Theory of cascade third harmonic generation in the strong wave-interaction approximation

A theory of cascade third harmonic generation is developed using the strong wave-interaction approximation. This can be used to determine the maximum radiation conversion efficiency in real situations. The capabilities of two different cascade generation systems based on KDP crystals are compared and the conditions under which it is more advantageous to use a particular interaction system are determined. The optimal conditions for maximizing the efficiency are considered in relation to the divergence and modulation profile of the pump radiation, the relationship between the energies of the mixed modulated waves, the crystal lengths, and so on. Good agreement between the theory and the experimental results is reported.