We demonstrate that the temporal profile of the transverse nanoseсond photovoltage pulse generated in the thin
semiсonduсtor СuSe/t-Se nanoсomposite film under irradiation with elliptiсally polarized femtoseсond pulse is determined
by the interplay of linear and сirсular photoсurrents. These photoсurrents have different durations indiсating the
dependenсe of the relaxation time of the photogenerated сarriers on their spin. The interplay of photoсurrent results in the
generation of either unipolar or bipolar pulse with temporal profile dependent on the handedness, shape, and orientation
of the polarization ellipse of the laser beam relative to the plane of incidence.
We propose a novel waveguide type based on the concept of strip-loaded waveguide. A strip-loaded waveguide is composed of a thin-film slab waveguide allowing a vertical confinement of the electromagnetic field. A lower refractive index strip provides the lateral confinement by inducing a slight modification of the effective index in the slab. By using such a generic device we will demonstrate how the limits of integrated photonics can be extended, especially, in terms of propagation losses while adding complex structure on the waveguide. Since light sees only a slight variation of effective index, and not an abrupt change of material, propagation losses of the device are fully determined by the film rather than by the structuration. Different micro- and nano-structures will be presented through simulation and experimental results. We will focus especially on the study of Y-junctions, ring resonators, interferometers, and Bragg gratings. Another advantage of strip-loaded waveguides is the simplicity of fabrication. In order to fabricate the devices we employed nano-imprinting of polymer, a fabrication technique suitable for mass production. The low refractive index of the polymer allows a large panel of materials for the slab waveguide, e.g., silicon, titanium dioxide, and lithium niobate. This diversity in the choice of the materials gives to the platform the potential to operate on a wide wavelength range from UV to IR, for multiple applications in telecommunications, sensing and bio-sensing, and medical devices.
We propose the nonlinear Fourier Modal Method (FMM) [J. Opt. Soc. Am. B 31, 2371 (2014)] as a convenient and versatile numerical tool for the design and analysis of grating based next generation all-optical devices. Here, we include several numerical examples where the FMM is used to simulate all-optically tunable functionalities in sub-wavelength periodic structures. At first, we numerically investigate a 1-D periodic nonlinear binary grating with amorphous TiO2. We plot the diffraction efficiency in the transmitted orders against the structure depth for normally incident plane wave. Change in diffraction efficiencies for different incident field amplitudes are evident from the plots. We verify the accuracy of our implementation by comparing our results with the results obtained with the nonlinear Split Field-Finite Difference Time Domain (SF-FDTD) method. Next we repeat the same experiment with vertically standing amorphous Titanium dioxide (TiO2) nanowire arrays grown on top of quartz which are periodic in two mutually perpendicular directions and examine the efficiencies in the direct transmitted light for different incident field amplitudes. Our third example includes analysis of a form birefringent linear grating with Kerr medium. With FMM we demonstrate that the birefringence of such a structure can be tuned by all-optical means. As a final example, we design a narrow band Guided Mode Resonance Filter (GMRF). Numerical experiments based on the nonlinear FMM reveal that the spectral tunability of such a filter can be obtained by all-optical means.
Using the Fourier Modal Method for gratings with Kerr media [J. Opt. Soc. Am. B 31, 2371 (2014)] we demonstrate that low energy Optical Bistability for normally incident light field can be observed by strong nonlinear light-matter interactions in a Silicon Nitride waveguide-grating with 2-D periodicity. Finite divergence of the incident light beam has been taken into account in our numerical study and the gratings are designed to observe bistable behavior in direct transmitted light inside the optical telecommunication C-band (1520 nm-1570 nm). The waveguide grating structures are fabricated from PECVD synthesized Silicon Nitride thin film on top of quartz with standard electron beam lithography and reactive ion etching techniques. We aim to demonstrate this phenomenon experimentally using a tunable narrow line-width pulsed laser. Our resonant nanostructures may find applications in free space all-optical information processing and all-optical switching.
We demonstrate that the integration of graphene strongly influences optical properties of the subwavelength gratings, opening a way toward nanophotonic devices. By using the Fourier-expansion modal method, we demonstrate that graphene–titanium dioxide nanostructures can be used for designing polarization-insensitive absorbers and biochemical sensors.
We introduce a numerically feasible method for rigorous modeling of crossed diffraction gratings with isotropic
third order nonlinear materials. The approach is based on an iterative solution of the crossed grating problem
with anisotropic linear materials. Several numerical experiments are performed to demonstrate the versatility
and numerical stability of our computation scheme. Resonance waveguide gratings made of isotropic cubic
nonlinear materials are investigated numerically using this newly developed technique. A polarization-sensitive
shift of resonance peak with variation of light intensity is numerically demonstrated.
