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Terahertz lensing effect in high-temperature superconductors

Amirparsa Zivari, Mohammad Reza Tavakol, Amin Khavasi, and Behzad Rejaei

Doc ID: 357821 Received 15 Jan 2019; Accepted 18 Mar 2019; Posted 20 Mar 2019  View: PDF

Abstract: We show that high-temperature superconductors can be used to build a terahertz superlens. These materials exhibit hyperbolic behavior at frequencies between their two plasma frequencies corresponding to electric fields parallel and perpendicular to their c-axis. Due to the large component of permittivity perpendicular to the c-axis, the resolution of the proposed lens is much below the diffraction limit (~$\lambda/1000$). In this letter we demonstrate this lensing phenomenon with a simple slab of a high-temperature superconductor.

Approach to Optical Communication Frequency Standard Using Fiber Laser Based on Cold Rb Two-Photons Transition with Enhancement

Jianxiao Leng, Hao Xu, Haoyuan Lu, Yaoyuan Fan, and Jy Zhao

Doc ID: 358261 Received 28 Jan 2019; Accepted 17 Mar 2019; Posted 20 Mar 2019  View: PDF

Abstract: We propose to utilize an Er-doped fiber laser locked to a cooled Rb TPT (two-photon transition) resonance as a frequency standard for fiber-based optical communication. We show experimentally that a CW (continuous wave) laser beam can effectively enhance the cooled Rb TPT resonance. The linewidth of the cooled Rb TPT resonance excited by the fiber frequency comb is measured about 900 kHz, which is narrower than the linewidth for the thermal Rb TPT. After locking the repetition rate of the fiber laser to the cooled Rb TPT resonance, the stability reaches 1.5×10^-13 with 100 s averaging time. The results demonstrate that the proposed method in this article is promising to provide frequency standard for fiber-based optical communication.

The effective role of Dirac mass in non-linear optical spectra ofsilicene

UPENDRA KUMAR

Doc ID: 347657 Received 12 Oct 2018; Accepted 15 Mar 2019; Posted 18 Mar 2019  View: PDF

Abstract: Silicene is a monolayer honeycomb system made of silicon. It is a two-dimensional topological insulator, which undergoes a topological phase transition to a band insulator by applying an external electromagnetic field. All topological phase transitions in silicene come by tuning of its Dirac mass. In this article, the tuning of Dirac mass of silicene has been done by application of Floquet theory. The nature of Dirac mass in Bloch-Seigert shift is shown in topological trivial and non-trivial phase of silicene. The collapse-revival spectra have been described by Floquet theory in silicene. The differential transmission coefficient of pump-probe spectra is shown, which have the capability of distinguishing Floquet theory oscillations in topological trivial and non-trivial phase of silicene. All these results are also valid for the germanene and stanene by changing material parameters.

Twist sensor based on surface plasmon resonance excitation using two spectral combs in one tilted fiber Bragg grating

Xuejun Zhang, jie chen, Alvaro Gonzalez-Vila, Fu Liu, Yuke Liu, Kaiwei Li, and Tuan Guo

Doc ID: 359214 Received 31 Jan 2019; Accepted 12 Mar 2019; Posted 12 Mar 2019  View: PDF

Abstract: An optical fiber twist sensor based on surface plasmon resonance (SPR) excitation and able to operate both in gaseous and liquid media is proposed and demonstrated. The use of a gold-coated 37.5° tilted fiber Bragg grating allows to generate two windows of cladding mode resonances, providing surrounding refractive index sensitivity in two different external media. The relative optical power of the SPR mode in each case exhibits a linear response to the twist angle of the fiber from 0° to 90°, as well as from 90° to 180°, as a consequence of the polarization dependency of these sensors. The results show sensitivities of 1.15%/° and 1.22%/° with the sensor working in air and liquids respectively, being suitable for deformation measurement and structural health monitoring applications.

Geometric phase diffractive waveplate singularity arrays

Gary Walsh, Luciano De Sio, and Nelson Tabiryan

Doc ID: 353353 Received 04 Dec 2018; Accepted 11 Mar 2019; Posted 13 Mar 2019  View: PDF

Abstract: A general geometric phase singularity array structure is presented and discussed. For any two-dimension point lattice, a singularity array is defined as a summation of helical phase singularities with alternating handedness. The phase angle is the slow-axis orientation of a varying half-waveplate. Arrays are demonstrated in photoaligned polymer liquid crystal films. Simple square and biomimetic spiral lattices are characterized for diffraction behavior. Pattern selection rules based on topological charge are discovered. Numerical decomposition show that diffracted beams are composites of a few ordered planewaves for square, and Bessel beams for spiral phase arrays. Orbital angular momentum spectra of spiral diffraction is directly measured.

