Nonresonant Light Research Articles

In-plane photoelectric effect in phosphorene nanoribbons

Recently, a new photoelectric phenomenon dubbed in-plane photoelectric (IPPE) effect has been demonstrated experimentally. In this work, we investigate the IPPE effect in a zigzag-edged or armchair-edged phosphorene nanoribbons (ZPNRs or APNRs) that is modulated by a step barrier. Based on the Floquet theory, we calculate the directed photocurrent Ī|| (Ī⊥) generated by a non-resonant linearly-polarized light with polarization vector in parallel with (perpendicular to) the nanoribbon direction. We find that such a photocurrent depends on the edge type of the nanoribbon and the polarization direction of light. At high Fermi energies, the IPPE current Ī|| in APNRs is significantly stronger than that in ZPNRs under the same conditions. In APNRs, both Ī|| and Ī⊥ always have the same direction and |Ī||:Ī⊥|>10. In contrast, in ZPNRs Ī⊥ can reverse its direction (becoming negative) and is comparable to Ī|| in amplitude. The negative photocurrent arises from both the photon-emission and photon-absorption process related to the quasi-flat-band in ZPNRs. This indicates that the mid-gap states can be detected by the IPPE effect. The energy scope and amplitude of negative photocurrent can be tuned by adjusting the height of the step barrier, the light frequency, and the light intensity.

Momentum-dependent intraband high harmonic generation in a photodoped indirect semiconductor

Nonlinear optical response of solid-state materials exposed to strong non-resonant light fields leads to the generation of harmonic frequencies as a consequence of interband polarization and coherent intraband dynamics of the electrons. The efficient production of a macroscopic wave requires the preservation of the mutual phase between the driving wave and the individual microscopic sources of radiation. Here, we experimentally and theoretically show that the yield of high harmonic generation in a photodoped silicon crystal is enhanced by the nonlinear intraband current whose amplitude depends not only on the volume density of the photogenerated carriers but also on their momentum distributions within the bands. The strongest enhancement is reached when the carrier system is relaxed to the band minima before interacting with the strong nonresonant wave, which drives the high harmonic generation. These results extend the possibilities of high harmonic spectroscopy towards the investigation of ultrafast carrier relaxation in condensed matter.

Topologically protected optical pulling force on synthetic particles through photonic nanojet

Abstract A dielectric microsphere concentrates light into a photonic nanojet (PNJ), and swims towards the near-infrared laser in response to the nanojet-mediated force. In contrast, a Janus particle with an opaque metal layer was thought to be impossible to concentrate light into a stable nanojet. However, the Janus particle may experience optical torque owing to the inhomogeneous composition on both sides even in linearly polarized non-resonant light. Herein, we report on topologically protected PNJ produced by a synthetic Janus particle, and observed the backaction force on the Janus particle. Due to symmetry, the counter-propagating beams can both form PNJ on the respective opposite sides, and pull Janus particles towards respective sources. Furthermore, we unveil that the hysteresis on backaction force with respect to the injection power also exists on synthetic Janus particle compared with their dielectric counterparts. Additionally, the magnitude of the backaction force varies between power increase and decrease stages even with the same laser power. We anticipate that the observation offers great possibilities to pull irregular particles by concentrating light with the particle, and such scheme may be applied for parallel particle manipulation and classification.

Role of surface damping on hybrid modes and electric field enhancement distribution of ultrathin metal-coated dielectric microspheres illuminated by non-resonant light

Herein, we report a theoretical investigation on the characteristic parameters of hybrid plasmonic–photonic modes (or simply hybrid modes) and electric field enhancement (EFE) distribution of ultrathin Au- and Ag-coated dielectric microspheres illuminated by non-resonant light obtained with and without consideration of the size-dependent damping (SDD) or surface damping in ultrathin metal nanoshells. From the obtained scattering and absorption spectra, the role of SDD on characteristic parameters such as wavelength locations, full width at half maximum, and EFE of the hybrid modes is investigated for the first time, to our knowledge. In addition, the effect of metal shell thickness (t) on the hybrid modes is studied. The EFE distribution inside/outside the ultrathin metal-coated dielectric microspheres illuminated by non-resonant light is investigated. More importantly, the sensitivity of the EFE distribution of bare and metal-coated microspheres is explored by slightly varying the resonant and non-resonant wavelengths.

