Showing papers in "Journal of The Optical Society of America B-optical Physics in 2006"
TL;DR: In this paper, the authors present a homogenization technique in which macroscopic fields are determined via averaging the local fields obtained from a full-wave electromagnetic simulation or analytical calculation.
Abstract: Over the past several years, metamaterials have been introduced and rapidly been adopted as a means of achieving unique electromagnetic material response. In metamaterials, artificially structured—often periodically positioned—inclusions replace the atoms and molecules of conventional materials. The scale of these inclusions is smaller than that of the electromagnetic wavelength of interest, so that a homogenized description applies. We present a homogenization technique in which macroscopic fields are determined via averaging the local fields obtained from a full-wave electromagnetic simulation or analytical calculation. The field-averaging method can be applied to homogenize any periodic structure with unit cells having inclusions of arbitrary geometry and material. By analyzing the dispersion diagrams and retrieved parameters found by field averaging, we review the properties of several basic metamaterial structures. © 2006 Optical Society of America OCIS codes: 160.0160, 160.1190, 260.2110, 350.5500.
581 citations
TL;DR: In this paper, a combined theoretical and experimental investigation of the generation of few-cycle terahertz (THz) pulses via the nonlinear effect of optical rectification and of their coherent detection via electro-optic sampling is presented.
Abstract: We present a combined theoretical and experimental investigation of the generation of few-cycle terahertz (THz) pulses via the nonlinear effect of optical rectification and of their coherent detection via electro-optic sampling. The effects of dispersive velocity matching, absorption of the optical and the THz waves, crystal thickness, pulse diameter, pump pulse duration, and two-photon absorption are discussed. The theoretical calculations are compared with the measured spectra of THz pulses that have been generated and detected in crystals of the highly nonlinear organic salt 4-N,N-dimethylamino-4′-N′-methyl stilbazolium tosylate (DAST). The results are found to be in agreement with the theory. By the selection of the optical pump wavelength between 700 and 1600 nm, we achieved several maxima of the overall generation and detection efficiency in the spectral range between 0.4 and 6.7 THz, with an optimum at 2 THz generated with 1500 nm laser pulses.
378 citations
TL;DR: In this article, a femtosecond pulse characterization and compensation using multiphoton intrapulse interference phase scan (MIIPS) was rigorously tested and was found to have 3 mrad precision within the 90 nm bandwidth of the pulses.
Abstract: Femtosecond pulse characterization and compensation using multiphoton intrapulse interference phase scan (MIIPS) [Opt. Lett.29, 775 (2004)] was rigorously tested. MIIPS was found to have 3 mrad precision within the 90 nm bandwidth of the pulses. Group-velocity dispersion measurements of glass and quartz provided independent accuracy tests. Phase distortions from high-numerical-aperture objectives were measured and corrected using MIIPS, an important requirement for reproducible two-photon microscopy. Phase compensation greatly improved the pulse-shaping results through a more accurate delivery of continuous and binary phase functions to the sample. MIIPS measurements were possible through the scattering of biological tissue, a consideration for biomedical imaging.
283 citations
TL;DR: In this article, the problem of optical nanotransmission lines (NTLs) that can be envisioned by properly joining together arrays of these basic nanoscale circuit elements was investigated.
Abstract: Following our recent theoretical development of the concepts of nanoinductors, nanocapacitors, and nanoresistors at optical frequencies and the possibility of synthesizing more complex nanoscale circuits, we theoretically investigate in detail the problem of optical nanotransmission lines (NTLs) that can be envisioned by properly joining together arrays of these basic nanoscale circuit elements. We show how, in the limit in which these basic circuit elements are closely packed together, NTLs can be regarded as stacks of plasmonic and nonplasmonic planar slabs, which may be designed to effectively exhibit the properties of planar metamaterials with forward (right-handed) or backward (left-handed) operation. With the proper design, negative refraction and left-handed propagation are shown to be possible in these planar plasmonic guided-wave structures, providing possibilities for subwavelength focusing and imaging in planar optics and laterally confined waveguiding at IR and visible frequencies. The effective material parameters for such NTLs are derived, and the connection and analogy between these optical NTLs and the double-negative and double-positive metamaterials are also explored. Physical insights and justification for the results are also presented.
