Two-dimensional metamaterial structure exhibiting reduced visibility at 500 nm

Metamaterials provide unprecedented freedom and flexibility in the creation of new structures, which control electromagnetic wave propagation in very unusual ways. Very recently various theoretical designs for an electromagnetic cloak were suggested and an experimental realization of a partial cloak operating in a two-dimensional cylindrical geometry were reported in the microwave frequency range. We report on an experimental two-dimensional reduced visibility structure that approximates the distribution of the radial component of the dielectric permittivity necessary to achieve nonmagnetic cloaking in the visible frequency range.

High-optical-throughput individual nanoscale aperture in a multilayered metallic film

The optical transmission of an individual subwavelength aperture in a multilayered metal film is shown to be enhanced compared with that of a homogeneous metal film. The enhancement effect is due to the light coupling to surface plasmon excitation facilitated by a film periodicity. The sensitivity of the transmission to the dielectric filling of the aperture is also shown. The latter effect can be used to switch and control the transmittance. Devices based on enhanced transmission through nanosized apertures can find applications in high-density optical and magneto-optical data storage, high-resolution microscopy, and photolithography, where nanoscale light sources with high-optical-power throughput are required, as well as in sensor applications.

Single-photon tunneling via localized surface plasmons

Strong evidence of a single-photon tunneling effect, a direct analog of single-electron tunneling, has been obtained in the measurements of light tunneling through individual subwavelength pinholes in a gold film covered with a layer of polydiacetylene. The transmission of some pinholes reached saturation because of the optical nonlinearity of polydiacetylene at a very low light intensity of a few thousand photons per second. This result is explained theoretically in terms of a "photon blockade," similar to the Coulomb blockade phenomenon observed in single-electron tunneling experiments. Single-photon tunneling may find applications in the fields of quantum communication and information processing.

Micromachining of diamond with a near-field scanning optical microscope

Direct-write laser micromachining of diamond on a submicrometer scale with a near-field scanning optical microscope with an uncoated tapered fiber tip has been demonstrated. Micromachined structures can be imaged in situ immediately after modification of the sample. An early stage of the ablation process, which is believed to be conversion of diamond into graphite, has been visualized.

High resolution study of permanent photoinduced reflectivity changes and charge-order domain switching in Bi(0.3)Ca(0.7)MnO(3)

We report near-field and far-field optical microscopic studies of photoinduced effects in charge-ordered Bi(0.3)Ca(0.7)MnO(3). Unlike previously reported transient photoinduced effects in manganites, we have observed permanent reflectivity changes following local sample illumination with 488 nm light. High-resolution images of exposed regions reveal optical contrast on a submicrometer scale. This observation indicates that photonic band-gap structures may be created using holographic recording in manganites. We also present images of photoinduced charge-order domain switching in Bi(0.3)Ca(0.7)MnO(3).

Near-field second harmonic imaging of the c/a/c/a polydomain structure of epitaxial PbZrxTi(1-x)O3 thin films

Near-field optical second harmonic microscopy has been applied to imaging of the c/a/c/a polydomain structure of epitaxial PbZrxTi1-xO3 thin films in the 0 < x < 0.4 range. Comparison of the near-field optical images and the results of atomic force microscopy and X-ray diffraction studies show that an optical resolution of the order of 100 nm is achieved. Symmetry properties of the near-field second harmonic signal allow us to obtain good optical contrast between the local second harmonic generation in c- and a-domains. Experimentally measured near-field second harmonic images have been compared with the results of theoretical calculations. Good agreement between theory and experiment is demonstrated.

Supercooling molecular hydrogen down through the superfluid transition

Recent calculations by Vorobev and Malyshenko [JETP Lett. 71, 39 (2000)] show that molecular hydrogen may stay liquid and superfluid in strong electric fields of the order of 4x10(7) V/cm. I demonstrate that strong local electric fields of similar magnitude exist beneath a two-dimensional layer of electrons localized in the image potential above the surface of solid hydrogen. Even stronger local fields exist around charged particles (ions or electrons) if the surface or bulk of a solid hydrogen crystal is statically charged. Measurements of the frequency shift of the 1 --> 2 photoresonance transition in the spectrum of a two-dimensional layer of electrons above a positively or negatively charged solid hydrogen surface performed in the temperature range 7-13.8 K support the prediction of electric field induced surface melting. The range of surface charge density necessary to stabilize the liquid phase of molecular hydrogen at the temperature of superfluid transition is estimated.