Zone-Folded Quasi-bound State Metasurfaces with Customized, Symmetry-Protected Energy-Momentum Relations

Energy-momentum (dispersion) relations are a foundational framework for photonic device design, but our incomplete command thereof still limits key technologies. For instance, narrowband optical combiners for augmented reality should ideally reflect with unitary efficiency selected wavelengths that encode the artificial information over a large range of oblique incident angles, yet they are conventionally severely limited in field of view by dispersion. Here, we engineer nonlocal metasurfaces to support quasi-bound states in continuum with zero first-order resonant frequency dispersion at any desired quasi-momentum by exploiting a zone-folding technique that leverages a change in the lattice family. Our platform thereby advances photonic devices by enabling unprecedented control over the energy-momentum properties of nonlocal states, rationally controlled through a perturbation scheme that produces minimal distortion to non-resonant light.

Ultrafast valley-selective coherent optical manipulation with excitons in WSe2 and MoS2 monolayers

Increasing the speed limits of conventional electronics requires innovative approaches to manipulate other quantum properties of electrons besides their charge. An alternative approach utilizes the valley degree of freedom in low-dimensional semiconductors. Here we demonstrate that the valley degeneracy of exciton energies in transition metal dichalcogenide monolayers may be lifted by coherent optical interactions on timescales corresponding to few tens of femtoseconds. The optical Stark and Bloch-Siegert effects generated by strong nonresonant circularly-polarized light induce valley-selective blue shifts of exciton quantum levels by more than 30 meV. We show these phenomena by studying the two most intensive exciton resonances in transiton metal dichalcogenide monolayers and compare the results to a theoretical model, which properly includes the Coulomb interaction and exciton dispersion. These results open the door for ultrafast valleytronics working at multiterahertz frequencies.

Role of Van Hove singularities and effective mass anisotropy in polarization-resolved high harmonic spectroscopy of silicon

Nonlinear optical response of materials exposed to strong nonresonant light fields leads to production of high energy photons whose spectra contain fingerprints of the coherent electron dynamics in the material. In this paper we investigate how the high harmonic spectra generated in crystalline silicon are linked to specific properties of its band structure. By comparing the polarization anisotropy of high harmonic spectra for two distinct frequencies of the driving pulses we show that the anisotropy has two sources. When driven by mid-infrared light, the signal at specific photon energies is enhanced by the presence of Van Hove singularities in the joint density of states of silicon. With near-infrared driving pulses, in contrast, the high harmonic yield is mainly influenced by the anisotropy of the reduced mass of electron-hole pair, which is related to the nonresonant excitation probability. The experimental results are compared with numerical calculations using time-dependent density functional theory.

Improved optical standing-wave beam splitters for dilute Bose–Einstein condensates

Bose–Einstein condensate (BEC)-based atom interferometry exploits low temperatures and long coherence lengths to facilitate high-precision measurements. Progress in atom interferometry promises improvements in navigational devices like gyroscopes and accelerometers, as well as applications in fundamental physics such as accurate determination of physical constants. Previous work demonstrates that beam splitters and mirrors for coherent manipulation of dilute BEC momentum in atom interferometers can be implemented with sequences of non-resonant standing-wave light pulses. While previous work focuses on the optimization of the optical pulses’ amplitude and duration to produce high-order momentum states with high fidelity, we explore how varying the shape of the optical pulses affects optimal beam-splitter performance, as well as the effect of pulse shape on the sensitivity of optimized parameters in achieving high fidelity in high-momentum states. In simulations of two-pulse beam splitters utilizing optimized square, triangle, and sinc-squared pulse shapes applied to dilute BECs, we, in some cases, reduce parameter sensitivity by an order of magnitude while maintaining fidelity.

