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Inelastic collision of self-formed chirped solitons at a laser pulse propagation in a medium with nonlinear absorption and gold nanorods

Tatiana Lysak and V. Trofimov

Doc ID: 317913 Received 18 Dec 2017; Accepted 15 Feb 2018; Posted 16 Feb 2018  View: PDF

Abstract: We investigate the self-formation of new type solitons - chirped solitons, occurring at a pico- or femtosecond pulse propagation in a medium with noble metal nanoparticles, and their inelastic collision. The solitons are formed due to the laser radiation trapping by the nanorod reshaping fronts if a positive phase-amplitude grating is induced by laser radiation. We take into account the dependence of TPA (two-photon absorption) on the nanorod aspect ratio and time-dependent nanorod aspect ratio changing due to their reshaping because of laser energy absorption.

Direct Generation of Hybrid Entangled Photon Pairs inWaveguides

Divya Bharadwaj and Krishna Thyagarajan

Doc ID: 307216 Received 15 Sep 2017; Accepted 14 Feb 2018; Posted 16 Feb 2018  View: PDF

Abstract: In this paper we propose a scheme for direct generation of hybrid spatial modal – polarization entangled photon pairs using type-II spontaneous parametric down conversion process and the electro optic effect in a domain engineered potassium titanyl phosphate (KTP) nonlinear waveguide. Such hybrid entangled states must find applications in quantum information processing using integrated photonic circuits.

Scaling relations for soliton compression and dispersive-wave generation in tapered optical fibers

Jesper Laegsgaard

Doc ID: 314804 Received 01 Dec 2017; Accepted 14 Feb 2018; Posted 16 Feb 2018  View: PDF

Abstract: Scaling relations for soliton compression in tapered optical fibersare derived and discussed. The relations allow simple and semi-accurateestimates of the compression point and output noise level, which is useful fore.g. tunable dispersive-wave generation with an agile femtosecond pump laser.

Near-resonant light propagation in an absorptive spatially anisotropic ultracold gas

Jonathan Gilbert, Colin Roberts, and Jacob Roberts

Doc ID: 315708 Received 14 Dec 2017; Accepted 14 Feb 2018; Posted 16 Feb 2018  View: PDF

Abstract: A collection of ultracold atoms has an index of refraction that varies depending on the spatial density distribution of the gas. For many confined gases commonly found in ultracold atom experiments, there can be a substantial gradient in the spatial density distribution and hence the index of refraction. In addition, these gases can have a smaller spatial extent than that of the cross section of a laser beam that illuminates them. With a sufficient gradient in density under these conditions, the resulting index variation leads to frequency-dependent focusing or defocusing of incident near-resonant light as demonstrated by the calculations in this work. Non-intuitive intensity pattern formations result within the gas from the combination of refraction and diffraction of the incident light, including focusing effects that substantially increase the intensity of the light as compared to its incident value despite the nominally absorptive nature of the gas.

Entangled multi-mode spin coherent states of trapped ions

Yusef Maleki and Alireza Maleki

Doc ID: 315874 Received 18 Dec 2017; Accepted 13 Feb 2018; Posted 16 Feb 2018  View: PDF

Abstract: Multi-mode macroscopic states consisting of asuperposition of spin coherent states that are generated in a trapped ion system are introduced. The role of various parameters that control the entanglement of the system are exposed and their effects are quantified.In particular, it is shown that the generated states exhibit different entanglement characteristics for odd and even $2nj$, where jis the spin of each mode and $n$ is the number of modes.

Design of mid-infrared nonlinear silicon-germanium waveguides for broadband/discrete-band wavelength conversion

Shiming Gao, Dongsheng Lyu, and Qiang Jin

Doc ID: 313373 Received 13 Nov 2017; Accepted 13 Feb 2018; Posted 16 Feb 2018  View: PDF

