Development of Visible-to-LWIR multispectral chalcogenide glasses

Abstract

In the last four decades, Gallium Lanthanum Sulphide (GLS) glasses have been studied and proposed as material for active and passive applications. In this thesis, the effect of Se, Te, In and Cs on GLS is described presenting a new class of chalcogenide glasses with transparency from Visible to Long Wave IR range (500 nm – 16 μm). The addition of the new component was done by exchanging S with Se and Te, Ga with In and La with Cs in a variety of combinations to probe the glass forming ability of the new systems. The glasses were prepared mixing the precursors in a dry-N₂ glovebox and adopting a melt-quench method in a Ar-purged furnace. The powders were melted at 1150 °C for 24 hours and then annealed at 490 °C for 24 hours. Glass formation in Se, Te and In samples was observed and the optical, thermal and mechanical properties of these samples were characterised. The addition of the new components resulted in an extension of the transmission towards the LWIR. Particularly, the largest improvement was observed for the sample containing 60 mol% Ga₂Se₃ which transmitted light up to 15 μm. This sample also exhibited transmission in the visible range up to 550 nm. Although modest improvements were observed for Te-GLS and In-GLS, these compositions exhibited phase separation and large losses in mass during the melting process. The thermal and mechanical properties of the samples were studied to investigate the possibility to produce optical components such as multispectral lenses. The results obtained showed superior properties than the commercial chalcogenide glasses. Indeed, higher characteristic temperatures, mechanical strength and comparable thermal expansion were observed. The effect of the temperature on the optical properties was studied up to 500 °C for high temperature applications. The properties in the THz spectrum were studied to study the dielectric properties of the glasses. The n2 was measured for supercontinuum generation and other applications in non-linear optics. The spectral properties of Nd³⁺ and Er³⁺ were studied for applications as amplifiers and middle-IR lasers. For these samples, mathematical models supported the experimental results to better understand the mechanism of light emission.

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ORCID for Daniel Hewak: orcid.org/0000-0002-2093-5773

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