Energy recycling under ambient illumination for internet-of-things using metal/oxide/metal-based colorful organic photovoltaics

Colorful indoor organic photovoltaics (OPVs) have attracted considerable attention in recent years for their autonomous function in internet-of-things (IoT) devices. In this study, a solution-processed TiO2 layer in a metal–oxide–metal (MOM) color filter electrode is used for light energy recycling in P3HT:ICBA-based indoor OPVs. The MOM electrode allows for tuning of the optical cavity mode to maximize photocurrent production by modulating the thickness of the TiO2 layer in the sandwich structure. This approach preserves the OPVs’ optoelectronic properties without damaging the photoactive layer and enables them to display a suitable range of vivid colors. The optimized MOM-OPVs demonstrated an excellent power conversion efficiency (PCE) of 8.8% ± 0.2%, which is approximately 20% higher than that of reference opaque OPVs under 1000 lx light emitting diode illumination. This can be attributed to the high photocurrent density due to the nonresonant light reflected from metals into the photoactive layer. Additionally, the proposed MOM-OPVs exhibited high external quantum efficiency and large parasitic shunt resistances, leading to improved fill factor and PCE values. Thus, the study’s MOM electrode provides excellent feasibility for realizing colorful and efficient indoor OPVs for IoT applications.

In Situ Label-Free Study of Protein Adsorption on Nanoparticles.

Improving the design of nanoparticles for use as drug carriers or biosensors requires a better understanding of the protein–nanoparticle interaction. Here, we present a new tool to investigate this interaction in situ and without additional labeling of the proteins and/or nanoparticles. By combining nonresonant second-harmonic light scattering with a modified Langmuir model, we show that it is possible to gain insight into the adsorption behavior of blood proteins, namely fibrinogen, human serum albumin, and transferrin, onto negatively charged polystyrene nanoparticles. The modified Langmuir model gives us access to the maximum amount of adsorbed protein, the apparent binding constant, and Gibbs free energy. Furthermore, we employ the method to investigate the influence of the nanoparticle size on the adsorption of human serum albumin and find that the amount of adsorbed protein increases more than the surface area per nanoparticle for larger diameters.

Broadband and Tunable Light Harvesting in Nanorippled MoS2 Ultrathin Films.

Nanofabrication of flat optic silica gratings conformally layered with two-dimensional (2D) MoS2 is demonstrated over large area (cm2), achieving a strong amplification of the photon absorption in the active 2D layer. The anisotropic subwavelength silica gratings induce a highly ordered periodic modulation of the MoS2 layer, promoting the excitation of Guided Mode Anomalies (GMA) at the interfaces of the 2D layer. We show the capability to achieve a broadband tuning of these lattice modes from the visible (VIS) to the near-infrared (NIR) by simply tailoring the illumination conditions and/or the period of the lattice. Remarkably, we demonstrate the possibility to strongly confine resonant and nonresonant light into the 2D MoS2 layers via GMA excitation, leading to a strong absorption enhancement as high as 240% relative to a flat continuous MoS2 film. Due to their broadband and tunable photon harvesting capabilities, these large area 2D MoS2 metastructures represent an ideal scalable platform for new generation devices in nanophotonics, photo- detection and -conversion, and quantum technologies.

Symmetry breaking in the Stark Control of Electrons at Interfaces (SCELI).

Ultrafast control of electron dynamics is essential for future innovations in nanoelectronics, catalysis, and molecular imaging. Recently, we developed a general scheme (Stark Control of Electrons at Interfaces or SCELI) to control electron dynamics at interfaces [A. J. Garzón-Ramírez and I. Franco, Phys. Rev. B 98, 121305 (2018)] that is based on using few-cycle lasers to open quantum tunneling channels for interfacial electron transfer. SCELI uses the Stark effect induced by non-resonant light to create transient resonances between a donor level in material B and an acceptor level in material A, resulting in B → A electron transfer. Here, we show how SCELI can be employed to generate net charge transport in ABA heterojunctions without applying a bias voltage, a phenomenon known as laser-induced symmetry breaking. The magnitude and sign of such transport can be controlled by simply varying the time asymmetry of the laser pulse through manipulation of laser phases. In particular, we contrast symmetry breaking effects introduced by manipulation of the carrier envelope phase with those introduced by relative phase control in ω + 2ω laser pulses. The ω + 2ω pulse is seen to be far superior as such pulses exhibit a larger difference in field intensity for positive and negative amplitudes. The results exemplify the power of Stark-based strategies for controlling electrons using lasers.

Multiscale coupled Maxwell's equations and polarizable molecular dynamics simulation based on charge response kernel model.