Abstract: A dispersion-engineered silicon-germanium (Si0.8Ge0.2) waveguide is designed for mid-infrared (MIR) broadband or discrete-band wavelength conversion by using its advantages of high nonlinearity and tight mode-field confinement. The dispersion of this waveguide is engineered by optimizing the waveguide geometry. The zero-dispersion wavelength is tuned to about 2 μm and the dispersion curve is flattened to reduce the dispersion slope. In MIR band, the 3-dB bandwidth for the four-wave mixing effect reaches 795 nm and the peak conversion efficiency is -25.0 dB when the pump power is 500 mW, which can support the broadband all-optical wavelength conversion for the next-generation MIR optical communications. Discrete-band wavelength conversion between the MIR 2.5-4.0 μm and telecommunication 1.30-1.72 μm are realized by using the pair of phase-matching wavelengths far away from the pump. Moreover, by choosing proper waveguide geometries, the signals in the band of 2.0-4.0 μm can be efficiently converted to the idler with the fixed wavelength of 1.55 μm, which exhibits the potential to realize the indirect detection using telecommunication-band detectors to detect MIR signals.

Wannier Functions and the Calculation of Localized Modes in One-dimensional Photonic Crystals

Maria Romano, Arianne Vellasco-Gomes, and Alexys Alfonso

Doc ID: 319538 Received 10 Jan 2018; Accepted 13 Feb 2018; Posted 16 Feb 2018  View: PDF

Abstract: The localized modes of a layered photonic crystal with a substitutional defect are calculated by expanding the magnetic-field over a truncated set of Wannier functions. Good agreement is found with the results obtained by the transfer-matrix technique. It is shown that frequencies converge very fast (slowly) as the number of unit cells (photonic bands) in the truncated set is increased.

Numerical simulation of nonlinear second harmonic wave generation by the Finite Difference Frequency Domain method

Tamás Szarvas and Zsolt Kis

Doc ID: 314888 Received 04 Dec 2017; Accepted 10 Feb 2018; Posted 12 Feb 2018  View: PDF

Abstract: Nonlinear second harmonic wave generation (SHG) has been thoroughly examined in one dimension both in analytical and numerical ways. Recently, the application of advanced domain poling techniques enabled the fabrication of two dimensional patterns of the sign of the nonlinear coefficient in certain nonlinear crystals, such as LiNbO3 and LiTaO3. This method can be used to achieve quasi phase matching in second harmonic generation (SHG) and hence amplification of the second harmonic fields in 2D. In this study we present a true vectorial numerical method for the simulation of SHG by extending the Finite Difference Frequency Domain method (FDFD). Our non-linear method (NL-FDFD) operates directly on the electromagnetic fields, uses two meshes for the simulation (for ω and 2ω fields) and handles the nonlinear coupling as an interaction between the two meshes. Final field distributions can be obtained by a small number of iteration steps. NL-FDFD can be applied in arbitrarily structured linear media with an arbitrarily structured χ(2) component both in the small conversion efficiency and the pump depleted cases.

Spectral shifts and asymmetries in mid-infrared assisted high-order harmonic generation

Balazs Major, Emeric Balogh, Katalin Kovács, Songhee Han, Bernd Schuette, Paul Weber, Marc Vrakking, Valer Tosa, Arnaud Rouzée, and Katalin Varjú

Doc ID: 312526 Received 15 Nov 2017; Accepted 09 Feb 2018; Posted 12 Feb 2018  View: PDF

Abstract: We study high-order harmonics generated by an intense multi-cycle 800 nm laser pulse in the presence of a weaker 1300 nm mid-infrared (MIR) pulse. Additionally to the previously observed effects of yield enhancement, cutoff extension and continuum generation, we report here a spectral shift of harmonic peaks controlled by the delay of the MIR pulse. We explain this effect considering the half-cycle to half-cycle behavior of the two-color field.

Intensity based measuring of the topological charge alteration by the diffraction of vortex beams from amplitude sinusoidal radial gratings

Davud Hebri, Saifollah Rasouli, and Mohammad Yeganeh

Doc ID: 314315 Received 27 Nov 2017; Accepted 07 Feb 2018; Posted 12 Feb 2018  View: PDF

Abstract: For convenient optical communications by the aid of vortex beams, topological charge alterations should be translated to the change in intensity of the output light. In this paper, we formulate and experimentally investigate diffraction of vortex beams from amplitude radial gratings having sinusoidal profile. We show that, the diffraction pattern simply renders both topological charge and twist direction of the impinging vortex beam. When, topological charge of the vortex beam and the radial grating spokes number are equal, intensity on the optical axes of the Fraunhofer pattern gets a maximum value. Otherwise, its value on the optical axes remains zero. We examined the method on different vortex beams, the measured topological charge of generated beams are in an excellent agreement with the excepted values. We show that an alteration between two vortex beams, in which one has a topological charge of equal to the grating spokes number, is translated to a binary change in intensity of the output light on the optical axes. This feature might find wide applications in optical communications.