199 citations
TL;DR: In this paper, a low-loss negative-index metamaterial with the magnitude of the real part of the index comparable with the imaginary part is demonstrated, where over 40% transmission is achieved in the negative-Index region by structural adjustment of the impedance matching between the metammaterial and the air-substrate claddings.
Abstract: We experimentally demonstrate a comparatively low-loss negative-index metamaterial with the magnitude of the real part of the index comparable with the imaginary part. Over 40% transmission is achieved in the negative-index region by structural adjustment of the impedance matching between the metamaterial and the air-substrate claddings. This structure has the potential of achieving high transmission and small loss in the negative-index region.
195 citations
TL;DR: In this article, a non-magnetic negative-refractive-index system for optical and near-infrared frequency bands is proposed. But the design does not require periodicity and thus is highly tolerant to fabrication defects.
Abstract: We develop an approach to use nanostructured plasmonic materials as a nonmagnetic negative-refractive-index system at optical and near-infrared frequencies. In contrast to conventional negative-refraction materials, our design does not require periodicity and thus is highly tolerant to fabrication defects. Moreover, since the proposed materials are intrinsically nonmagnetic, their performance is not limited to the proximity of a resonance, so the resulting structure has relatively low loss. We develop the analytical description of the relevant electromagnetic phenomena and justify our analytic results via numerical solutions of Maxwell equations.
186 citations
TL;DR: The work was supported by the Australian Research Council and the Russian Fund for Basic Research (grant N05-02-16357) as discussed by the authors, and the authors acknowledge the warm hospitality of the Nonlinear Physics Centre during their stay in Canberra.
Abstract: The work was supported by the Australian Research
Council. Alexander Zharov acknowledges the warm hospitality
of the Nonlinear Physics Centre during his stay in
Canberra, as well as a support from the Russian Fund for
Basic Research (grant N05-02-16357).
177 citations
TL;DR: In this paper, surface-plasmon (SP) coupling was used to increase the photoluminescence (PL) intensities and decay rates of CdSe quantum dots.
Abstract: We obtained very bright light emission from CdSe quantum dots (QDs) by using the surface-plasmon (SP) coupling technique. 23-fold enhanced photoluminescence (PL) intensities and two-fold increased PL decay rates are observed when the QDs are located on evaporated gold films. This enhancement is not effective for CdSe cores with ZnS shells (ZnS/CdSe). The reason for this difference can be explained by using the SP dispersion diagram and by considering the SP coupling mechanism. We discuss the inherent merits and demerits of this technique to increase the emission efficiency. This technique will enable high-speed and efficient light emission for optically as well as electrically pumped light emitters.
162 citations
TL;DR: In this article, the negative refractive index of metal dielectric composites was found to be negative in the optical range, and it was shown that arrays of single and paired nanorods can provide such negative refraction.
Abstract: Specially designed metal-dielectric composites can have a negative refractive index in the optical range. Specifically, it is shown that arrays of single and paired nanorods can provide such negative refraction. For pairs of metal rods, a negative refractive index has been observed at 1.5 µm. The inverted structure of paired voids in metal films can also exhibit a negative refractive index. A similar effect can be accomplished with metal strips in which the refractive index can reach −2. The refractive index retrieval procedure and the critical role of light phases in determining the refractive index are discussed.
160 citations
TL;DR: In this paper, the authors proposed an optical far-field superlens (FSL) for imaging beyond the diffraction limit, which is composed of a properly designed periodically corrugated metallic slab-based super-lens with a specific strong-broadband wavenumber excitation of surface-plasmon polaritons supported by the nanostructured metallic grating.
Abstract: A conventional optical superlens for imaging beyond the diffraction limit produces images only in the near-field zone of the superlens. In contrast, an optical far-field superlens (FSL) device has a remarkable transmission property that leads to a one-to-one relationship between the far-field and the near-field angular spectra. This property makes the device suitable for imaging beyond the diffraction limit from far-field measurement. This specific FSL is composed of a properly designed periodically corrugated metallic slab-based superlens. Through the numerical design and parameter study, we show that the transmission property of this FSL is based on a specific strong-broadband wavenumber excitation of surface-plasmon polaritons supported by the nanostructured metallic grating.
