Showing papers on "Wavelength published in 2015"
TL;DR: An on-chip integrated wavelength demultiplexer designed using an inverse computational algorithm is experimentally demonstrated in this paper, where 1,300 and 1,550 nm wavelength light is sorted in a device area of just 2.8 µm2.
Abstract: An on-chip integrated wavelength demultiplexer designed using an inverse computational algorithm is experimentally demonstrated. 1,300 and 1,550 nm wavelength light is sorted in a device area of just 2.8 × 2.8 μm2.
817 citations
TL;DR: In this article, the authors study the generation of high-harmonic radiation by Bloch electrons in a model transparent solid driven by a strong midinfrared laser field and find that the resulting harmonic spectrum exhibits a primary plateau due to coupling of the valence band to the first conduction band, with a cutoff energy that scales linearly with field strength and laser wavelength.
Abstract: We study the generation of high-harmonic radiation by Bloch electrons in a model transparent solid driven by a strong midinfrared laser field. We solve the single-electron time-dependent Schr\"odinger equation (TDSE) using a velocity-gauge method [M. Korbman et al., New J. Phys. 15, 013006 (2013)] that is numerically stable as the laser intensity and number of energy bands are increased. The resulting harmonic spectrum exhibits a primary plateau due to the coupling of the valence band to the first conduction band, with a cutoff energy that scales linearly with field strength and laser wavelength. We also find a weaker second plateau due to coupling to higher-lying conduction bands, with a cutoff that is also approximately linear in the field strength. To facilitate the analysis of the time-frequency characteristics of the emitted harmonics, we also solve the TDSE in a time-dependent basis set, the Houston states [J. B. Krieger and G. J. Iafrate, Phys. Rev. B 33, 5494 (1986)], which allows us to separate interband and intraband contributions to the time-dependent current. We find that the interband and intraband contributions display very different time-frequency characteristics. We show that solutions in these two bases are equivalent under a unitary transformation but that, unlike the velocity-gauge method, the Houston state treatment is numerically unstable when more than a few low-lying energy bands are used.
287 citations
Patent•
AT&T1
TL;DR: In this article, the authors described a transmission device that includes a transmitter that generates a first electromagnetic wave to convey data, the first wave having at least one carrier frequency and corresponding wavelength.
Abstract: Aspects of the subject disclosure may include, for example, a transmission device that includes a transmitter that generates a first electromagnetic wave to convey data, the first electromagnetic wave having at least one carrier frequency and corresponding wavelength. A coupler couples the first electromagnetic wave to a transmission medium having at least one inner portion surrounded by a dielectric material, the dielectric material having an outer surface and a corresponding circumference, wherein the coupling of the first electromagnetic wave to the transmission medium forms a second electromagnetic wave that is guided to propagate along the outer surface of the dielectric material via at least one guided-wave mode that can include an asymmetric mode, wherein the at least one carrier frequency is within a microwave or millimeter-wave frequency band and wherein the at least one corresponding wavelength is less than the circumference of the transmission medium. Other embodiments are disclosed.
276 citations
TL;DR: In this paper, a method to constrain the grain size in protoplanetary disks with polarization observations at millimeter wavelengths is presented. But the method is limited to the case where the maximum grain size is set to be and the observing wavelength to be 870.
Abstract: We present a new method to constrain the grain size in protoplanetary disks with polarization observations at millimeter wavelengths. If dust grains are grown to the size comparable to the wavelengths, the dust grains are expected to have a large scattering opacity, and thus the continuum emission is expected to be polarized due to self-scattering. We perform 3D radiative transfer calculations to estimate the polarization degree for the protoplanetary disks having radial Gaussian-like dust surface density distributions, which have been recently discovered. The maximum grain size is set to be and the observing wavelength to be 870 . We find that the polarization degree is as high as 2.5% with a subarcsec spatial resolution, which is likely to be detected with near-future ALMA observations. The emission is polarized due to scattering of anisotropic continuum emission. The map of the polarization degree shows a double-peaked distribution, and the polarization vectors are in the radial direction in the inner ring and in the azimuthal direction in the outer ring. We also find the wavelength dependence of the polarization degree: the polarization degree is the highest if dust grains have a maximum size of , where λ is the observing wavelength. Hence, multi-wave and spatially resolved polarization observations toward protoplanetary disks enable us to put a constraint on the grain size. The constraint on the grain size from polarization observations is independent of or may be even stronger than that from the opacity index.