A computational scheme of coupled Maxwell's equations and polarizable molecular dynamics simulation has been developed based on a multi-scale model to describe the coupled dynamics of light electromagnetic waves and molecules in crystalline solids, where the charge response kernel model is employed to incorporate electronic polarization of the molecules. The method is applicable to electronically non-resonant light-matter interaction systems that involve atomic motions in spectroscopy and photonics. Since the scheme simultaneously traces the light propagation in a medium on a macroscopic scale and the microscopic molecular motion under the light electric field, this enables us to treat the experimental setup and mimic its measurement process. As the first applications, we demonstrate three numerical examples of basic spectroscopies of an ice crystalline solid: simulations of reflection and transmission of visible light, infrared absorption measurement, and stimulated Raman scattering measurement. These examples show the detailed behaviors of the interacting light fields and molecules in the spectroscopic processes.

Double-sided and omnidirectional absorption of visible light in tapered dielectric nanostructure coated with non-noble metal.

The common complex architecture constitutes the major bottleneck of optical absorber operating on broadband spectrum. Here we demonstrate a super absorber consisting of tapered dielectric nanostructure coated with a thin-layer of non-noble metal chromium on flexible poly(ethylene terephthalate) substrate. The proposed device yields double-sided, omnidirectional, and polarization-independent absorption over the entire visible spectrum with an average efficiency more than 90% at normal incidence, and 80% at a tilt incident angle of 60°. It can be easily realized by nanoimprinting lithography combined with physical vapor deposition technique. Theoretical analysis demonstrates that the superior optical performance is ascribed to the non-resonant light absorption by using the metal-covered, closed-packed tapered nanostructure via adiabatic nanofocusing of the metal-dielectric-metal (MDM) guided modes excited by scattering of the gradually changing nanostructure. For the cost-effective fabrication and material strategy, the super absorber has potential applications in a wide range of passive and active photonic devices, including inkless printing, harvesting solar energy, as well as thermal emitter and optical detector.

Research of magnetic resonance quality factor dependence on cesium distribution in quantum rotation sensor cell

Subject of Research. The paper presents results of the experimental and theoretical studies on cesium distribution effect along the vapor cell walls of quantum rotation sensor on the quality of parametric resonance in cesium. Methods. Theoretical and experimental studies were performed using the mathematical model, quantum rotation sensor layout and the laboratory setup for the vapor cell parameters research. The mathematical model was used for calculation of cesium relaxation rate theoretical value at various temperatures and further comparison of these data with experimental ones. For the experimental determination of cesium relaxation rate, the data on the parametric resonance width in cesium obtained on the of the quantum rotation sensor model were used. Studies of the cell optical properties were carried out on a laboratory setup in non-resonant light. A laser with a vertical emitter similar to the one used in the quantum rotation sensor is applied as a source of non-resonant light, tuned away from the nominal wavelength. The optimal detuning of the optical radiation frequency from the cesium resonance was determined on the laboratory setup, that reduces the dependence of the measurement results on the cell temperature. Selection of laser radiation optimal parameters is performed for the normal mode of the laser operation and freedom from fluctuations in its power and polarization. Main Results. During the research it was shown that undesirable cesium redistribution in the vapor cell leads to the optical paths transparency change, which causes the deterioration of the signal-to-noise ratio and the decrease in the resonance line quality factor. In addition, it was shown that cesium resonance line broadening due to sedimentation of the cesium vapor on the cell walls is insignificant and is at the level of the measurement error. Practical Relevance. We have proposed and tested non-resonant light intensity control method for the laser emitter after passing through a vapor cell. This method provides for an operative state monitoring of the optical pumping channels and detecting of quantum rotation sensor layout.

Controlling ultracold p -wave collisions with nonresonant light: Predictions of an asymptotic model

Interactions in a spin-polarized ultracold Fermi gas are governed by $p$-wave collisions and can be characterized by the $p$-wave scattering volume. Control of these collisions by Feshbach resonances is hampered by huge inelastic losses. Here, we suggest non-resonant light control of $p$-wave collisions, exploiting the anisotropic coupling of non-resonant light to the polarizability of the atoms. The $p$-wave scattering volume can be controlled by strong non-resonant light, in close analogy to the $s$-wave scattering length. For collision partners that are tightly trapped, the non-resonant light induces an energy shift directly related to the generalized scattering volume. This effect could be used to climb the ladder of the trap. We also show that controlling the generalized scattering volume implies control, at least roughly, over the orientation of the interparticle axis relative to the polarization direction of the light at short interatomic distances. Our proposal is based on an asymptotic model that explicitly accounts for the anisotropic dipole-dipole interaction which governs the ultracold collision dynamics at long-range.

