Showing papers on "Kerr effect published in 2016"
20 Aug 2016
TL;DR: In this article, the combination of nonlinear and integrated photonics enables Kerr frequency comb generation in stable chip-based micro-resonators, where optical parametric oscillations are achieved with milliwatt-level pump threshold powers, which paves the way for on-chip pumped comb generation.
Abstract: The combination of nonlinear and integrated photonics enables Kerr frequency comb generation in stable chip-based micro-resonators. Such a comb system will revolutionize applications, including multi-wavelength lasers, metrology, and spectroscopy. Aluminum gallium arsenide (AlGaAs) exhibits very high material nonlinearity and low nonlinear loss. However, difficulties in device processing and low device effective nonlinearity made Kerr frequency comb generation elusive. Here, we demonstrate AlGaAs-on-insulator as a nonlinear platform at telecom wavelengths with an ultra-high device nonlinearity. We show high-quality-factor (Q>105) micro-resonators where optical parametric oscillations are achieved with milliwatt-level pump threshold powers, which paves the way for on-chip pumped comb generation.
208 citations
TL;DR: It is demonstrated that attosecond metrology extends the resolution to petahertz frequencies of visible light and Quantitative determination of dissipation within a signal manipulation cycle of only a few femtoseconds duration reveals the feasibility of dielectric optical switching at clock rates above 100 teraherz.
Abstract: Petahertz-bandwidth metrology is demonstrated in the measurement of nonlinear polarization in silica. Recent years have seen an increased interest in light–matter interactions in solid-state systems at ultrafast timescales. Ferenc Krausz and colleagues study the nonlinear polarization of silica in response to intense infrared light fields with a spectroscopy method in the attosecond time range. The method makes it possible to unravel details of the reversible and irreversible energy exchange between infrared light and electrons and points to the feasibility of using light-based switching techniques for signal processing in solid-state devices above 100 terahertz. Electric-field-induced charge separation (polarization) is the most fundamental manifestation of the interaction of light with matter and a phenomenon of great technological relevance. Nonlinear optical polarization1,2 produces coherent radiation in spectral ranges inaccessible by lasers and constitutes the key to ultimate-speed signal manipulation. Terahertz techniques3,4,5,6,7,8 have provided experimental access to this important observable up to frequencies of several terahertz9,10,11,12,13. Here we demonstrate that attosecond metrology14 extends the resolution to petahertz frequencies of visible light. Attosecond polarization spectroscopy allows measurement of the response of the electronic system of silica to strong (more than one volt per angstrom) few-cycle optical (about 750 nanometres) fields. Our proof-of-concept study provides time-resolved insight into the attosecond nonlinear polarization and the light–matter energy transfer dynamics behind the optical Kerr effect and multi-photon absorption. Timing the nonlinear polarization relative to the driving laser electric field with sub-30-attosecond accuracy yields direct quantitative access to both the reversible and irreversible energy exchange between visible–infrared light and electrons. Quantitative determination of dissipation within a signal manipulation cycle of only a few femtoseconds duration (by measurement and ab initio calculation) reveals the feasibility of dielectric optical switching at clock rates above 100 terahertz. The observed sub-femtosecond rise of energy transfer from the field to the material (for a peak electric field strength exceeding 2.5 volts per angstrom) in turn indicates the viability of petahertz-bandwidth metrology with a solid-state device.
197 citations
TL;DR: In this paper, the magnon Kerr effect in a cavity-magnon system where magnons in a small yttrium iron garnet (YIG) sphere are strongly but dispersively coupled to the photons in a three-dimensional cavity was demonstrated.
Abstract: We experimentally demonstrate magnon Kerr effect in a cavity-magnon system where magnons in a small yttrium iron garnet (YIG) sphere are strongly but dispersively coupled to the photons in a three-dimensional cavity. When the YIG sphere is pumped to generate considerable magnons, the Kerr effect yields a perceptible shift of the cavity's central frequency and more appreciable shifts of the magnon modes. We derive an analytical relation between the magnon frequency shift and the drive power for the uniformly magnetized YIG sphere and find that it agrees very well with the experimental results of the Kittel mode. Our study paves the way to explore nonlinear effects in the cavity-magnon system.
187 citations
20 May 2016
TL;DR: In this paper, an all-optical, all-fiber optical modulator with a Mach-Zehnder interferometer structure was proposed. But it is based on the idea of converting optically induced phase modulation in the graphene-cladded arm of the inter-ferometer to intensity modulation at the output of the IC.