We experimentally investigated the electrical and electromagnetic (EM) properties of
pyrolytic carbon (PyC) ultrathin films synthesized on a quartz substrate by chemical vapor deposition at 1100°C using low pressure CH4∶H2 gas mixture as carbon source. PyC films consist of randomly oriented and intertwined graphene ribbons, which have a typical size of a few nanometers. We discovered that the manufactured PyC films of 35-nm thickness provided remarkably high attenuation caused by absorption of 37% to 24% of incident microwave power. The temperature dependence of PyC’s direct-current (DC) conductivity represents typical behavior for disordered systems. Being semitransparent in visible and infrared spectral range and highly conductive at room temperature, PyC films emerge as a promising material for manufacturing ultrathin microwave (e.g., Ka band) coatings to be used in aerospace applications.
Ultrathin pyrolytic carbon films were synthesized in a single step on dielectric substrates, using a methane-based chemical vapor deposition technique. The developed technique enables the production of wafer scale transparent conductive films suitable for applications in optics and optoelectronics.
Recently a remarkable phenomenon in ultrafast laser processing of transparent materials has been reported manifesting
itself as a change in material modification by reversing the writing direction. It has been experimentally demonstrated
that the pulse front tilt is responsible for the occurrence of directional dependence. Additionally, an anisotropic
cavitation was observed in the vicinity of the focus at high fluences. The bubbles, formed in the bulk of the glass, can be
trapped and manipulated in the plane perpendicular to the light propagation direction by controlling the laser writing
direction relative to the tilt of the pulse front. Another intriguing effect recently discovered occurs when the direction of
the femtosecond laser beam is reversed from +Z to - Z directions, the structures written in a lithium niobate crystal are
mirror images when translating the beam along the +Y and -Y directions. In contrast to glass, the directional dependence
of writing in lithium niobate depends on the orientation of the crystal with respect to the direction of the beam movement
and the light propagation direction. A theoretical model was created to demonstrate how in the lithium niobate, the
nonreciprocal photosensitivity manifests itself as a changing the sign of the light-induced current when the light
propagation direction is reversed. Therefore, in a non-centrosymmetric medium, modification of the material can be
different when light propagates in opposite directions.
When a linearly polarized light wave propagates in a chiral medium, the polarization plane azimuth rotates
clockwise or counter-clockwise depending on the handedness of the material. This effect is called optical activity.
It can be observed in a number of crystals and organic liquids, however the rotatory power of chiral materials
available in nature is useally very small. That is why chiral planar micro- or nano-structures, which possess a
much stronger rotatory power than natural chrial media, have attracted a considerable attention in recent years.
We demonstrate large optical activity of chiral subwavelength gratings having no in-plane mirror symmetry and
fabricated with metal thin films. For zeroth-order transmitted light, the chirality of these gratings manifests itself
in the non-coplanarity of the electric field vectors at the air- and substrate-sides of the metal layer and can be
interpreted in terms of the surface pllasmon enhanced non-local
light-matter interaction. We demonstrate also
that in all-dielectric subwavelength chiral gratings, the optical activity can be enhanced even stronger by using
waveguide resonance. In the terahertz (THz) region, we obtain rotation of the polarization zimuth of a linearly
polarized THz wave by using double-layered metal chiral structure with complimentary patterns.
We studied performance of a fast-response nanographite film photodetector (PD) in the temperature range of 300-
1000 K. In experiment, we measured the magnitude of the electric signal generated in nanographite film (NGF) under
irradiation of intense nanosecond laser pulses at λ=1.064 μm. In vacuum, the measurements of the PD sensitivity were
performed in the temperature range of 300-800 K. We showed experimentally that the PD sensitivity at 300 K was about
30% higher than that at 625 K and 50% higher than that at 740 K. At T>625 K, the magnitude of the light-induced signal
decreases as a linear function of temperature and vanish at T ≈ 1000 K. In atmospheric conditions, we observed a stable
operation of the NGF-based PD during several tens of hours in the temperature range from 300 to 580 K. However, at
higher temperature, degradation of the NG film resulted in a drop in the PD sensitivity.
We present a comprehensive multipolar tensor analysis to investigate the roles of dipolar and higher-order
multipoles to second-harmonic radiation from a regular array of noncentrosymmetric L-shaped gold nanoparticles.
We find the nonlinear response to be dominated by a tensor component which is associated with chiral symmetry
breaking and has strong multipolar character. These findings substantiate our interpretation that one of the
major contributors to the optical response of the present sample are structural defects, which break the symmetry
and make multipolar contributions to the SH response important.
Nanoscale variations in the local fields and material properties can enable higher-multipole (magnetic-dipole and
electric-quadrupole) contributions to the nonlinear response in addition to electric-dipole contributions. Moreover,
the local-field distribution in the structure is important to achieve favorable interaction with the locally varying
nonlinearity. Local-field enhancement is particularly important for nonlinear optical effects. Extremely
small features of a few nm, such as nanogaps between two particles, are expected to be particularly beneficial
for field localization and enhancement. Here, we provide evidence of multipole interference in polarized secondharmonic
generation from arrays of L-shaped gold nanoparticles. We also prepare T-shaped gold nanodimers
and vary the size of the nanogap between their vertical and horizontal bars. Surprisingly, the second-harmonic
signals do not decrease trivially with increasing gap size, because the gap region is nearly centrosymmetric,
thereby forbidding second-order effects. Instead, asymmetric local fundamental field distributions along the
dimer perimeter are favorable, in accordance with the symmetry rule.