153 citations
TL;DR: In this article, a perturbation theory for the frequency shift of highly resonant photonic whispering gallery modes in a transparent sphere is presented, and a general formula for the shifts in TE and TM polarization by adsorption of another dielectric medium is derived.
Abstract: A perturbation theory is presented for the frequency shift of highly resonant photonic whispering gallery modes in a transparent sphere. Using a vector wave equation, we derive a general formula for the shifts in TE and TM polarization by adsorption of another dielectric medium. The adsorbed medium can have an arbitrary shape and refractive-index profile. The formula is applied to adsorption of a thin layer and deposition of a small spherical particle, many such particles, and thin cylindrical particles on the resonator surface. We found that the ratio of the TM mode shift to the TE mode shift is sensitive to the shape of the adsorbates and their orientation. Calculation results are discussed in terms of a dipolar field.
TL;DR: In this article, the omnidirectional total reflection range using a binary (BaF2/PbS) periodic structure was enhanced by sandwiching a thin layer of ZrO2 between every two layers, constituting a period of the lattice.
Abstract: Here we demonstrate by theoretical analysis a novel way to enhance the omnidirectional total-reflection wavelength range in one-dimensional photonic bandgap material by using a ternary periodic structure (i.e., three material layers constituting a period of the lattice). The omnidirectional total reflection range using a binary (BaF2/PbS) periodic structure was enhanced by 108 nm when the structure was modified by sandwiching a thin layer of ZrO2 between every two layers, constituting a period of the lattice. A shift of the omnidirectional range toward higher wavelengths was also observed. When the sandwiched layer was CeF3, the enhancement in the range was 120 nm. As the sandwiched layer is very thin, there will not be any significant increase in the size of the reflector, contrary to the case of heterostructured photonic crystals (PCs) where two or more PCs are clubbed together to achieve enhancement.
TL;DR: In this paper, a theoretical study of clusters of evanescently coupled 2D whispering-gallery mode optical microcavities (termed "photonic molecules") as chemosensing and biosensing platforms is presented.
Abstract: We report a theoretical study of clusters of evanescently coupled 2D whispering-gallery mode optical microcavities (termed "photonic molecules") as chemosensing and biosensing platforms. Photonic molecules (PMs) supporting modes with narrow linewidths, wide mode spacing, and greatly enhanced sensitivity to the changes in the dielectric constant of their environment and to the presence of individual subwavelength-sized nanoparticles in the PM evanescent-field region are numerically designed. This type of optical biosensor can be fabricated in a variety of material platforms and integrated on a single chip that makes it a promising candidate for a small and robust laboratory-on-a-chip device. Possible applications of the developed methodology and the designed PM structures to near-field microscopy, single nanoemitter microcavity lasing, and cavity-controlled single-molecule fluorescence enhancement are also discussed.
TL;DR: In this paper, a novel design of all-optical logic gates based on nonlinear slot-waveguide couplers is proposed, which can be realized by a simple single optical-directional coupler configuration.
Abstract: A novel design of all-optical logic gates based on nonlinear slot-waveguide couplers is proposed. NOT, OR, and AND logic gates can be realized by a simple single optical-directional coupler configuration. Strong polarization dependencies of slot waveguides are effectively utilized for realizing polarization-independent optical-directional couplers in the linear regime and polarization-dependent all-optical switches in the nonlinear regime. All the simulations performed in this paper were performed for three-dimensional nonlinear channel waveguide structures by using rigorous numerical schemes based on the full-vector finite-element method specially formulated for nonlinear optical waveguides.
TL;DR: In this article, the authors measured the threshold energy for supercontinuum generation and bulk damage in fused silica using numerical apertures (NAs) ranging from 0.01 to 0.65.
Abstract: Competing nonlinear optical effects are involved in the interaction of femtosecond laser pulses with transparent dielectrics: supercontinuum generation and multiphoton-induced bulk damage. We measured the threshold energy for supercontinuum generation and bulk damage in fused silica using numerical apertures (NAs) ranging from 0.01 to 0.65. The threshold for supercontinuum generation exhibits a minimum near 0.05NA and increases quickly above 0.1 NA. For NAs greater than 0.25, we observe no supercontinuum generation. The extent of the blue broadening of the supercontinuum spectrum decreases significantly as the NA is increased from 0.01 to 0.08, showing that weak focusing is important for generating the broadest supercontinuum spectrum. Using a light-scattering technique to detect the onset of bulk damage, we confirmed bulk damage at all NAs studied. At a high NA, the damage threshold is well below the critical power for self-focusing.
