Inorganic Glasses with Second-order Optical Response
Thermal poling constitutes an effective method for inducing second-order optical nonlinearity in inorganic glasses, which are otherwise optically passive materials. This process involves the application of high voltage at an elevated temperature, followed by cooling the sample to room temperature while keeping the field on. Poled glasses are characterized by second harmonic generation (SHG) measurements to evaluate their second-order susceptibility, ÷(2), through simulations of Maker-fringe patterns.
Thermal poling-induced NLO properties offer the possibility to use glasses as very versatile and inexpensive materials in active photonic devices. The effects of thermal poling parameters and glass chemistry, as well as the microscopic physical mechanisms associated with the poling process, are not well understood at present and this makes the full exploitation of glasses in photonics difficult.
Research activities in this project involve the development of selected ionic glasses in bulk and thin film forms and their processing by thermal poling. Using expertise and techniques available in house and in collaborating laboratories, SHG measurements are complemented by further investigations to understand the effects of poling on local structural rearrangements and related NLO responses as a means for optimizing the efficiency of poled glasses. To this aim we investigate glasses ranging from sodium-niobium borophoshates and sodium-borosilicates to germanates and aluminophosphates, and employ micro-Raman and infrared spectroscopy to establish correlations between structure/chemistry and NLO response. Micro-infrared reflectance measurements are also employed to probe the spatial distribution and depth-profile of the refractive index in the NLO layer of the poled glass.