Abstract: Graphene-based optical modulators have recently attracted much attention because of their characteristic ultrafast and broadband response. Their modulation depth (MD) and overall transmittance (OT), however, are often limited by optical loss arising from interband transitions. We report here an all-optical, all-fiber optical modulator with a Mach–Zehnder interferometer structure that has significantly higher MD and OT than graphene-based loss modulators. It is based on the idea of converting optically induced phase modulation in the graphene-cladded arm of the interferometer to intensity modulation at the output of the interferometer. The device has the potential to be integrable into a photonic system in real applications.
164 citations
TL;DR: This paper characterize the thermal tuning of a coherent Kerr frequency comb generated from an on-chip silicon nitride microring, and the time-dependent thermal response of the microheater based tuning scheme is characterized.
Abstract: Microresonator based Kerr frequency comb generation has many attractive features, including ultrabroad spectra, chip-level integration, and low power consumption. Achieving precise tuning control over the comb frequencies will be important for a number of practical applications, but has been little explored for microresonator combs. In this paper, we characterize the thermal tuning of a coherent Kerr frequency comb generated from an on-chip silicon nitride microring. When the microring temperature is changed by ~70 °C with an integrated microheater, the line spacing and center frequency of the comb are tuned respectively by −253 MHz (−3.57 MHz/°C) and by −175 GHz (−2.63 GHz/°C); the latter constitutes 75% of the comb line spacing. From these results we obtain a shift of 25 GHz (362.07 MHz/°C) in the comb carrier-envelope offset frequency. Numerical simulations are performed by taking into account the thermo-optic effects in the waveguide core and cladding. The temperature variation of the comb line spacing predicted from simulations is close to that observed in experiments. The time-dependent thermal response of the microheater based tuning scheme is characterized; time constants of 30.9 μs and 0.71ms are observed.
158 citations
TL;DR: In this article, it was shown that methylammonium lead iodide, prepared by solution processing at temperatures not exceeding 100 °C, exhibits a highly nonlinear intensity-dependent refractive index due to changes in the free-carrier concentration and for femtosecond excitation at higher intensities undergo saturation that can be attributed to the Pauli blocking effect.
Abstract: With solar conversion efficiencies surpassing 20%, organometallic perovskites show tremendous promise for solar cell technology. Their high brightness has also led to demonstrations of lasing and power-efficient electroluminescence. Here we show that thin films of methylammonium lead iodide, prepared by solution processing at temperatures not exceeding 100 °C, exhibit a highly nonlinear intensity-dependent refractive index due to changes in the free-carrier concentration and for femtosecond excitation at higher intensities undergo saturation that can be attributed to the Pauli blocking effect. Nonlinear refractive index and nonlinear absorption coefficients were obtained by the Z-scan technique, performed simultaneously in open- and closed-aperture configurations. Both nanosecond- and femtosecond-pulsed lasers at multiple wavelengths were used in order to distinguish between the mechanisms inducing the nonlinearities. The magnitude and sign of the nonlinear refractive index n2 were determined. For resonan...
125 citations
TL;DR: A novel concept of magnetoplasmonic sensor with ultranarrow resonances and high sensitivity based on the combination of a specially designed one-dimensional photonic crystal and a ferromagnetic layer to realize ultralong-range propagating magnetoplasmons and to detect alteration of the environment refractive index via observation of the modifications in the Transversal Magnetooptical Kerr Effect spectrum.
Abstract: Currently, sensors invade into our everyday life to bring higher life standards, excellent medical diagnostic and efficient security. Plasmonic biosensors demonstrate an outstanding performance ranking themselves among best candidates for different applications. However, their sensitivity is still limited that prevents further expansion. Here we present a novel concept of magnetoplasmonic sensor with ultranarrow resonances and high sensitivity. Our approach is based on the combination of a specially designed one-dimensional photonic crystal and a ferromagnetic layer to realize ultralong-range propagating magnetoplasmons and to detect alteration of the environment refractive index via observation of the modifications in the Transversal Magnetooptical Kerr Effect spectrum. The fabrication of such a structure is relatively easy in comparison with e.g. nanopatterned samples. The fabricated heterostructure shows extremely sharp (angular width of 0.06°) surface plasmon resonance and even sharper magnetoplasmonic resonance (angular width is 0.02°). It corresponds to the propagation length as large as 106 μm which is record for magnetoplasmons and promising for magneto-optical interferometry and plasmonic circuitry as well as magnetic field sensing. The magnitude of the Kerr effect of 11% is achieved which allows for detection limit of 1∙10−6. The prospects of further increase of the sensitivity of this approach are discussed.
