Optical beam induced current microscopy of photonic quantum ring lasers

We explore developing graded-grating-loaded plasmonic waveguide for “trapped rainbow” at telecom frequencies by modulating feature sizes of gratings to extend its operational frequencies to the infrared domain. We show that such a structure is capable of localizing light waves of different infrared frequencies at different spatial positions. Such a slow-light device offers the advantages including a wide spectral band, a long photon lifetime and strong confinement, which may enable practical applications in various nanophotonic circuits.     

Novel spatial solitons in light-induced photonic bandgap structures

The study of wave propagation in periodic systems is at the frontiers of physics, from fluids to condensed matter physics, and from photonic crystals to Bose-Einstein condensates. In optics, a typical example of periodic system is a closely-spaced waveguide array, in which collective behavior of wave propagation exhibits many intriguing phenomena that have no counterpart in homogeneous media. Even in a linear waveguide array, the diffraction property of a light beam changes due to evanescent coupling between nearby waveguide sites, leading to normal and anomalous discrete diffraction. In a nonlinear waveguide array, a balance between diffraction and self-action gives rise to novel localized states such as spatial “discrete solitons” in the semi-infinite (or total-internal-reflection) gap or spatial “gap solitons” in the Bragg reflection gaps. Recently, in a series of experiments, we have “fabricated” closely-spaced waveguide arrays (photonic lattices) by optical induction. Such photonic structures have attracted great interest due to their novel physics, link to photonic crystals, as well as potential applications in optical switching and navigation. In this review article, we present a brief overview on our experimental demonstrations of a number of novel spatial soliton phenomena in light-induced photonic bandgap structures, including self-trapping of fundamental discrete solitons and more sophisticated lattice gap solitons. Much of our work has direct impact on the study of similar discrete phenomena in systems beyond optics, including sound waves, water waves, and matter waves (Bose-Einstein condensates) propagating in periodic potentials.      

Quasi-phase-matched optical activity effect in “gyroelectric” crystals and its applications

“Quasi-phase matching” is first introduced to the optical activity (OA) effect and a wave coupling theory for the quasi-phase-matched (QPM) OA effect in periodically poled “gyroelectric” crystals is developed. The OA effect is observed clearly even though the propagating direction of light deviates far from the optical axis in the QPM crystal with both optical activity and natural birefringence. The QPM OA effect provides a special way to determine the gyration coefficients that cannot be observed by the normal OA effect, and it provides a principle for building optical filters without external field.     

Pattern of flow around a sphere oscillating an neutrally buoyancy horizon in a continuously stratified fluid

The flow pattern produced by a sphere freely sinking to the neutral buoyancy horizon in a continuously stratified liquid is visualized with different schlieren methods. Dispersion of light in the brine produces colouring of conventional schlieren images when cutting diaphragm is at the edge of blade or thread and is used to form “natural rainbow” colour schlieren image. With sensitive schlieren methods a new structural element is distinguished in the flow pattern. That is a narrow jet covered with a high gradient envelope forming in the neighbourhood of the turning points on the trajectory of the oscillating body. Due to the interaction of the body with the emitted internal waves, and also with the wake and secondary jets, the rate of amplitude damping decreases with time     

Polarization-bistable vertical-cavity surface-emitting lasers: application for optical bit memory

We summarize recent results on polarization-bistable vertical-cavity surface-emitting lasers (VCSELs) and their application to optical buffer memory. All-optical flip-flop operation with very low switching energies and high repetition rates is achieved. An optical buffer memory consisting of a two-dimensional array of polarization-bistable VCSELs, in which the bit state of the optical signal, “0” or “1”, is stored as a lasing linear polarization state of 0 or 90°. Input data stored as the polarization states of the first VCSEL are transferred to the polarization states of the second VCSEL. In our experiments with 980 nm polarization-bistable VCSELs, 10 Gbit/s optical buffering, 2-bit optical buffering, and a shift register function have been successfully demonstrated.     

Plasmonic nanoparticle monomers and dimers: from nanoantennas to chiral metamaterials

We review the basic physics behind light interaction with plasmonic nanoparticles. The theoretical foundations of light scattering on one metallic particle (a plasmonic monomer) and two interacting particles (a plasmonic dimer) are systematically investigated. Expressions for the effective particle susceptibility (polarizability) are derived, and applications of these results to plasmonic nanoantennas are outlined. In the long-wavelength limit, the effective macroscopic parameters of an array of plasmonic dimers are calculated. These parameters are attributable to an effective medium corresponding to a dilute arrangement of nanoparticles, i.e., a metamaterial where plasmonic monomers or dimers have the function of “meta-atoms”. It is shown that planar dimers consisting of rod-like particles generally possess elliptical dichroism and function as atoms for planar chiral metamaterials. The fabricational simplicity of the proposed rod-dimer geometry can be used in the design of more cost-effective chiral metamaterials in the optical domain.     

