The effect of Na3(PO3)3 on the growth of KDP crystal (101) faces was studied by the Michelson interference technique and atomic force microscopy. The experimental results show that the growth rates were near zero at low supersaturation when Na3(PO3)3 was doped into solution, i.e., there was a supersaturation interval similar to the “growth dead zone”. The growth rates began to increase rapidly as the supersaturation crossed the “growth dead zone” and continued to increase. The “growth dead zone” increased as the doping concentration was increased. In addition, the anisotropy of growth hillocks decreased and the competition of growth hillocks became more intense when the doping concentration of Na3(PO3)3 was gradually increased in solution at confirmed supersaturation. The calculated surface free energies of three adjacent planes show that they increased with the increase of doping concentration and always αI, αII > αIII.
Wang Tian-Yu,Yang Wei,Hui Hao-Hao,Lei Xiang-Yang,Zhang Qing-Hua,Wang Jian,Xu Qiao,Deng Xue-Ran
The sol–gel method is an important process for the preparation of laser frequency conversion components, such as dihydrogen phosphate (KDP), which are often employed in high-power laser facility. Methyltriethoxysilane (MTS) precursor is a typical matrix to prepare polysiloxane under hydrolysis and polycondensation process. Further coating and curing procedure is applied to obtain desired polysiloxane coating which acts as the moisture-proof and refractive index matching layer. Subsequently, an antireflective coating is prepared over this polysiloxane coating (a bilayer coating system) to realize ultrahigh transmission at desired wavelengths. Due to the low curing temperature (limited by the phase transition temperature of KDP), current MTS-polysiloxane coating could not be completely cured and inter-coating permeation between this bilayer coating system would lead to deterioration of coating properties. Thus, copolymerization of MTS and tetraethylorthosilicate (TEOS) is adopted to fabricate the polysiloxane coating with improved curing property (denser structure and higher hardness after curing). It is found that under certain molar ratio of MTS to TEOS, the structure of modified polysiloxane coating could be effectively densified and the coating hardness increases significantly. Meanwhile, the bilayer coating system still exhibits excellent transmission, high laser-induced damage threshold as well as satisfactory moisture resistance.
You Teng-Hui,Yang Wei,Hui Hao-Hao,Lei Xiang-Yang,Wang Tian-Yu,Zhang Qing-Hua,Ju Xin,Deng Xue-Ran
The purpose of this study is to analyze the damage of antireflective (AR) coating over potassium dihydrogen phosphate (KDP) crystal subjected to multi-pulse laser irradiation at low flux under vacuum. Fresh silica AR was characterized as a reference; Atomic Force Microscope (AFM), Scanning Electron Microscopy (SEM), profilometer, and Scanning Near-Field Optical Microscope Photo-induced Force Microscope (SNOM-PiFM) were employed to analyze the characteristics of coatings. The experimental results indicated that the damage of AR coating over the KDP crystal was mainly caused by partial exfoliation, which exposed silica particles beneath the surface. It was found that the accumulated tensile stress led to coating damage with the increase of laser pulse. The initial coating damage was observed to extend and interconnect to form large-area exfoliation. Splitting mechanism of SiO–Si TO 3 was observed at vibration mode peaks of 1064 cm −1 and 1096 cm −1 showing progressing irradiation damage. Based on this study, it would be helpful to suppress the damage probability of AR coating over KDP crystal applied in high-power laser systems. Moreover, the applicability of SNOM-PiFM method to study the Infrared Radiation (IR) spectra of ultra-thin coatings with transparent substrates was proposed.
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