114 citations
TL;DR: From measurements, a negative nonlinear refractive index for monolayer graphene is estimated, in contradiction to previously reported values, which leads to compare experimental measurements obtained by the OHD-OKE and the Z-scan method with theoretical and experimental values found in the literature and discuss the discrepancies.
Abstract: By means of the ultrafast optical Kerr effect method coupled to optical heterodyne detection (OHD-OKE), we characterize the third-order nonlinear response of graphene and compare it to experimental values obtained by the Z-scan method on the same samples. From these measurements, we estimate a negative nonlinear refractive index for monolayer graphene, n2=−1.1×10−13 m2/W. This is in contradiction to previously reported values, which leads us to compare our experimental measurements obtained by the OHD-OKE and the Z-scan method with theoretical and experimental values found in the literature and to discuss the discrepancies, taking into account parameters such as doping.
88 citations
TL;DR: THz conductivity measurements point towards the influence of lattice disorder in amorphous CoFeB as the driving force for enhanced spin-lattice scattering, significantly faster than optical laser-induced demagnetization.
Abstract: We use single-cycle THz fields and the femtosecond magneto-optical Kerr effect to, respectively, excite and probe the magnetization dynamics in two thin-film ferromagnets with different lattice structures: crystalline Fe and amorphous CoFeB. We observe Landau-Lifshitz-torque magnetization dynamics of comparable magnitude in both systems, but only the amorphous sample shows ultrafast demagnetization caused by the spin-lattice depolarization of the THz-induced ultrafast spin current. Quantitative modeling shows that such spin-lattice scattering events occur on similar time scales than the conventional spin conserving electronic scattering (∼30 fs). This is significantly faster than optical laser-induced demagnetization. THz conductivity measurements point towards the influence of lattice disorder in amorphous CoFeB as the driving force for enhanced spin-lattice scattering.
84 citations
TL;DR: In this article, the gate control of the magneto-optic Kerr effect (MOKE) in bilayer MnPSe_{3} using first-principles calculations was demonstrated.
Abstract: Using symmetry arguments and a tight-binding model, we show that for layered collinear antiferromagnets, magneto-optic effects can be generated and manipulated by controlling crystal symmetries through a gate voltage. This provides a promising route for electric field manipulation of the magneto-optic effects without modifying the underlying magnetic structure. We further demonstrate the gate control of the magneto-optic Kerr effect (MOKE) in bilayer MnPSe_{3} using first-principles calculations. The field-induced inversion symmetry breaking effect leads to gate-controllable MOKE, whose direction of rotation can be switched by the reversal of the gate voltage.
78 citations
TL;DR: In this article, a theoretical analysis of the non-classical behavior of the Kerr optical frequency combs is presented, where the authors use quantum Langevin equations to provide a theoretical understanding of nonclassical behaviour of these combs when pumped below and above threshold.
Abstract: The dynamical behavior of Kerr optical frequency combs is very well understood today from the perspective of the semiclassical approximation. These combs are obtained by pumping an ultrahigh-$Q$ whispering-gallery mode resonator with a continuous-wave laser. The long-lifetime photons are trapped within the toruslike eigenmodes of the resonator, where they interact nonlinearly via the Kerr effect. In this article, we use quantum Langevin equations to provide a theoretical understanding of the nonclassical behavior of these combs when pumped below and above threshold. In the configuration where the system is under threshold, the pump field is the unique oscillating mode inside the resonator, and it triggers the phenomenon of spontaneous four-wave mixing, where two photons from the pump are symmetrically up- and down-converted in the Fourier domain. This phenomenon, also referred to as parametric fluorescence, can only be understood and analyzed from a fully quantum perspective as a consequence of the coupling between the field of the central (pumped) mode and the vacuum fluctuations of the various side modes. We analytically calculate the power spectra of the spontaneous emission noise, and we show that these spectra can be either single- or double-peaked depending on the value of the laser frequency, chromatic dispersion, pump power, and spectral distance between the central mode and the side mode of interest. We also calculate as well the overall spontaneous noise power per side mode and propose simplified analytical expressions for some particular cases. In the configuration where the system is pumped above threshold, we investigate the phenomena of quantum correlations and multimode squeezed states of light that can occur in the Kerr frequency combs originating from stimulated four-wave mixing. We show that for all stationary spatiotemporal patterns, the side modes that are symmetrical relative to the pumped mode in the frequency domain display quantum correlations that can lead to squeezed states of light under some optimal conditions that are analytically determined. These quantum correlations can persist regardless the dynamical state of the system (rolls or solitons), regardless of the spectral extension of the comb (number side modes) and regardless of the dispersion regime (normal or anomalous). We also explicitly determine the phase quadratures leading to photon entanglement and analytically calculate their quantum-noise spectra. For both the below- and above-threshold cases, we study with particular emphasis the two principal architectures for Kerr comb generation, namely the add-through and add-drop configurations. It is found that regardless of the configuration, an essential parameter is the ratio between out-coupling and total losses, which plays a key role as it directly determines the efficiency of the detected fluorescence or squeezing spectra. We finally discuss the relevance of Kerr combs for quantum information systems at optical telecommunication wavelengths below and above threshold.