264 citations
TL;DR: In this article, a full-range complex spectral domain optical coherence tomography with an ultra-broadband light source based on sinusoidal modulation is presented, where a lead zirconate titanate stack actuator is employed to achieve the sinusoid vibration of a mirror and therefore to get a series of spectral interferogram with different phase delays.
Abstract: We present a full-range complex spectral domain optical coherence tomography with an ultra-broadband light source based on sinusoidal modulation. For the sinusoidal modulation strategy, a lead zirconate titanate stack actuator is employed to achieve the sinusoidal vibration of a mirror and therefore to get a series of spectral interferogram with different phase delays. The purpose of this strategy is to get higher performance complex-conjugate artifact elimination. Bessel separation of the signal sequence at each wavelength of the spectrometer was used to reconstruct the real and imaginary components of interference fringes; however, the sinusoidal modulation method is independent of light source wavelength. The experimental results demonstrated that the method had an excellent performance in a complex-conjugate suppression of 50 dB for a full width at half maximum bandwidth of 236 nm, and it has better anti-artifact ability and more flexible range in phase shifting than the conventional wavelength-dependent phase-shifting method on a full-range complex spectral optical coherence tomography system. Furthermore, the effect of the hysteresis error of lead zirconate titanate actuators on the performance of complex-conjugate artifact elimination was investigated and the solution of lead zirconate titanate positioning performance for both conventional phase-shifting and sine-modulation methods was suggested.
260 citations
TL;DR: S semiconducting single-walled carbon nanotubes with large diameters were used for in vivo fluorescence imaging in the long-wavelength NIR region (1500-1700 nm, NIR-IIb) and 3-4 μm wide capillary blood vessels at a depth of about 3 mm could be resolved.
Abstract: Compared to imaging in the visible and near-infrared regions below 900 nm, imaging in the second near-infrared window (NIR-II, 1000-1700 nm) is a promising method for deep-tissue high-resolution optical imaging in vivo mainly due to the reduced scattering of photons traversing through biological tissues. Herein, semiconducting single-walled carbon nanotubes with large diameters were used for in vivo fluorescence imaging in the long-wavelength NIR region (1500-1700 nm, NIR-IIb). With this imaging agent, 3-4 um wide capillary blood vessels at a depth of about 3 mm could be resolved. Meanwhile, the blood-flow speeds in multiple individual vessels could be mapped simultaneously. Furthermore, NIR-IIb tumor imaging of a live mouse was explored. NIR-IIb imaging can be generalized to a wide range of fluorophores emitting at up to 1700 nm for high-performance in vivo optical imaging.
249 citations
TL;DR: Silva et al. as mentioned in this paper proposed reflective metasurfaces consisting of arrayed gold nanobricks atop a subwavelength-thin dielectric spacer and optically thick gold film, a configuration that supports gap-surface plasmon resonances.
Abstract: Motivated by the recent renewed interest in compact analog computing using light and metasurfaces ( Silva, A. et al. Science 2014 , 343, 160 - 163), we suggest a practical approach to its realization that involves reflective metasurfaces consisting of arrayed gold nanobricks atop a subwavelength-thin dielectric spacer and optically thick gold film, a configuration that supports gap-surface plasmon resonances. Using well-established numerical routines, we demonstrate that these metasurfaces enable independent control of the light phase and amplitude, and design differentiator and integrator metasurfaces featuring realistic system parameters. Proof-of-principle experiments are reported along with the successful realization of a high-quality poor-man's integrator metasurface operating at the wavelength of 800 nm.
214 citations
TL;DR: In this paper, a 2D dense and large network with about 2500 receivers with 100m spacing was used to estimate 3D P wave velocities from a single depth image.
