RUI: Atomic Physics with Rapidly Frequency Chirped Laser Light

该项目将研究如何通过外部激光场控制超冷原子之间的碰撞。 这些实验将使我们更好地理解光辅助碰撞和简单的化学反应。 该项目的主要进展是激光将在时间尺度上产生脉冲，并在与原子碰撞过程相称的频率范围内啁啾。 使用超快激光，在更快的时间尺度上进行的相关实验使人们对光辅助化学反应有了更深入的了解。 然而，由于计划中的实验中的原子将非常冷，新实验可以在明显较慢的时间尺度上进行。 该团队已经为这些实验开发了一种新型的振幅和相位调制激光系统。 该激光系统也将用于探索控制原子激发的新方法。 这对减慢原子的速度很重要，也是一条有趣的途径，可以让分子慢下来。 这些活动为本科物理学生提供了一个理想的环境，进行令人兴奋的物理和实验，使用激光控制量子力学激发态碰撞，并探索制备超冷分子的新技术。 让学生参与本科研究是一种高影响力的教学实践，有助于培养训练有素的科学家。 这两个项目都集中在一个新的激光系统，以产生强烈的频率啁啾激光脉冲。 这种激光将用于影响原子物理学中的各种动力学，包括相干控制超冷碰撞和研究快速绝热通道。 在第一个项目中，该团队将使用磁光阱的损耗作为工具，探索原子之间非弹性光辅助碰撞中的相干控制轨迹。 最近的研究表明，两个铷原子之间的超冷碰撞可以用频率啁啾激光控制;通常整个过程需要大约一纳秒。 通过在相同的时间尺度上调整激光频率和振幅，可以影响碰撞的行为，并且整个过程可以是相干的。 最初的实验表明，这是使用100 ns的1 GHz激光脉冲的情况;然而，实验不够快，无法观察到对碰撞过程的完全控制。 该团队使用半经典模拟表明，啁啾率的适度增加导致对这种类型的碰撞过程的完全控制（20 ns内1 GHz）。 该项目现在的目标是表明，在一纳秒时间尺度上成形激光脉冲可以以一种新的方式控制碰撞。 在第二个项目中，该团队将探索成形的频率啁啾激光作为加速原子气体的一种手段。 他们将通过使用一对反向传播的频率啁啾脉冲来实现这一点，这些脉冲的延迟远小于跃迁的寿命。 这将适用于多普勒展宽的气体，因为啁啾的范围很大，铷很重。该项目的成功开发可能会增加相干过程用于减缓分子束（SrF，CaF等）的可能性，用于冷和超冷分子实验。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This project will study the how collisions between ultracold atoms can be controlled by an external laser field. These experiments will lead to a greater understanding of light-assisted collisions and simple chemical reactions. The major advancement in this project is that the laser will be pulsed on a time scale, and chirped over a frequency range, commensurate with the atomic collision process. Using ultrafast lasers, related experiments on much faster time scales have led to a greater understanding of light-assisted chemical reactions. However, because atoms in the planned experiments will be very cold, the new experiments can be conducted on significantly slower time scales. This team has already developed a novel amplitude and phase modulated laser system for these experiments. This laser system will also be used to explore new methods for controlling atomic excitations. This is important for slowing atoms and is an interesting avenue toward slowing molecules to a stop. These activities provide an ideal environment for undergraduate physics students to conduct exciting physics and experiments, use lasers to control quantum mechanical excited-state collisions, and explore new techniques for preparing ultracold molecules. Engaging students in undergraduate research is a high-impact teaching practice and helps to generate trained scientists. Both of the projects are centered on a novel laser system to generate intense frequency-chirped pulses of laser light. This laser will be used to affect a variety of dynamics in atomic physics, including coherently controlling ultracold collisions and studying rapid adiabatic passage. In the first project, this team will use loss from a magneto-optical trap as a tool to explore coherently controlling trajectories in inelastic light-assisted collisions between atoms. Recent work has shown that ultracold collisions between two rubidium atoms can be controlled with frequency-chirped laser light; typically the entire process takes about one nanosecond. By tuning the laser frequency and amplitude on that same time scale, one can influence the behavior of the collision and the entire process can be coherent. The initial experiments have shown that this is the case using a 1 GHz in 100 ns laser pulse; however, the experiments weren't fast enough to observe total control over collisional processes. This team has shown, using semi-classical simulations, that a modest increase in the chirp-rate leads to full control over collisional processes of this type (1 GHz in 20 ns). This project now aims to show that shaping laser pulses on the one nanosecond time scale can lead to control over collisions in a novel way. In the second project, this team will explore shaped frequency-chirped laser light as a means to accelerate atomic gases. They will do this by using a pair of counter propagating frequency-chirped pulses delayed by much less than the lifetime of the transition. This will work with a Doppler broadened gas because the range of chirp is large and rubidium is heavy. Successful developments on this project may increase the likelihood that coherent processes will be used to slow molecular beams (SrF, CaF, etc), for cold and ultracold molecule experiments.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.