Peak emission of terahertz waves from (110)-oriented ZnTe by interacting phase-matched phonon resonances

Osama Hatem

Doc ID: 358112 Received 18 Jan 2019; Accepted 11 Mar 2019; Posted 11 Mar 2019  View: PDF

Abstract: We demonstrate the measurements and assignments of the phonon resonances responsible for observed peak emission of THz waves from (110)-ZnTe. We show that optical rectification in ZnTe using femtosecond pulses centered at 790 nm involves phase-matched fundamental and difference-phonon resonances at 1.7, 1.95, 2.25, and 2.55 THz, which produce peak THz emission at 2.1 THz and damped oscillations for ~ 6 ps after the main THz pulse. The phase-matched phonon resonances are measured and assigned using THz-TDS and mathematical modelling. The refractive index and the absorption coefficient of ZnTe are also extracted over the frequency range (0.1- 3 THz) from the measured THz-TDS data. The results are of great significance for understanding the dynamics of ZnTe in ultrafast optoelectronic systems and for designing tunable THz sources.

A Phase-correction algorithm for Fourier Transform Spectroscopy of a Laser Frequency Comb

Philipp Huke, Michael Debus, and Ansgar Reiners

Doc ID: 352702 Received 21 Dec 2018; Accepted 11 Mar 2019; Posted 12 Mar 2019  View: PDF

Abstract: Fourier-transform spectrographs (FTS) are among the most important tools for high-resolution spectroscopy over a broad spectral bandwidth. Traditionally, the frequency axis of an FTS has been calibrated with relatively few atomic lines and an absolute wavelength reference, which is often a stabilized HeNe-laser. Normally, the phase-spectrum is measured using a continuous light source to enable phase correction. Laser Frequency Combs (LFC) provide a much higher stability. Their spectrum consists of closely spaced, narrow lines which are very well suited for the characterization and calibration of an FTS. Due to thepulsed nature of the LFC, the phase spectrum can not be measured easily and a good phase correction becomes impossible. We show how a proper phase spectrum from an FTS-measurement of an LFC can be obtained and how the strongly-varying phase spectrum noise can be filtered. Therefore, we analyze a narrow spectral band-width σσ=10.200−12.700cm¯¹ in which we can measure∼ 70.000 lines with sufficient intensity. Only with an accurate truncation of the interferogram and a proper shifting, the complex structure of the phase spectrum is revealed. For phase filtering we adapted Mertz’ algorithm and show how the instrumental line shape (ILS) is significantly improved.

Full Wave Analysis of Terahertz Dispersive and Lossy Plasmonic HEMT using Hydrodynamic Model

Farzaneh Daneshmandian, Abdolali Abdipour, and Amir Nader Askarpour

Doc ID: 357113 Received 07 Jan 2019; Accepted 11 Mar 2019; Posted 12 Mar 2019  View: PDF

Abstract: Full-wave dispersive analysis and modeling of 2-D plasmon propagation in the channel of a biased ungated HEMT are presented. The numerical analysis is based on the simultaneous solution of the hydrodynamic transport model and the Maxwell’s equations using the FDTD method. The dispersive Drude-Lorentz model is employed to study the propagation of 2-D plasmons in the 2DEG layer embedded in an InGaAs substrate in THz frequencies. The effect of the dispersion on the phase and attenuation constants is investigated. Moreover, the proposed dispersive full-wave model is applied to a lossy metallic grating HEMT which can be used in a THz detector. The results demonstrate strong influence of the dispersion characteristics of InGaAs on the electromagnetic field distribution in the channel.

Detection of anomalies inside microcavities through parametric fluorescence: a formalism based on modulated commutation relations and consequences on the concept of density of states

Serge Gauvin, Joseph Zyss, and Cory Walker

Doc ID: 349974 Received 05 Nov 2018; Accepted 08 Mar 2019; Posted 08 Mar 2019  View: PDF

Abstract: It has been previously shown [Phys. Rev. A 50, 89 (1994)] that cavity-based electromagnetic confinement leads to an “anomalous” fields operators commutation relation that is undetectable by probing the cavity with a beam splitter. However, using this commutator in the case of parametric fluorescence (spontaneous parametric down conversion) when it occurs inside an open cavity implies a strong intensification of this process. This prediction can validate, or not, this commutation relation. The ab initio approach used is entirely based on vacuum field fluctuations and does not resort to the concept of density of states. Finally, through a generalization of creation and annihilation operators in presence of noise, this approach raises fundamental questions about quantum modes. We expect this work to stimulate new theoretical developments and related experiments, which might lead to new applications in quantum nonlinear optics.

