Nonlinear Optical and Laser Damage Properties of KDP Crystal with Trace Impurities in Bulk

Abstract

Small-sized potassium dihydrogen phosphate (KDP) samples cut from the pyramid sector of a large KDP boule are observed to have different impurity content. The nonlinear absorption properties of two KDP samples containing different impurities are characterized by Z-scan technique with picosecond laser at 355 nm wavelength. Reverse saturable absorption effects are found in samples, with nonlinear absorption coefficients of 7.35 × 10 −2 cm GW −1 and 15.91 × 10 −2 cm GW −1 . The sample with more impurity contents exhibits stronger nonlinear absorption. Such behavior is considered to be a result of nonlinear energy coupling under 355 nm laser irradiation assisted by impurity defects. Nanosecond laser-induced damage test at 355 nm of the two KDP samples is further investigated. The bulk damage thresholds of the two samples are 4.7 and 0.423 J cm −2 respectively, indicating that impurity-induced nonlinear absorption might play an important role in laser-induced damage processes.

Study on the defects of KDP crystal with different states by the positron spectroscopy method

“…Researchers paid more attention to the changes in optical properties caused by Fe 3+ , ignoring the changes in defects themselves. 11,17…”

“…Therefore, the LIDT of the KDP crystal was reduced. 10,11 Runkel et al 12 had studied the influence of these impurity cations on the laser damage for KDP crystals and found that the LIDT of doped crystals could not meet the requirements for application in National Ignition Facility (NIF) engineering. Fe 3+ , as the most typical impurity ion, existed in the raw material in a small amount.…”

“…Researchers paid more attention to the changes in optical properties caused by Fe 3+ , ignoring the changes in defects themselves. 11,17 There are some experimental methods to investigate the state of defects in crystals, such as electron paramagnetic resonance (EPR) and positron technology. The EPR technique could qualitatively and quantitatively detect unpaired electrons in crystals and explore the structural properties of the surrounding environment.…”