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Summary

Possibilities of holographic recording and laser lithography usage for forming of Diffractive Microoptical Elements into thin films of As-S system were studied in present thesis. Both theoretical and experimental aspects of problem were investigated. In the literature review section is brief explanation of diffractive elements principles, holographic recording and previous use of As based amorphous thin films as a recording media. The diffractive properties, in particular diffractive efficiency (DE), of expected diffractive elements were simulated numerically for both sinusoidal and rectangular grating shape and for the wavelengths of 632.8, 1064 and 1500 nm, chosen with regard to possible applications. From the simulations is clear that high DE's to chosen order can be achieved, even for the considered normal incidence. The set of As-S system bulk samples was prepared from pure elements by melt quenching. The compositions of systems investigated were chosen with regard to previous research and were As$_x$S$_{100-x}$, where the $x$ was $28,33,35,38$ and 40. Thin films of various thicknesses and compositions were deposited by thermal evaporation. Sensitivity, etching selectivity and characteristics were studied. The best results were observed on samples of As$_{35}$S$_{65}$ system. Selective etching phenomenon was used to transform exposed mixed amplitude/phase elements to phase (surface corrugated) elements. As etchants the Triethylamine or Propylamine were tested and Dimethylsulfoxide or Dimethylformamide were tested as solvents, all in various concentrations. For various film thicknesses the optimal exposure dose, etching time and concentration were found. Compared to holographic recording (514.5 nm), approximately 100 times higher sensitivity of used system was observed for the wavelength of 441 nm used for the laser lithography. Some of prepared elements were characterized by usage of DE, AFM and REM measurements. Observed DE's were in good agreement with numerical simulations for accordant depth, period and profile. From the collected theoretical and experimental data can be concluded that, after minor problems will be solved, both techniques are highly usable for diffractive elements preparation. Used amorphous As-S films have numerous advantages, compared to conventional materials, in particular very high index of refraction and wide spectral region of high transmission, practically from 0.6 to 12 $\mu$m. It was proven that highly efficient elements, diffracting the most energy to any arbitrary diffractive order, could be designed and prepared by both used techniques.
next up previous
Next: Introduction Up: jirka Previous: jirka
root 2002-05-23