Noncritical phase-matched fourth harmonic generation properties of traditional grown large-size DKDP crystal

Noncritical phase-matched (NCPM) fourth harmonic generation (FHG) of 1053 nm was conducted at different regions of a traditional grown large-size 65.8% deuterated potassium dihydrogen phosphate (DKDP) crystal. NCPM FHG was realized at the temperature of 32.1–32.4 °C. The 0.3 °C variation of the temperature is induced by the 0.12% inhomogeneity of deuterium content. Comparing with 2.3 °C of temperature acceptance, the 0.3 °C variation is acceptable. Thus, the traditional grown DKDP crystal is in good homogeneity of deuterium content in view of NCPM FHG. On the other hand, the linear absorption coefficient varies from 0.08 cm⁻¹ to 0.12 cm⁻¹. When driven with 0.85 GW/cm² of second harmonic radiation, the FHG conversion efficiency reaches 68.9%. Larger linear absorption leads to 3% reduction of the conversion efficiency. Therefore, measures should be taken to suppress the linear absorption.