Abstract: We retrieve P diving waves by applying seismic interferometry to ambient-noise records observed at Long Beach, California, and invert travel times of these waves to estimate 3-D P wave velocity structure. The ambient noise is recorded by a 2-D dense and large network, which has about 2500 receivers with 100 m spacing. Compared to surface wave extraction, body wave extraction is a much greater challenge because ambient noise is typically dominated by surface wave energy. For each individual receiver pair, the cross-correlation function obtained from ambient-noise data does not show clear body waves. Although we can reconstruct body waves when we stack correlation functions over all receiver pairs, we need to extract body waves at each receiver pair separately for imaging spatial heterogeneity of subsurface structure. Therefore, we employ two filters after correlation to seek body waves between individual receiver pairs. The first filter is a selection filter based on the similarity between each correlation function and the stacked function. After selecting traces containing stronger body waves, we retain about two million correlation functions (35% of all correlation functions) and successfully preserve most of body wave energy in the retained traces. The second filter is a noise suppression filter to enhance coherent energy (body waves here) and suppress incoherent noise in each trace. After applying these filters, we can reconstruct clear body waves from each virtual source. As an application of using extracted body waves, we estimate 3-D P wave velocities from these waves with travel time tomography. This study is the first body wave tomography result obtained from only ambient noise recorded at the ground surface. The velocity structure estimated from body waves has higher resolution than estimated from surface waves.
206 citations
TL;DR: In this paper, a simple model was proposed to describe the interaction between waves that propagate across the Pacific Ocean and the Equatorial Undercurrent (EUC) in terms of the attenuation factor for short, intermediate and long waves.
Abstract: We propose a new, simple model – but one which has far-reaching consequences – to describe the interaction between waves that propagate across the Pacific Ocean and the Equatorial Undercurrent (EUC). This involves a detailed discussion of the full linear problem as it relates to the dynamic coupling between the surface waves and the internal waves on the thermocline. The result is a comprehensive description of the system close to the Equator, and how the structure of the EUC affects the wave properties; in particular, the analysis holds for arbitrary wavelengths and finite depths. Although the final expressions, for general wavelengths, are too cumbersome for direct interpretation, we are able to produce simple formulae for the speeds of the waves, and the attenuation factor between the two families of waves, for short, intermediate and long waves. Further, our results predict the appearance of critical layers under certain circumstances; by reverting to our original system of governing equations, we are...
206 citations
TL;DR: In this article, a combination of new measurements and analysis of historical data from several geographic regions was used to address four issues that affect the reliability and interpretation of colored dissolved organic matter (CDOM) measured by remote sensing of inland waters.
201 citations
TL;DR: In this paper, an ultrabroadband superoscillatory lens (UBSOL) is proposed and realized by utilizing the metasurface-assisted law of refraction and reflection in arrayed nanorectangular apertures with variant orientations.
Abstract: Conventional optics is diffraction limited due to the cutoff of spatial frequency components, and evanescent waves allow subdiffraction optics at the cost of complex near-field manipulation. Recently, optical superoscillatory phenomena were employed to realize superresolution lenses in the far field, but suffering from very narrow working wavelength band due to the fragility of the superoscillatory light field. Here, an ultrabroadband superoscillatory lens (UBSOL) is proposed and realized by utilizing the metasurface-assisted law of refraction and reflection in arrayed nanorectangular apertures with variant orientations. The ultrabroadband feature mainly arises from the nearly dispersionless phase profile of transmitted light through the UBSOL for opposite circulation polarization with respect to the incident light. It is demonstrated in experiments that subdiffraction light focusing behavior holds well with nearly unchanged focal patterns for wavelengths spanning across visible and near-infrared light. This method is believed to find promising applications in superresolution microscopes or telescopes, high-density optical data storage, etc.
TL;DR: A simple and fail-proof procedure to determine the orientation of a BP crystal by combining polarized Raman scattering with polarized optical microscopy is proposed.
