Demonstration of broadband frequency tripling based on cascaded partially deuterated KDP crystals

The cascaded KDP crystal scheme with different deuteration levels for enhancing the bandwidth of third-harmonic generation (THG) is experimentally demonstrated in this paper. The deuteration level of a partially deuterated KDP crystal is used as a degree of freedom to alter the phase-matching (PM) wavelength. The experimental results show that this scheme can increase the bandwidth acceptance in broadband frequency tripling. In addition, the spacing between the two cascaded crystals has significant influence on the THG spectrum as well as THG conversion efficiency, and a relatively ideal THG spectrum can be obtained by the optimized parameters. Meanwhile, nonlinear-coupled wave equations are used to theoretically analyze the experimental results, and the experimental results are consistent with the numerical simulation.