Ultrafast Laser Processing of Hybrid Micro- and Nano-structures in Silicate Glasses
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Ultrafast Laser Processing of Hybrid Micro- and Nano-structures in Silicate Glasses Pavel Mardilovich1, Luke Fletcher2, Neil Troy2, Lihmei Yang3, Huan Huang3, Subhash Risbud1 and Denise M. Krol2 1 Department of Chemical Engineering and Materials Science, University of California, Davis One Shields Ave, Davis, CA 95616, U.S.A. 2 Department of Applied Science, University of California, Davis One Shields Ave, Davis, CA 95616, U.S.A. 3 PolarOnyx Inc., 2526 Qume Drive, Suites 17 & 18, San Jose, CA 95131 ABSTRACT This study describes the fabrication of hybrid micro- and nanostructures of semiconductor nanocrystals arranged in microscopic lines inside of a borosilicate glass doped with CdSxSe1-x. This was performed using a two step process of (1) ultrafast laser modification and (2) heat treatment. The glass was photomodified using focused sub-picosecond infra-red pulses with 1 MHz repetition rate to create linear domains with local compositional variations. Heat treating the sample at temperatures near glass transition preferentially precipitated semiconductor in the modified regions, as evidenced by confocal fluorescence microscopy. The optical properties of the precipitated nanocrystals varied with heat treatment duration. INTRODUCTION Ultrafast laser processing of glasses has potential for applications in a host of photonic devices [1]. Short pulses, in the femtosecond to picosecond range, when focused inside a normally transparent glass produce extremely high electromagnetic fields at the focal point, which leads to non-linear effects and absorption of laser energy. The rapid absorption and dissipation of energy leads to structural changes [2], which can be induced with a great degree of control in three dimensions. This micron scale modification lies at the heart of a lot of currently investigated photonic devices, such as basic waveguides [3,4] interferometers [5], couples and splitters [6], etc.. Recently there has been interest and notable advances in using active glasses, i.e. glasses that can exhibit signal gain [7], and that can be used either for signal amplification along the waveguide, or, with proper cavity construction, compact waveguide lasers [8]. The focus of active glass waveguides so far has been on glasses doped with ions, such as Er and Yr. One shortcoming of such systems, is that in rare earth ions optical transitions, dictating gain bandwidth, are narrow and do not easily yield themselves to tuning. Previously, quantum dots (QDs) have been considered as good candidates for gain media due to being easily invertible, thus having low lasing threshold, and, perhaps more importantly, having optical properties tunable with particle size [9]. In this light, quantum dot doped glasses make intriguing candidates for the aforementioned photonic applications, as the particle size in these glasses, and therefore their optical properties, can be easily controlled by adjusting simple processing conditions that govern their nucleation and growth, such as heat treatment temperature and duration [10, 11].
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