J. Weiner

Surface wave generation and propagation on metallic subwavelength structures measured by far-field interferometry

Transmission spectra of metallic films or membranes perforated by arrays of subwavelength slits or holes have been widely interpreted as resonance absorption by surface plasmon polaritons. Alternative interpretations involving evanescent waves diffracted on the surface have also been proposed. These two approaches lead to divergent predictions for some surface wave properties. Using far-field interferometry, we have carried out a series of measurements on elementary one-dimensional subwavelength structures with the aim of testing key properties of the surface waves and comparing them to predictions of these two points of view.

Polarization state of the optical near field

The polarization state of the optical electromagnetic field lying several nanometers above complex dielectric-air interfaces reveals the intricate light-matter interaction that occurs in the near-field zone. From the experimental point of view, access to this information is not direct and can only be extracted from an analysis of the polarization state of the detected light. These polarization states can be calculated by different numerical methods, well suited to near-field optics. In this paper, we apply two different techniques (localized Greens function method and differential theory of gratings) to separate each polarization component associated with both electric and magnetic optical near fields produced by nanometer sized objects. A simple dipolar model is used to get an insight into the physical origin of the near-field polarization state. In a second stage, accurate numerical simulations of field maps complete data produced by analytical models. We conclude this study by demonstrating the role played by the near-field polarization in the formation of the local density of states.

Phase shifts and interference in surface plasmon polariton waves.

A pi phase shift between the incident wave and surface Plasmon polariton (SPP) waves launched from a one-dimensional (slit or groove) subwavelength structure has been found in numerical simulations and invoked to explain recent measurements of optical transmission in slit arrays. Although groove launchers exhibit an overall phase shift that depends on the groove depth, it is shown here how magnetic field induction at the incident surface, and oscillating dipoles from the accumulated charge at the slit or groove edges on the entrance facet lead to an intrinsic pi phase shift, independent of the groove or slit depth. Destructive interference between the pi-shifted surface wave and the incident wave explains the observed transmission minima when the pitch of an array of slits becomes equal to an integer multiple of the SPP wavelength.

Atomic nanolithography patterning of submicron features: writing an organic self-assembled monolayer with cold, bright Cs atom beams

Cs atom beams, transversely collimated and cooled, passing through material masks in the form of arrays of reactive-ion-etched hollow Si pyramidal tips and optical masks formed by intense standing light waves, write submicron features on self-assembled monolayers (SAMs). Features with widths as narrow as 43 ± 6n m and spatial resolution limited only by the grain boundaries of the substrate have been realized in SAMs of alkanethiols. The material masks write two-dimensional arrays of submicron holes; the optical masks result in parallel lines spaced by half the optical wavelength. Both types of feature are written to the substrate by exposure of the masked SAM to the Cs flux and a subsequent wet chemical etch. For the arrays of pyramidal tips, acting as passive shadow masks, the resolution and size of the resultant feature depends on the distance of the mask array from the SAM, an effect caused by the residual divergence of the Cs atom beam. The standing wave optical mask acts as an array of microlenses focusing the atom flux onto the substrate. Atom ‘pencils’ writing on SAMs have the potential to create arbitrary submicron figures in massively parallel arrays. The smallest features and highest resolutions were realized with SAMs grown on smooth, sputtered gold substrates.

Modelling resonant coupling between microring resonators addressed by optical evanescent waves

In this paper we study the properties of microring resonator structures fabricated with high-index-of-refraction dielectric material. These structures concentrate light and can produce very strong optical potential gradients. They are of great interest for the trapping, manipulation and transport of cold atoms near surfaces. The study consists of two parts: in the first part we investigate the symmetry properties of the resonator response for simple models of the microring structures. In the second part we present detailed numerical calculations of the actual spectra for realistic microfabricated structures. We employ the direct space integral equation method (DSIEM). This method, based on a volume integral solving procedure, has already been found to cope successfully with nonresonant dielectric nanostructures. Such ab initio investigations of the optical near-field distributions only require a specification of the frequency-dependent dielectric constant and the precise shape of the fabricated structures. Consequently, these calculations can stand alone, or complement and inform anticipated experimental studies.

Atomic diffraction from nanostructured optical potentials

We develop a versatile theoretical approach to the study of ultracold atom diffractive scattering from light-field gratings by combining calculations of the optical near field generated by evanescent waves close to the surface of periodic nanostructured arrays with atom wavepacket propagation techniques. Nanometric one dimensional (1D) and 2D arrays with subwavelength periodicity deposited on a transparent surface and optically coupled to an evanescent wave source exhibit intensity and polarization gradients on the length scale of the object and can produce strong near-field periodic modulation in the optical potential above the structure. As a specific and experimentally practical example we calculate the diffraction of cold Cs atoms dropped onto a periodic optical potential crafted from a 2D nanostructure array. For an ``out-of-plane configuration we calculate a wide diffraction angle

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All-optical atom surface traps implemented with one-dimensional planar diffractive microstructures

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Optical response of nanostructured surfaces: experimental investigation of the composite diffracted evanescent wave model

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Advancing atomic nanolithography: cold atomic Cs beam exposure of alkanethiol self-assembled monolayers

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