Second Harmonic Generation from Complementary Au metasurfaces with Triangular resonators

Teruya Ishihara, Kengo Iwata, and Yusuf Habibullah

Doc ID: 357034 Received 07 Jan 2019; Accepted 07 Mar 2019; Posted 07 Mar 2019  View: PDF

Abstract: We demonstrate the contribution of local electric near-field enhancement around convex and concave corners at resonant fundamental excitation to second harmonic (SH) emission intensity using complementary Au metasurfaces with triangular resonators (i.e. square array of triangular particle and a square array of thin film of Au with a triangular hole). It is demonstrated that electric near-field enhancement at normal incident fundamental excitation around convex corners of a triangular particle is many times stronger than the one around concave corners of a complementary triangular hole. Notwithstanding, the SH emission intensity of the complementary structure is found to be comparable at their respective optimum resonant fundamental excitation. SH emission intensity is numerically estimated using nonlinear scattering theory. The comparable SH emission intensity is found to originate from the strong electric near-field enhancement on the sides of triangular hole with zero curvature, which compensate the field suppression around the concave corners of triangular hole. In addition, the strong electric near-field enhancement around convex corners of triangular particle (accompanied with suppression around side of the triangular particle) and field suppression around concave corners of triangular hole (accompanied with strong field enhancement around side of the triangular hole) is demonstrated using Babinet’s principle.

Numerical Investigation on Efficiency Improvement of Double Layer Anti-Reflection Coating AZO/buffer/Cu2O/CuO on BSF/FTO Heterostructure Solar Cells

Majid Toghyani Rizi and M.H. Shahrokh Abadi

Doc ID: 356597 Received 04 Jan 2019; Accepted 06 Mar 2019; Posted 07 Mar 2019  View: PDF

Abstract: Optical and electrical features of Cu2O solar cells from simple primitive bufferless AZO/Cu2O to complex Single/Double Layer-Anti-Reflection-Coating (S/DLARC) on Back-Surface-Fluorine-Doped-Tin-Oxide (BSF/FTO), were numerically studied. The simulated cells were optimized using low-conduction-band-offset (CBO) buffer, controlled-defect BSF and anti-reflection coating layers under compatible fabrication process. By considering the interlayers defects, the optimized DLARC/AZO/buffer/Cu2O/CuO on BSF/FTO exhibits an improved efficiency of 9.17% with a JSC ≈11.45 mA/cm2, a VOC ≈1.191 V, and a fill factor of 67.22%, under simulated illumination (AM 1.5G, 100 mW/cm2). The results are shown that the models can be adapted for prediction the Cu2O-based-cell behavior, prior to fabricating.

Modeling propagation in deformed step index fibers using a finite operator method

Das Kumar, Stephen Creagh, Slawomir Sujecki, and Trevor Benson

Doc ID: 352412 Received 20 Nov 2018; Accepted 05 Mar 2019; Posted 06 Mar 2019  View: PDF

Abstract: A finite operator model is applied to the propagation of light in a deformed step-index fibers. The distribution of the light captured by the fiber from an arbitrary initial excitation is illustrated in the phase space for each fiber boundary. The method proves to be promising in modeling the transmission of light in the presence of fiber asymmetries. Simulations are made of the captured power in the core in the presence of fiber deformations.

Bond model of Second Harmonic Generation in Wurtzite ZnO(0002) Structures with Twin Boundaries

Hendradi Hardhienata, Ignu Priyadi, Husin Alatas, MUHAMMAD DANANG BIROWOSUTO, and Philippe Coquet

Doc ID: 356128 Received 28 Dec 2018; Accepted 02 Mar 2019; Posted 04 Mar 2019  View: PDF

Abstract: We offer a comprehensive explanation of second harmonic generation in ZnO (0002) wurtzite structures with [1$\overline{1}$00]/(1102) twin boundaries using the simplified bond hyperpolarizability model (SBHM). We show explicitly how the reflective second harmonic generation (RSHG) intensity profile for an s-incoming fundamental and s-outgoing SHG polarized light arise via superposition of the SHG dipole fields. The nonlinear fields originate from anharmonic motions of electric charges along each bond. The total dipole fields from within the ZnO bulk sum up to zero but produce a constructive SHG radiation from the twin boundary and from the unreduced surface. In addition, we compare the third order susceptibility tensor obtained from group theory and SBHM and calculate the values for the nonzero components. We found that the off resonance RSHG intensity data in diatomic wurtzite structures even with the presence of twin boundaries can be modelled using only three independent fitting parameters namely the effective bulk, reduced surface, and twin boundary SHG hyperpolarizability. The results shows that SBHM can be used to investigate impurities and surface reconstruction in ZnO as well as their contribution to nonlinear radiation with potential application of frequency conversion in nanoscale optical circuitry.

