Non-critical phase-matching fourth harmonic generation of a 1053-nm laser in an ADP crystal

Abstract

In current inertial confinement fusion (ICF) facilities, KDP and DKDP crystals are the second harmonic generation (SHG) and third harmonic generation (THG) materials for the Nd:glass laser (1053 nm). Based on the trend for the development of short wavelengths for ICF driving lasers, technical solutions for fourth harmonic generation (FHG) will undoubtedly attract more and more attention. In this paper, the rapid growth of an ADP crystal and non-critical phase-matching (NCPM) FHG of a 1053-nm laser using an ADP crystal are reported. The NCPM temperature is 33.7°C. The conversion efficiency from 526 to 263 nm is 70%, and the angular acceptance range is 55.4 mrad; these results are superior to those for the DKDP crystals. This research has shown that ADP crystals will be a competitive candidate in future ICF facilities when the utilisation of high-energy, high-efficiency UV lasers at wavelengths shorter than the present 351 nm is of interest.

Raman spectral characterization of NH 4 H 2 PO 4 single crystals: Effect of pH on microstructure

“…In the Raman spectra of ADP crystal samples at different pH, the position and intensity of the peaks in the range 300-900 cm À 1 did not change; the peaks in the range 1400-1700 cm À 1 shifted their position, although they had the same intensity. This indicates that the structure of ( ) − PO 4 3 did not change with pH, whereas the structure of + NH 4 changed with pH. In the Raman study in the range 1700-4000 cm À 1 , the primary discrimination occurred for the intensity of the peaks at 3050 cm À 1 and 3147 cm À 1 , which is attributed to the vibration of O-H⋯O hydrogen bond, it can be inferred that pH slightly affected the O-H⋯O hydrogen bonding.…”

“…ADP contains + NH 4 and ( ) − PO 4 3 groups and two hydrogen bonds. The N-H⋯O hydrogen bond connects + NH 4 and ( ) − PO 4 3 groups, and the O-H⋯O hydrogen bond lies between the ( ) − PO 4 3 groups. The structural changes in ADP crystals and stages of crystal growth at different pH were studied using Raman spectroscopy.…”

“…Ammonium dihydrogen phosphate (NH 4 H 2 PO 4 , ADP) is an important isomorph of the KDP-type crystal. ADP has a higher nonlinear optical coefficient, conversion efficiency, and laser damage threshold [3,4]. pH is an important crystal growth parameter, affecting the stability of solution and crystal defects.…”

Stability and electronic structure of hydrogen vacancies in ADP: hybrid DFT with vdW correction

“…In our experiment, we also observe the optical absorption at 355 nm (3.49 eV) that has been detected in many other experiments, such as ref. 3. It is not expected to come from the intrinsic H vacancy as the calculated transition energy is not consistent with the measured absorption energy (more than 1 eV difference).…”

“…[1][2][3][4] As compared to its analogue potassium dihydrogen phosphate (KH 2 PO 4 , KDP), ADP exhibits a higher laser damage threshold (LDT) and larger nonlinear optical (NLO) coefficient than KDP, and can thus be treated as a promising alternative material to break the present KDP monopoly of Inertial Connement Fusion (ICF) applications.…”