The present work is concerned with a fundamental study of the metal photodissolution effect in chalcogenide glasses and in particular of those aspects which are relevant to one of the main application areas, the fabrication of diffractive optical elements for operation in the infrared. This study has dealt exclusively with glasses in the As-S system and has used mainly Ag as the source for photodoping. The optical constants of undoped and photodoped As-S films of various compositions have been measured over a wide wavelength range. Pre-annealing the undoped As-S films produced an overall increase of about 3% in the refractive index, n, from the visible to the far-infrared region. The magnitude of the pre-annealing effect was found to increase with increasing As content, being most pronounced at As<SUB>40</SUB>S<SUB>60</SUB>. The maximum overall increase in n produced by photodoping was 20%. The single oscillator and dispersion energies, E<SUB>o</SUB> and E<SUB>d</SUB>, were obtained by fitting the measured dispersion relations using the Wemple-Didomenico model. The optical gap and E<SUB>o</SUB> were found to decrease and E<SUB>d</SUB> and the refractive index to increase with increasing Ag content. Regarding the dependence on As-S composition, for the most heavily Ag-doped films, n, E<SUB>o</SUB> and E<SUB>d</SUB> all exhibited a peak at 30 at.% As but the change in the optical gap was similar to that of the undoped films. The time dependence of the process was examined and found to be definitely linear for the conditions used. It was also found that the photodissolution process does not stop when the Ag is exhausted.
|University of Edinburgh
|Electronic Thesis or Dissertation
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