Matthews Mary, Morales Felipe, Patas Alexander, Lindinger Albrecht, Gateau Julien, Berti Nicolas, Hermelin Sylvain, Kasparian Jerome, Richter Maria, Bredtmann Timm, Smirnova Olga, Wolf Jean-Pierre, Ivanov Misha
GAP, University of Geneva, 22 chemin de Pinchat, 1211 Geneva 4, Switzerland.
Max Born Institute, Max Born Strasse 2a, 12489 Berlin, Germany.
Nat Phys. 2018 Jul;14(7):695-700. doi: 10.1038/s41567-018-0105-0. Epub 2018 Apr 16.
Light can be used to modify and control properties of media, as in the case of electromagnetically induced transparency or, more recently, for the generation of slow light or bright coherent XUV and X-ray radiation. Particularly unusual states of matter can be created by light fields with strengths comparable to the Coulomb field that binds valence electrons in atoms, leading to nearly-free electrons oscillating in the laser field and yet still loosely bound to the core [1,2]. These are known as Kramers-Henneberger states [3], a specific example of laser-dressed states [2]. Here, we demonstrate that these states arise not only in isolated atoms [4,5], but also in rare gases, at and above atmospheric pressure, where they can act as a gain medium during laser filamentation. Using shaped laser pulses, gain in these states is achieved within just a few cycles of the guided field. The corresponding lasing emission is a signature of population inversion in these states and of their stability against ionization. Our work demonstrates that these unusual states of neutral atoms can be exploited to create a general ultrafast gain mechanism during laser filamentation.
光可用于改变和控制介质的性质，如在电磁感应透明的情况下，或者更近一些，用于产生慢光或明亮的相干极紫外和X射线辐射。强度与束缚原子价电子的库仑场相当的光场能够创造出特别不寻常的物质状态，导致近自由电子在激光场中振荡，但仍与原子核松散地结合在一起[1,2]。这些状态被称为克拉末-亨内贝格态[3]，是激光修饰态[2]的一个具体例子。在这里，我们证明这些状态不仅出现在孤立原子中[4,5]，而且出现在大气压力及以上的稀有气体中，在那里它们在激光成丝过程中可以作为增益介质。使用整形激光脉冲，在引导场的几个周期内就能实现这些状态下的增益。相应的激光发射是这些状态下粒子数反转及其抗电离稳定性的标志。我们的工作表明，这些中性原子的不寻常状态可被利用来在激光成丝过程中创造一种通用的超快增益机制。
