Kathleen Richardson

Raman gain measurements and photo-induced transmission effects of germanium- and arsenic-based chalcogenide glasses

The Raman gain spectra of millimeter thick As(2)S(3) and As(24)S(38)Se(38) glasses and Ge((23 - x))Ga(x)Sb(7)S((70 - y))Se(y) with x = 0 and 5 and y = 0, 2, 5 have been measured using a direct nonlinear optics technique. The pump light originated from a picosecond Nd:YAG laser operating at 1064 nm and a tunable optical parametric generator and amplifier (OPG/OPA) was used as a source for the probe light. A peak material Raman gain coefficient of (155 +/- 11) x 10(-13) m/W has been measured for the As(24)S(38)Se(38) glass. A reversible photodarkening effect which responds to picosecond pulses is also reported. Finally, surface optical damage threshold measurements were found to be less than 9 GW/cm(2) for the reported samples, values which are comparable to some TeO(2)-based glasses with lower nonlinearities.

Broadband low-loss optical phase change materials and devices (Conference Presentation)

Optical phase change materials (O-PCMs) are a unique class of materials which exhibit extraordinarily large optical property change (e.g. refractive index change > 1) when undergoing a solid-state phase transition. These materials, exemplified by Mott insulators such as VO2 and chalcogenide compounds, have been exploited for a plethora of emerging applications including optical switching, photonic memories, reconfigurable metasurfaces, and non-volatile display. These traditional phase change materials, however, generally suffer from large optical losses even in their dielectric states, which fundamentally limits the performance of optical devices based on traditional O-PCMs. In this talk, we will discuss our progress in developing O-PCMs with unprecedented broadband low optical loss and their applications in novel photonic systems, such as high-contrast switches and routers towards a reconfigurable optical chip.

Ultra-thin, reconfigurable meta-optics using optical phase change materials (Conference Presentation)

The dramatic optical property change of optical phase change materials (O-PCMs) between their amorphous and crystalline states potentially allows the realization of reconfigurable photonic devices with enhanced optical functionalities and low power consumption, such as reconfigurable optical components, optical switches and routers, and photonic memories. Conventional O-PCMs exhibit considerable optical losses, limiting their optical performance as well as application space. In this talk, we present the development of a new group of O-PCMs and their implementations in novel meta-optic devices. Ge-Sb-Se-Te (GSST), obtained by partially substituting Te with Se in traditional GST alloys, feature unprecedented broadband optical transparency covering the telecommunication bands to the LWIR. A drastic refractive index change between the amorphous and crystalline states of GSST is realized and the transition is non-volatile and reversible. Optical metasurfaces consist of optically-thin, subwavelength meta-atom arrays which allow arbitrary manipulation of the wavefront of light. Capitalizing on the dramatically-enhanced optical performance of GSST, transparent and ultra-thin reconfigurable meta-optics in mid-infrared are demonstrated. In one example, GSST-based all-dielectric nano-antennae are used as the fundamental building blocks for meta-optic components. Tunable and switchable metasurface devices are developed, taking advantage of the materials phase changing properties.

Thermal conductivity of chalcogenide glasses measured by Raman spectroscopy

We review the potential and limitations of a temperature-dependent Raman Scattering Technique (RST) as a nondestructive optical tool to investigate the thermal properties of bulk Chalcogenide Glasses (ChGs). Conventional thermal conductivity measurement techniques employed for bulk materials cannot be readily extended to thin films created from the parent bulk. This work summarizes the state of the art, and discusses the possibility to measure more accurately the thermal conductivity of bulk ChGs with micrometer resolution using RST. Using this information, we aim to extend the method to measure the thermal conductivity on thin films. While RST has been employed to evaluate the thermal conductivity data of 2D materials such as graphene, molybdenum disulfide, carbon nanotubes and silicon, it has not been used to effectively duplicate data on ChGs which have been measured by traditional measurement tools. The present work identifies and summarizes the limitations of using RST to measure the thermal conductivity on ChGs. In this technique, the temperature of a laser spot was monitored using Raman Scattering Spectra, and efforts were made to measure the thermal conductivity of bulk AMTIR 1 (Ge33As12Se55) and Ge32.5As10Se57.5 ChGs by analyzing heat diffusion equations. To validate the approach, another conventional technique - Transient Plane Source (TPS) has been used for assessing the thermal conductivity of these bulk glasses. Extension to other more complicated materials (glass ceramics) where signatures from both the glassy matrix and crystallites, are discussed.

Advances in infrared GRIN: a review of novel materials towards components and devices

Novel optical materials capable of advanced functionality in the infrared will enable optical designs that can offer lightweight or small footprint solutions in both planar and bulk optical systems. UCF’s Glass Processing and Characterization Laboratory (GPCL) with our collaborators have been evaluating compositional design and processing protocols for both bulk and film strategies employing multi-component chalcogenide glasses (ChGs). These materials can be processed with broad compositional flexibility that allows tailoring of their transmission window, physical and optical properties, which allows them to be engineered for compatibility with other homogeneous amorphous or crystalline optical components. This paper reviews progress in forming ChG-based GRIN materials from diverse processing methodologies, including solution-derived ChG layers, poled ChGs with gradient compositional and surface reactivity behavior, nanocomposite bulk ChGs and glass ceramics, and meta-lens structures realized through multiphoton lithography (MPL).

Cavity-Enhanced Photosensitivity in As 2 S 3 Chalcogenide Glass

Cavity-enhanced photosensitivity of As2S3chalcogenide glass films is measured using planar micro-disk resonators. We determine the origin of such photosensitivity to be optical absorption arising from sub-gap defects.