Incident Optical Radiation Research Articles

Reduced ITO for transparent superconducting electronics

Absorption of light in superconducting electronics is a major limitation on the quality of circuit architectures that integrate optical components with superconducting components. A 10 nm thick film of a typical superconducting material like niobium can absorb over half of any incident optical radiation. Instead, we propose using superconductors that are transparent to the wavelengths used elsewhere in the system. In this paper, we investigated reduced indium tin oxide (ITO) as a potential transparent superconductor for electronics. We fabricated and characterized superconducting wires of reduced ITO. We also showed that a thick film of this material would only absorb about 1%–20% of light between 500 and 1700 nm.

Carbon nanotube electron blackbody and its radiation spectra

An optical blackbody is an ideal absorber for all incident optical radiation, and the theoretical study of its radiation spectra paved the way for quantum mechanics (Planck's law). Herein, we propose the concept of an electron blackbody, which is a perfect electron absorber as well as an electron emitter with standard energy spectra at different temperatures. Vertically aligned carbon nanotube arrays are electron blackbodies with an electron absorption coefficient of 0.95 for incident energy ranging from 1 keV to 20 keV and standard electron emission spectra that fit well with the free electron gas model. Such a concept might also be generalized to blackbodies for extreme ultraviolet, X-ray, and γ-ray photons as well as neutrons, protons, and other elementary particles.

Electro-optically tunable cascaded second-order nonlinearity induced (2 + 1)D spatial optical soliton using bulk β-barium borate crystal: a theoretical approach

This paper deals with the development of an effective theoretical approach to generate spatial optical soliton in exceptionally beneficial bulk beta-barium-borate crystal by utilizing cascaded second-order nonlinearity through electro-optic tuning. The proposed methodology paves the way for novel nonlinear optical interactions conceptualized in bulk material depending upon an effective nonlinear refractive index for a broad range of crystal lengths. The development of ( 2 + 1 ) D spatial bright soliton has been analytically demonstrated at 800 nm wavelength of the incident continuous-wave optical radiation, and the implication of tunable electro-optic effect to the crystal’s nonlinear response is also presented here. Involvement of the generalized nonlinear Schrödinger equation has been utilized to develop the necessary and sufficient criteria for self-trapping optical beams considering both linear and nonlinear absorption losses. In conformity with the findings of the simulation, the beam diameter of a generated spatial soliton within this anisotropic crystal is near 56 µm while maintaining precise peak intensity ∼ 0.8 G W / c m 2 .

Gold Coated VO2 Nanogratings Based Plasmonic Switches

This paper presents 2 dimensional (2D) and 1 dimensional (1D) gold (Au) coated VO2 (Vanadium Dioxide) nanogratings based tunable plasmonic switch. VO2 is a phase changing material and hence exhibits phase transition from semiconductor to metallic phase approximately at 67 ºC or 340 K (critical temperature) which can be achieved by exposure to IR radiation, application of voltage, heating, etc. and there is a huge contrast between optical properties of its metallic and insulating phases and hence that can be utilized to implement VO2 based optical switches. These VO2 based gratings couple the incident optical radiation to plasmonic waveguide modes which in turn leads to high electromagnetic field enhancement in the gaps between the nanogratings. The proposed Au coated VO2 nanogratings can be fabricated by using current state of art fabrication techniques and provides switchability of the order of femtoseconds. Hence the optical switching explained in our paper can be used fast switching applications. For an optimum switch our aim is to maximize its differential reflectance spectra between the 2 states of VO2, i.e., metallic and semiconductor phases. Rigorous Coupled Wave Analysis (RCWA) reveals that wavelengths for maximum differential reflectance can be optimized over a large spectral regime by varying various parameters of nanogratings for example groove height (h), width (w), gap (g) between the gratings, and thickness (t) of Au coating over VO2 by simulation using RCWA for maximum differential reflectance between VO2 metal and semiconductor phase, i.e., the switching wavelengths can be tuned by varying grating parameters and thus we can have optimum optical switch.

