Slowing, Cooling, and Spectroscopy with Stimulated Optical Forces

在正常情况下，空气中的分子运动速度接近每秒500米，如果它们不经常相互碰撞，它们只会在千万分之一秒内移动一英寸。这笔拨款将支持研究使用激光使原子或分子在同样一英寸的范围内静止的新方法，通过产生一百万倍于重力的减速。对于原子来说，目标是通过大大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，使用单氟化钙分子（CaF）作为测试系统。最佳方法将由数值模拟和实验测试相结合来确定，使用激光束同时包含多种颜色的光。由此产生的冷原子和分子将使用激光来探测它们的内部能量结构。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。提出的研究有三个主要动机：发展和理解受激光力的物理特性，在原子和分子光束的直接激光减速和冷却方面取得重大进展，以及研究原子He和分子CaF的激发态结构和动力学。选择氦和CaF部分是因为它们的基本利益，部分是因为它们是受激光力操纵的优秀候选者。受激双色力（BCF）和新提出的多色力（PCF）是来自多频激光束的整流相干光力，其强度可达传统辐射力的数百倍。作为拟议研究的一部分，他将完成一个原型啁啾- bcf减速器，并将测试一个有前景的新四色PCF版本，并与计算进行比较。类似的减速剂将用于CaF分子，这一物种最近作为直接激光减速和冷却的候选物引起了相当大的兴趣。对于分子来说，利用相干光力有一个额外的优势，而不仅仅是增加力。由于每次辐射衰变事件都会发生数百次BCF动量交换，因此在分子衰变到无法进入的“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。将对得到的冷原子和分子进行几项光谱实验，包括对CaF高激发态的冷气体的研究，以及He和CaF的精确激光光谱。对里德伯态冷分子的研究是一个很少被探索的话题，可能涉及新的物理现象。氦气的精确光谱将有助于基础理论的测试，并为未来的超精确测量铺平道路。亚稳氦束的新应用也将被探讨。

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.