Franciscus B. Segerink

Influence of hole size on the extraordinary transmission through subwavelength hole arrays

We show that the extraordinary transmission of light through an array of square subwavelength holes is strongly influenced by the size of the holes. For small, square holes (air fraction below 20%), the dependence of the normalized transmission (transmissivity) on hole width greatly exceeds the expectations on the basis of conventional aperture theory. For larger holes, the transmissivity saturates. Moreover, the positions of the transmission maxima shift when the size is varied.

Near‐field optical microscope using a silicon‐nitride probe

Operation of an alternative near‐field optical microscope is presented. The microscope uses a microfabricated silicon‐nitride probe with integrated cantilever, as originally developed for force microscopy. The cantilever allows routine close contact near‐field imaging on arbitrary surfaces without tip destruction. The effect of adhesion forces on the coupling to the evanescent wave has been observed. Images with a lateral resolution of about 50 nm are presented and compared with atomic force images. A specific sample area can be selected using an integrated conventional light microscope.

High resolution imaging of dielectric surfaces with an evanescent field optical microscope

An evanescent field optical microscope (EFOM) is presented which employs frustrated total internal reflection oxadn a localized scale by scanning a dielectric tip in close proximity to a sample surface. High resolution images of dielectric gratings and spheres containing both topographic and dielectric information have been obtained. The resolution obtained is 30 nm in the lateral directions and 0.1 nm in height depending oxadn proper tip fabrication

Evanescent-field optical microscopy: effects of polarization, tip shape and radiative waves

Recent results in evanescent-field optical microscopy are presented. A resolution of 30 nm in the lateral directions and 0.1 nm in height has been obtained by suitable tip fabrication. Both the direction of the exciting field and the tip shape are shown to affect the optical coupling efficiency and resolution. Near-field diffraction patterns are observed with high lateral resolution by interference between evanescent and propagating waves.

A Monopole Antenna at Optical Frequencies: Single-Molecule Near-Field Measurements

We present a monopole antenna for optical frequencies (~600 THz) and discuss near-field measurements with single fluorescent molecules as a technique to characterize such antennas. The similarities and differences between near-field antenna measurements at optical and radio frequencies are discussed in detail. Two typical antenna properties, polarization selectivity and resonances, are studied for the optical monopole by direct near-field measurements and finite integration technique calculations. The antenna is driven by the local field of a sub-wavelength aperture. This gives rise to a dependence of the antenna response on the orientation of the local field vector, in an analogous way to the polarization selectivity of linear wire antennas. The antenna resonances are studied by varying the antenna length. Typical monopole resonances are demonstrated. The finite conductivity of metals at optical frequencies (in combination with the antenna radius) causes the wavelength of the surface charge density oscillation (surface plasmon polariton) along the antenna to be shortened in comparison to the free space wavelength. As a result, resonances for the optical monopole antenna occur at much shorter relative lengths than for conventional radio monopole antennas

Novel instrument for surface plasmon polariton tracking in space and time

We describe the realization of a phase-sensitive and ultrafast near-field microscope, optimized for investigation of surface plasmon polariton propagation. The apparatus consists of a homebuilt near-field microscope that is incorporated in Mach-Zehnder-type interferometer which enables heterodyne detection. We show that this microscope is able to measure dynamical properties of both photonic and plasmonic systems with phase sensitivity.

Fabrication of three-dimensional nanostructures by focused ion beam milling

The fabrication of an extended three-dimensional nanostructure with dimensions much larger than the feature size using a focused ion beam is described. By milling two identical patterns of pores with a designed diameter of 460 nm in orthogonal directions, a photonic crystal with an inverse woodpile structure was made in a gallium phosphide single crystal. The patterns are aligned with an unprecedented accuracy of 30 nm with respect to each other. The influence of GaP redeposition on the depth, shape, and size of the pores is described. A literature study revealed that the redeposition of GaP during milling is more pronounced than that of Si found in previous studies. An explanation for this phenomenon is given.

Enhanced surface plasmon polariton propagation length using a buried metal grating

We report an enhancement in the propagation length of surface plasmon polaritons (SPPs) on a metallic grating when the grating is buried in the substrate. A template-stripping technique has been used to fabricate the buried grating. Near-field measurements on the buried and an exposed grating show that the full width at half maximum of the surface plasmon resonances are reduced to 57% for the prism-coupled SPPs and 77% for the grating-coupled SPPs. The reduction in the full width at half maximum is attributed to a decrease in the in-plane directional scattering of the SPPs on the buried grating. The propagation lengths of the SPPs measured beyond the gratings are close to the theoretical SPP propagation length on an ideal gold surface. The buried grating with a significant reduction in the full width at half maximum of the surface plasmon resonances is theoretically shown to improve the figure of merit of grating-incorporated SPR sensors.

An atomic force microscope operating at hypergravity for in situ measurement of cellular mechano-response

We present a novel atomic force microscope (AFM) system, operational in liquid at variable gravity, dedicated to image cell shape changes of cells in vitro under hypergravity conditions. The hypergravity AFM is realized by mounting a stand‐alone AFM into a large‐diameter centrifuge. The balance between mechanical forces, both intra‐ and extracellular, determines both cell shape and integrity. Gravity seems to be an insignificant force at the level of a single cell, in contrast to the effect of gravity on a complete (multicellular) organism, where for instance bones and muscles are highly unloaded under near weightless (microgravity) conditions. However, past space flights and ground based cell biological studies, under both hypogravity and hypergravity conditions have shown changes in cell behaviour (signal transduction), cell architecture (cytoskeleton) and proliferation. Thus the role of direct or indirect gravity effects at the level of cells has remained unclear. Here we aim to address the role of gravity on cell shape. We concentrate on the validation of the novel AFM for use under hypergravity conditions. We find indications that a single cell exposed to 2 to 3u2003×u2003g reduces some 30–50% in average height, as monitored with AFM. Indeed, in situ measurements of the effects of changing gravitational load on cell shape are well feasible by means of AFM in liquid. The combination provides a promising technique to measure, online, the temporal characteristics of the cellular mechano‐response during exposure to inertial forces.

Near-field observation of spatial phase shifts associated with Goos-Hänschen and Surface Plasmon Resonance effects

We report the near-field observation of the phase shifts associated with total internal reflection on a glass-air interface and surface plasmon resonance on a glass-gold-air system. The phase of the evanescent waves on glass and gold surfaces, as a function of incident angle, is measured using a phase-sensitive Photon Scanning Tunneling Microscope (PSTM) and shows a good agreement with theory.