The investigated functional materials make it possible to visualize, register, and digitize the volumetric picture of highly nonlinear interaction of light and matter. Using highly nonlinear photographs, including luminescent microtomograms, it is possible to reconstruct the configuration of intense light fields in self-action modes. Crystals with a wide band gap, in which the exciton mechanism of radiation-induced defect formation is realized, are investigated. The generated radiation defects are capable of photoluminescence, they are thermally and optically stable. These media are excellent materials for the manufacture of optical storage media in the form of images and in digital codes.
The paper presents the results of experimental and theoretical studies of the role of avalanche ionization in the process of highly nonlinear generation of electron-hole pairs in the interaction of intense femtosecond laser radiation with dosimetric crystals LiF:Mg,Ti. We assume that the effective formation of defects of hole-interstitial type, which consist of molecular halogen ions placed in one cationic and two anionic vacancies, distinguished by high-temperature peaks in the thermally stimulated luminescence curves, is feasibly connected with avalanche ionization processes occurring in the regions of passage of light filaments. The calculated dependences of the plasma density on time during the laser pulse made with taking into account the avalanche ionization for this type of crystals show that the contribution of avalanche ionization to the electron-hole plasma density is comparable to that of the multiphoton tunneling mechanism.
Non-stationary mechanisms of spatial modulation of luminescence intensity in anisotropic quantum systems within birefringent crystals under their interaction with ultrashort polarized laser pulses were studied. We have found connection between this phenomenon and phase relaxation of excited quantum systems. We have as well grounded a new method for investigation of coherency of quantum systems based on study of characteristic properties of modulation phenomena. It was shown that the influence of the frequency dispersion on the clarity of the modulation picture in insignificant at durations of 100 fs and greater, even for crystals with strong dispersion. Due to the existence of chirp in femtosecond pulses exciting the luminescence, modulation period in instant distribution of absorbed power decreases over distance. In the time-integrated picture of spatial distribution of luminescence intensity, the rate of decrease of modulation depth grows. This leads to new possibilities in experimental investigation of the value of chirp of femtosecond pulses.
Spatial intensity modulation of luminescence in crystals excited by ultrashort pulses decays with respect to distance due to outrunning of the wave packets corresponding to the ordinary and extraordinary waves. The dispersion spreading of the packets introduces distortions into this picture. It is shown that these distortions become significant at pulse duration less than 0.1 ps.
Hidden spatially periodic oscillations of energy absorption by orientation groups of anisotropic quantum systems in birefringent crystals were calculated. Conditions favoring experimental detection of modulation phenomena were determined, and their features have been studied under nonstationary excitation by ultrashort light pulses.
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