Non-Uniform Narrow Groove Plasmonic Nano-Gratings for SPR Sensing and Imaging

A surface plasmon resonance sensing and imaging platform based on plasmonic non-uniform nano-gratings with narrow groove (sub-10 nm) is presented. In these nanogratings, normally incident optical radiation is directly coupled to surface plasmons without the requirements of any other conventional surface plasmon coupling mechanisms such as prism-based or grating-based coupling. Theoretical analysis of practically realizable plasmonic non-uniform nano-gratings with rounded tops and slanted sidewalls is carried out to numerically to determine reflectance and differential reflectance signals when the localized refractive index of the medium around the gold layer present in these nano-gratings is changed. This change in the localized refractive index can occur due to the binding of biomolecules to the gold layer. Two kinds of plasmonic non-uniform nano-gratings are studied using finite difference time domain (FDTD) modelling: gold nano-gratings (GNGs) and gold-coated silicon nano-gratings (GSNGs). The plasmonic non-uniform nano-gratings being proposed, more specifically the GSNGs, can be easily fabricated with the presently existing nanofabrication and thin film deposition methods as opposed to uniform nano-gratings (with parallel sidewalls) that are very difficult to fabricate. The plasmonic non-uniform nano-gratings with narrow grooves eliminate the strict requirements on the angle of incidence for coupling of light into surface plasmons, which are needed in conventional prism-based coupling mechanisms. By employing FDTD calculations, we demonstrate that these plasmonic non-uniform nano-gratings provide very high differential reflectance amplitude values, which are indicative of high sensitivities of the SPR or SPRi sensors when the localized refractive index around the sensors is varied. Moreover, the sensors being proposed in this article provide a maximum sensitivity of localized refractive index sensing (i.e. surface sensitivity or $\text{S}_{\mathrm {S}}$ ) of 70 nm/nm with a figure of merit of the localized sensor (FOMS) of 1.5 nm $^{-1}$ . This sensitivity of localized refractive index sensing is the highest reported thus far in comparison with previously reported plasmonic sensors. Moreover, these plasmonic non-uniform nano-grating based sensors exhibit significantly better performance when compared with conventional SPR or SPRi sensors based on the Kretschmann configuration.

Computer simulation of optical radiation scattering by aerosol media

Development of the technologies simulating optical processes in an arbitrary dispersed medium is one of the important directions in the field of optical instrumentation and can provide computer simulation of the processes instead of using expensive equipment in physical experiments. The goal of the study is simulation of scattering of optical radiation by aerosol media using the finite element method to show a practical significance of the results of virtual experiments. We used the following initial conditions of the model: radius of a spherical particle of distilled water is 1 μm, wavelength of the incident optical radiation is 0.6328 μm, air is a medium surrounding the particle. An algorithm for implementation of the model by the finite element method is proposed. A subprogram has been developed which automates a virtual experiment for a group of particles to form their random arrangement in the model and possibility of changing their geometric shape and size within predetermined intervals. Model dependences of the radiation intensity on the scattering angle for single particle and groups of particles are presented. Simulation of the light transmission through a dispersed medium provides development of a given photosensor design and determination of the minimum number of photodetectors when measuring the parameters of the medium under study via analysis of the indicatrix of scattering by a group of particles.

Far-Field Control of Nanoscale Hotspots by Near-Field Interference

Optical nanoantennas coherently scatter incident optical radiation, creating a localized electromagnetic near-field imprinted with subwavelength phase distribution, rapidly changing in space. The n...

Optical properties of nanowires synthesized in regular nanochannels of porous matrices

Arrays of nanowires were synthesized in a matrix of natural chrysotile. It was found that the diameter of the nanowires was about 5 nm, the length was close to 1 cm. X-ray diffraction showed that the nanowires have a polycrystalline structure. The results of an experimental study of Raman scattering in Se and InSb nanowires are presented. Analysis of the experimental results showed that the frequencies of optical phonons in Se nanowires are close to the frequencies of phonons in bulk samples. The frequencies of optical phonons in InSb nanowires differ significantly from those in bulk samples, which are apparently related to the interaction of optical phonons and conduction electrons. The properties of conduction electrons differ greatly when they propagate along or across the nanowire. Therefore, Raman scattering is anisotropic in nature. As result, the experimental spectra vary depending on the polarization of the incident optical radiation along or across the nanowires.

Sensitivity comparison of surface plasmon resonance (SPR) and magneto-optic SPR biosensors