Analytic description of four-wave mixing in silicon-on-insulator waveguides

Søren Friis, Jacob Koefoed, Kai Guo, and Karsten Rottwitt

Doc ID: 312570 Received 08 Nov 2017; Accepted 03 Feb 2018; Posted 05 Feb 2018  View: PDF

Abstract: We develop an analytic description of continuous wave four-wave mixing in silicon-on-insulator (SOI) waveguides including linear loss, two-photon absorption, and free-carrier absorption. Under the undepleted pump approximation, the pump equation decouples from the signal and idler equations and becomes a nonlinear differential equation that we solve analytically without further approximations. The signal and idler equations have no known solutions for arbitrary pump power evolution but we calculate approximate field expressions based on a Magnus expansion, which has been used to study time-ordering effects in quantum optics. Lastly, we show that the phase-matching condition changes through the waveguide and that this explains the shape of the wavelength-conversion-efficiency spectrum in SOI waveguides and why it differs from that of highly nonlinear silica fibers.

Suppression of quantum noises in coherent atom lithography through squeezing

Zeyang Liao, Anqi Zhang, Da-Wei Wang, and Rongxin Chen

Doc ID: 314955 Received 06 Dec 2017; Accepted 03 Feb 2018; Posted 05 Feb 2018  View: PDF

Abstract: The Abbe's diffraction limit restricts the resolution of an optical imaging and lithography system. Coherent Rabi oscillation is shown to be able to overcome the diffraction limit in both optical and atom lithography. In previous studies, semiclassical theory is applied where the driving field is treated as a classical light and quantum fluctuation is neglected. Here, we show that the quantum fluctuation may reduce the visibility of the superresolution pattern. However, by squeezing the photon number fluctuation we are able to significantly increase its visibility.

A multitude of photonic stopbands due tomorphological perturbation in structurally chiralmaterials

David Wang

Doc ID: 314407 Received 01 Dec 2017; Accepted 02 Feb 2018; Posted 09 Feb 2018  View: PDF

Abstract: The periodic morphology of a structurally chiral material(SCM) can be perturbed periodically in order to displaya multitude of photonic stopbands similar to thecircular Bragg phenomenon display by an unperturbedSCM. Perturbation can be continuous or disrupted inphase; when perturbation is phase–disruptive, moreand tighter photonic stopbands occur in the defectmode.

Effects of structure parameters on high-order diffraction suppression of quasi-periodic gratings

Tanchao Pu, Ziwei Liu, Lina Shi, Guanya Wang, Jiebin Niu, and Changqing Xie

Doc ID: 313951 Received 22 Nov 2017; Accepted 02 Feb 2018; Posted 02 Feb 2018  View: PDF

Abstract: We introduce the design and implementation of quasi-periodic gratings for high-order diffraction suppression. The effects of hole shape (circle, rectangle, diamond and hexagon) and location distribution on the diffraction properties are investigated. We theoretically, and experimentally demonstrate that the quasi-triangle array with hexagonal holes is highly advantageous for suppressing high-order diffractions. Additionally, the quasi-periodic location distribution also helps to suppress high order diffraction. Remarkably, the analytical results show that the 2nd, 3rd, 4th, 5th and 6th order diffractions can be completely suppressed for the special structure parameters of the quasi-periodic gratings, and the 7th order diffraction intensity is as low as 2.2×10-⁵ of the 1st order. The experimental results show there exists only 0th and ±1st order diffraction peaks along ξ axis, which qualitatively agreed with the theoretical and numerical predictions. Comparing to the traditional 1:1 grating, the quasi-triangle array with hexagonal holes can effectively suppress high-order diffractions. We except the quasi-periodic gratings may find significant applications in high-accuracy wide spectral measurement ranging from the far infrared to the x-ray regions.

