Ultrafast coherent control of molecular dynamics with shaped laser pulses

我们的研究重点是利用高功率超短激光脉冲控制分子动力学。具体地说，我们发展了激发极端旋转态的新方法--所谓的分子超级旋转器，并研究了超快旋转对孤立分子、分子团簇和稠密分子气体的化学和物理性质的影响。长期以来，分子旋转控制一直被认为是指导化学反应、成像单个分子轨道、产生阿秒激光脉冲和分离分子同位素的有力工具。最近的理论研究表明，在将旋转控制的范围扩展到超高旋转状态方面具有巨大的潜力。超快分子自旋被认为可以改变分子与固体表面的碰撞特性，改变分子在外场中的运动轨迹。提出了通过诱导超转动实现分子冷却和选择性化学键断裂的新途径。然而，由于多重技术挑战，加拿大目前没有开展关于分子超级转子的研究。在最近的一系列工作中，我们的研究团队成功地展示了控制分子旋转的新方法。我们建造了一台“光学离心机”，并成功地制造、观测和控制了分子超级旋翼。我们还发展了一种用高功率超短脉冲串激发极端旋转态的方法。这两种方法是互补的，并提供了不同的旋转控制方案。我们打算在极限转速下探索分子科学的以下独特方面。(1)离心力扭曲的影响和通过可控超快分子自旋选择性化学键断裂的可能性；(2)反磁和顺磁超级转子的旋转诱导磁性质，包括离心分子在外磁场中的行为；(3)极性超级转子的旋转诱导电学性质，包括新的THz辐射源的可能性；(4)分子表面散射对分子角动量方向和大小的依赖；(5)分子旋转对氦纳米液滴超流动性的影响；(6)经典混沌动力学条件下量子分子旋转的控制；(7)分子超级旋转器的碰撞特性和从孤立分子旋转到集体气体涡旋的旋转能量转移方面；(8)在极高的角频率范围内通过调节分子旋转来控制化学反应的前景。类似于物质的其他奇异状态，如超冷原子或反物质，超级转子将提供对目前建立的边界以外的基本自然规律的新见解。我们计划研究氢、氮、氧和二氧化碳的超级自转--这些都是自然界最基本的组成部分。超级转子的独特性表明，它将对普通科学产生立竿见影的影响，并对现代技术产生深远影响。从化学的角度来看，超快分子转动对化学反应的影响需要详细研究。从物理学的角度，我们期待发现超级转子的新的电学、磁学和光学性质。对于天文学来说，对恒星周围极热气体的分析可能会受益于桌面实验室实验中可以获得的超高速旋转分子的光谱。在纳米科学中，超旋转对纳米沉积和分子-表面散射的影响具有实际意义。

Our research is focused on controlling molecular dynamics with high-power ultra-short laser pulses. Specifically, we develop new methods of exciting extreme rotational states – the so called “molecular super rotors”, and investigate the effects of ultra-fast rotation on chemical and physical properties of isolated molecules, molecular clusters and dense molecular gases. Control of molecular rotation has been long recognized and successfully used as a powerful tool for steering chemical reactions, imaging individual molecular orbitals, generating attosecond laser pulses and separating molecular isotopes. Recent theoretical studies have indicated enormous potential in extending the reach of rotational control to ultra-high rotational states. Ultrafast molecular spinning has been predicted to change the character of molecular collisions with solid surfaces and alter molecular trajectories in external fields. New ways of molecular cooling and selective chemical bond breaking by inducing super rotation have been suggested. Yet, owing to multiple technological challenges, no research on molecular super rotors is currently pursued in Canada. In a series of recent works, our research team has successfully demonstrated new approaches to controlling molecular rotation. We have built an “optical centrifuge” and succeeded in producing, observing and controlling molecular super rotors. We also develop a method of exciting extreme rotational states with high-power ultra-short pulse trains. The two methods are complementary and offer different schemes of rotational control. We intend to explore the following unique aspects of molecular science at the limit of extreme rotational speed. (1) Effects of centrifugal distortion and the possibility of selective chemical bond breaking by means of controlled ultrafast molecular spinning; (2) Rotation-induced magnetic properties of diamagnetic and paramagnetic super rotors, including the behaviour of centrifuged molecules in external magnetic field; (3) Rotation-induced electrical properties of polar super rotors, including the possibility for new sources of THz radiation; (4) Dependence of molecule-surface scattering on the orientation and magnitude of the molecular angular momentum; (5) Effects of molecular rotation on superfluidity of helium nanodroplets; (6) Control of quantum molecular rotation in the regime of classically chaotic dynamics; (7) Collisional properties of molecular super rotors and the aspects of rotational energy transfer from isolated molecular rotation to collective gas vortices; (8) Prospects of controlling chemical reactions by tuning molecular rotation in the extreme range of angular frequencies. Similarly to other exotic states of matter, such as ultra-cold atoms or anti-matter, super rotors will provide new insights into the fundamental laws of nature beyond currently established boundaries. We plan to investigate super rotation of hydrogen, nitrogen, oxygen and carbon dioxide - some of the nature’s most fundamental building blocks. The uniqueness of super rotors suggests an immediate impact on general science, and far-reaching effects on modern technology. From a chemistry viewpoint, the effect of ultrafast molecular rotation on chemical reactions begs detailed investigation. From the perspective of physics, we anticipate to find out new electrical, magnetic and optical properties of super rotors. For astronomy, the analysis of extremely hot gases around stars may benefit from the spectroscopy of ultrafast rotating molecules accessible in table-top laboratory experiments. In nano-science, the effects of super rotation on nano-deposition and molecule-surface scattering are of practical interest.