Abstract
We study waveguide fabrication in lithium-niobo-phosphate glass, aiming at a practical method of single-stage fabrication of nonlinear integrated-optics devices. We observed chemical transformations or material redistribution during the course of high repetition rate femtosecond laser inscription. We believe that the laser-induced ultrafast heating and cooling followed by elements diffusion on a microscopic scale opens the way toward the engineering non-equilibrium sates of matter and thus can further enhance Refractive Index (RI) contrasts by virtue of changing glass composition in and around the fs tracks.
Highlights
Micro-fabrication of photonics devices by means of intense femtosecond laser pulses has emerged as a novel technology during the last decade [1, 2]
Its uniqueness is based on three physical facts: i) nonlinear absorption, which triggers the energy deposition only at or around a focal point inside a sample; ii) the density of energy deposited in such processes can exceed that typically achieved by the majority of other methods; iii) the rates of energy deposition and following cooling are extremely high, potentially leading to non-equilibrium phase transitions and states of materials, which otherwise cannot be obtained in a laboratory
The glass sample with written waveguides was first studied by optical microscope (Zeiss, AxioScope-2MOT), equipped with Differential Interference Contrast (DIC) optics, as well as Quantitative Phase Microscopy (QPM) software with the possibility for Refractive Index (RI) contrast reconstruction by using Abel inversion and inhouse software, assuming a cylindrical symmetry in the structures obtained
Summary
Micro-fabrication of photonics devices by means of intense femtosecond (fs) laser pulses has emerged as a novel technology during the last decade [1, 2]. Ultrafast cooling of a borosilicate glass [4, 5] after an exposure to either a multiple pulses or after just a single pulse in sapphire [6], revealed a creation of a nano-crystalline precursors of phases, which can only be obtained in bulk materials under very high pressures and temperatures. Local ions diffusion in bulk glass can be induced by laser ultrafast heating and highly localised melting of the material, at that the diffusion length and rate are determined by temperature gradient, time of treatment (e.g. cooling rate) and nature of chemical species As these parameters can be controlled by optimizing laser power, sample translation speed and glass chemical composition, laser induced elements/ions diffusion can be considered as efficient way of high contrast optical phase elements creation. We believe that the laser-induced heating followed by elements diffusion can be efficient way to increase Refractive Index (RI) contrasts by virtue of changing glass composition around the fs tracks
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