All-Optical Wavelength Conversion Based on Four-Wave Mixing in Dispersion-Engineered Silicon Nanowaveguides

We demonstrate experimentally all-optical wavelength conversion based on four-wave mixing in dispersion-engineered silicon nanowaveguides with a picosecond pulse pump. We find that the conversion efficiency is significantly limited by nonlinear losses induced by the two-photon absorption and freecarrier absorption. Using a picosecond pulse pump centered at 1,550 nm, we show that the input continuous-wave signals can efficiently be converted into a broadband idler pulse in silicon waveguides with various dimensions. Conversion efficiencies versus signal wavelengths are different for silicon waveguides with different dimensions due to the variation in the phase mismatch; we obtain a conversion efficiency of – 32 dB in silicon nanowaveguides with a length of 5.8 mm. Such on-chip optical wavelength converters can find important potential applications in highly-integrated optical circuits for all-optical ultrafast signal processing.     

Guided-wave methods for optical configurations

Guided-wave methods used in the past to treat electromagnetic problems and applications in the microwave area have recently been extended to cover work in fiber and integrated optics. The basic principles of these methods are reviewed briefly and, in particular, the “open” properties of optical configurations are contrasted to the “closed” characteristics that describe most microwave applications. These aspects are illustrated in the context of beam couplers of uniform and periodic varieties, which are shown to lend themselves to rigorous treatment by microwave guided-wave methods that include both theoretical and experimental facets.     

Optical breakdown threshold in the electron-thermal model of defect generation

An investigation is made of the conditions for the nucleation of optical breakdown in transparent material when recombination-stimulated defect-formation reactions occur in it. It is shown that a positive feedback between the conduction electron concentration and point defects activates defect formation even if the medium is not heated. Under real conditions, where heating of the medium by the light is important, lowering of the activation barrier by thermal defect generation aided by conduction electrons results in optical breakdown of the medium at light intensities much lower than predicted in the classical “semiconductor” or “thermochemical” models of thermal breakdown. The analysis confirms that optical breakdown of transparent condensed media is due to electron-aided defect formation reactions over a broad range of illumination conditions. Zh. Tekh. Fiz. 67, 48–53 (May 1997)     

Effective collection of Brillouin scattered light in liquids

Devices for the collection of Brillouin scattered light in liquids are discussed. Optical systems have hitherto employed conical mirrors; their angular acceptance functions are presented. Novel devices proposed and discussed are the cylinder lens and the “scattering tube” (a cylindrical mirror). Results of applications are reported. This work was supported by the “Deutsche Forschungsgemeinschaft”.     

QCD in the nuclear medium and effects due to Cherenkov gluons

The equations of in-medium gluodynamics are proposed. Their classical lowest-order solution is explicitly shown for a color charge moving with constant speed. For chromopermittivity larger than 1 it describes emission of Cherenkov gluons resembling results of classical electrodynamics. The values of the real and imaginary parts of the chromopermittivity are obtained from the fits to experimental data on the double-humped structure around the away-side jet obtained at RHIC. The dispersion of the chromopermittivity is predicted by comparing the RHIC, SPS, and cosmic-ray data. This is important for LHC experiments. Cherenkov gluons may be responsible for the asymmetry of dilepton mass spectra near ρ meson observed in the SPS experiment with excess in the low-mass wing of the resonance. This feature is predicted to be common for all resonances. The “color rainbow” quantum effect might appear according to higher-order terms of in-medium QCD if the chromopermittivity depends on color.     

Threshold reduction of stimulated Brillouin scattering (SBS) using fiber loop schemes

SBS mirrors as self-pumped and easy to handle non-linear optical devices are frequently used in high-power laser systems for improving the beam quality based on optical phase conjugation. Because of the non-linear behaviour, a certain pulse energy or power of incident light is needed to generate enough reflectivity for practical purposes. Therefore, reducing this “threshold” is still a main topic in the development of new schemes for optical phase conjugation. In addition to the taper concept reported earlier, this paper deals with loop schemes for reducing the power requirements. A reduction of the so-called “threshold” by a factor of between two and four was obtained with the schemes investigated using liquids and fibers. Received: 4 September 2001 / Revised version: 22 October 2001 / Published online: 23 November 2001     

Laser induced micro-photoluminescence of marble and application to authenticity testing of ancient objects