Resonance enhancement of Faraday rotation in double-periodic gyromagnetic layers analyzed by the method of integral functionals

Vladimir Yachin, Tatiana Zinenko, and Sergey Mizrakhy

Doc ID: 305112 Received 21 Aug 2017; Accepted 31 Jan 2018; Posted 01 Feb 2018  View: PDF

Abstract: Extraordinary enhancement of the Faraday rotation (over 1000 times) for a PEC-like layer with square-shaped apertures filled with YIG and its smaller enhancement (17 times) for YIG layer perforated with square-shaped air apertures are revealed at the grating-mode resonance frequencies. At the same time the periodic perforation of a PEC-like layer with C-shaped apertures filled with YIG does not influence the Faraday effect. For our theoretical study, we develop the full-wave solution of three-dimensional problem of the plane wave scattering from a double–periodic gyromagnetic layer obtained by the Method of Integral Functionals. The method is based on the 3-D volume integral equations for the electric and magnetic polarization currents on the periodic layer

Light masks for atom diffraction created from twisted beams with a Gaussian intensity envelope

Vassilis Lembessis

Doc ID: 313685 Received 20 Nov 2017; Accepted 31 Jan 2018; Posted 01 Feb 2018  View: PDF

Abstract: We show how we can construct light masks from twisted beams with Gaussian envelopes. These masks can be used for the diffraction of cold atoms and lead to the generation of atom vortex beams. We show that these type of masks are more efficient in the generation of twisted atom beams than the corresponding light masks created with Gaussian-Laguerre beams.

Interferometric control of the ellipticity of a femtosecond extreme ultraviolet source

Vincent Gruson, Sebastien Weber, Lou Barreau, Jean-Francois Hergott, Fabien Lepetit, T. Auguste, Bertrand Carre, Pascal Salieres, and Thierry Ruchon

Doc ID: 312527 Received 01 Nov 2017; Accepted 30 Jan 2018; Posted 30 Jan 2018  View: PDF

Abstract: A method for ultrafast ellipticity modulation of femtosecond intense lasers is introduced and demonstrated. It is based on the coherent superimposition of two linearly polarized visible/infrared (Vis-IR) laser beams with orthogonal polarizations. Tuning their delay by a quarter of the wavelength, i.e. a few hundreds nanometers, achieves the same function as the rotation of a quarter wave plate by 45º, switching the polarization from linear to circular. We demonstrate the portability of this method to high intensity processes by upconverting a femtosecond Vis-IR laser beam to the Extreme UltraViolet (EUV) spectral ranges through High Harmonic Generation (HHG). These results opens the way to lock-in detection of small absorption chiroptical signals in the EUV spectral range, including pump probe signals.

Multiphoton Knill-Laflamme-Milburn states generated by nonlinear optics

Cai-Peng Shen, Xiao-Fei Gu, Qi Guo, Xiao-Yu Zhu, Shi-Lei Su, and Erjun Liang

Doc ID: 312838 Received 06 Nov 2017; Accepted 29 Jan 2018; Posted 30 Jan 2018  View: PDF

Abstract: Knill-Laflamme-Milburn (KLM) entangled state proposed in Ref.~[Knill \emph{et al.}, Nature \textbf{409}, 46 (2001)] has unique advantages for linear optics quantum information processing tasks since it is able to decrease the error rate. In this paper, we propose scalable schemes to generate the multi-qubit KLM entangled states with single-photon resources and weak cross-Kerr nonlinearity theoretically. We first construct the two- and three-qubit KLM states, through which the multi-qubit KLM state is generated. For the schemes using weak cross-Kerr nonlinearity, P homodyne measurement has higher success rate than X homodyne measurement but narrow applications since $|\alpha e^{i\theta}\rangle$ and $|\alpha e^{-i\theta}\rangle$ are distinguished from each other, which is undesirable for most of the entanglement generation schemes. To avoid this disadvantage, Ref.~[Jin \emph{et al}., Phys. Rev. A \textbf{75}, 054302 (2007)] introduces the coherent superposition state~(CSS) $c(|\alpha\rangle+|-\alpha\rangle)$ to generate Greenberger-Horne-Zeilinger(GHZ) state but with a rapid oscillation term and needs to be ignored. Through designing the optical path uniquely and choosing the phase of cross-Kerr nonlinearity suitably, our P homodyne measurement and CSS probe mode based schemes to generate KLM state avoid the needless terms. The present scalable schemes have high mission success rates and utilization ratios of the single photon resources, and may find potential applications in the future with the further development of the nonlinear optics.

