Andrea Ravagli

Ga-La-S-Se glass for visible and thermal imaging

Abstract Chalcogenide glasses are emerging as important enabling materials for low-cost infrared imaging by virtue of their transparency in the key short-wave infrared (SWIR) to long-wave infrared (LWIR) bands and the ability to be mass produced and molded into near-net shape lenses. In this paper, we introduce a new family of chalcogenide glasses, which offer visible as well as infrared transmission and improved thermal and mechanical properties. These glasses are based on Ga2S3-La2S3 with added Ga2Se3-up to complete the substitution of Ga2S3 for Ga2Se3. The samples are prepared via the melt-quench method in an argon-purged atmosphere. All the studied compositions showed a lower glass transition temperature and an extended transmission window. Particularly, the LWIR transmission was extended from about 9 μm for gallium lanthanum sulfide (Ga-La-S) glass to about 15 μm for Se-added Ga-La-S retaining visible transmission from around 463 nm. The thermal and mechanical properties were investigated to prove the suitability of these novel materials for the production of optical components such as visible to LWIR lenses. Their suitability for drawing into optical fibers is also discussed.

Nonlinear refractive index of ultrafast laser inscribed waveguides in gallium lanthanum sulphide

We demonstrate ultrafast all-optical switching in femtosecond laser inscribed nonlinear directional couplers in gallium lanthanum sulphide operated at 1.55 μm. We report on the evaluation of the nonlinear refractive index of the waveguides forming the directional couplers by making use of the switching parameters. The nonlinear refractive index is reduced by the inscription process to about 4-5 times compared to bulk material.

Optical, Thermal, and Mechanical Characterization of Ga2Se3‐Added GLS Glass

Gallium lanthanum sulfide glass (GLS) has been widely studied in the last 40 years for middle-infrared applications. In this work, the results of the substitution of selenium for sulphur in GLS glass are described. The samples are prepared via melt-quench method in an argon-purged atmosphere. A wide range of compositional substitutions are studied to define the glass-forming region of the modified material. The complete substitution of Ga2 S3 by Ga2 Se3 is achieved by involving new higher quenching rate techniques compared to those containing only sulfides. The samples exhibiting glassy characteristics are further characterized. In particular, the optical and thermal properties of the sample are investigated in order to understand the role of selenium in the formation of the glass. The addition of selenium to GLS glass generally results in a lower glass transition temperature and an extended transmission window. Particularly, the IR edge is found to be extended from about 9 µm for GLS glass to about 15 µm for Se-added GLS glass defined by the 50% transmission point. Furthermore, the addition of selenium does not affect the UV edge dramatically. The role of selenium is hypothesized in the glass formation to explain these changes.

Structural and spectral characterisation of Er3+ and Nd3+ doped Ga-La-S-Se glasses

In this work, the spectroscopy of Er3+ and Nd3+ doped Se-GLS glasses was studied. A structural comparison between doped and non-doped samples was done to assess the differences between the glasses. For this comparison, Raman spectroscopy and thermal analysis were employed. The spectral properties of the samples were studied in order to identify the mechanisms responsible for quenching the fluorescence lifetime of the dopants. In particular, cross-relaxation and concentration quenching were observed in Nd3+ doped samples, whilst co-operative upconversion, radiation trapping and concentration quenching were observed in Er3+ doped samples. The results obtained demonstrated the fundamental role of the phonon energy in the mechanism of fluorescence. The low phonon energy of chalcogenides decreased the rate of non-radiative processes promoting co-operative upconversion. This effect could be exploited to design new lasers and sensitizers for solar energy harvesters.

Spatially controlled doping of silver in chalcogenide glass by thermal, photo and electron beam effects

For the first time, silver doping of bulk Gallium-Lanthanum-Sulphide (GLS) and Gallium-Lanthanum-Sulphur-Selenide (GLSSe) glass is demonstrated, presenting potential for a huge array of optoelectronic applications. Previously, silver doping of chalcogenide glasses were mostly based upon toxic, arsenic containing thin films [1-3]. GLS and GLSSe, however, offer a toxic free alternative, made by a safer and more economic technique, with infrared and nonlinear optic capacity [4].

Structural modification of Ga-La-S glass for a new family of chalcogenides

In this work, the effect of adding Se, Te, In, Cs, Y to gallium lanthanum sulphide glass was studied. Structural modifications to the glassy network were achieved by substitution of sulphur, gallium or lanthanum using a melt-quench method in an inert atmosphere. Optical, thermal and mechanical characterisation of the samples revealed tailorable features according to the nature and the amount of glass modifier. In particular, the addition of selenium and tellurium resulted in an extended transmission in the infrared up to 12 μm. Furthermore, for small amounts of selenium, the position of the bandgap did not change significantly, maintaining visible transmission. The addition of indium led to the formation of glasses with longer transmission in the infrared and a cut-off edge around 600nm in the UV-visible range. Over-all, the addition of these modifiers resulted in stronger materials with improved thermal stability and similar mechanical properties to original Ga-La-S glass. The outcome of this work aims to bring a new family of chalcogenide glasses for applications in the infrared and visible range.

Ga-La-S-Se glass for visible and thermal imaging - dataset

Experiments on novel chalcogenide glass. Data is all included in GLSSe.xlsx. It includes thermal, mechanical and optical measurements. Data was plotted using Microsoft Excel 2013.