TL;DR: In this paper, a 2D Fourier transform was used to measure transient changes of a GaAs surface irradiated with intense femtosecond laser pulses with fluences near the ablation threshold.
Abstract: �2 rad and amplitude changes 1% with micrometer spatial resolution 1 m. Interferograms are processed using a 2D-Fourier transform algorithm. We discuss the image formation and the physical interpretation of the measured interferograms. The technique is applied to measure transient changes of a GaAs surface irradiated with intense femtosecond laser pulses with fluences near the ablation threshold. © 2006 Optical Society of America OCIS codes: 000.2170, 100.2650, 110.2990, 120.5050, 180.3170, 320.7100.
TL;DR: In this article, high-quality LuAG:Yb3+ crystals with 0.75, 3.8, 10, 12, 15, 20, and 50 at. % were grown using the vertical Bridgman method.
Abstract: We have grown high-quality LuAG:Yb3+ crystals with 0.75, 3.8, 10, 12, 15, 20, and 50 at. % concentrations by the vertical Bridgman method. With low-temperature spectroscopy the Stark sublevel structure of the 2F7/2 ground state and the 2F5/2 excited state has been determined. With room-temperature spectroscopy, the emission cross section was found to be 3×10−20 cm2, being 1.5 times the YAG:Yb3+ emission cross section. The luminescence quantum efficiency was measured in samples with different Yb3+ concentrations. Its value was found to be 90% for 3.8 and 10 at. %, 84% for 20 at. %, and 70% for 50 at. % Yb3+. The laser-emission tunability under diode pumping was found to extend from 1045 up to 1095 nm in a 12 at. % sample with 3.15 mm thickness.
TL;DR: In this paper, the spectrally resolved two-beam coupling technique was extended to include higher-order nonlinearities, and the governing equations of the extended technique were derived and applied to the analysis of the experimental measurements.
Abstract: We extend the spectrally resolved two-beam coupling technique for measurements of cubic nonlinearities of materials to include higher-order nonlinearities. The governing equations of the extended technique are derived and applied to the analysis of the experimental measurements. We report the observation of saturation of the cubic optical nonlinearity of several glasses. Fifth- and seventh-order nonlinearities are required to account for the measured nonlinear phase shifts. The observation of saturable nonlinear indices accompanied by only moderate nonlinear absorption will be relevant to some applications.
TL;DR: In this paper, a spherical glass cell of 3 mm diameter containing Cs metal with inner walls coated with paraffin was used for nonlinear magneto-optical-rotation signals with frequency and amplitude-modulated laser light.
Abstract: Dynamic nonlinear magneto-optical-rotation signals with frequency- and amplitude-modulated laser light have been observed and investigated with a spherical glass cell of 3 mm diameter containing Cs metal with inner walls coated with paraffin. Intrinsic Zeeman relaxation rates of γ/(2π)≈20 Hz and lower have been observed. Favorable prospects of using millimeter-scale coated cells in portable magnetometers and secondary frequency references are discussed.
TL;DR: In this paper, a comparison between homodyne and heterodyne near-field optical microscopy (ASNOM) is made through near field analysis of gold nanowells, integrated waveguides, and a single evanescent wave generated by total internal reflection.
Abstract: In coherent homodyne apertureless scanning near-field optical microscopy (ASNOM) the background field cannot be fully suppressed because of the interference between the different collected fields, making the images difficult to interpret. We show that implementing the heterodyne version of ASNOM allows one to overcome this issue. We present a comparison between homodyne and heterodyne ASNOM through near-field analysis of gold nanowells, integrated waveguides, and a single evanescent wave generated by total internal reflection. The heterodyne approach allows for the control of the interferometric effect with the background light. In particular, the undesirable background is shown to be replaced by a controlled reference field. As a result, near-field information undetectable by a homodyne ASNOM is extracted by use of the heterodyne approach. Additionally, it is shown that field amplitude and field phase can be detected separately.
TL;DR: In this article, a new type of optical-fiber surface-plasmon-resonance (SPR) sensor based on a thin metallic film and long-period fiber gratings for measuring small changes of refractive index of analyte is presented.