Tunable circular dichroism created by surface plasmons in Bi-layer twisted tetramer nanostructure arrays

Mingdi Zhang, Lu Qieni, and Hairong Zheng

Doc ID: 313943 Received 20 Nov 2017; Accepted 28 Jan 2018; Posted 30 Jan 2018  View: PDF

Abstract: Optical chirality of Bi-layer twisted tetramer nanostructure are investigated theoretically. The difference of transmission spectra under left-handed circularly polarized (LCP) and right-handed circularly polarized (RCP) extinction produces very large optical chirality which reaches 91% due to the different plasmonic hybridization patterns between the nanorods. This structure also allows the generation of a perfectly right/left-handed system at certain mode because this mode nearly vanish under illumination of the left/right-handed light. Moreover, tunable optical chirality is achieved, which is found to be easily affected by geometric parameters such as the separation distance between the two layers, the length of the nanorod, and the arrangement of nanorods. We consider the charge vibrations of four nanorods at the same layer as an equivalent dipole and explain the dependence of the circular dichroic spectrum on the geometric parameters. This work suggests that the Bi-layer twisted tetramer nanostructure can be considered a potential candidate for achieving giant optical chirality applicable in the field of polarization polarizer and biological detection.

Tunable Multiband Metasurfaces Based on Plasmonic Core-Shell Nano-Particles

Soheil Farazi, Farhad Namin, and Douglas Werner

Doc ID: 313453 Received 14 Nov 2017; Accepted 27 Jan 2018; Posted 30 Jan 2018  View: PDF

Abstract: Metasurfaces which can act as wavelength selective surfaces with multiple pass-bands or stop-bands have numerous applications including modulating electromagnetic (EM) radiation, and transmitarray or reflectarray antennas. In this paper, the feasibility of such metasurfaces, using plasmonic core-shell nano-particles (NPs) has been studied. By analyzing the polarizability of such particles, it is shown that they are capable of possessing two plasmonic resonances which can be tuned by manipulating the core-shell properties. In addition, a pass-band exists in between these two bands. The surface susceptibilities of the metasurface are determined using “sparse approximation formulas”. Analytical scattering coefficients were compared and found to agree with numerical results obtained using full-wave simulation.

Dynamics of a green high-power tunable external-cavity broad-area GaN diode laser

Mingjun Chi, Ole Jensen, Anders Hansen, and Paul Petersen

Doc ID: 315853 Received 21 Dec 2017; Accepted 26 Jan 2018; Posted 30 Jan 2018  View: PDF

Abstract: Although external-cavity feedback with a grating is widely used to achieve tunable high-power narrow-linewidth broad-area diode laser (BAL) system, the dynamics of such system is seldom studied. In this paper, the temporal dynamics of a tunable high-power green external-cavity diode laser system based on a GaN BAL and Littrow external-cavity is investigated experimentally. The regular pulse package oscillation (PPO) is observed just above the threshold. The oscillating period of the pulse package decreases with the increasing injected current. As the current increases further, the pulse package oscillates irregularly, and finally changes to a chaotic state. The PPO is observed, for the first time to our knowledge, in a BAL with a long external-cavity grating feedback.

Enhanced quadratic nonlinearity with parametric amplifications

Wenju Gu, Zhen Yi, lihui Sun, and Yan Yan

Doc ID: 312978 Received 08 Nov 2017; Accepted 26 Jan 2018; Posted 30 Jan 2018  View: PDF

Abstract: The realization of quantum nonlinearity in quadratic optomechanics including optical and mechanical nonlinearity at the single-photon level is crucial to explore the extraordinary quantum features. Here we investigate an exponential enhancement of quadratic optomechanical interaction via parametric amplifications. The parametric process can form an in-phase amplified quadrature, and the coupling rate to the in-phase quadrature will be exponentially increased even to the single-photon strong-coupling regime. Concretely, to achieve the optical nonlinearity mediated by the quadratic optomechanical interaction, we can employ a mechanical parametric process, and the in-phase mechanical quadrature can strongly couple to the cavity mode, leading to an enhanced optical nonlinearity such as photon blockade. Similarly, via employing the optical parametric process, the in-phase optical quadrature can also effectively mediate the quadratic interaction, leading to an enhanced mechanical nonlinearity such as mechanical squeezing, bi-excitation exchange interaction and feasibility of QND detection of mechanical motion. However, parametric process can also enlarge the noise and a squeezing vacuum with the phase matching condition should be introduced to suppress the noise.