For the last 70 years, the authenticity of disputable marble objects has been tested by using a black light lamp. According to empirical observations “fresh marbles are purple while ancient ones are blue under the lamp”. This discrimination lacks scientific basis but is very popular because sculptured stone dating is impossible. This work aims to test the reliability of the “UV method” by studying the laser excited photoluminescence (PL) of marble surfaces. An argon ion laser beam was focused through a microscope objective onto the sample, offering a PL spatial resolution of 3 μm. Newly-cut marbles show an intense emission at 610 nm ascribed to Mn²⁺ and a less intense one at 390 nm. Excavated surfaces show the 610 nm emission and a broadband (380–530 nm) one. Similar broadband emissions due to humic (HAs) and fulvic acids (FAs) are typical in soil PL spectra and were observed in the spectra of samples taken from the soil surrounding the excavated surfaces. Additionally, electron paramagnetic resonance (EPR) spectra of excavated surfaces show a peak at g=2.0045, typical in calcite doped with humic acids. We presume that the 380–550 nm emission originates from HA and FA salts existing in the infiltrated soil or the recrystallised calcite developed in marble patinas. Finally, the application of the “UV method” on twelve ancient and modern surfaces proved that the technique is only partly reliable and should be used together with other analytical techniques. PACS 78.55.-m; 78.55.Hx; 81.70.Fy; 87.64.Hd     

A unified framework for the algebra of unsharp quantum mechanics

On the basis of the concrete operations definable on the set of effect operators on a Hilbert space, an abstract algebraic structure of sum Brouwer-Zadeh (SBZ)-algebra is introduced. This structure consists of a partial sum operation and two mappings which turn out to be Kleene and Brouwer unusual orthocomplementations. The Foulis-Bennett effect algebra substructure induced by any SBZ-algebra, allows one to introduce the notions of unsharp “state” and “observable” in such a way that any “state-observable” composition is a standad probability measure (classical state). The Cattaneo-Nisticò BZ substructure induced by any SBZ-algebra permits one to distinguish, in an equational and simple way, the sharp elements from the really unsharp ones. The family of all sharp elements turns out to be a Foulis-Randall orthoalgebra. Any unsharp element can be “roughly” approximated by a pair of sharp elements representing the best sharp approximation from the bottom and from the top respectively, according to an abstract generalization introduced by Cattaneo of Pawlack “rough set” theory (a generalization of set theory, complementary to fuzzy set theory, which describes approximate knowledge with applications in computer sciences). In both the concrete examples of fuzzy sets and effect operators the “algebra” of rough elements shows a weak SBZ structure (weak effect algebra plus BZ standard poset) whose investigation is set as an interesting open problem.     

New possibilities for producing photon echoes from a homogeneous ensemble of atoms and with the use of a single light pulse

In investigations of predicted new types of photon echoes — an echo from a homogeneous ensemble of atoms and an echo of a single light pulse — have established that the magnitude and form of these new types of photon echoes are completely determined by the type of optical transition and by the “area” and polarization of the exciting light pulses (and the form can be controlled by varying the magnetic field). It is also established that the echo amplitude decreases for both small (compared to 1) and large light-pulse areas, and the optimal areas for which the maximum echo is obtained have been found. Investigations show that such photon echoes can also appear under conditions when an ordinary photon echo is absent (in atomic or molecular gases at high pressure, in the far-IR region of the spectrum, from cooled trapped atoms or ions, and so on). Pis’ma Zh. éksp. Teor. Fiz. 65, No. 10, 738–743 (25 May 1997)     

Optical vortices in the scattering field of magnetic domain holograms

Experimental investigations and theoretical-model analyses have been made of the magnetooptic diffraction of light at ferrite garnet magnetic films with a banded domain structure which includes isolated magnetic grating defects in the form of “forks” and “breaks.” An analysis of the magnetic grating structure and the light diffraction field shows that in terms of its action on laser radiation, a banded domain grating is similar to a computer-synthesized phase hologram of an isolated pure screw-wavefront dislocation. It is shown that as a result of magnetooptic diffraction at a magnetic hologram, optical vortices may be reconstructed with a helicoidal wavefront carrying the topological charge l=±1,±2. Zh. Tekh. Fiz. 68, 54–58 (December 1998)     

Electro-optical properties and photopolarization anisotropy of methacrylic azopolymer films

We have synthesized polymethacrylates with azobenzene side moieties and “spacers” of different lengths. We have studied the spectra and kinetics of the electro-optical effect appearing in films of such azopolymers after they are exposed to linearly polarized light. The nature of the electro-optical effect is explained by the appearance of photoinduced optical anisotropy in the films, due to a change in the ratio of the concentrations of trans and cis isomers of the azobenzene moieties. The characteristic time required for establishment and relaxation of photoinduced optical anisotropy correlates with the times required for a change in the dielectric characteristics of the studied films when exposed to linearly polarized light. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 2, pp. 307–310, March–April, 2009.     

The optical sum rule in strongly correlated systems

We discuss the problem of a possible “violation” of the optical sum rule in the normal (nonsuperconducting) state of strongly correlated electronic systems, using our recently proposed DMFT + Σ approach applied to two typical models: the “hot spot” model of the pseudogap state and the disordered Anderson-Hubbard model. We explicitly demonstrate that the general Kubo single-band sum rule is satisfied for both models, but the optical integral itself is in general dependent on temperature and characteristic parameters, such as the pseudogap width, correlation strength, and disorder scattering, leading to an effective “violation” of the optical sum rule, which may be observed in experiments. The text was submitted by the authors in English.