Near-field-light lens for nano-focusing of atoms

It is an important subject to make a nano-scale structure with an arbitrary shape at an arbitrary position. To this end, we are developing several near-field optical devices for precise atom control and deposition [1]. Here, we describe a near-field-light lens for focusing of atoms on a nano-size spot. Figure 1 is a sketch of the near-field-light lens. Repulsive dipole forces from near-field lights focus atoms passing through a small aperture, The upper SEM image shows the top view of the device fabricated from a Silicon-on-Insulator substrate by photolithography and anisotropic chemical etching. Near-field lights are generated around the aperture at the bottom by illuminating each side with four blue-detuned light beams guided through optical fibers. As shown in the lower SEM image, the was of window is 400 nm × 500 inn. The radius of curvature of the edge is 50 nm, which almost equals the decay length of the near-field lights. The near-field optical device works as a lens with a focal length of 10 um, a focal depth of 10 nm, and NA of 0.14 for Rb atoms with the velocity of 10 m/s in the case where the incident light intensity is 10 ⁷ mW/cm² and the blue detuning is 1.5 GHz. Figure 2 shows the distribution of the Rb atoms at the focal point obtained from Fourier optics under Fraunhofer-diffradion conditions, in this case, the FWHM is estimated to be about 1 nm, which is comparable to the de Broglie wavelength. We will also report the experimental progress.