SIDI1
TL;DR: In this paper, a novel approach to design an all optical 4 × 2 encoder is proposed by employing Kerr effect in 2D square lattice of silicon rods in photonic crystals.
TL;DR: In this paper, the cross-Kerr effect on an optomechanical system driven by two-tone fields was studied and it was shown that a bistable behavior of the mean photon number in the cavity becomes more robust against the fluctuations of the frequency detuning between the cavity mode and the control field.
Abstract: We study the cross-Kerr (CK) effect on an optomechanical system driven by two-tone fields. We show that in the presence of the CK effect, a bistable behavior of the mean photon number in the cavity becomes more robust against the fluctuations of the frequency detuning between the cavity mode and the control field. The bistability can also be turned into a tristability within the experimentally accessible range of the system parameters. Also, we find that the symmetric profile of the optomechanically induced transparency is broken and the zero-absorption point is shifted in the presence of the CK effect. This shift can be used to measure the strength of the CK effect and the asymmetric absorption profiles can be employed to engineer a high quality factor of the cavity.
TL;DR: In this article, the current-induced spin-orbit torques (SOTs) in the perpendicularly magnetized Ir22Mn78/Co20Fe60B20/MgO structures are investigated.
Abstract: The current-induced spin-orbit torques (SOTs) in the perpendicularly magnetized Ir22Mn78/Co20Fe60B20/MgO structures are investigated. The damping- and field-like torques are characterized using a harmonic technique. The spin Hall angle of Ir22Mn78 is determined to be θSHE = +0.057 ± 0.002. The SOT-driven magnetization switching is also demonstrated with the assistance of an external in-plane field. Furthermore, the magneto-optical Kerr effect imaging experiments show that the magnetization switching is realized through domain nucleation and domain wall motion. These results may promise potential practical applications in high-performance SOT devices based on the antiferromagnetic materials.
TL;DR: In this article, the terahertz magnetic field induces a large change in spontaneous magnetization and the frequency of the antiferromagnetic resonance decreases in proportion to the square of the magnetization change.
Abstract: We report on the nonlinear magnetization dynamics of a HoFeO3 crystal induced by a strong terahertz magnetic field resonantly enhanced with a split ring resonator and measured with magneto-optical Kerr effect microscopy. The terahertz magnetic field induces a large change (~40%) in the spontaneous magnetization. The frequency of the antiferromagnetic resonance decreases in proportion to the square of the magnetization change. A modified Landau–Lifshitz–Gilbert equation with a phenomenological nonlinear damping term quantitatively reproduced the nonlinear dynamics.
TL;DR: In this article, the anomalous Hall effect and magneto-optical Kerr effect were combined in crossbar geometry for a current-induced magnetization reversal in Pt/[Co/Ni]3/Al multilayers.
Abstract: We experimentally investigate the current-induced magnetization reversal in Pt/[Co/Ni]3/Al multilayers combining the anomalous Hall effect and magneto-optical Kerr effect techniques in crossbar geometry. The magnetization reversal occurs through nucleation and propagation of a domain of opposite polarity for a current density of the order of 3 × 1011 A/m2. In these experiments, we demonstrate a full control of each stage: (i) the Orsted field controls the domain nucleation and (ii) domain-wall propagation occurs by spin torque from the Pt spin Hall effect. This scenario requires an in-plane magnetic field to tune the domain wall center orientation along the current for efficient domain wall propagation. Indeed, as nucleated, domain walls are chiral and Neel-like due to the interfacial Dzyaloshinskii-Moriya interaction.
