What is it about?
In this work, a physical justification is given for the technology for recording color 3D images in a transparent optical carrier based on a lithium fluoride crystal. This technology is based on the found possibilities of creating voxels of three basic colors: red, green and blue under the influence of laser radiation. The technology includes three stages of femtosecond laser irradiation and three stages of heat treatment of the optical medium.
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Why is it important?
Methods for recording monochromatic images with laser radiation in transparent media have been developed long ago. However, attempts to record full color images did not give good results. In our work, this problem was solved for the first time.
Read the Original
This page is a summary of: Laser recording of color voxels in lithium fluoride, Optics & Laser Technology, November 2020, Elsevier, DOI: 10.1016/j.optlastec.2020.106430.
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Creating of luminescent defects in crystalline media by a scanning laser beam
Line-by-line two-dimensional step small-scale scanning irradiation of a transparent cubic LiF crystal was carried out by intense linearly polarized femtosecond laser radiation in the multiple filamentation mode. As a result, isolated longitudinal extended tracks consisting of induced color centers were formed in the medium. It was found that no transverse periodicity associated with the scanning step is observed in the arrangement of tracks formed by laser filaments. This is because inhomogeneities that stimulate filamentation are not contained in the laser beam itself but are formed randomly when the medium interacts with the first laser pulses and are supported and amplified by subsequent pulses. The efficiency of color center formation in crystals at normal laser beam incidence on the cube face depends periodically on the azimuth angle θ between the electric vector and the cube edge on the face, with the period of π/2. It was found that azimuthal dependences for defect formation (maximum at θ = π/4) and for carrier photogeneration (maximum at θ = 0) are in the antiphase. Calculations showed that the processes of self-focusing and filamentation controlled by the components of the third-order nonlinear susceptibility tensor are most effective at the orientation where θ = π/4. The experiment showed that at such an orientation, the critical power and the length of self-focusing decrease, and therefore, the density of the number of filaments in the beam section increases and, as a result, the average concentration of the color centers created by laser filaments increases.
Nonlinear volumetric fluorescent photographic media
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.
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