Abstract: We investigated polarization dependence of the Raman modes in black phosphorus (BP) using five different excitation wavelengths. The crystallographic orientation was determined by comparing polarized optical microscopy with high-resolution transmission electron microscopy analysis. In polarized Raman spectroscopy, the B2g mode shows the same polarization dependence regardless of the excitation wavelength or the sample thickness. On the other hand, the Ag1 and Ag2 modes show a peculiar polarization behavior that depends on the excitation wavelength and the sample thickness. The thickness dependence can be explained by considering the anisotropic interference effect due to the birefringence and dichroism of the BP crystal, but the wavelength dependence cannot be explained. We propose a simple and fail-proof procedure to determine the orientation of a BP crystal by combining polarized Raman scattering with polarized optical microscopy.
TL;DR: Surprisingly, the high ultraviolet refractive indices of both neutral atoms and ions enabled effective phase matching, even in a multiply ionized plasma, which could presage a more generally efficient means of creating x-ray pulses for fundamental dynamics studies as well as technological applications.
Abstract: High-harmonic generation is a universal response of matter to strong femtosecond laser fields, coherently upconverting light to much shorter wavelengths. Optimizing the conversion of laser light into soft x-rays typically demands a trade-off between two competing factors. Because of reduced quantum diffusion of the radiating electron wave function, the emission from each species is highest when a short-wavelength ultraviolet driving laser is used. However, phase matching--the constructive addition of x-ray waves from a large number of atoms--favors longer-wavelength mid-infrared lasers. We identified a regime of high-harmonic generation driven by 40-cycle ultraviolet lasers in waveguides that can generate bright beams in the soft x-ray region of the spectrum, up to photon energies of 280 electron volts. Surprisingly, the high ultraviolet refractive indices of both neutral atoms and ions enabled effective phase matching, even in a multiply ionized plasma. We observed harmonics with very narrow linewidths, while calculations show that the x-rays emerge as nearly time-bandwidth-limited pulse trains of ~100 attoseconds.
TL;DR: In this article, the authors experimentally report perfect acoustic absorption through the interplay of the inherent losses and transparent modes with high Q factor generated in a two-port, one-dimensional waveguide, which is sideloaded by isolated resonators of moderate Q factor.
Abstract: We experimentally report perfect acoustic absorption through the interplay of the inherent losses and transparent modes with high Q factor. These modes are generated in a two-port, one-dimensional waveguide, which is side-loaded by isolated resonators of moderate Q factor. In symmetric structures, we show that in the presence of small inherent losses, these modes lead to coherent perfect absorption associated with one-sided absorption slightly larger than 0.5. In asymmetric structures, near perfect one-sided absorption is possible (96%) with a deep sub-wavelength sample ( λ/28, where λ is the wavelength of the sound wave in the air). The control of strong absorption by the proper tuning of the radiation leakage of few resonators with weak losses will open possibilities in various wave-control devices.
TL;DR: In this article, Faraday and Joule numbers have been defined to quantify the ability of a nanoparticle to enhance the optical near field and produce heat, which can be used to compare the plasmonic capabilities of different materials.
Abstract: Following recent advances in nanoplasmonics related to high-temperature applications, hot-electron processes, nanochemistry, sensing, and active plasmonics, new materials have been introduced, reducing the supremacy of gold and silver in plasmonics. The variety of possible materials in nanoplasmonics is now so wide that selecting the best material for a specific application at a specific wavelength may become a difficult task. In this context, we introduce in this Article two dimensionless parameters acting as figures of merit to simply compare the plasmonic capabilities of different materials. These numbers, which we named Faraday and Joule numbers, aim at quantifying the ability of a nanoparticle to respectively enhance the optical near field and produce heat. The benefit of these numbers compared to previously defined figures of merit is that (i) they possess simple close-form expressions and can be simply calculated without numerical simulations, (ii) they give quantitative estimations in the nonretar...
TL;DR: Nikolov et al. as discussed by the authors reported the optical to near-infrared transmission spectroscopy of the hot-Jupiter WASP-6b, measured with the Space Telescope Imaging Spectrograph and Spitzer's InfraRed Array Camera.
