Ryuji Uchimura

Damage threshold of fluoride HR coatings at 352 nm

Laser damage thresholds of fluoride HR coating were investigated at 352 nm, 10 ns pulses. Additionally, an effective method to reduce the crazing in fluoride HR coatings is studied. A high threshold greater than 30 J/cm2 was achieved in LaF3/AlF3 coating when the laser conditioning procedure was used. The IAD process or double stack design with a combination of fluoride and HfO2SiO2 coating was effective in reducing the crazing.

Highly Damage-Resistant Reflectors for 248 nm Formed by Fluorides Multilayers

we investigated the laser damage thresholds and optical performances of fluorides multi-layered reflectors, consisting of middle index fluoride and Na3AlF, for high power KrF laser applications. It was found the damage thresholds of those reflectors are significantly improved by laser annealing. Those reflectors with annealing resisted against the fluence of 18-27 J/cm2 (this fluence varies on combinations of various fluorides) for 248 n, 15 nsec, 10Hz pulses.

Damage thresholds and optical stabilities of fluoride HR coatings for 193 nm

We investigated the damage thresholds and optical stabilities of 193 nm fluoride HR coatings consisting of NdF3/Na3AlF6 and LaF3/Na3AlF3. These coatings were deposited on fused silica substrates by conventional electron beam (EB) and ion assisted deposition process (IAD). Damage thresholds of LaF3/Na3AlF6 HRs were significantly increased by laser conditioning procedure and low index overcoating when they were deposited by EB and low energy IAD process. NdF3/Na3AlF6 HRs showed negligible laser conditioning effect except certain few case, and had considerably lower damage thresholds than LaF3/Na3AlF6 HRs with conditioning (1.8 J/cm2). Optical stabilities of these HRs were significantly improved by low energy IAD process (50 - 100 eV) which had not harmful influence on damage thresholds.

Efficient diode bar-pumped intracavity-doubled Nd:YVO/sub 4/ laser using stacked-glass plate beam shaper

We describe efficient operation in an intracavity-doubled, diode bar-pumped Nd:YVO/sub 4/ laser using a newly designed stacked-glass plate (SGP) beam shaper. We used 20-W diode bars as pump source. It has 10 mm/spl times/1 /spl mu/m emitting dimensions with a divergence of 20/spl deg//spl times/50/spl deg/ (full angle) for horizontal and vertical dimensions. The SGP beam shaper consists of two sets of 15 SGPs. Each plate (25 mm square) is 1.5 mm thick and is stacked with a twist offset. The diode bar beam collimated in the vertical plane is condensed at the entrance of the first SGP and divided into 15 beams. Each beam is refracted at a different angle and transmitted in a different direction in a glass plate. As a result, each beam is emitted with a 1.5-mm gap in the vertical plane from the first SGP is exactly the same as the first one but positioned at a right angle to the first one. The second SGP causes all 15 beams from the SGP to be overlapped in the horizontal plane. As a result, M/sup 2/ of the diode bar beam is improved by a factor of about 15 in the horizontal dimension. Additionally, this beam shaper has a high transmission of 93% for the diode bar beam. The 15 stacked beams are then focused with a cylindrical and a spherical lens.

Light scattering of highest damage resistant fluoride HR coating for KrF laser

Fluoride HR coatings consisting of middle and low refractive index fluorides often show a higher damage threshold than oxide coatings in the UV range. However, the light scattering level of fluoride HR coatings tend to be higher than oxide ones. In this study, the scattering and surface roughness of fluoride HR coatings for KrF laser were investigated, and also compared with those of oxide HR coatings using Al2O3 as high index materials.

High-quality optical coatings and their scaling

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High-threshold fluoride AR coatings for KDP crystal at 352 nm

The laser damage thresholds and other properties of 352 nm fluoride AR coatings for KDP substrate were investigated. The HoF3 (or LaF3)/AlF3 AR coating deposited by IAD process had a high threshold of 24 J/cm2 (10 ns) when the laser conditioning procedure was used. These fluoride ARs were durable for wiping and also did not degrade during more than one year under room atmosphere.