Method for traveling-wave deceleration of buffer-gas beams of CH
Method for traveling-wave deceleration of buffer-gas beams of CH
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DOI：
10.1103/physreva.90.033418
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发表时间：
2014-09-17
影响因子：
2.9
通讯作者：
Lewandowski, H. J.
中科院分区：
文献类型：
--
作者：
Fabrikant, M. I.;Li, Tian;Lewandowski, H. J.
低温缓冲气体束流是一种很有前途的产生冷分子自由基亮光源的方法，可用于冷碰撞和化学反应实验。为了将这些光束用于研究具有受控碰撞能量的反应或在俘获实验中使用，人们需要一种控制光束前进速度的方法。斯塔克减速器可以成为控制超音速喷流产生的分子平均速度的有效工具，但由于脉冲长度较长，有效减速缓冲气体光束带来了新的挑战。行波减速器特别适合于应对这些挑战，因为它们能够在减速过程中将分子限制在三维空间，而且电极的模拟控制提供了它们的多功能性。我们在低温缓冲气体室中产生了基态CH(X-2PI)自由基，有可能产生10(11)个分子/脉冲的冷分子束。我们提出了一种用于行波减速器的大位置大速度散射束的斯塔克减速的通用协议。我们的方法包括在减速之前用六极杆横向限制分子一段优化的距离。这旋转了分子包的相空间分布，从而使包与减速器的时变相空间接受度相匹配。我们通过模拟和一维解析模型证明，这种方法可以使行波减速器连续势垒中的相当一部分分子减速，从而产生用于冷态和受控分子实验的能量调谐光束。
Cryogenic buffer-gas beams are a promising method for producing bright sources of cold molecular radicals for cold-collision and chemical-reaction experiments. In order to use these beams in studies of reactions with controlled collision energies or in trapping experiments, one needs a method of controlling the forward velocity of the beam. A Stark decelerator can be an effective tool for controlling the mean speed of molecules produced by supersonic jets, but efficient deceleration of buffer-gas beams presents new challenges due to longer pulse lengths. Traveling-wave decelerators are uniquely suited to meet these challenges because of their ability to confine molecules in three dimensions during deceleration and their versatility afforded by the analog control of the electrodes. We have created ground-state CH(X-2 Pi) radicals in a cryogenic buffer-gas cell with the potential to produce a cold molecular beam of 10(11) molecules/pulse. We present a general protocol for Stark deceleration of beams with a large position and velocity spread for use with a traveling-wave decelerator. Our method involves confining molecules transversely with a hexapole for an optimized distance before deceleration. This rotates the phase-space distribution of the molecular packet so that the packet is matched to the time-varying phase-space acceptance of the decelerator. We demonstrate with simulations and an analytic one-dimensional model that this method can decelerate a significant fraction of the molecules in successive wells of a traveling-wave decelerator to produce energy-tuned beams for cold and controlled-molecule experiments.