TL;DR: This article reports the simultaneous excitation of these three fundamental interactions in mm-size ultra-high Q whispering gallery mode resonators under continuous wave pumping and proposes a unified theory based on a spatiotemporal formalism for the understanding of this phenomenology.
Abstract: Universal nonlinear scattering processes such as Brillouin, Raman, and Kerr effects are fundamental light-matter interactions of particular theoretical and experimental importance. They originate from the interaction of a laser field with an optical medium at the lattice, molecular, and electronic scale, respectively. These nonlinear effects are generally observed and analyzed separately, because they do not often occur concomitantly. In this article, we report the simultaneous excitation of these three fundamental interactions in mm-size ultra-high Q whispering gallery mode resonators under continuous wave pumping. Universal nonlinear scattering is demonstrated in barium fluoride and strontium fluoride, separately. We further propose a unified theory based on a spatiotemporal formalism for the understanding of this phenomenology.
TL;DR: In this article, the authors discuss the physics of Kerr comb generation in the normal dispersion regime and review recent experimental advances, and discuss the potential advantages and future directions of normal-dispersion combs.
Abstract: Abstract Optical microresonator-based Kerr frequency comb generation has developed into a hot research area in the past decade. Microresonator combs are promising for portable applications due to their potential for chip-level integration and low power consumption. According to the group velocity dispersion of the microresonator employed, research in this field may be classified into two categories: the anomalous dispersion regime and the normal dispersion regime. In this paper, we discuss the physics of Kerr comb generation in the normal dispersion regime and review recent experimental advances. The potential advantages and future directions of normal dispersion combs are also discussed.
13 Apr 2016
TL;DR: In this paper, strong third order nonlinear optical properties exhibited by WS2 layers are presented and optical Kerr effect is identified as the dominant physical mechanism responsible for these third order optical nonlinearities.
Abstract: In this work, strong third order nonlinear optical properties exhibited by WS2 layers are presented. Optical Kerr effect was identified as the dominant physical mechanism responsible for these third order optical nonlinearities. An extraordinary nonlinear refractive index together with an important contribution of a saturated absorptive response was observed to depend on the atomic layer stacking. Comparative experiments performed in mono- and few-layer samples of WS2 revealed that this material is potentially capable of modulating nonlinear optical processes by selective near resonant induced birefringence. In conclusion, we envision applications for developing all-optical bidimensional nonlinear optical devices.
TL;DR: A simple setup suitable for excitation and time resolved measurements of high frequency magnetoelastic waves, which is based on the transient grating technique, andumerical solution of thermal diffusion in two dimensions provides the basis on which to understand the sensitivity in the magnetooptic detection.
Abstract: Surface magnetoelastic waves are coupled elastic and magnetic excitations that propagate along the surface of a magnetic material. Ultrafast optical techniques allow for a non-contact excitation and detection scheme while providing the ability to measure both elastic and magnetic components individually. Here we describe a simple setup suitable for excitation and time resolved measurements of high frequency magnetoelastic waves, which is based on the transient grating technique. The elastic dynamics are measured by diffracting a probe laser pulse from the long-wavelength spatially periodic structural deformation. Simultaneously, a magnetooptical measurement, either Faraday or Kerr effect, is sensitive to the out-of-plane magnetization component. The correspondence in the response of the two channels probes the resonant interaction between the two degrees of freedom and reveals their intimate coupling. Unraveling the observed dynamics requires a detailed understanding of the spatio-temporal evolution of temperature, magnetization and thermo-elastic strain in the ferromagnet. Numerical solution of thermal diffusion in two dimensions provides the basis on which to understand the sensitivity in the magnetooptic detection.
TL;DR: It is found that the fifth-order nonlinear optical susceptibility in the Rydberg-EIT system may be five orders of magnitude larger than that obtained in traditional EIT systems.