Temperature sensing of a plasmonic nanocylinder array by a polymer film containing chameleon complex

Shunsuke Murai, Motoharu Saito, Yuki Kawachiya, Satoshi Ishii, takayuki nakanishi, and Katsuhisa Tanaka

Doc ID: 357372 Received 11 Jan 2019; Accepted 02 Mar 2019; Posted 04 Mar 2019  View: PDF

Abstract: Chameleon complex, a coordination polymer containing Eu3+ and Tb3+ as emitting centers, is a temperature sensor whose photoluminescence (PL) intensity ratio between Eu3+ and Tb3+ varies with the temperature. Although the performance of this complex has been verified in a form of powders, it has not been used as a film, which is a commonly used form for various applications. In this study, we fabricate a temperature-sensing thin film by dissolving a chameleon complex powder in poly(methyl methacrylate) (PMMA). The chameleon complex retains the responsivity to temperature after the dispersion in PMMA. The PL intensity ratio changes almost linearly with the temperature in the experimental range of 20 to 40 °C. In order to further demonstrate the temperature sensing ability of the film, we deposit the film on a plasmonic periodic array of Al nanocylinders. We simultaneously use two laser lines to excite both localized surface plasmon resonances (LSPRs) in the array and the chameleon complex in the film. The LSPRs decay into heat increasing the temperature, which is then detected through the PL intensity ratio between Eu3+ and Tb3+. The temperature increase is in agreement with numerical calculations. The results show that the film is applicable for temperature sensing in a local area defined by the excitation spot.

Refractive index profile tailoring of multimode optical fibers for the spatial and spectral shaping of parametric sidebands

Katarzyna Krupa, Vincent COUDERC, Alessandro Tonello, Daniele Modotto, Alain Barthelemy, Guy Millot, and Stefan Wabnitz

Doc ID: 354890 Received 10 Dec 2018; Accepted 28 Feb 2019; Posted 28 Feb 2019  View: PDF

Abstract: We introduce the concept of spatial and spectral control of nonlinear parametric sidebands in multimode optical fibers by tailoring their linear refractive index profile. In all cases, the pump experiences Kerr self-cleaning,leading to a bell-shaped profile close to the fundamental mode. Geometric parametric instability, owing to quasi-phase-matching from the grating generated via the Kerr effect by pump self-imaging, leads to frequency multicasting of beam self-cleaning across a wide-band array of sidebands. Our experiments show that introducing a gaussian dip in the refractive index profile of a graded index fiber permits to dramatically change the spatial content of spectral sidebands into higher-order modes. This is due to the breaking of oscillation synchronism among fundamental and higher-order modes. Hencemodal-four-wave mixing prevails over geometric parametric instability as the main sideband generation mechanism. Observations agree well with theoretical predictions based on a perturbative analysis, and with full numerical solutions of the (3D + 1) nonlinear Schrödinger equation.

The energy point of view in plasmonics

Antoine Moreau, Rabih Ajib, Armel Pitelet, Rémi Pollès, emmanuel centeno, and Ziad Ajaltouni

Doc ID: 349020 Received 23 Oct 2018; Accepted 27 Feb 2019; Posted 28 Feb 2019  View: PDF

Abstract: The group velocity of a plasmonic guided mode can be written as the ratio of the flux of the Poynting to the integral of the energy density along a the profile of the mode. This theorem, linking the way energy propagates in metals to the properties of guided modes and Bloch modes in a multilayer, provides a unique physical insight in plasmonics. It allows to better understand the link between the negative permittivity of metals and the wide diversity of exotic phenomenon that occur in plasmonics -- like the slowing down of guided modes, the high effective index and the negative refraction.

The role of diffraction in the Casimir effect beyond the proximity force approximation

Vinicius Henning, Benjamin Spreng, Michael Hartmann, Gert Ingold, and Paulo Maia Neto

Doc ID: 352270 Received 19 Nov 2018; Accepted 25 Feb 2019; Posted 26 Feb 2019  View: PDF

Abstract: We derive the leading-order correction to the proximity force approximation (PFA) result for the electromagnetic Casimir interaction in the plane-sphere geometry by developing the scattering approach in the plane-wave basis. Expressing the Casimir energy as a sum over round trips between plane and sphere, we find two distinct contributions to the correction. The first one results from the variation of the Mie reflection operator, calculated within the geometric optical WKB approximation, over the narrow Fourier interval associated to specular reflection at the vicinity of the point of closest approach on the spherical surface. The second contribution, accounting for roughly 90% of the total correction, results from the modification of the geometric optical WKB Mie scattering amplitude due to diffraction. Our derivation provides a clear physical understanding of the nature of the PFA correction for spherical surfaces.

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