Nonlinear propagations and high power THz generations using ultrashort pulses

Theoretical studies on nonlinear propagations involving Kerr effects as well as experimental demonstrations on high power THz generations based on optical rectification in nonlinear crystals are presented. Theoretical investigation of supercontinuum generation in photonic crystal fibers (PCFs) and its application to pulse compression have been undertaken, and from which an optimum length of PCF has been found for single-cycle pulse compression.; We also investigate the limits imposed by stimulate Raman scattering (SRS) and finite gain bandwidth on power scaling in an Yb-doped fiber based parabolic amplifiers. Our results show that the maximum achievable parabolic pulse energies are limited by SRS at low amplifier gains and by the finite gain bandwidth at high gains.; We generalize the concept of temporal parabolic similaritons and discover new types of self-similar propagation phenomena, i.e. spatial parabolic similaritons and incoherent parabolic similaritons. Solving the amplified nonlinear Schrodinger equation (NLSE) in a general context, the physical mechanisms behind the formation of parabolic similaritons are revealed. It is found that incoherent parabolic similaritons can be amplified and compressed as have been done for its coherent counterpart.; In addition to the theoretical work on nonlinear propagations, we conducted experiments on THz generations based on optical rectification. A high power compact THz source is constructed using <110> cut GaP pumped by an Yb-doped parabolic pulse amplifier. Using 10-W average optical pump power, up to 6.5 muW average THz power is obtained, which to our knowledge is the highest reported THz power achieved with a compact laser. This work also represents the first demonstration of optical rectification in GaP pumped by femtosecond pulses.; We also demonstrate for the first time to our knowledge, that velocity-mismatched optical rectification can be employed to generate radially polarized THz pulses. It has been a popular conception that optical rectification always generates to the linearly polarized THz radiation. Our experimental work breaks this incorrect perception and leads to many possible designs of high power compact THz sources.