Numerous innovations in photonics were realized on the base of nonlinear optical properties and notably in information technologies. To take advantage of nonlinear optical properties of glass, multi-disciplinary research efforts were necessary combining optics, glass chemistry, material science as well as development of optical or electrical polarizations processes.
This presentation addresses fundamental aspects of the second order optical properties in glasses, but will also give more details on recent progresses demonstrating that amorphous inorganic material can now compete with lithium niobate single crystal. By using a thermo-electrical imprinting process, the possibility to manage at the micrometer scale geometry and location of efficient second order optical responses. (χ(2)= 29 pm.V−1 at 1.06 µm) is demonstrated on amorphous niobate optical thin films. This paves the way for the future design of integrated nonlinear photonic circuits based on amorphous inorganic materials enabled by the spatially selective and efficient second order optical susceptibility of these promising and novel optical materials.
A thermo-electrical imprinting process has been employed to induce second-order optical nonlinear (SONL) response in amorphous sodo-niobate optical thin films. By characterizing the geometry and the magnitude of the SONL response, a key aspect of thin film’s poling mechanisms compared with bulk glasses was established. This lies in the appearance of a charge accumulation at the film/substrate interface, described by the Maxwell–Wagner effect. A way to minimize this effect was then proven by promoting an induced built-in static field in the plane of the film using a microstructured electrode. A SONL susceptibility as high as 29 pm/V was measured, and its geometry and location were controlled at the micrometer scale. This work paves the way for the future design of integrated nonlinear photonic circuits based on amorphous inorganic poled materials.
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.
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).
Secondary Ion Mass Spectroscopy (SIMS), Electron Probe Micro Analysis (EPMA) and X-Ray Photoelectron
Spectroscopy (XPS) were used to analyze the polishing induced contamination layer at the fused silica optics surface.
Samples were prepared using an MRF polishing machine and cerium-based slurry. The cerium and iron penetration and
concentration were measured in the surface out of defects. Cerium is embedded at the surface in a 60 nm layer and
concentrated at 1200 ppmw in this layer while iron concentration falls down at 30 nm. Spatial distribution and
homogeneity of the pollution were also studied in scratches and bevel using SIMS and EPMA techniques. An
overconcentration was observed in the chamfer and we saw evidence that surface defects such as scratches are specific
places that hold the pollutants. A wet etching was able to completely remove the contamination in the scratch.
Effects of deep wet etching on the surface quality and the laser induced damage probability have been studied on fused
silica samples. Results obtained with a HF/HNO3 solution and a KOH solution were compared on both polished pristine
surface and scratched surfaces. The hydrofluoric solution radically deteriorated the surface quality creating a haze on the
whole surface and increasing considerably the roughness. For both solutions, neither improvement nor deterioration of
the laser damage performances has been observed on the etched surfaces while the laser damage resistance of scratches
has been increased to the level of the surface. We conclude that laser damage performances are equivalent with both
solutions but an acid etching induces surface degradation that is not experienced with basic etching.
We report on two-photon excited fluorescence in the oriented Eu3+-doped LYB monoclinic crystal under femtosecond laser tight focusing. Due to spatial walk-off, the two polarization modes of the incident femtosecond beam simultaneously provide the independent excitation of two distinct focuses, leading to a single-beam dual-voxel nonlinear excitation of fluorescence below material modification threshold. These observations emphasize on the anisotropy of both two-photon absorption as well as fluorescence emission. They demonstrate the localized control of the nonlinear energy deposit, thanks to the adjustment of both the input power and polarization, by properly balancing the injected energy in each voxel. Such approach should be considered for future direct laser writing of waveguides in propagation directions out of the dielectric axes, so as to optimally cope with the highly probable anisotropy of laser-induced material modification thresholds in these crystals. These results open new ways for further potential developments in direct laser writing as the simultaneous inscription of double-line structures for original waveguides processes.
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