Efficient fourth harmonic generation of Nd:YAG laser in DKDP crystals

In the present work we investigated the conditions of the 4th harmonic stable high effective pulse generation with the energy up to 100 mJ, efficiency approximately 50 percent and pulse repetition rate 10 Hz in DKDP crystals with noncritical phase matching. On the basis of experimental data we carried out the numerical modeling of thermal self- action effects influencing on the efficiency of the 4th harmonic single-shot pulse generation and received the solution of non-stationary heat conduction equation, describing radial temperature profile in crystal as a function of time. It was shown that maximum efficiency of the 4th harmonic generation in the thermal self-actions conditions is reached when initial crystal temperature is less than noncritical phase matching temperature and in the process of heating during the pulse inside the crystal radial temperature profile close to the noncritical phase matching temperature.