Picosecond and Nanosecond Pulse Shaping for State-Selective Chemistry

沃伦教授得到了实验物理化学计划的资助，他使用形状激光脉冲来定向或排列分子束中的分子，在低温晶体中产生人口反转，并通过光子锁定实验来定位键中的能量。研究计划的重点之一是发展技术，以有效地填充一个电子激发态与一个单一的激光，或转移人口到基态的高振动激发态与两个激光。这项工作的动机是研究碰撞动力学，这需要选择性激励来监测速度变化的碰撞。完全的人口转移增强了信号并使干扰最小化。成功地将热分布的大部分转移到高振动状态将有助于探索化学反应的动力学。一个目标是设计辐射场，驱动双原子分子在基态到旋转态的叠加，这样双原子分子在实验室中是定向的。通过特定扫频脉冲形状的Stark移动先前稳定的水平来调节IBr分子的解离率的效果的演示将是将该技术应用于多原子分子的第一步。通过制备特别定制的光脉冲，可以产生简单且可解释的分子状态。Warren教授将使用这些技术来控制它们在分子束中的排列，甚至在实验室中控制它们的方向，并调节它们分裂成碎片的速度。

Professor Warren is supported by a grant from the Experimental Physical Chemistry Program to use shaped laser pulses to orient or align molecules in a molecular beam, to generate population inversion in low-temperature crystals, and to localize energy in a bond by a photon-locking experiment. One of the thrusts of the research program is the development of techniques to efficiently populate an electronically excited state with a single laser, or to transfer population to highly vibrationally excited levels of the ground state with two lasers. The motivation for this work is the study of collisional dynamics which require selective excitation to monitor velocity changing collisions. Complete population transfer enhances the signal and minimizes interferences. Success in transferring large fractions of the thermal distribution into high vibrational states will be useful for exploring the kinetics of chemical reactions. One goal is to design radiation fields which drive diatomic molecules in their ground state to a superposition of rotational states such that the diatomic molecule is oriented in the laboratory. A demonstration of the effect of modulating the dissociation rate of the IBr molecule by Stark shifting previously stable levels with specific frequency-swept pulse shapes will be the first step towards applying this technique to polyatomic molecules. %%% By preparing specially tailored pulses of light, it is possible to produce simple and interpretable states of molecules. These techniques will be used by Prof. Warren to control their alignment in a molecular beam and even their orientation in the laboratory, and to modulate the rate at which they break apart into fragments.