Abstract: A new type of optical-fiber surface-plasmon-resonance (SPR) sensor based on a thin metallic film and long-period fiber gratings for measuring small changes of refractive index of analyte is presented. This sensor simply employs a long-period fiber grating with a proper period to couple a core mode (HE11) to the copropagating cladding mode that can excite a surface-plasmon wave (SPW). The mainly theoretical base used to analyze this new structure is the unconjugated form of coupled-mode equations. In this new SPR sensor, the variation of the refractive index of analyte is determined by monitoring the change of the transmitted core mode power, which is calculated by unconjugated two-mode coupled-mode equations at a fixed wavelength. The numerical results have demonstrated that this new and simple configuration may be used as a highly sensitive amplitude sensor. As far as the excitation of SPW, the model of numerical simulation, and the complexity of measurement equipment are concerned, this new structure is superior to the proposed sensor, consisting of a bent polished single-mode SPR optical fiber. Furthermore, the structure can be easily adapted for a SPR fiber optical probe if a mirror is deposited on the fiber tip.
TL;DR: In this paper, an analytical solution to the mode dispersion equation is derived, and it is shown that the quarter-wave Bragg reflection waveguide is polarization degenerate, although the TE and TM mode profiles differ significantly as the external Brewster's angle condition in the cladding is approached.
Abstract: The Bragg reflection waveguide (BRW), or one-dimensional photonic crystal waveguide, has recently been proposed for a wide spectrum of applications ranging from particle acceleration to nonlinear frequency conversion. Here, we conduct a thorough analytical investigation of the quarter-wave BRW, in which the layers of the resonant cladding have a thickness corresponding to one quarter of the transverse wavelength of a desired guided mode. An analytical solution to the mode dispersion equation is derived, and it is shown that the quarter-wave BRW is polarization degenerate, although the TE and TM mode profiles differ significantly as the external Brewster's angle condition in the cladding is approached. Analytical expressions for waveguide properties such as the modal normalization constants, propagation loss, and overlap factors between the mode and each waveguide layer are derived, as are dispersion and tuning curves.
TL;DR: In this paper, the exact expression of the radially polarized light beams, which is valid for the fields to be predicted for an arbitrary transverse beam size, has been derived in closed-form terms for any on-axis point.
Abstract: Starting from the vectorial Rayleigh-Sommerfeld formulas, the nonparaxial propagation of radially polarized light beams in free space is investigated analytically and numerically. The paraxial case can be treated as a special case of the general result. The exact expression of the radially polarized light beams, which is valid for the fields to be predicted for an arbitrary transverse beam size, has been derived in closed-form terms for any on-axis point. The validity of the analytical results is confirmed by the numerical results.
TL;DR: In this article, it was shown that 2D photonic crystals in semiconductor membranes strongly modify the radiative decay of dipole emitters, and that they can be used to simulate the local mode density in a simple 2D model.
Abstract: We show theoretically that two-dimensional (2D) photonic crystals in semiconductor membranes strongly modify the radiative decay of dipole emitters. Three-dimensional finite-difference time-domain calculations show over 7 times inhibition and 15 times enhancement of the emission rate compared with vacuum for judiciously oriented and positioned dipoles. Emission rate modifications inside the membrane mimic the local mode density in a simple 2D model. The inhibition of emission saturates with crystal size around the source, with a 1/e size that scales as the inverse gap bandwidth. Owing to the vertically guided mode structure, inhibition occurs only near the slab center, but enhanced emission persists also outside the membrane. We find that emission changes can even be observed in experiments with ensembles of randomly oriented dipoles.
TL;DR: Shokooh-Saremi et al. as discussed by the authors used the assistance of the Australian Research Council (ARC) for the development of ultrahigh-bandwidth devices for optical systems.
Abstract: This work was produced with the assistance of the Australian
Research Council (ARC). The Centre for
Ultrahigh-bandwidth Devices for Optical Systems is an
ARC Centre of Excellence. M. Shokooh-Saremi appreciates
the partial support of the Iranian Ministry of Science,
Research and Technology.
Journal Article•
TL;DR: It is found that the image metrics make it possible to determine the axis position reliably at well below the resolution of one detector bin in an automated procedure.
