Melt property variation in GeSe₂‐As₂Se₃‐PbSe glass ceramics for infrared gradient refractive index (GRIN) applications

Abstract

Melt size‐dependent physical property variation is examined in a multicomponent GeSe2‐As2Se3‐PbSe chalcogenide glass developed for gradient refractive index applications. The impact of melting conditions on small (40 g) prototype laboratory‐scale melts extended to commercially‐relevant melt sizes (1.325 kg) have been studied and the role of thermal history variation on physical and optical property evolution in parent glass, the glass’ crystallization behavior and postheat‐treated glass ceramics, is quantified. As‐melted glass morphology, optical homogeneity and heat treatment‐induced microstructure following a fixed, two‐step nucleation and growth protocol exhibit marked variation with melt size. These attributes are shown to impact crystallization behavior (growth rates, resulting crystalline phase formation) and induced effective refractive index change, neff, in the resulting optical nanocomposite. The magnitude of these changes is discussed based on thermal history related melt conditions.

Infrared Glass–Ceramics with Multidispersion and Gradient Refractive Index Attributes

“…As previously noted, these GAP‐Se base glasses exhibit a systematic variation in thermomechanical and other physical properties with PbSe addition as reported for bulk glasses and can be used to form ultralow dispersion GRIN optics as demonstrated in films . Glasses within the same system have served as a basis for demonstration of a 3D GRIN structure, and can be scaled from laboratory to commercial scale demonstrating the manufacturability of low‐loss GRIN materials suitable for the mid‐wave IR (MWIR) …”

Monolithic Chalcogenide Optical Nanocomposites Enable Infrared System Innovation: Gradient Refractive Index Optics

“…The size of the secondary Pb‐rich and Pb‐deficient amorphous phases typically range from ≈100 to ≈250 nm; as the reduced glass stability of the Pb‐rich phase undergoes thermodynamic transformation to nuclei first (due to a lower activation energy barrier), the size of the resulting crystalline phase(s) created upon subsequent growth can remain sub‐wavelength with precise selection of growth time and temperature, thereby maintaining low loss and broadband transparency across the IR spectral region. [ 28,33–35,37,42–44 ]…”

“…The segregation of Pb at the sub‐wavelength scale has a particular importance since Pb‐containing crystalline phases such as PbSe and Ge 0.1 Pb 0.9 Se, which are formed dominantly within the Pb‐rich regions upon HT, possess refractive indices far greater than those of other resulting crystalline phases, including As 2 Se 3 and Se as well as that of the surrounding amorphous counterpart, thereby increasing the effective refractive index of a resulting glass‐ceramic nanocomposite. [ 33–37,42,44 ] Furthermore, while the spatial segregation of Pb is universally shown in GAP‐Se glasses with a given mol% of PbSe in the immiscibility zone, the extent of the segregation varies with the average diameter of the secondary phases (see Figure S1, Supporting Information), indicating the metastable, non‐equilibrium kinetic nature of the phase separation. [ 45 ]…”

“…[ 1,12,14–16,33,37–39 ] Recent activities have demonstrated how their crystallization behavior can be tailored through composition, morphology, and microstructural modification. [ 28,33–38,40–44 ] Recently, composites based upon Ge‐As‐Pb‐Se chalcogenide glasses have been shown to yield high refractive index Pb‐containing nanocrystalline phases in an amorphous matrix which can remain stable at elevated temperatures or under photo/electronically excited states. [ 28,33–37,40–44 ] In the present approach, we exploit this simple yet effective process to transform multicomponent GeSe 2 ‐As 2 Se 3 ‐PbSe (GAP‐Se) bulk glasses from an amorphous structure into an optical nanocomposite where the volume fraction of high refractive index Pb‐rich nanocrystals is spatially varied in a low refractive index amorphous matrix, thereby realizing a GRIN structure with smoothly varying index and dispersion properties.…”

“…[ 28,33–38,40–44 ] Recently, composites based upon Ge‐As‐Pb‐Se chalcogenide glasses have been shown to yield high refractive index Pb‐containing nanocrystalline phases in an amorphous matrix which can remain stable at elevated temperatures or under photo/electronically excited states. [ 28,33–37,40–44 ] In the present approach, we exploit this simple yet effective process to transform multicomponent GeSe 2 ‐As 2 Se 3 ‐PbSe (GAP‐Se) bulk glasses from an amorphous structure into an optical nanocomposite where the volume fraction of high refractive index Pb‐rich nanocrystals is spatially varied in a low refractive index amorphous matrix, thereby realizing a GRIN structure with smoothly varying index and dispersion properties. Specifically, we explore the mechanism whereby thermal processing of GAP‐Se glasses influences the nanocomposite's resulting microstructural and compositional evolution defining their post‐processed transmissive and optical properties.…”