Manipulating molecules with optical fields

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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.