Optical absorption properties of laser-driven matter

Characterizing and controlling matter driven far from equilibrium represents a major challenge for science and technology. Here, we develop a theory for the optical absorption of electronic materials driven far from equilibrium by resonant and nonresonant lasers. In it, the interaction between matter and the driving light is treated exactly through a Floquet analysis, while the effects of the probing light are captured to first order in perturbation theory. The resulting equations are reminiscent to those for equilibrium absorption but with the Floquet modes playing the role of the pristine eigenstates. The formalism is employed to characterize the optical properties of a model nanoscale semiconductor dressed by nonresonant light of intermediate intensity (nonperturbative, but nonionizing). As shown, nonresonant light can reversibly turn this transparent semiconductor into a broadband absorber and open strong absorption and stimulated emission bands at very low frequencies ($\ensuremath{\sim}\mathrm{meV}$). Further, the absorption spectra of the driven material exhibit periodic features energetically spaced by the photon energy of the driving light that reflect the periodic structure of the Floquet bands. These developments offer a platform to understand and predict the emergent optical properties of materials dressed by the electric field of light, and catalyze the design of laser-driven materials with desired optical properties.

Non-resonant light scattering in dispersions of 2D nanosheets

Extinction spectra of nanomaterial suspensions can be dominated by light scattering, hampering quantitative spectral analysis. No simple models exist for the wavelength-dependence of the scattering coefficients in suspensions of arbitrary-sized, high-aspect-ratio nanoparticles. Here, suspensions of BN, talc, GaS, Ni(OH)2, Mg(OH)2 and Cu(OH)2 nanosheets are used to explore non-resonant scattering in wide-bandgap 2D nanomaterials. Using an integrating sphere, scattering coefficient (σ) spectra were measured for a number of size-selected fractions for each nanosheet type. Generally, σ scales as a power-law with wavelength in the non-resonant regime: σ(λ)∝[λ/〈L〉]−m, where 〈L〉 is the mean nanosheet length. For all materials, the scattering exponent, m, forms a master-curve, transitioning from m = 4 to m = 2, as the characteristic nanosheet area increases, indicating a transition from Rayleigh to van der Hulst scattering. In addition, once material density and refractive index are factored out, the proportionality constant relating σ to [λ/〈L〉]−m, also forms a master-curve when plotted versus 〈L〉.

Extremely sharp transmission peak in optically thin aluminum film with hexagonal nanohole arrays

Extraordinary transmission is the most attractive phenomenon, that has been studied in recent decades, for optically thick metal film with nanohole arrays. On the contrary, in optically thin metal film with nanohole arrays, it has been found that the interaction between excited surface plasmon polariton and non-resonant direct propagation light introduces a strong light absorption and causes a suppressed transmission dip. Here, we explore the optical properties of a free standing optically thin aluminum film with a hexagonal large filling ratio nanohole array and find an extremely sharp extra extraordinary transmission peak within the suppressed transmission dip which is originated from the interaction of the excited surface plasmon polariton and the non-resonant directly scattered light. Simulation results show that the nanohole-array-based biosensor that were proposed have an excellent sensitivity, with a figure of merit of 87, beyond that of nanohole-array-based biosensors reported previously for normal incidence.

Actively mode-locked all-fiber laser by 5 MHz transmittance modulation of an acousto-optic tunable bandpass filter

Active mode-locking of an all-fiber ring laser by transmittance modulation of an in-fiber acousto-optic tunable bandpass filter (AOTBF) is reported. Cavity loss modulation is achieved by full acousto-optic mode re-coupling cycle induced by standing flexural acoustic waves. The modulator permits the implementation of 28 dB of nonresonant light suppression, 1.4 nm of modulation bandwidth, 74% of modulation depth and 4.11 dB of optical loss in a 72.5 cm-long all-fiber configuration. The effects of the modulated AOTBF on the laser performance are investigated. Transform-limited optical pulses of 8.8 ps temporal width and 6.0 W peak power were obtained at 4.87 MHz repetition rate.