Characterisation of compositional photosensitivity dependence of Ga-La-S thin films fabricated by pulsed laser deposition

Thin films of chalcogenide glasses of Ga-La-S composition (GLS) have recently been grown via the technique of pulsed laser deposition (PLD). These non-oxide glasses have many attractive features including a wide transmission range which extends from visible wavelengths up to ~10 micron, and low phonon energies, which drastically reduce non-radiative relaxation rates, thus making them interesting candidates for infra-red laser hosts. Furthermore, under irradiation with light in the blue/uv wavelength region, these glasses can exhibit several photostructural effects including photobleaching, photodoping, and more complicated reconfiguration behaviour, in which refractive index variations of the order of 1% can easily be produced. The exact cause of such index changes is uncertain, but the possibility of writing diffractive grating structures with sub-micron resolution in waveguide GLS structures holds out much potential for distributed feedback integrated optical devices. Previous results on both laser and e-beam grating writing have revealed the ease with which gratings can be produced in GLS films, but so far, no systematic study has been undertaken on how the induced refractive index change depends on exact compositional properties of the GLS glasses