Slowing, Cooling, and Spectroscopy with Stimulated Optical Forces

在正常情况下，空气中的分子以每秒近500米的速度移动，如果它们不是不断地相互碰撞，它们会在50百万分之一秒内移动一英寸。这笔拨款将支持研究利用激光在同样一英寸的范围内通过产生一百万倍重力的减速来使原子或分子处于停顿状态的新方法。对于原子的情况，目标是通过极大地增加力和力可用的速度范围来改进现有的方法。对于分子，由于分子内部量子结构的相对复杂性，应用标准方法已被证明是极其困难的。因此，将特别强调减速和冷却分子的有效方案，使用一氟化钙分子CaF作为测试系统。最佳方法将通过使用同时包含多种颜色的激光的激光的数值建模和实验测试相结合来确定。由此产生的冷原子和分子将用激光探测其内部能量结构进行研究。该装置还将用于研究在特殊条件下分子之间的相互作用。它可能应用于化学物理、冷等离子体形成、电场校准和量子计算。该项目将有助于培养和教育本科生和研究生。这项研究涉及三个主要动机：发展和理解受激光学力的物理学，在原子和分子束的直接激光减速和冷却方面取得重大进展，以及研究He原子和分子CaF中的激发态结构和动力学。之所以选择氦和CaF，部分是因为它们的根本利益，部分是因为它们是通过受激发的光学力进行操纵的极佳候选者。受激双色力(BCF)和新提出的多色力(PCF)是由多频激光产生的相干光学力修正而来的，其强度可以比传统的辐射力强数百倍。作为拟议研究的一部分，将完成一个用于He的啁啾-BCF减速器的原型，并将测试一个有前景的新的四色光子晶体光纤版本，并与计算进行比较。将为CaF分子开发类似的减速器，CaF分子最近吸引了相当大的兴趣，成为直接激光减速和冷却的候选物种。对于分子来说，除了增加作用力之外，利用相干光学力还有一个额外的优势。由于每个辐射衰变事件可能会发生数百次BCF动量交换，因此在分子衰变到难以接近的“暗”状态之前，BCF可以将速度降低数百倍，而不是非相干辐射力。几个光谱实验将在产生的冷原子和分子上启动，包括对CaF的高激发里德堡态的冷气体的研究，以及对He和CaF的精确激光光谱的研究。里德堡态中冷分子的研究是一个很少被探索的话题，可能会涉及新的物理现象。氦的精确光谱将有助于基础理论的测试，并为未来的超精密测量铺平道路。亚稳氦束的新应用也将被探索。

Under normal conditions, molecules in the air move at speeds of nearly 500 meters per second, and if they were not constantly bumping into one another, they would travel an inch in just 50 millionths of a second. This grant will support research on new methods for using lasers to bring atoms or molecules to a standstill within this same one-inch range, by producing decelerations a million times the force of gravity. For the case of atoms, the objective is to improve upon existing methods, by greatly increasing the force and the velocity range over which the force is usable. For molecules, it has proven to be extremely difficult to apply standard methods, owing to the relative complexity of the internal quantum structure of molecules. Thus a particular emphasis will be placed on effective schemes for decelerating and cooling molecules, using as a test system the calcium monofluoride molecule, CaF. Optimal approaches will be determined by a combination of numerical modeling and experimental tests using laser beams that contain light at multiple colors simultaneously. The resulting cold atoms and molecules will be investigated using lasers to probe their internal energy structure. The apparatus will also be used to study the interaction of molecules with each other under unusual conditions. There are possible applications to chemical physics, cold plasma formation, electric field calibration, and quantum computation. The project will help train and educate undergraduate and graduate students. The proposed research addresses three main motivations: to develop and understand the physics of stimulated optical forces, to achieve large improvements in direct laser slowing and cooling of atomic and molecular beams, and to investigate excited-state structure and dynamics in atomic He and molecular CaF. Helium and CaF are chosen partially for their fundamental interest, and partially because they are excellent candidates for manipulation by stimulated optical forces. The stimulated bichromatic force (BCF) and the newly-proposed polychromatic force (PCF) are rectified coherent optical forces from multi-frequency laser beams that can be hundreds of times stronger than the conventional radiative force. As part of the proposed research, a prototype chirped-BCF decelerator for He will be completed, and a promising new four-color PCF version will be tested and compared with calculations. A similar decelerator will be developed for the CaF molecule, a species that has attracted considerable recent interest as a candidate for direct laser slowing and cooling. For molecules, there is an additional advantage to utilizing coherent optical forces beyond merely increasing the force. Because hundreds of BCF momentum exchanges can occur for each radiative decay event, the BCF can reduce the velocity by hundreds of times more than incoherent radiative forces before the molecule decays into an inaccessible "dark" state. Several spectroscopic experiments will be initiated on the resulting cold atoms and molecules, including studies of cold gases of highly-excited Rydberg states of CaF, and precise laser spectroscopy of both He and CaF. The study of cold molecules in Rydberg states is a little-explored topic likely to involve new physical phenomena. Precise spectroscopy of helium will facilitate tests of basic theory and pave the way for future ultra-precise measurements. Novel applications of metastable helium beams will also be explored.