Lasers consist of an active medium of excitable atoms, a pumping mechanism for exciting those atoms, and a cavity for building up a pulse of coherent radiation. At the Institute for Heavy Ion Research (Gesellschaft für Schwerionenforschung, or GSI) in Darmstadt, Germany, scientists have succeeded for the first time in using a beam of uranium ions as the pump for producing ultraviolet laser light.
It works like this: the uranium beam ionizes argon atoms, which ionize krypton atoms, which in turn form excited molecules with fluorine. The krypton fluoride molecules are the excited entities which emit coherent light at a wavelength of 248 nanometers. A laser that uses this rare gas-halide mixture is called an excimer (excited dimer) laser.
This is not the shortest laser wavelength ever achieved, and the uranium pumping scheme is not all that energy efficient. So why then use this approach to producing laser light, especially when electrically pumped commercial krypton fluoride lasers are available? Because this was a test run for producing laser light in excimers that can't be electrically pumped.
According to Andreas Ulrich of the Technical University of Munich (andreas.ulrich@ph.tum.de), the goal is to excite excimers of pure rare gases for producing radiation in the VUV (vacuum ultraviolet) and soft X-ray region of the spectrum. Only now have uranium beams at GSI been powerful enough to provide the pumping power for lasers in this wavelength region. Being so heavy, uranium atoms deposit their energy into a gas much more efficiently that lighter particles such as electrons.
Ulrich et al., Physical Review Letters, 13 October 2006
Contact Andreas Ulrich
Technical University of Munich
andreas.ulrich@ph.tum.de
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用铀原子驱动紫外激光
作者：Phil Schewe；Ben Stein, 葛韶锋 译
注释：Uranium Beam-Pumped UV Laser, AIP Physics News Update, Number 796 #2, October 11, 2006 by Phil Schewe and Ben Stein.(561字)
相关网址：http://www.aip.org/pnu/2006/split/796-2.html
摘要/内容：
激光是由含有激发态原子的活性介质、激发这些原子的机制以及产生相干辐射脉冲的谐振腔组成的。在位于德国达姆斯塔特（Darmstadt）的重离子研究所（Institute for Heavy Ion Research or GSI: Gesellschaft für Schwerionenforschung），科学家们第一次成功地使用一束铀离子（Uranium Ion）作为激发原子的能量泵产生了紫外激光（Ultraviolet Laser Light）。
这种激光器的工作原理是，首先铀离子束将氩原子（Argon Atom）电离，然后氩原子电离氪原子（Krypton Atom），最后利用氪原子形成含氟的激发态分子。氪氟化物分子（Krypton Fluoride Molecule）是一种激发态的分子，可以辐射出波长为248纳米（Nanometer）的相干光（Coherent Light）。这种利用稀有气体（Rare Gas）和卤化物（Halide）混合材料的激光器称为激发态二聚物（Excited Dimer）激光器。
这种激光器产生的激光并不是目前已经达到的最短波长的激光，而用铀原子来驱动的方案并不能有效率的利用能量。因此什么时候用这种机制来产生激光，特别是什么时候制造出电能运行的商用氪氟化物激发态二聚化物激光并不十分清楚，因为这仅仅是产生激光的一次试运行。
根据来自德国慕尼黑技术大学（Technical University of Munich）的Andreas Ulrich所言，最后的目标是实现激发纯稀有气体的激发态二聚化物来产生真空中的紫外（VUV: Vacuum Ultraviolet）以及软X射线波段的激光。现在只有德国重离子研究所采用的铀原子束才具有足够的能量来为这个波段的激光提供能量。由于其质量比较大，铀原子比起比较轻的粒子，比如电子，更容易将能量释放出来传递给气体。
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