P B Sergeev

Electron-beam induced absorption in crystals of the alkaline-earth fluorides

The absorption behavior has been studied in the 120-1000-nm region in modern high-purity samples of MgF2,CaF2, and BaF2 crystals when they undergo prolonged irradiation in air by an electron beam with energy less than 280 keV (about 104 pulses, total fluence about 20 kJ/cm2). The induced optical density in CaF2 and BaF2 in the 200-1000-nm region was about 0.04-0.1 after such irradiation. Absorption in the UV region in MgF2 samples monotonically increases with irradiation, and they have almost completely lost their transparency in the 260-nm region at fluences of about 500 J/cm2. The studies of the crystals showed that the electron-beam induced absorption is largely determined by impurities that were either already present or that entered the samples while they were being irradiated.

How the absorption-band intensities in high-purity quartz glasses depend on the electron-beam fluence

To study the formation of defects in quartz glasses of type KS-4V, KU-1, and Corning 7980 under the action of an electron beam (EB), the induced absorption spectra is decomposed into individual bands (IBs) with maxima at 163.5, 183.5, 213, 225, 244, and 260 nm. In all the glasses, the intensities of most of the IBs saturated at doses around 90 MGy as the EB fluence increased. The steady-state absorption at 260, 213, and 183 nm was a factor of 2–4 less in KS-4V than in KU-1. The intensity of the bands at 163 nm virtually coincided in these glasses and monotonically increased with increasing EB fluence. This indicates an impact mechanism for the throughput of the oxygen-deficient centers responsible for this band.

Nonlinear and electron-beam-induced absorption in pure quartz glasses at the wavelengths of excimer lasers

The two-photon absorption coefficients β at wavelengths 248 and 193nm with pulse widths 80 and 60ns, respectively, have been measured in KS-4V, KU-1, and Corning 7980 glasses. The value of β at 248nm in KS-4V was 0.16cm∕GW, which was about 30% higher than in the other glasses. At a wavelength of 193nm, the value of β virtually coincided at a level of 1.1cm∕GW in all the samples. The coupling factors between the electron-beam (EB)-induced quasi-steady-state optical density at wavelengths 353, 248, and 193nm and the EB power density on the samples were measured for the same glasses, using the radiations of XeF, KrF, and ArF lasers. These factors in KS-4V were 1, 4, and 6cm2∕GW, respectively. The measurement error did not exceed 50%.

Nonlinear absorption and optical strength of BaF{sub 2} and Al{sub 2}O{sub 3} at the wavelength of 248 nm

An experimental investigation was made of the dependence of the transmission of BaF{sub 2} and Al{sub 2}O{sub 3} samples on the intensity of KrF-laser radiation ({lambda} = 248 nm) pulses of 85 ns duration. The two-photon absorption coefficients were found at {lambda} = 248 nm and their values for these two crystals were 0.5 {+-} 0.2 and 2 {+-} 1 cm Gw{sup -1}. The surface and bulk laser breakdown thresholds were determined for these samples. (nonlinear optical phenomena)An experimental investigation was made of the dependence of the transmission of BaF2 and Al2O3 samples on the intensity of KrF-laser radiation (λ = 248 nm) pulses of 85 ns duration. The two-photon absorption coefficients were found at λ = 248 nm and their values for these two crystals were 0.5 ± 0.2 and 2 ± 1 cm Gw-1. The surface and bulk laser breakdown thresholds were determined for these samples.

Electron-beam-induced absorption of laser radiation at λ = 193, 248, and 353 nm in quartz glass

The absorption of laser radiation at λ = 193, 248, and 353 nm in KU-1 quartz glass has been measured during the application to the test samples of an electron beam with an energy density up to 1 J/cm2 in a pulse 80 ns long. The induced optical density is a linear function of the specific power of the ionizing radiation applied to the sample. The coefficients of these linear proportionalities are 8, 4.6, and 0.5 cm2/GW at the specified wavelengths. Analysis shows that this coefficient gives the most comprehensive characterization of the optical properties of the material at the time at which the intense ionizing radiation is applied.