Compensation for Self-Focusing of Picosecond Pulses in Nd：Glass by Using Cascaded Quadratic Nonlinearity

One of the obstacles in obtaining high power/energy laser sources is self-focusing, which stems from the nonlinear phase shift (B-integral) accumulated during beam propagation in Kerr media. Phase-mismatched secondharmonic generation may impose a nonlinear phase shift on the fundamental with controllable sign and magnitude,which can be used to compensate for self-focusing with a single-pass configuration. We have demonstrated such a possibility for picosecond pulses theoretically and experimentally, and both configurations of pre- and postcompensation by a β-barium borate crystal have been studied in detail. Cascaded second-order nonlinearity-based compensation for self-focusing may provide an auxiliary means to the conventional B-integral control techniques.     

二维光子晶体

光子晶体是一种介电常数周期变化的功能材料,其基本特征是具有光子带隙。光子晶体理论诞生已三十年,基于理论及实验的研究取得了许多成绩。当所制备的光子带隙与光波的波长相当时,光子晶体材料抑制光子在一定频段内的传播。由于在光学、电学、热学、磁学等方面均有优良特性和潜在应用,光子晶体作为一种新型材料也越来越受到科研人员的青睐。不论在可加工性方面还是在传播特性方面,二维光子晶体的优势正逐渐体现出来。本文重点阐述二维光子晶体的研究进展,分别介绍了二维光子晶体的结构与性能特点以及近年来发展出的新型制备方法,如自组装法、刻蚀法、多光束干涉法等,并着重列举其在传感器、波导、光纤、太赫兹技术等领域的发展现状,表明二维光子晶体作为超材料具有巨大的发展空间和潜力。最后,本文对二维光子晶体今后的研究方向和发展前景作了展望。