Abstract: Author(s): Nikolov, N; Sing, DK; Burrows, AS; Fortney, JJ; Henry, GW; Pont, F; Ballester, GE; Aigrain, S; Wilson, PA; Huitson, CM; Gibson, NP; Desert, JM; Lecavelier des Etangs, A; Showman, AP; Vidal-Madjar, A; Wakeford, HR; Zahnle, K | Abstract: We report Hubble Space Telescope optical to near-infrared transmission spectroscopy of the hot-Jupiter WASP-6b, measured with the Space Telescope Imaging Spectrograph and Spitzer's InfraRed Array Camera. The resulting spectrum covers the range 0.29-4.5 μm. We find evidence for modest stellar activity of WASP-6 and take it into account in the transmission spectrum. The overall main characteristic of the spectrum is an increasing radius as a function of decreasing wavelength corresponding to a change of Δ (Rp/R*) = 0.0071 from 0.33 to 4.5 μm. The spectrum suggests an effective extinction cross-section with a power law of index consistent with Rayleigh scattering, with temperatures of 973 ± 144K at the planetary terminator. We compare the transmission spectrum with hot-Jupiter atmospheric models including condensate-free and aerosol-dominated models incorporating Mie theory. While none of the clear-atmosphere models is found to be in good agreement with the data, we find that the complete spectrum can be described by models that include significant opacity from aerosols including Fe-poor Mg2 SiO4, MgSiO3, KCl and Na2S dust condensates.WASP- 6b is the second planet after HD 189733b which has equilibrium temperatures near ~1200K and shows prominent atmospheric scattering in the optical.
TL;DR: An Yb:YAG thin-disk multipass laser amplifier delivering sub-8 ps pulses at a wavelength of 1030 nm with 1420 W of average output power and 4.7 mJ of pulse energy is reported on.
Abstract: We report on an Yb:YAG thin-disk multipass laser amplifier delivering sub-8 ps pulses at a wavelength of 1030 nm with 1420 W of average output power and 4.7 mJ of pulse energy. The amplifier is seeded by a regenerative amplifier delivering 6.5 ps pulses with 300 kHz of repetition rate and an average power of 115 W. The optical efficiency of the multipass amplifier was measured to be 48% and the beam quality factor was better than M2 = 1.4. Furthermore we report on the external second harmonic generation from 1030 nm to 515 nm using an LBO crystal leading to an output power of 820 W with 2.7 mJ of energy per pulse. This corresponds to a conversion efficiency of 70%. Additionally, 234 W of average power were obtained at the third harmonic with a wavelength of 343 nm.
TL;DR: By exciting particles at their optimized sizes with the corresponding optimized laser wavelengths, the authors achieved a detection limit of roughly around 100 pM and 80 pM for NCs and NBs, respectively.
Abstract: We systematically investigated the size- and shape-dependent SERS activities of plasmonic core–shell nanoparticles towards detection of the pesticide thiram. Monodisperse Au@Ag nanocubes (NCs) and Au@Ag nanocuboids (NBs) were synthesized and their Ag shell thickness was precisely adjusted from ∼1 nm to ∼16 nm. All these nanoparticles were used as SERS substrates for thiram detection, and the Raman intensities with three different lasers (514 nm, 633 nm and 782 nm) were recorded and compared. Our results clearly show that: (1) the excitation wavelength discriminated particle shapes regardless of particle sizes, and the maximized Raman enhancement was observed when the excitation wavelength approaches the SERS peak (provided there is significant local electric field confinement on the plasmonic nanostructures at that wavelength); (2) at the optimized laser wavelength, the maximum Raman enhancement was achieved at a certain threshold of particle size (or silver coating thickness). By exciting particles at their optimized sizes with the corresponding optimized laser wavelengths, we achieved a detection limit of roughly around 100 pM and 80 pM for NCs and NBs, respectively.
TL;DR: The results presented in this paper could be considered as an important contribution to the understanding of the enhanced transmission phenomenon based on the excitation of guided modes.