Abstract: We investigate the optical Kerr nonlinearities of an ensemble of cold Rydberg atoms under the condition of electromagnetically induced transparency (EIT). By using an approach beyond mean-field theory, we show that the system possesses not only enhanced third-order nonlinear optical susceptibility, but also giant fifth-order nonlinear optical susceptibility, which has a cubic dependence on atomic density. Our results demonstrate that both the third-order and the fifth-order nonlinear optical susceptibilities consist of two parts, contributed respectively by photon-atom interaction and Rydberg-Rydberg interaction. The Kerr nonlinearity induced by the Rydberg-Rydberg interaction plays a leading role at high atomic density. We find that the fifth-order nonlinear optical susceptibility in the Rydberg-EIT system may be five orders of magnitude larger than that obtained in traditional EIT systems. The results obtained may have promising applications in light and quantum information processing and transmission at weak-light level.
TL;DR: In this paper, a representative two-dimensional layered material, bismuth telluride (Bi2Te3) nanosheets, exhibit obvious broadband nonlinear absorption and large nonlinear refraction investigated by Z-scan technique.
Abstract: We experimentally observed that a representative two-dimensional layered material, bismuth telluride (Bi2Te3) nanosheets, exhibit obvious broadband nonlinear absorption and large nonlinear refraction investigated by Z-scan technique. Our study may not only verify the giant nonlinear refractive index of Bi2Te3 (~10−8 cm2/W), but also provide some new insights for topological insulator-based photonics, potentially leading to the emergence of several new conceptual optoelectronics devices.
Journal Article•
TL;DR: In this paper, an all-optical 3-input 3-output NOR gate based on photonic crystals is proposed, which employs high intensity optical power into the device based on Kerr effect, the refractive index of the rods has been varied and the coupling of light into output has been controlled.
Abstract: In the present paper, an all-optical 3-Input NOR gate based on photonic crystals is proposed. In designing this gate, three resonant rings have been used. By employing high intensity optical power into the device based on Kerr effect, the refractive index of the rods has been varied and the coupling of light into output has been controlled. The consistency of simulation results with the logical table of NOR gate confirms the suitable functionality of the device.
TL;DR: In this article, the authors used a basic structure of photonic crystal ring resonators and designed all optical logic gates which are working using the Kerr effect for all-optical devices.
Abstract: Photonic crystal based ring resonators are best choice for designing all-optical devices. In this paper, we used a basic structure of photonic crystal ring resonators and designed all optical logic gates which are working using the Kerr effect. The proposed gates consisted of upper and lower waveguides coupled through a resonator which was designed for dropping of special wavelength. The resonance wavelength was designed for 1550 nm telecom operation wavelength. We used numerical methods such as plane wave expansion and finite difference time domain (FDTD) for performing our simulations and studied the optical properties of the proposed structures. Our results showed that the critical input power for triggering the gate output was lower compared to previously reported gates.
TL;DR: The engineering of the magnetic response based on the plasmon-induced modification of the optical properties introduces the concept of a magneto-plasmonic meta-structure.
Abstract: We reveal an explicit strategy to design the magneto-optic response of a magneto-plasmonic crystal by correlating near- and far-fields effects. We use photoemission electron microscopy to map the spatial distribution of the electric near-field on a nanopatterned magnetic surface that supports plasmon polaritons. By using different photon energies and polarization states of the incident light we reveal that the electric near-field is either concentrated in spots forming a hexagonal lattice with the same symmetry as the Ni nanopattern or in stripes oriented along the Γ–K direction of the lattice and perpendicular to the polarization direction. We show that the polarization-dependent near-field enhancement on the patterned surface is directly correlated to both the excitation of surface plasmon polaritons on the patterned surface as well as the enhancement of the polar magneto-optical Kerr effect. We obtain a relationship between the size of the enhanced magneto-optical behavior and the polarization and wave...
TL;DR: In this paper, the magneto-optic-Kerr effect with normal light incidence was used to obtain quantitative optical measurements of both components of spin-orbit induced torque (both the antidamping and effective field components) in heavy-metal/ferromagnet bilayers.
Abstract: We demonstrate that the magneto-optic-Kerr effect with normal light incidence can be used to obtain quantitative optical measurements of both components of spin-orbit-induced torque (both the antidamping and effective-field components) in heavy-metal/ferromagnet bilayers. This is achieved by analyzing the quadratic Kerr effect as well as the polar Kerr effect. The two effects can be distinguished by properly selecting the polarization of the incident light. We use this all-optical technique to determine the spin-orbit torques generated by a series of Pt/Permalloy samples, finding values in excellent agreement with spin-torque ferromagnetic resonance measurements.