Plasmonic Cloaking for Irregular Inclusions Using an Epsilon-Near-Zero Region Comprised of Graphene-Silica Stack

Ramin Emadi, Abolghasem Zeidaabadi Nezhad, and Reza Safian

Doc ID: 308147 Received 28 Sep 2017; Accepted 25 Jan 2018; Posted 26 Jan 2018  View: PDF

Abstract: A reconfigurable epsilon-near-zero (ENZ) region comprised of alternative layers of a graphene nano-ribbon (GNR)-silica stack is designed for realizing a plasmonic cloak at 1.55 um. The ENZ point is tuned via applying an electrostatic bias to the GNRs for a certain structure. The ENZ region's boundaries are sealed by Au material with optimized thicknesses to avoid the energy loss from them. This cloak is robust against the inclusion's shape that to show this fact an arbitrary shape is chosen for the embedded inclusion in the ENZ region. Moreover, by selecting a sufficiently large length for the ENZ region, such a cloak provides an exceptionally large bandwidth because graphene possesses a very high carrier mobility. As a result, this platform is superior in comparison to other platforms made of thin film oxides for realizing an ENZ region. Previous plasmonic cloaks in the literature have some drawbacks including: a narrow bandwidth, the sensitivity to the inclusion's shape, and a non-reconfigurable operation. Finally, the robustness of the plasmonic cloak with respect to oblique incidence is investigated and an acceptable performance is achieved, indicating that this plasmonic cloak has not the fundamental limitations of previous plasmonic cloaks in the literature.

Spatio-spectral structures in high harmonic generation driven by tightly focused high repetition rate lasers

Aura Gonzalez, gaëtan jargot, Philippe Rigaud, Loïc Lavenu, Florent Guichard, Antoine Comby, Thierry Auguste, Olivier Sublemontier Sublemontier, Michel Bougeard, Yoann Zaouter, Patrick Georges, Marc Hanna, and Thierry Ruchon

Doc ID: 310222 Received 30 Oct 2017; Accepted 25 Jan 2018; Posted 25 Jan 2018  View: PDF

Abstract: We investigate the spatio-spectral properties of extreme ultraviolet high-harmonic radiation driven by high repetition rate femtosecond laser systems. In the spatio-spectral domain, ring-shaped structures at each harmonic order associated with long-trajectories electron are found to form arrow-shaped structures at the cutoff. These structures are observed with two different laser systems: an optical parametric chirped-pulse amplifier system at a central wavelength of 1.55 µm and 125 kHz repetition rate, and a temporally compressed femtosecond ytterbium fiber amplifier at 1.03 µm wavelength and 100 kHz repetition rate. As recently pointed out, the observed structures are well explained by considering the space-time atomic dipole-induced phase for short and long electron trajectories in the generation plane. The tighter focusing geometry and longer wavelength associated with these emerging driving laser systems increases the ring-like divergence and spectral broadening for high harmonics. Cutoff energies and photon fluxes obtained in argon and neon are also reported. Overall, these results shed new light on the properties of XUV radiation driven by these recently developed high average power laser systems, paving the way to high photon-flux XUV beamlines.

Asymmetric optical transmission through silver film with a hyperbolic air hole

Weilong She, xin li, and Wanguo Liu

Doc ID: 308854 Received 27 Oct 2017; Accepted 25 Jan 2018; Posted 30 Jan 2018  View: PDF

Abstract: Asymmetric optical transmission is one of the most important functionality in modern optical communication system. However, it has been impeded due to the low transmission ratio of forward transmittance to backward one. Here, we propose asymmetric optical transmission through a silver film with a hyperbolic air hole (HAH), of which the ratio is as high as 24.5 at a proper wavelength. The mechanism is the fact that the steep inner wall of the silver film HAH can inhibit guided mode reflection. This kind of silver film HAH is expected to have the potential served as asymmetric optical transmission device.