Near-field second-harmonic microscopy of thin ferroelectric films

We present a near-field optical technique for second-harmonic imaging by use of tapered optical fiber tips externally illuminated with femtosecond laser pulses. Enhancement of the electric field at the tip of the fiber results in enhanced second-harmonic (SH) generation from the sample region near the tip. This SH emission is collected by the same tapered fiber. The spatial distribution and polarization properties of SH generation from thin ferroelectric films and a poled single crystal of BaTiO(3) have been studied. A spatial resolution of the order of 80 nm was achieved. Symmetry properties of the near-field SH signal allow us to recover the local poling direction of individual ferroelectric domains in the film. Thus the technique provides a novel tool for nanometer-scale crystal analysis of polycrystalline samples.

Near-field optical study of photorefractive surface waves in BaTiO(3)

Near-field optical microscopy has been used to study photorefractive surface waves in BaTiO(3). The field distribution of the photorefractive surface wave near the crystal-air interface has been measured and compared with theory. Experimental data indicate that a micrometer-wide transition layer with dielectric and photorefractive properties that are different from the properties of the bulk BaTiO(3) exists near the interface.

Near-field second harmonic imaging of lead zirconate titanate piezoceramic

Near-field optical microscopy has been used to image variations in local optical second harmonic generation (SHG) from the surface of lead zirconate titanate (PZT) piezoceramic. As PZT ceramic is a strongly scattering medium. SHG occurs in the thin layer near the surface of the ceramic. Thus, individual crystalline grains and grain boundaries located near the surface are the main features visible in the images. In general, this technique allows us to determine the local poling direction of individual submicrometre-sized crystalline grains of ceramic by near-field SH imaging at different angles of incidence and polarization states of the fundamental excitation light. In some cases 'hot spots' of submicrometre size showing enhanced SHG have been observed. This enhancement is believed to result from local cavity resonances.

Near-field imaging of surface-enhanced second harmonic generation

Surface-enhanced second harmonic generation from individual topographical defects of an otherwise flat gold film and from metal-coated diffraction gratings was measured using a near-field optical microscope. Experimentally measured second harmonic field distributions were compared with theoretical calculations.

Apparent superresolution in near-field optical imaging of periodic gratings

A superresolution phenomenon in images of diffraction gratings obtained with a near-field optical microscope probe positioned at distances of the order of 1>mu;m from the surface was recently reported [Appl. Opt. 33, 876 (1994)]. This experiment was interpreted in terms of evanescent waves observed in the far field. We show that the effect observed in that experiment is a very well known far-field optical phenomenon called the Talbot effect. The existence of self-imaging Talbot planes for gratings with periods of the order of a few micrometers appears promising for many practical applications.

Near-field second-harmonic imaging of ferromagnetic and ferroelectric materials

A novel scanning probe technique that is able to image surface magnetic and electric properties has been developed. It is based on the near-field microscopy of surface second-harmonic generation. We have demonstrated the capability of the technique by imaging the domain structure of a Ni single crystal and a piezoelectric ceramic.

Correlation between optical and topographical images from an external reflection near-field microscope with shear force feedback

An external reflection scanning near-field optical microscope with shear force regulation of the tip-surface distance is described. Near-field optical and shear force topographical images are compared for various samples. It is shown that the most important correlative relationships between these images can be deduced from symmetry considerations. The possibility of extracting additional information from the optical images is demonstrated on images of human blood cells.

Phase conjugation of an optical near field

Using degenerate four-wave mixing in an Fe:LiNbO(3) 0.04-wt. % crystal and an external-reflection near-field optical microscope, we have achieved phase conjugation of light emitted by a fiber tip. We observe that the phase-conjugated light at a wavelength of 633 nm can reach a power of ~0.1 nW and produce a 180-nm-wide spot image in the near-field microscope. This is the first direct demonstration, to our knowledge, of the phase conjugation of near-field components of optical fields.