SG-II-Up prototype final optics assembly: optical damage and clean-gas control

Abstract

The Shenguang-II Upgrade (SG-II Up) facility is an under-construction high-power laser driver with eight beams, 24 kJ energy, 3 ns pulse duration and ultraviolet laser output, in the Shanghai Institute of Optics and Fine Mechanics, China. The prototype design and experimental research of the prototype final optics assembly (FOA), which is one of the most important parts of the SG-II Up facility, have been completed on the ninth beam of the SG-II facility. Thirty-three shots were fired using 1-ω energy from 1000 to 4500 J and 3-ω energy from 500 to 2403 J with a 3 ns square pulse. During the experiments, emphasis was given to the process of optical damage and to the effects of clean-gas control. A numerical model of the FOA generated by the Integrated Computer Engineering and Manufacturing code for Computational Fluid Dynamics (ICEMCFD) demonstrated that a flux within 1-5 l s −1 and a 180 s period is effectual to avoid contaminant sputtering to the optics. The presence of surface 'mooning' damage and surface spots located outside the clear aperture are induced by contaminants such as wire, silica gel and millimeter order fiber and metal.

Status and development of high-power laser facilities at the NLHPLP

“…Meanwhile, two confocal spatial filters, namely the transport spatial filter (TSF) and cavity spatial filter (CSF), are used to restrain the beam modulation. As the pulse again propagates through the power amplifier, after passing the TSF and transport mirrors, it enters the final optics assembly (FOA) [50] and it is frequency converted to 351 nm light, before being focused to the target chamber using the wedged focus lens. In addition, the measurement system [51][52][53] , centralized control system [54,55] , and automatic alignment system [56,57] are all involved to enable the effective operation of the facility.…”

“…Various problems, such as the high-energy acquisition of pulses with Figure 29. Pulse contrast measurement result of picosecond laser system [50] .…”

“…(6) An apparatus to measure the pulse contrast with a high dynamic range has been developed. The apparatus [50] was based on the single-shot cross-correlation with a fiber array detector. A schematic diagram of the pulse contrast measurement is shown in Figure 36.…”

Characteristics of Local Modulation Beam Propagating through Spatial Filter System

“…The amplitude and phase modulations caused by damage defects and contamination particles can result in downstream intensification, which can damage certain optical components in the systems [1][2][3][4][5]. As one of the crucial factors restricting the output power of high-power laser systems, the research of defects in optical components has aroused great interest for a long time.…”

Study on low-refractive-index sol-gel SiO2 antireflective coatings

“…SiO 2 antireflective (AR) coatings prepared by the sol-gel method have good optical properties and high laser-induced damage thresholds. There are many optical elements that require SiO 2 AR coatings in large high-power laser devices around the world [2] , such as the National Ignition Facility in the USA [3] , the Laser MégaJoules in France [4,5] , and the "Shenguang" systems in China [6][7][8] . Compared with films of high-refractive-index media made by physical vapor deposition, the refractive index of SiO 2 AR coatings made by the sol-gel method are not only low but also controllable [9,10] .…”