Abstract: Tomographic reconstruction requires precise knowledge of the position of the center of rotation in the sinogram data; otherwise, artifacts are introduced into the reconstruction. In parallel-beam microtomography, where resolution in the 1 μm range is reached, the center of rotation is often only known with insufficient accuracy. We present three image metrics for the scoring of tomographic reconstructions and an iterative procedure for the determination of the position of the optimum center of rotation. The metrics are applied to model systems as well as to microtomography data from a synchrotron radiation source. The center of rotation is determined using the image metrics and compared with the results obtained by the center-of-mass method and by image registration. It is found that the image metrics make it possible to determine the axis position reliably at well below the resolution of one detector bin in an automated procedure.
TL;DR: In this paper, the validity of the theory of McCumber has been tested by applying it to a number of ground state transition in various rare-earth-doped glasses, and the results suggest that, at room temperature, the McCumber theory is not restricted to crystalline hosts but remains valid for the broader transitions characteristic of rare earth doped glass.
Abstract: The validity of the theory of McCumber [Phys. Rev.136, A954-A957 (1964)] has been tested by applying it to a number of ground-state transition in various rare-earth-doped glasses. Special attention was given to those aspects of the experimental procedure that can lead to systematic errors, such as reabsorption of fluorescence and baseline subtraction uncertainties in the absorption measurements. To ensure consistency between absorption and fluorescence measurements, we used the same geometry for light collection and measurement. With these experimental procedures properly implemented, we find that in all cases there is excellent agreement between the spectral shape of calculated and measured cross-section spectra at room temperature. This is true even for the thermally coupled (2H9/2,4F5/2) and 4F3/2 levels of Nd, which span an energy range of ∼2000 cm−1, much larger than the typical width of a single Stark level manifold. The results suggest that, at room temperature, the McCumber theory is not restricted to crystalline hosts but remains valid for the broader transitions characteristic of rare-earth-doped glass.
TL;DR: In this paper, the authors examined the kinetic behavior involved within the photopolymer material during recording to obtain a clearer picture of the photochemical processes present, and the results support their description of the inhibition process in an acrylamide-based photopolymers and can be used to predict behavior under certain conditions.
Abstract: Photopolymer materials are practical materials for use as holographic recording media, as they are inexpensive and self-processing (dry processed). Understanding the photochemical mechanisms present during recording in these materials is crucial to enable further development. One such mechanism is the existence of an inhibition period at the start of grating growth during which the formation of polymer chains is suppressed. Some previous studies have indicated possible explanations for this effect and approximate models have been proposed to explain the observed behavior. We examine in detail the kinetic behavior involved within the photopolymer material during recording to obtain a clearer picture of the photochemical processes present. Experiments are reported and carried out with the specific aim of understanding these processes. The results support our description of the inhibition process in an acrylamide-based photopolymer and can be used to predict behavior under certain conditions.
TL;DR: In this article, a two-beam mode-mismatched thermal lens experiment aimed at determination of the absorption coefficient and the photothermal parameters of a nearly transparent material is described.
Abstract: We describe a calibrated two-beam mode-mismatched thermal lens experiment aimed at determination of the absorption coefficient and the photothermal parameters of a nearly transparent material. The use of a collimated probe beam in the presence of a focused excitation beam optimizes the thermal lens experiment. The signal becomes independent from the Rayleigh parameters and waist positions of the beams. We apply this method to determine the absolute value of the thermal diffusivity and absorption coefficient of distilled water at 533 nm.
TL;DR: In this paper, a negative-permittivity material (silicon carbide) sandwiched between two layers of positive-permittivity materials was used for enhancement of the resolution of near-field imaging via the superlensing effect.
Abstract: We demonstrate that a negative-permittivity material (silicon carbide) sandwiched between two layers of positive-permittivity material (silicon oxide) can be used for enhancement of the resolution of near-field imaging via the superlensing effect. The resulting three-layer metamaterial is also shown to exhibit an enhanced transmission when its effective dielectric permittivity matches that of the vacuum. Experimental far-field diagnostics of the superlensing based on measuring transmission coefficients through the metal-coated superlens is implemented using Fourier-transformed infrared microscopy. Superlensing is shown to be a highly resonant phenomenon manifested in a narrow frequency range.