Abstract: This paper is devoted to the study of the transmission properties of Slanted Annular Aperture Arrays made in perfectly conducting metal. More precisely, we consider the transmission based on the excitation of the cutoff-less guided mode, namely the TEM mode. We numerically and analytically demonstrate some intrinsic properties of the structure showing a transmission coefficient of at least 50% of an unpolarized incident beam independently of the illumination configuration (angle and plane of incidence). The central symmetry exhibited by the structure is analytically exploited to demonstrate the existence of a polarization state for which all the incident energy is transmitted through the sub-wavelength apertures when the eigenmode is excited, whatever are the illumination and the geometrical parameters. For this state of polarization, the laminar flow of the energy through the structure can exhibit giant deviation over very small distances. An example of energy flow deviation of 220° per wavelength is presented for illustration. The results presented in this paper could be considered as an important contribution to the understanding of the enhanced transmission phenomenon based on the excitation of guided modes.
TL;DR: The results show that the Mie resonance can be continuously tuned across a wide range of wavelength by varying the diameter of the nanopillars, and Si nanocone arrays can strongly interact with the incident light in the broadband spectrum and the absorbance is higher than 95% over the wavelength from 300 to 2000 nm.
Abstract: Nanostructure arrays such as nanowire, nanopillar, and nanocone arrays have been proposed to be promising antireflection structures for photovoltaic applications due to their great light trapping ability. In this paper, the optical properties of Si nanopillar and nanocone arrays in visible and infrared region were studied by both theoretical calculations and experiments. The results show that the Mie resonance can be continuously tuned across a wide range of wavelength by varying the diameter of the nanopillars. However, Si nanopillar array with uniform diameter exhibits only discrete resonance mode, thus can't achieve a high broadband absorption. On the other hand, the Mie resonance wavelength in a Si nanocone array can vary continuously as the diameters of the cross sections increase from the apex to the base. Therefore Si nanocone arrays can strongly interact with the incident light in the broadband spectrum and the absorbance by Si nanocone arrays is higher than 95% over the wavelength from 300 to 2000 nm. In addition to the Mie resonance, the broadband optical absorption of Si nanocone arrays is also affected by Wood-Rayleigh anomaly effect and metal impurities introduced in the fabrication process.
TL;DR: In this article, a bulk acoustic wave (BAW)-mediated multiferroic antenna structure is proposed and its potential for efficient radiation of electromagnetic waves is evaluated by analytically deriving the lower bound of its radiation quality factor ( $Q$ factor).
Abstract: Time-varying magnetic flux can be induced from the dynamic mechanical strain of acoustic waves in multiferroic devices that are comprised of piezoelectric and magnetostrictive material. Such devices can be used to create electromagnetic radiation and to alleviate the platform effect associated with low-profile conformal antennas. In this paper, a bulk acoustic wave (BAW)-mediated multiferroic antenna structure is proposed. Its potential for efficient radiation of electromagnetic waves is evaluated by analytically deriving the lower bound of its radiation quality factor ( $Q$ factor). A one-dimensional (1-D) multiscale finite-difference time-domain (FDTD) technique is developed to predict the bilateral, dynamic coupling between the acoustic waves and electromagnetic waves. The simulation shows a decaying stress profile in the BAW resonator structure, which implies that the radiation of the electromagnetic waves acts as a damping load to the acoustic resonance. The simulated radiation $Q$ factor matches well with the analytical derivations and the agreement validates both the operating principle of the proposed antenna and the FDTD algorithm developed. The study concludes that efficient antennas may be realized at GHz frequencies with thin film multiferroic material that has thicknesses of the order of $10^{-5}$ wavelength.
TL;DR: Second harmonic spectroscopy of aluminum nanoantenna arrays that exhibit plasmonic resonances at the second harmonic wavelength is performed by focusing sub-30 fs laser pulses tunable from 900 to 1140 nm onto the nanoantennas.