High-order harmonic generation in disordered semiconductors

Gianfranco Orlando, Chang-Ming Wang, Tak-San Ho, and Shih-I Chu

Doc ID: 314515 Received 30 Nov 2017; Accepted 24 Jan 2018; Posted 25 Jan 2018  View: PDF

Abstract: We analyze high order harmonic generation in a disordered semiconductor. The semiconductor is simu- lated through a one dimensional two band tight-binding Hamiltonian. We neglect both Coulomb interac- tion between electrons and electron-phonon interactions. The disorder is modeled using a site diagonal potential in the context of the Anderson model of disorder. We show that, when a moderate amount of disorder is present in the semiconductor, the resultant high-order harmonics spectra present clean peaks corresponding to odd harmonics of the frequency of the driving laser field. Our results suggest that dis- order is a probable cause for the well-resolved HHG spectra observed in experiments.

Constraints on down-conversion in atomically-thick films

Loris Marini, Luke Helt, Yuerui Lu, Benjamin Eggleton, and Stefano Palomba

Doc ID: 313660 Received 20 Nov 2017; Accepted 23 Jan 2018; Posted 25 Jan 2018  View: PDF

Abstract: Spontaneous parametric downconversion (SPDC) has been predicted in atomically-thick crystals, though not yet observed. In this work we uncover physical and experimental constraints of photon-pair generation in such planar nonlinear films with a free-space illumination/collection geometry. We measure the material nonlinear response of mono-layer tungsten diselenide (WSe2) via second harmonic generation (SHG) and subsequently calculate the expected SPDC efficiency from appropriate quantum-classical relations. Energy and momentum conservation shape the wavevectors of photon pairs in free-space and allow us to calculate the loss and coincidence-to-accidental ratio (CAR) in various configurations. This work improves the understanding of the nonlinear quantum optical potential of these crystals, guides their experimental validation, and provides a performance benchmark for these ultra-thin materials.

Multi-Color Plasmonic Probes for Improvement of Scanning Near-Field Optical Microscopy

Hesam Heydarian, Afsaneh Shahmansouri, Payam Yazdanfar, and Bizhan Rashidian

Doc ID: 312327 Received 30 Oct 2017; Accepted 22 Jan 2018; Posted 25 Jan 2018  View: PDF

Abstract: Design and modeling of a class of Scanning Near-field Optical Microscope (SNOM) probe for improving the performance is reported. The basic idea is to generate more than one hot spot with well-known spatial distribution. This not only enables one to calibrate out many sorts of errors in conventional SNOM, but also results in the increase in the speed of imaging. We utilize plasmonic nano-color sorter structures to design aperture probes that create two spatially distinct hot spots. The method of moment analysis technique is employed to tune the probe for operation at standard Ar-ion laser wavelengths (457.9 and 514.5 nm).

Adjusting third-order nonlinear properties in silicon triply-resonant nanobeam cavities

Xin CUI, Weiwei Zhang, Samuel Serna Otálvaro, Carlos Alonso Ramos, Laurent Vivien, Jian-Jun He, Eric Cassan, and Delphine Marris-Morini

Doc ID: 308806 Received 10 Oct 2017; Accepted 28 Dec 2017; Posted 26 Jan 2018  View: PDF

Abstract: We propose the use of a triply resonant silicon photonic structures, based on a set of three coupled silicon nanobeam cavities, to engineer third order nonlinearities. We show that a judicious selection of the opto-geometrical parameters allows a nearly independent tuning of the linear and nonlinear properties of the system. We demonstrate that longitudinally shifting the central cavity weakly affects the system nonlinear properties while strongly changes its resonance wavelengths. On the contrary, longitudinally shifting one of the side cavities leads to a significant variation of the self-phase modulation, cross-phase modulation, and four-wave-mixing nonlinear overlaps while the linear properties of the three cavity photonic molecule are then only moderately tuned. This geometrical control of the nonlinear properties of photonic molecules opens new degrees of freedom for the realization of small footprint and efficient optical switching and frequency conversion devices.

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