Reentry Point Match Broadband Second Harmonic Generation Study

Frequency conversion system is one of the critical parts in the inertial confinement fusion (ICF) high power laser facility. Currently, in order to improve the uniformity of illumination on target, and restrain influence of the B-integral on the laser facility, high conversion efficiency broadband frequency conversion technology must be implemented. In this thesis the spectrally noncritical phase-matching broadband second harmonic generation (SHG) is researched systematically. The conversion bandwidth and conversion efficiency are the two main topics of this thesis.The major research work can be listed as follows:1. The development, application and general status of broadband frequency conversion technology are summarized. Limitation of efficient broad-bandwidth frequency conversion is demonstrated, and several broadband frequency conversion techniques, such as achromatic phase matching, chirp-matching, multi-crystal sequence and spectrally noncritical phase-matching, are elaborated. The spectrally noncritical phase-matching technique is preferred in the ICF high power laser facility based on comprehensive consideration and comparison.2. A theoretical model of broadband SHG, which includes group-velocity mismatching, group-velocity dispersion (GVD) and third-order nonlinearity is established. The physics in broadband SHG at the retracing point of phase-matching is illustrated. We conclude that the "two compensations" (i.e. birefringent compensating phase mismatching and abnormal dispersion compensating group-velocity mismatching) are the essence of spectrally noncritical phase-matching SHG technique. The possibility of making materials that have spectrally noncritical behaviour at other wavelengths is further discussed.3. The spectrally noncritical phase-matching SHG in the low-drive regime is studied detailedly. In this case, SHG process is mainly affected by GVD. A novel "time-focusing" SHG scheme is proposed to compensate for the effects of GVD. The physical insight of "time-focusing" SHG is to actively control the fundamental harmonic (FH) pulse duration by introducing a proper pre-chirp to the FH pulse. Detailed simulations are conducted and results show that this method can improve the' conversion efficiency effectively. Optimizations of the "time-focusing" SHG scheme are also investigated, which can be achieved by choosing proper pre-chirp, phase-matching condition and dispersion parameter. The "time-focusing" SHG scheme is also applicable in the medium and high pump intensity regime, while the compensation effect is not as remarkable as that in low pump intensity regime.4. The spectrally noncritical phase-matching SHG in the pump depletion regime is...