Focusing of atomic beams by near-field atom microlenses: The Bethe-type and the Fresnel-type microlenses

We analyze focusing of atomic beams by the atom near-field microlenses produced by the laser fields diffracted on the apertures in the metallic screens. Analysis of the focusing properties of the atom microlenses is given in a model describing dipole interaction of atoms with a far-off-resonance laser light. Two types of the atom microlenses are considered: The Bethe-type microlens with aperture less than the light wavelength and the Fresnel-type microlens with aperture about the wavelength. It is shown that both types of the atom microlenses are able to produce strong dipole gradient forces which can focus the atomic beams. However, while the Bethe-atom microlens is able to produce sharp focusing of the beams the Fresnel-atom microlens possesses weak focusing property due to high anharmonicity of the gradient force. We conclude that the Bethe-atom microlens can be considered as a promising tool of the atom optics potentially able to focus atomic beams into spot sizes about nanometers.