective population transfer in two-photon transitions. A simple theoretical model is used to illustrate effective population transfer in two-photon transitions, which can be experimentally validated.(3) An optimal feedback control of second harmonic generation (SHG) in BBO crystal excited by shaping femtosecond laser pulses based on genetic algorithm is demonstrated experimentally, and SHG in BBO crystal can be enhanced by -16%. SPIDER results show that the optimal laser pulses have shorter pulse-width with the little negative chirp than the original pulse with the little positive chirp. By modulating the spectral phase with periodic square distribution on SLM, the SHG can be effectively controlled, and the experimental results indicate that the SHG with ultra-short pulse is related to sum frequency generation both between the same frequencies (harmonic generation) and different frequencies, where the former depends on the peak intensity, and the latter depends on not only the peak intensity but also the...