Manipulating molecules with optical fields

将气体冷却到比绝对零度（-273摄氏度）高不到百万分之一度的温度的能力在科学界引起了极大的兴奋。在这个温度下，原子几乎是静止的，其行为与我们所熟悉的日常气体非常不同。例如，在非常低的温度下，组成气体的许多原子在某些方面的行为就好像它们是一个原子。在这种奇怪的情况下，一种叫做玻色-爱因斯坦凝聚物的新物质状态就形成了。这些极低温的原子气体是通过使用激光从气体中提取能量来达到的。许多人喜欢用同样的方法冷却任何气体，尤其是由分子组成的气体。然而，对于许多原子物种来说已经成功的既定方法并不适用于分子。非常冷的分子气体的行为可能与原子气体非常不同，并且已经预测了一些非常有趣的效应。这些包括由极性分子形成的气体晶体的产生，以及分子之间不寻常的反应的发生，这些反应在我们正常的“热”世界中不会发生。冷分子已经可以用其他方法制造出来，但它们的移动速度非常快。制造静止冷分子的一种方法是使用高强度激光束快速使其减速。这位研究人员直到最近才第一次减慢和冷却苯分子。同样的激光束也被用来聚焦一束分子，就像聚焦光一样，只是在这种情况下，光和物质的角色颠倒了，光是透镜，物质被聚焦。这项提议的目的是在这项研究的基础上，利用激光减慢分子束的速度，直到它们几乎静止。激光也将被用来捕获和保持分子，而不同的激光束将被用来从被捕获的分子中提取能量，使它们变得足够冷，以观察上述新现象。这项研究还旨在将分子和原子束聚焦到大约500亿分之一米的宽度。这种小光束可以用来在纳米光刻的过程中将特殊分子“写”到表面上。聚焦光束也可用于测量从表面反射的原子或分子的数量；它可以提供关于表面大小、形状和类型的信息，分辨率接近500亿分之一米。它也有可能发展成为一种新型的显微镜。最后，通过研究分子在激光束中的详细运动，研究人员旨在开发一种新技术，将不同分子的混合物分离成它们各自独立的部分。这将在污染监测等领域发挥作用，在这些领域，科学家们目前很难分离出一些不同的气体。

The ability to cool a gas to temperatures that are less than 1 millionth of degree above absolute zero (-273 degrees celcius) has created great excitement in the scientific community. At this temperature the atoms are almost stationary and behave very differently to everyday gases that we are familiar with. For example, at very low temperatures the many atoms that make up the gas act in some ways as if they are one single atom. In this strange situation a new state of matter called a Bose-Einstein condensate is formed. These very low temperature atomic gases have been reached by using lasers to take energy out of the gas. Many people would like to cool any gas and particularly a gas made of molecules in the same way. However, the established method that has been successful for many atomic species does not work for molecules. Very cold molecular gases are likely to behave very differently to atomic gases and some very interesting effects have been predicted. These include the creation of gaseous crystals formed by polar molecules and the occurrance of unusual reactions between molecules that would not occur in our normal 'hot' world. Cold molecules can already be created using other methods but they move at very high speeds. One way to create stationary cold molecules is to slow them rapidly using high intensity laser beams. This researcher has only recently slowed and cooled benzene molecules, for the first time. The samelaser beams have also been used to focus a beam of molecules in a similar way to the focusing of light, except in this case the roles of light and matter are reversed and the light is the lens and the matter is focused. This proposal aims to build on this research by using laser light to slow beams of molecules until they are almost stationary. Laser light will also be used to trap and hold the molecules while different laser beams will be used to take energy out of the trapped molecules so that they become cold enough to observe the new phenomena mentioned above. This research also aims to focus beams of molecules and atoms to a width of approximately 50 billionths of a metre. This small beam may be used to 'write' specialized molecules onto a surface in a process called nanolithography. The focused beam may also be used to measure the number of atoms or molecules reflected from a surface; this can give information about the size, shape and type of surface with an resolution approaching 50 billionths of a metre. It may also be able to be developed as a new type of microscopy. Finally, by studying the detailed motion of molecules in the laser beams, the researcher aims to develop a new technique for separating a mixture of different molecules into their separate parts. This would be useful in areas such as pollution monitoring, where scientists currently find it difficult to separate some different gases.