Manipulating external degrees of freedom with intense light: Laser focusing and trapping of molecules

The possibility of focusing and trapping molecules in the intensity gradient of a moderately intense laser field is shown. A fully quantum-mechanical and a hybrid quantum-classical model are developed and both the case of a near-resonance and that of a far-off-resonance field are studied numerically and analytically. Molecular focusing is obtained when the ratio between the kinetic energy and the field-matter interaction exceeds unity (but remains small). In this energy regime the laser beam serves as a lens for a beam of molecules. The properties of the "molecular lens" are analyzed and the experimental conditions required to focus molecules are examined. We propose the application of laser focusing to nanoscale deposition onto, and etching of a substrate and describe a possible setup to that end. Molecular trapping is obtained as the strong interaction limit of a general "molecular optics" scheme.