KU1 Glasses Research Articles

A New Insight into High-Aspect-Ratio Channel Drilling in Translucent Dielectrics with a KrF Laser for Waveguide Applications.

A new insight into capillary channel formation with a high aspect ratio in the translucent matter by nanosecond UV laser pulses is discussed based on our experiments on KrF laser multi-pulse drilling of polymethyl methacrylate and K8 silica glass. The proposed mechanism includes self-consistent laser beam filamentation along a small UV light penetration depth caused by a local refraction index increase due to material densification by both UV and ablation pressure, followed by filamentation-assisted ablation. A similar mechanism was shown to be realized in highly transparent media, i.e., KU-1 glass with a multiphoton absorption switched on instead of linear absorption. Waveguide laser beam propagation in long capillary channels was considered for direct electron acceleration by high-power laser pulses and nonlinear compression of excimer laser pulses into the picosecond range.

Infrared Spectra of KU1 and KS-4V Quartz Glass Irradiated by Fast Neutrons

IR absorption spectra of quartz glass with varying contents of hydroxyl OH groups, namely, KU1 (1000 ppm OH) and KS-4V (≤0.1 ppm OH) are compared prior to and after exposure to fast neutron fluences of 1018–5 × 1019 cm–2. The appearance of the IR absorption band of 2260 cm–1 regardless of the large difference in the content of OH groups in nonirradiated KU1 and KS-4V glass is related to the bending vibrations of the bridging ≡Si−O−Si≡ bonds. A decrease in the amplitude of the band at 2260 cm–1 and shift of its maximum by 20 cm–1 to the IR range is caused by the decrease in the bridging ≡Si−O−Si≡ bond angle with the growth of the neutron fluence. The asymmetric band at 3674 cm–1, which is related to OH groups, is observed only in nonirradiated KU1 glass. An increase in the number of OH groups in KU1 glass and the formation of OH groups in KS-4V glass after the accumulation of the neutron fluence of ≥1019 cm–2 rationalizes the slow accumulation of the intrinsic defects such as nonbridging oxygen atoms and oxygen vacancies in both brands of the glass in the range of the neutron fluence.

Formation of a carbon nanofilm on oil-coated KU-1 glass annealed by KrF laser radiation

The annealing of an oil layer on the output face of a KU-1 glass substrate in air by a high-power 80 ns KrF laser pulse is studied. A polymer-like hydrocarbon film up to 40 nm thick is found to form at laser radiation fluences F above 2 J cm−2 on the glass surface. The upper limit of F ≈ 6 J cm−2 is determined by the damage of the glass samples whose size is approximately equal to the laser spot diameter (1 cm).

Nature and Formation Mechanism of γ-Induced Color Centers with Optical Absorption Band 665 nm in KS-4V and KI Quartz Glasses

The aim of the experiment was to elucidate the formation mechanism of color centers with optical absorption band in the region 660–680 nm, which are induced in KS-4V and KI quartz glasses under irradiation by 60Co γ-rays at dose rate 2.5 Gy/sec and temperature 77, 273, and 310 K in the dose range 30–105 Gy. The 665 nm band is induced efficiently in KI samples, which contain more metallic impurities ( 4·102 Gy is caused by rupture of the M+O–Si≡ bond near aluminum ≡Al3+. In contrast to KS-4 and KI glasses, KU-1 glass is recommended for small windows in the ITR reactor for the visible part of the spectrum.

Electron-beam-induced absorption in quartz glasses

Electron-beam-induced absorption in quartz glasses of types KS-4V, KU-1, and Corning 7940 has been experimentally investigated in the 150-1000-nm region. Samples of optical materials were irradiated in regimes similar to the operating conditions of the windows of electron-beam excimer lasers, in particular, powerful KrF lasers for laser thermonuclear synthesis. It is shown that the electron-beam-induced absorption in all the quartz glasses that were tested reaches a steady-state level during irradiation that is determined by the mean specific power density of the electron beam. Under identical irradiation conditions, the steady-state absorption level in KS-4V glass in the UV region is about a factor of 4 less than in KU-1 glass and a factor of 2 less than in Corning 7940. © 2004 Optical Society of America

Dependence of the POR and NBOHC defects as function of the dose in hydrogen-treated and untreated KU1 glass fibers

We evaluated the performances of the hydrogen-loading technique to reduce the radiation-induced absorption in optical fibers in the visible part of the spectrum. A reduction factor as large as one order of magnitude can be obtained in high dose-rate regime. Based on a spectral deconvolution method, we showed that hydrogen preferentially interacts with NBOHC defects while the number of POR defects is not affected.

Neutron irradiation studies on window materials for EC wave systems

Fast neutron irradiation experiments are reported to study tolerable fluence levels of the primary window of electron cyclotron (EC) wave systems near the torus. Model discs of CVD diamond grades (30/40 mm diameter) were irradiated to fluences between 10 20 and 10 22 n/m 2 ( E>0.1 MeV). For a torus window demonstrator, a large area diamond disc of (106 mm diameter) was irradiated to 0.9.×10 21 n/m 2. Mechanical strength tests were performed with specimens (11 mm diameter) cut from medium size diamond discs (62 mm diameter). In contrast to dielectric and mechanical properties, the most sensitive material parameter is thermal conductivity for which at 10 −4 dpa a significant reduction by about a factor of 2 has to be accounted for. Comparative dielectric measurements for Quartz discs and special silica glass grades (Infrasil, KU1) showed that loss in quartz stayed at the tan δ-level of 10 −4 at least up to 10 22 n/m 2; loss in the unirradiated KU1 glass reached the 10 −3 level.

Investigation of the Effect of Radiation and High-Temperature Treatment on the x-Ray Luminescence of Quartz Glasses

The x-ray luminescence of KI, KV, and KU-1 quartz glasses, irradiated with γ and n–γ radiation in the dose range 102–107 Gy and neutron fluence range 1015–1017 cm–2 and subjected to high-temperature annealing in air at 450 and 900°C is investigated. It is shown that the spectra of the nonirradiated and the γ and n–γ irradiated glasses of the first two types are a superposition of bands with λmax = 410 and 460 nm, which are due to an impurity center initially present in the glasses (λmax = 410 nm) and the initial and radiation-generated with dose ≥106 Gy and fluence ≥1016 cm–2E' centers (λmax = 460 nm). X-Ray luminescence is not observed in nonirradiated KU-1 glasses; a band with λmax = 460–470 nm, due to radiation-generated E' centers, appears in the spectra of γ and n–γ irradiated glasses. As the γ radiation dose and the neutron fluence increase, the number of impurity centers decreases and the number of E' centers increases. It is established that the 410 nm band is due to the γ component of the n–γ radiation. High-temperature annealing in air at 900°C induces in the spectra new bands with λmax = 470 and 520–540 nm, which are believed to be due to interstitial defects of the type O– and O2–, formed when oxygen from air diffuses into the glass and localizes in interstices. 6 figures, 7 references.

Some properties of a precursor film

The optical, rheological, and topological properties of a precursor film, which is created by a drop lying on a surface, were studied by means of ellipsometry. The investigated liquid is glycerin; the investigated substrates were type K8 and KU1 glass. The results are in good qualitative agreement with DLFO theory.