Atom Nanolithography with Atom Pinhole Camera
The most efficient method for controlling the motion of material particles in experimental physics is the use of interaction potentials with electromagnetic fields. The static magnetic and electric interaction potentials are used in the optics of charged particles. In the optics of neutral atoms, the various interaction potentials of atoms with laser and electromagnetic fields are used in addition to the static fields. The effective methods of diffraction, interference, mirror reflection of atoms are implemented in atom optics. The most difficult problem in atom optics is the problem of high-resolution focusing of neutral atoms, which is promising for the nondestructive method for probing the surface at the atomic level, as well as for the creation of nanostructures on the surface. Although there are many proposals for focusing of atomic beams, this problem is experimentally unsolved. The main difficulty is the creation of the interaction potential of the atom with the electromagnetic field that is close to an ideal lens for atoms.In this paper, we experimentally implement another approach to the problem of focusing and construction of an image in atom optics, which is based on a well known idea of optical pinhole camera. The pinhole camera in optics is a camera without lens. Light forming an image passes through a small hole. In our experiment with the atom pinhole camera the Cr atomic beam passes through a set of holes in a metal mask and thereby forms, by analogy with optics, a glowing object of a given geometry. The atoms pass through the holes in the mask, propagate in vacuum along rectilinear trajectories, similar to light rays, and are incident on a thin film (thickness 5 mum) placed at a distance of 90 mm from the mask with a large number (n =107-108 /cm2) of nanoholes (50 nm diameter). Each hole of the film is a pinhole camera for atoms, which forms its individual image of the object on the substrate surface placed at a distance of l = 5mum behind the film.
Atom “pinhole camera” with nanometer resolution
An atom “pinhole camera” with nanometer resolution has been experimentally implemented for the first time. Owing to the use of this camera, an array of ∼106 identical nanostructures of Cr atoms with a characteristic size of the nanostructure of less than 50 nm has been created on a glass surface. Nanostructures of arbitrary shapes have been created.
Atom focusing by far-detuned and resonant standing wave fields: Thin-lens regime
The focusing of atoms after interacting with both far-detuned and resonant standing wave fields in the thin-lens regime is considered. Exact quantum expressions for the Fourier components of the density (that include all spherical aberration) are used to study the focusing numerically. The following lens parameters and density profiles are calculated as functions of the pulsed field area $\ensuremath{\theta}:$ the position of the focal plane, peak atomic density, atomic density pattern at the focus, focal spot size, depth of focus, and background density. The lens parameters are compared to asymptotic, analytical results derived from a scalar diffraction theory for which spherical aberration is small but non-negligible $(\ensuremath{\theta}\ensuremath{\gg}1).$ Within the diffraction theory analytical expressions show that the focused atoms in the far-detuned case have an approximately constant background density $0.5(1\ensuremath{-}0.635{\ensuremath{\theta}}^{\ensuremath{-}1/2})$ while the peak density behaves as $3.83{\ensuremath{\theta}}^{1/2},$ the focal distance as ${\ensuremath{\theta}}^{\ensuremath{-}1}(1+1.27{\ensuremath{\theta}}^{\ensuremath{-}1/2})$ ${L}_{T}/2\ensuremath{\pi},$ the depth of focus as ${0.304L}_{T}{\ensuremath{\theta}}^{\ensuremath{-}3/2},$ and the focal spot size $0.0592\ensuremath{\lambda}{\ensuremath{\theta}}^{\ensuremath{-}3/4},$ where ${L}_{T}$ is the Talbot distance and \ensuremath{\lambda} is the wavelength of the light. Focusing by the resonant standing wave field leads to a new effect, a Rabi-like oscillation of the atom density. For the far-detuned lens, chromatic aberration is studied quantitatively with the exact Fourier results. Similarly, the degradation of the focus that results from angular divergence in beams or thermal velocity distributions in traps is studied quantitatively with the exact Fourier method and understood analytically using the asymptotic results. Overall, we show that strong thin-lens focusing is possible with modest laser powers and with currently achievable atomic beam characteristics.