Abstract: We perform second harmonic spectroscopy of aluminum nanoantenna arrays that exhibit plasmonic resonances at the second harmonic wavelength between 450 and 570 nm by focusing sub-30 fs laser pulses tunable from 900 to 1140 nm onto the nanoantenna arrays. We find that a plasmonic resonance at the second harmonic wavelength boosts the overall nonlinear process by more than an order of magnitude. In particular, in the measurement the resonant second harmonic polarization component is a factor of about 70 stronger when compared to the perpendicular off-resonant second harmonic polarization. Furthermore, the maximum of the second harmonic conversion efficiency is found to be slightly blue-shifted with respect to the peak of the linear optical far-field spectrum. This fact can be understood from a simple model that accounts for the almost off-resonant absorption at the fundamental wavelength and the resonant emission process at the second harmonic.
TL;DR: In this paper, a new structural color generation mechanism that produces colors by the Fano resonance effect on thin photonic crystal slab was proposed, and the resonance-induced colors can be dynamically tuned by stretching the photonic laser slab fabricated on an elastic substrate.
Abstract: Structural coloration is an interference phenomenon where colors emerge when visible light interacts with nanoscopically structured material and has recently become a most interesting scientific and engineering topic. However, current structural color generation mechanisms either require thick (compared to the wavelength) structures or lack dynamic tunability. This report proposes a new structural color generation mechanism that produces colors by the Fano resonance effect on thin photonic crystal slab. We experimentally realize the proposed idea by fabricating the samples that show resonance-induced colors with weak dependence on the viewing angle. Finally, we show that the resonance-induced colors can be dynamically tuned by stretching the photonic crystal slab fabricated on an elastic substrate.
TL;DR: A method to control the behaviors of different light waves through a metasurface which is able to generate achromatic geometric phase is proposed and may open a new door to the design of subminiature optical components and integrated optical system operating at multiple wavelengths.
Abstract: The independent control of electromagnetic waves with different oscillating frequencies is critical in the modern electromagnetic techniques, such as wireless communications and multispectral imaging. To obtain complete control of different light waves with optical materials, the chromatic dispersion should be carefully controlled, which is however extremely difficult. In this paper, we propose a method to control the behaviors of different light waves through a metasurface which is able to generate achromatic geometric phase. Using this approach, a doughnut-shaped and a solid light spot were achieved at the same focal plane using two light sources with different wavelengths as used in the stimulation emission depletion (STED) microscope system. In order to reveal the full capacity of such method, tight focusing at multiple wavelengths is also represented, where the focal spots of different wavelengths are located at the same position. The results provided here may open a new door to the design of subminiature optical components and integrated optical system operating at multiple wavelengths.
TL;DR: In this paper, the authors extended the super-oscillation concept into the vectorial-field regime to work with circularly polarized light, and experimentally demonstrated a circularly polarized optical needle with sub-diffraction transverse spot size (0.45l) and axial long depth of focus (DOF) of 15l using a planar SOL at a violet wavelength of 405 nm.
Abstract: Planar optical lenses are fundamental elements of miniaturized photonic devices. However, conventional planar optical lenses are constrained by the diffraction limit in the optical far-field due to the band-limited wavevectors supported by free-space and loss of high-spatial-frequency evanescent components. As inspired by Einstein’s radiation ‘needle stick’, electromagnetic energy can be delivered into an arbitrarily small solid angle. Such sub-diffraction optical needles have been numerically investigated using diffractive optical elements (DOEs) together with specially polarized optical beams, but experimental demonstration is extremely difficult due to the bulky size of DOEs and the required alignment precision. Planar super-oscillatory lenses (SOLs) were proposed to overcome these constraints and demonstrated that sub-diffraction focal spots can actually be formed without any evanescent waves, making far-field, label-free super-resolution imaging possible. Here we extend the super-oscillation concept into the vectorial-field regime to work with circularly polarized light, and experimentally demonstrate, for the first time, a circularly polarized optical needle with sub-diffraction transverse spot size (0.45l) and axial long depth of focus (DOF) of 15l using a planar SOL at a violet wavelength of 405 nm. This sub-diffraction circularly polarized optical needle has potential applications in circular dichroism spectroscopy, super-resolution imaging, high-density optical storage, heat-assisted magnetic recording, nano-manufacturing and nano-metrology.
TL;DR: In this article, a demultiplexing grating is proposed to separate O-band and C-band light into separate waveguides, where the user specifies design constraints in the form of target fields rather than a dielectric constant profile.