TL;DR: In this paper, a detailed computational study of the wavelength-dependent efficiency of optical second-harmonic generation in plasmonic nanostructures is presented based on a discontinuous Galerkin Maxwell solver that utilizes a hydrodynamic material model.
Abstract: A detailed computational study of the wavelength-dependent efficiency of optical second-harmonic generation in plasmonic nanostructures is presented. The computations are based on a discontinuous Galerkin Maxwell solver that utilizes a hydrodynamic material model to calculate the free-electron dynamics in metals without any further approximations. Besides wave-mixing effects, the material model thus contains the full nonlocal characteristics of the electromagnetic response, as well as intensity-dependent phenomena such as the Kerr effect. To be specific, two prototypical nanostructures are studied in depth with the help of two independent computer codes. For an infinitely long metal cylinder, it is found that the spectral position of linear particle plasmon modes (dipolar modes, higher-order modes, and, for frequencies above the plasma frequency also bulk plasmon modes) and their associated relative strengths for scattering and absorption both at the fundamental and second-harmonic wavelengths largely con...
TL;DR: In this article, a magnetophotonic plasmonic heterostructure with an ultra-high-Q resonance is considered, which corresponds to a Q factor of 700 and is a record value for magnetoplasmonics sensors.
Abstract: A novel type of a plasmonic sensor based on a magnetophotonic plasmonic heterostructure with an ultrahigh-Q resonance is considered. A magnetoplasmonic resonance with an angular width of 0.06°, which corresponds to a Q factor of 700 and is a record value for magnetoplasmonic sensors, is experimentally demonstrated. It is shown that, owing to the excitation of long-propagation-range plasmons, the transverse magneto-optical Kerr effect is considerably enhanced and, thus, the sensitivity of the magnetoplasmonic sensor to variations in the refractive index increases to 18 RIU–1, where RIU is the refractive index unit. Numerical calculations indicate that the parameters of the magnetoplasmonic structure can be further optimized to attain sensitivities up to 5 × 103 RIU–1.
TL;DR: It is shown that with an increase in laser power the radial component of the trapping potential becomes progressively more stable but the axial component is dramatically modulated due to increased Kerr nonlinearity, and the relevant parameter to quantify the trapping efficiency is not the absolute depth of the highly asymmetric axial trapping potential but the height of the potential barrier along the beam propagation direction.
Abstract: The use of low-power high-repetition-rate ultrafast pulsed excitation in stable optical trapping of dielectric nanoparticles has been demonstrated in the recent past; the high peak power of each pulse leads to instantaneous trapping of a nanoparticle with fast inertial response and the high repetition-rate ensures repetitive trapping by successive pulses However, with such high peak power pulsed excitation under a tight focusing condition, nonlinear optical effects on trapping efficiency also become significant and cannot be ignored. Thus, in addition to the above mentioned repetitive instantaneous trapping, trapping efficiency under pulsed excitation is also influenced by the optical Kerr effect, which we theoretically investigate here. Using dipole approximation we show that with an increase in laser power the radial component of the trapping potential becomes progressively more stable but the axial component is dramatically modulated due to increased Kerr nonlinearity. We justify that the relevant parameter to quantify the trapping efficiency is not the absolute depth of the highly asymmetric axial trapping potential but the height of the potential barrier along the beam propagation direction. We also discuss the optimal excitation parameters leading to the most stable dipole trap. Our results show excellent agreement with previous experiments.
21 Mar 2016
TL;DR: In this article, the main results that have been achieved over the past decade in the new field of liquid-crystal micro-photonics are presented, and optical microfibres can be self-grown in water/liquid-crystals dispersions and present their waveguiding and lasing properties.
Abstract: This review presents the main results that were achieved over the past decade in the new field of liquid-crystal micro-photonics. After a general introduction to some aspects of state-of-the-art micro-photonics technologies, nematic colloids are discussed in terms of their self-assembly and photonic properties. Liquid-crystal lasers, based on spatially periodic, liquid-crystal phases, are reviewed, and microlasers based on liquid-crystal microdroplets are presented and discussed. We show that optical microfibres can be self-grown in water/liquid-crystal dispersions and present their waveguiding and lasing properties. The review concludes with a discussion of the resonant transfer of light across different liquid-crystal micro-objects and presents the ultra-fast optical Kerr and STED effects in bulk nematic liquid crystals.