Analysis of the relationship between variations in detuning angle and the harmonic generation efficiency of a KDP crystal

The harmonic generation efficiency of a large aperture KDP (KH2PO4) crystal that is used in the Final Optics Assembly of high-energy solid-state lasers is one of the key points to achieve inertial confinement fusion. The variations in the detuning angle of a KDP crystal are achieved by interferometer and calculation. The harmonic generation efficiency is calculated using variations in the detuning angle. The theoretical prediction model of harmonic generation efficiency based on small-signal approximation theory was built. In the experiment, Crystal off-line Debugging System was used to measure the actual harmonic generation efficiency of a KDP crystal. The predictive harmonic generation efficiency of a KDP crystal and the actual efficiency was compared, which concluded that the theoretical prediction model of harmonic generation efficiency was correct. A simple method to predict the harmonic generation efficiency of a KDP crystal was provided. The method can also be applied to other harmonic generation crystals.