基于调制光晶格的中性分子束光学Stark减速与囚禁的理论研究

本文基于分子束光学Stark减速理论，提出采用调制的红失谐光晶格来减速和囚禁任意脉冲超声分子束方案，并予以理论研究.以CH₄超声分子束为例，利用Monte-Carlo方法模拟了调制光晶格中的分子减速与囚禁的动力学过程，给出减速级数、同步分子初始位相角与减速效果的关系.研究结果表明：随着减速级数的增加，被减速的分子波包逐渐从原来的分子速度分布的大波包中分离开来，且减速级数越高，减速后的分子速度越小.在其他条件相同时同步分子初始位相角越大，减速波包内的分子数目越少，同时位相空间被压缩.与未调制的光晶格减速方案相比，本方案中无分子自由飞行过程，在相同的光晶格长度内完成了双倍的减速级数.当光晶格长度取3.71 mm时，模拟结果显示CH₄分子从280 m/s减速至172 m/s，而未调制光晶格只能将CH₄分子从280 m/s减速至232 m/s，减速效果提高了26%.本方案可以集分子的减速、囚禁于一体，是一种新型的分子光学功能器件，在冷分子光学、量子信息、冷化学等前沿研究领域中有潜在的应用.

Theoritical research on optical Stark deceleration and trapping of neutral molecular beams based on modulated optical lattices

According to the optical Stark deceleration theory of using a stationary quasi-cw red-detuned optical lattice to slow and trap an arbitrary pulsed molecular beam, we propose a novel idea of using a modulated optical lattice instead of a stationary one to realize a multistage optical Stark deceleration. We analyze the motion of the decelerated molecules inside the optical decelerator, and study the dependence of the velocity of the decelerated molecular packet on the synchronous phase angle and the number of the deceleration stages (i.e. half the number of the optical-lattice cells) by using the Monte-Carlo method. The simulation results show that it takes longer time for the molecules to reach the detector as the number of the deceleration stages increases. The decelerated molecular wave packets are gradually separated from the large wave packets of the original molecular velocity distribution. And the higher the number of the deceleration stages, the lower the decelerated molecular speed is. In addition, we also study the influence of the initial phase angle of synchronous molecules under the same conditions. It is demonstrated that the higher the initial phase angle of synchronous molecules, the lower the decelerated molecular speed is and the smaller the number of molecules in the deceleration wave packet, so the phase space is compressed. The result also shows that the modulated optical Stark decelerator does not have the process of molecular free flight, and thus improving the efficiency of deceleration for molecules. The ultra-cold molecules can be trapped in the optical lattice by rapidly turning off the modulation signal of the lattice. Comparing with the previous scheme, the doubled number of the deceleration stages is reached in the same optical lattice length since a modulated optical lattice is used. For a length of optical lattice of 3.71 mm, theoretical simulation results demonstrate that the speed of methane molecules is decelerated from 280 m/s to 172 m/s. Comparing with the previous results from 280 m/s to 232 m/s, the deceleration effect is improved by 26%. Our scheme can not only obtain an ultra-colder molecular packet under the same molecular-beam parameters and deceleration conditions, but also be directly used to trap the slowed cold molecules after the deceleration without needing to use other techniques for molecular trapping.