The influence of phase mismatching on output pulse temporal waveform in the process of second and third harmonic generation at various power densities with different detuning angles is studied based on nonlinear coupled-wave equations. The rules of different frequencies pulse width vary with the detuning angle have been analyzed quantitatively in potassium dihydrogen phosphate (KDP) crystals. The results of numerical simulation show that in high power laser frequency conversion system, the changes of fundamental pulse width are more sensitive to the detuning angle than second harmonic in the process of doubling, and the maximum variation of the full-width at half-maximum (FWHM) of fundamental at different detuning angles is about 19.0%. For tripling, the output pulse width changes of fundamental and second harmonic are sensitive to the detuning angle at high power density, and the maximum variation of their FWHM at different detuning angles are about 19.0% and 19.2%, respectively. However, the SH pulse width almost unchanged at low power density. The results of this study may provide a promising route to determine the best angle for phase matching in the angle adjusting process of experiment.
The non-collinear phase-matching in Potassium Dideuterium Phosphate (DKDP) crystal is analyzed in detail with signal pulse of center wavelength at 808 nm and pump pulse of wavelength at 526.5 nm. By numerical analysis, parametric bandwidths for various DKDP crystals of different deuteration level are presented. In particularly for DKDP crystals of 95% deuteration level, the optimal non-collinear angles, phase-matching angles, parametric bandwidths, walk-off angles, acceptance angles, efficiency coefficients, gain and gain bandwidths are provided based on the parameter concepts. Optical parametric chirped pulse amplifier based on DKDP crystal is designed and the output characteristics are simulated by OPA coupled wave equations for further discuss. It is concluded that DKDP crystals higher than 90% deuteration level can be utilized in ultra-short high power laser systems with compressed pulses broader than 30fs. The disadvantage is that the acceptance angles are small, increasing the difficulty of engineering regulation.