The methods of laser cooling of atoms have long been applied to obtain cold and ultracold atomic gases, including degenerate states and the atomic Bose–Einstein condensate in particular. Until recently the application of laser cooling methods to molecules was assumed to be impossible because of the complex structure of molecular levels and the absence of closed cooling cycles for transitions between the electron levels of molecules in the general case. However, it has recently become clear that laser cooling can be performed for a large class of molecules, including not only the simplest diatomic molecules but also polyatomic molecules. We here present the general principles for identifying suitable molecules and discuss current studies on and further developments in the laser cooling of molecules.

中文翻译：

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直接激光冷却分子

长期以来，人们一直采用激光冷却原子的方法来获得冷的和超冷的原子气体，包括简并状态，尤其是原子的玻色-爱因斯坦凝聚物。直到最近，由于分子能级的复杂结构以及在一般情况下分子的电子能级之间不存在用于分子间跃迁的封闭冷却循环，所以人们认为将激光冷却方法应用于分子是不可能的。然而，最近变得清楚的是，可以对包括最简单的双原子分子而且包括多原子分子在内的一大类分子进行激光冷却。我们在这里介绍识别合适分子的一般原理，并讨论分子激光冷却的当前研究和进一步发展。