Leonid B. Glebov

New possibilities of photosensitive glasses for three-dimensional phase hologram recording

Refractive index variation due to photothermoinduced crystallization of polychromatic glass has been found. This effect is used for 3-D phase hologram recording. Optical properties of holograms are stable in the wide spectral and temperature range. Holograms have high diffraction efficiency and angle selectivity.

Laser-induced damage of glasses by pulsed radiation in nano-picosecond region

The dependence of laser-induced damage threshold of K8 (Russia) and BK7 (USA) glasses on laser pulse duration in the wide region from 4 (DOT) 10-11 to 3 (DOT) 10-8 s has measured. Strong attention is paid to methods of measurements. It is indicated to strong influence of laser radiation statistics on the results of the threshold measurements. It is shown that intrinsic laser-induced damage threshold of glasses does not depend on pulse duration when there is not self-focusing. However the time dependence appears when spot size has become more than the wavelength of laser radiation. It is determined by Kerr nonlinearity in the region of pulse durations less than 10-9 s. For longer pulses the other types of nonlinearity are important as well. It is established that the critical power of the self-focusing is not constant for the same glass, and one depends on the concrete focusing conditions. Besides it is shown that the vector character of electric field strength of laser radiation must take into account under calculation of this value in the focal region under tight focusing conditions.

Influence of ion exchange treatment on laser-induced damage of glass surface

This work is devoted to the investigation of questions that can be useful for development of standard for the determination of laser induced damage threshold. It is shown that low- temperature ions exchange is a prospective approach for improving and stabilizing of laser damage thresholds of glasses surfaces. The radiation parameters and exposure conditions which are necessary to obtain the reproducible breakdown thresholds have formulated. The powerful laser system for damage testing designed on the basis of these requirements are described.

Formation of optical elements of glasses by ion-exchange method and photothermo-induced crystallization

It is found that a volume and a refractive index are varied as a result of an ion exchange process on glasses. This effect is used to produce microlenses and relief diffraction gratings. UV exposure and a thermal treatment result in a crystalline phase growth on photoglass- ceramics and polychromatic glasses. This effect leads to volume and refractive index exchange in the exposed zone. The exposure through masks enables the formation of volume phase holograms, gradient elements, and periodic relief structures on the photosensitive glasses surface and volume. The creation of ion-diffusants or microcrystals concentration gradients leads to a sample bending. This effect was used to produce the second order surface.

Intrinsic optical breakdown of glasses

In this paper the influence of multiphoton absorption, self-focusing, absorbing impurity, mode composition, and focusing conditions of laser radiation on the regularities and the absolute values of breakdown threshold of glasses have been studied. The conditions necessary for the realization of intrinsic optical breakdown have been determined. It is shown that under focusing of the neodymium laser radiation in spots of 0.4 - 0.8 micrometers diameters statistical spread in breakdown threshold values, temporal and size dependence are absent. Breakdown thresholds for alkali silicate glass K8 and fused quartz KY1 are similar and are almost 1013 W/cm2. On the basis of the obtained results a new model of intrinsic optical breakdown mechanism has been proposed.

Nonlinear coloration and damage of wide-gap glasses by femtosecond laser at 0.85 μm

The processes arising in glasses as an example of solid dielectrics under high-power femtosecond laser radiation have been investigated. In the investigation samples of fused silica were used as well as a wide selection of commercial borosilicate glasses K8 (Russia) and BK7 (USA) which have the band gap near 6 eV. The glass samples were irradiated with the output of a laser system allowing the production of laser pulses at 0.85 micrometer wavelength and duration approximately 10-13 s. It is found that color centers formation and intrinsic luminescence of borosilicate glasses are observed under high-power femtosecond radiation at 0.85 micrometer. These processes result from supercontinuum generation in the bulk glass and are followed by two-photon absorption of the short-wavelength part of this supercontinuum. These same processes lead to the damage of glasses under conditions of intensive ionization of material matrix, and show that the damage process is not connected with avalanche ionization.

Photostructural transformation of chalcogenide glasses under nonlinear absorption of laser radiation

The photoinduced change of transmittancy of chalcogenide glasses was investigated under exposure to the laser radiation at 1.064 and 1.318 micrometer. It was established that two- photon absorption in these glasses arises under exposure to radiation with irradiances of greater than or equal to 108 W/cm2. It results in irreversible structural transformation of the glasses in the interaction region. This process has threshold character over a narrow range of radiation irradiance (plus or minus 0.1Ithr) and results in appearance of a small-dispersion phase in the bulk glass. Formation of such regions has fluctuating character and causes the appearance of strong light scattering. The effect observed is similar phenomenologically to the known effect of photo-structural transformations in the thin films under exposure to near bandgap light. However, in contrast to the last, the emerged changes of the glass properties are not erased completely by the annealing at the glass transition temperature.

Photoinduced second-harmonic generation in titanium and cerium-doped lead silicate glasses

Photoinduced second harmonic generation in titanium and cerium doped lead-silicate glasses at different infrared preparation intensities is reported. The influence of dopants on second harmonic conversion efficiency is discussed.

Role of laser radiation statistics in the measurement of basic regularities of optical breakdown of glasses

The dependence of laser-induced damage (LID) threshold of K8 (Russia) and BK7 (USA) glasses on laser pulse duration in the wide region from 4 X 10-11 to 3 X 10-8 s has measured. Strong attention was paid to methods of measurements. It was indicated to strong influence of laser radiation statistics on the results of the threshold measurements. It was shown that intrinsic LID threshold of glasses does not depend on pulse duration when there is not self-focusing. However, the behavior of LID threshold time dependence is determined by different types of self-focusing under focusing in spots more than laser radiation wavelength. The self-focusing threshold power is changed with the increasing of spot diameter.

Mechanisms of multiple shot bulk damage of silicate glasses with and without conditions of multiphoton absorption

Accumulation effect in silicate glasses under single frequency laser radiation (0.53 and 1.06 micrometers ) has been investigated. It is shown that this effect in lead silicate glasses at 0.53 micrometers is the result of the multiphoton matrix ionization, the accumulation of color centers and radiation absorption by them, and the decrease of thermal self- focusing threshold. However, under radiation at 1.06 micrometers in the same materials the multiphoton ionization and color centers formation are not observed. It is established that in this case accumulation effect is connected with densification of glasses in the interaction bulk. This densification is the result of the action of large electrostrictional pressure. It leads to the modification of physical properties of glasses without electronic excitations and the decrease of the self-focusing threshold. In this connection, the accumulation effect takes place only if electrostrictional pressure exceeds threshold value of pressure required to densification of glasses.