Abstract: Nanophotonics has emerged as a powerful tool for manipulating light on chips. Almost all of today's devices, however, have been designed using slow and ineffective brute-force search methods, leading in many cases to limited device performance. In this article, we provide a complete demonstration of our recently proposed inverse design technique, wherein the user specifies design constraints in the form of target fields rather than a dielectric constant profile, and in particular we use this method to demonstrate a new demultiplexing grating. The novel grating, which has not been developed using conventional techniques, accepts a vertical-incident Gaussian beam from a free-space and separates O-band (1300 nm) and C-band (1550 nm) light into separate waveguides. This inverse design concept is simple and extendable to a broad class of highly compact devices including frequency filters, mode converters, and spatial mode multiplexers.
TL;DR: In this article, the dispersion relation of the wave propagating in narrow waveguides on one side of which quarter-wavelength resonators are plugged with a square lattice, whose periodicity is smaller than the wavelength, is analyzed.
Abstract: We demonstrate that the phenomenon of slow sound propagation associated with its inherent dissipation (dispersion + attenuation) can be efficiently used to design sound absorbing metamaterials The dispersion relation of the wave propagating in narrow waveguides on one side of which quarter-wavelength resonators are plugged with a square lattice, whose periodicity is smaller than the wavelength, is analyzed The thermal and viscous losses are accounted for in the modeling We show that this structure slows down the sound below the bandgap associated with the resonance of quarter-wavelength resonators and dissipates energy After deriving the effective parameters of both such a narrow waveguide and a periodic arrangement of them, we show that the combination of slow sound together with the dissipation can be efficiently used to design a sound absorbing metamaterial which totally absorbs sound for wavelength much larger than four times the thickness structure This last claim is supported by experimental results
TL;DR: This study investigates at room temperature the excited state lifetime of single NV(-)/NV0 in nanodiamonds at a variety of excitation wavelengths from 510 to 570 nm and concludes that the variation observed can be attributed to the specific nanod diamonds.
Abstract: In this paper we investigate at room temperature the excited state lifetime of single NV-/NV0 in nanodiamonds at a variety of excitation wavelengths from 510 to 570 nm. The average lifetimes of 25 nanodiamonds with similar sizes exhibit constant values over the entire investigated spectral window. We conclude that the variation observed can be attributed to the specific nanodiamonds. Therefore it is sample dependent, rather than related to the photo-physical properties of the defects. Our study is relevant for the potential use of nanodiamonds containing NV in application where the lifetime is used for sensing the local nano-environment.
TL;DR: In this paper, a field-deployable water vapor profiling instrument that builds on the foundation of the preceding generations of diode-laser-based differential absorption lidar (DIAL) laboratory prototypes was constructed and tested.
Abstract: . A field-deployable water vapor profiling instrument that builds on the foundation of the preceding generations of diode-laser-based differential absorption lidar (DIAL) laboratory prototypes was constructed and tested. Significant advances are discussed, including a unique shared telescope design that allows expansion of the outgoing beam for eye-safe operation with optomechanical and thermal stability; multistage optical filtering enabling measurement during daytime bright-cloud conditions; rapid spectral switching between the online and offline wavelengths enabling measurements during changing atmospheric conditions; and enhanced performance at lower ranges by the introduction of a new filter design and the addition of a wide field-of-view channel. Performance modeling, testing, and intercomparisons are performed and discussed. In general, the instrument has a 150 m range resolution with a 10 min temporal resolution; 1 min temporal resolution in the lowest 2 km of the atmosphere is demonstrated. The instrument is shown capable of autonomous long-term field operation – 50 days with a > 95% uptime – under a broad set of atmospheric conditions and potentially forms the basis for a ground-based network of eye-safe autonomous instruments needed for the atmospheric sciences research and forecasting communities.
TL;DR: In this article, a broadband, polarization-insensitive, and wide-angle terahertz metamaterial absorber is constructed by stacking multiple metal-dielectric layers with differently sized saw-shaped annular patch structures in the unit cell.