Pump-probe femtosecond transmission measurements in the vicinity of the first excitonic resonance are performed in a silicate glass embedded with Cd-S-Se semiconductor nanoparticles. In the experiment, the pump at 400 nm (duration 50 fs, energy up to 0.1 mJ) excites the sample, while the change of the optical absorption is probed by femtosecond continuum. The time-resolved spectrum of the absorption change in the wavelength range 450-650 nm is visualized using a two-channel imaging spectrometer. A strong optical nonlinearity of the glass containing Cd-S-Se nanoparticles results in the up to 50% bleaching of the first excitonic resonance via the depopulating of the ground state. The temporal evolution of the bleaching consists of fast (with relaxation time as small as 3 ps) and slow (>15 ps) components. The dependence of the nonlinear absorption on the detuning of the pump and probe wavelengths with respect to the exciton resonance is evaluated.
Great progress has been achieved in fabricating arbitrary metal nanoparticle shapes and geometries in order to control their linear optical properties. However, their nonlinear optical properties, particularly their second-order response, are frequently overlooked. Exploiting the nonlinear responses of metal nanoparticles opens another exciting avenue for developing nanoscale photonics applications. Second-harmonic generation (SHG) from metal nanoparticles is typically attributed to electric dipole excitations at their surfaces, but nonlinearities involving higher multipole effects, such as magnetic dipole interactions, electric quadrupoles, etc., may also be significant due to strong nanoscale gradients in the local material properties and fields. The nanoscale nonlinear optical processes in metal nanoparticles are not well-understood at present, and determining the sources of the SHG response can be arduous. In order to study the role of higher multipoles in the second-order response of gold nanoparticle arrays, we propose SHG measurements employed in both transmission and reflection geometries. Due to different radiative properties of the various multipoles in the forward and backward directions, the presence of multipoles should lead to opposing interference effects in the two directions. Strong polarization dependence of the response can modify the relative strengths of the interfering terms, thereby allowing electric-dipole and higher-multipole contributions to the overall SHG response to be distinguished. Analysis of the measured polarization dependencies would thus provide further knowledge of the mechanisms underlying the nanoscale SHG process in gold nanoparticles.
A simple high-speed photodetector of high-power laser radiation, based on the optical rectification effect in the nanographit film, is described. It operates without an external power source. The spectral dependence of the optical rectification effect in nanostructured carbon (nanographite) films obtained by plasmachemical deposition was studied in a wavelength range from 266 to 5000 nm. The performance of this device was demonstrated by detecting pulsed laser radiation using the second, third, and fourth harmonics of radiation from an YAG:Nd3+-laser with passive Q-switching, radiation from light oscillators based on stimulated Raman scattering in compressed hydrogen and parametric oscillator pumped by the second harmonic of the YAG:Nd3+-laser. It was shown that the photodetector response time is shorter than 0.5 ns. It is suggested that nanographite films are promising materials for detectors of ultrashort laser pulses in the IR, visible, and UV spectral intervals and for generators of electromagnetic radiation operating in the terahertz frequency range.
The physical processes underlying the complex nanoscale optical responses of metal nanoparticles must be understood
both experimentally and theoretically if they are to be developed for use in photonic devices. While
many linear optical measurements have been performed on gold nanoparticle arrays, only a handful of nonlinear
measurements have been reported. Here, we discuss a collection of experiments of both types on arrays of gold
nanoparticles. However, on nanoscale-rough metal surfaces, such as nanoparticles with small-scale defects, local
electric fields may vary rapidly and strong field gradients can induce significant multipolar contributions, making
a theoretical description of second-harmonic generation (SHG) from nanoparticle arrays infeasible at present.
A macroscopic nonlinear response tensor approach based on the input and output fields to the system avoids
with these complications. Contributions from higher multipoles are implicitly included, and electric-dipole-type
selection rules can be applied to address symmetry issues. While the experimental geometry constrains the
formalism, additional insight into the underlying physical processes is expected from experimental variations.
Good agreement with direct SHG tensor measurements validates the formalism, providing the framework for a
deeper understanding of the nanoscale optical responses of metal nanoparticles.
Planar chirality can lead to interesting polarization effects whose interpretation has invoked possible violation of reciprocity and time reversality. We show that a quasi-two-dimensional array consisting of gold nanoparticles with no symmetry plane and having sub-wavelength periodicity and thickness exhibits giant specific rotation (~104 °/mm) at normal incidence. The rotation is the same for light incident on the front and back sides of the sample. Such reciprocity manifests three-dimensionality of the structure arising from the asymmetry of light-plasmon coupling at the air-metal and substrate-metal interfaces of the structure. The structures thus enable nanoscale polarization control but violate no symmetry principle.
Metallic nanostructures can have strong effects on the polarization state of light and present significant polarization sensitivity. However, quite often these phenomena have only negligible effects thus passing our attention without careful analysis. We show that these effects can be enhanced by using resonance effects arising from waveguide modes propagating along the surface. This enables the use of metallic nanostructures as artificial media components modulating the polarization state of light.
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