Sensitivity of a biosensor is one of the most important parameters that determines its performance. It depends on many factors, such as excitation wavelength of incident optical radiation (\( \lambda\) , composition, type, and thickness of the ferromagnetic Co layer ( \( t_{\rm Co}\) , plasmonic Au, and high refractory metal, Ti, involved, and sensing/excitation configuration. In this paper, both the surface plasmon resonance (SPR at the magnetic field, H = 0 and magneto-optic SPR (MOSPR at H sensitivity of the sensors have been theoretically calculated in the visible wavelength regime using air-helium media as probing samples in the Kretschmann configuration, and their performances are compared side by side. The calculated MOSPR sensitivity of \( 1.25 \times 10^5\%\) /RIU (refractive index unit) at \( \lambda = 632.8\) nm is almost 12.5× larger as compared to the SPR sensitivity of \( 1.0 \times 10^4\%\) /RIU for the same geometry, excitation condition, and probing media. Likewise, the MOSPR sensitivity of \( 1.25 \times 10^5\%\) /RIU at \( \lambda\) = 632.8 nm is almost 10× larger as compared to the MOSPR sensitivity of \( 1.25 \times 10^4\%\) /RIU at \( \lambda\) = 515 nm for the same geometry and probing media. On decreasing the \( t_{\rm Co}\) , the sensitivity of the MOSPR sensor is further increased by almost 3× , from \( 1.25 \times 10^5\%\) /RIU at \( t_{\rm Co} = 8\) nm to \( 3.7 \times 10^5\%\) /RIU at \( t_{\rm Co} = 4\) nm. The sensitivity can be further improved by additional optimization of the material used and sensor configuration employed for detection.

New modulation method in acousto-optic spectrometers

A new method is proposed for modulating radiation in collinear acousto-optic (AO) spectrometers, which is based on the sequential diffraction of incident polarised optical radiation using two sound packets with the same frequencies and initial phases. A theory of diffraction of optical radiation on two successive packets of sound waves propagating in a crystal is constructed, and the instrumental function of the AO spectrometer is found. It is established that the instrumental function of such a spectrometer becomes time-dependent, and the modulation frequency of this dependence, in turn, depends on the intensity of the sound wave and on the detuning from the phase-matching conditions. The frequency dependence of the measured photocurrent for some finite number of sound packets is obtained explicitly, and it is shown that its measurement allows the spectral composition of the incident optical radiation to be determined with greater accuracy.

Light trapping plasmonic butterfly-wing-shaped nanostructures for enhanced absorption and efficiency in organic solar cells

This paper presents organic solar cells (OSCs) containing a one-dimensional (1D) periodic array of plasmonic butterfly-wing-shaped nanostructures, where silver butterfly-wing-shaped nanostructures are present in the back region of the active medium poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophene-4,6-diyl]] with [6,6]-phenyl-C71-butric acid methyl ester. Finite-difference time-domain (FDTD) modeling was employed to simulate the interaction of light with the plasmonic nanostructures, and it was demonstrated that these plasmonic nanostructures lead to a broadband enhancement of light absorption in the active medium. These plasmonic nanostructures lead to enhanced scattering and trapping of the incident optical radiation at multiple wavelengths due to surface plasmon excitation at these wavelengths. This enhanced scattering leads to an increased path length of light, as well as an enhanced intensity of the overall electric field in the active layer of the OSC, which further leads to an increase in absorption. The plasmonic butterfly-wing-shaped nanostructures-containing solar cells were also simulated with indium tin oxide (ITO) nanogratings (NGs) placed on the top surface of the solar cells. It was seen that the presence of the ITO NGs leads to a further enhancement in absorption. In these OSCs containing both the plasmonic butterfly-wing-shaped nanostructures and the ITO NGs, the highest values of enhancements in the absorption and cell efficiency were calculated to be ∼20% and ∼25%, respectively.

The study of quantum efficiency in PIN photodiodes in terms of temperature and capacitive effects under non-uniform illumination conditions

In this article the impacts of quantum efficiency and bandwidth of PIN photodiodes under non-uniform illumination conditions are investigated. An absorption region is divided into the number of arbitrary layers and the continuity equations for each layer are solved with assuming that the carrier’s drift velocity is constant in each layer. Also the impact of transit time and capacitive effects of bandwidth were studied with considering the bias voltage, width of absorption region and temperature. The results show that with considering the capacitive effects, the bandwidth is increased by increase in temperature and bias voltage. We observe the effect of incident optical radiation from two n and p sides and also its impact on bandwidth and quantum efficiency. The results show more impact of radiation from n region compared to p region.

Sol-gel coating of colloidal particles deposited glass surface pertinent to self-cleaning applications

A sol-gel coating using colloidal silica on a glass surface is carried out towards improving the self-cleaning properties. The optical transmittance and hydrophobic characteristics of the resulting coating are analyzed using analytical tools. Since the sol-gel coating reduces the optical transmittance of the glass samples, due to scattering and diffusion of the incident optical radiation at the coating surface, silicon oil (Sigma-Aldrich, 10 cSt) impregnation method is introduced to improve the optical transmittance. Silicon oil has good heat transfer characteristics, stable properties over range of temperatures, and optically transparent characteristics with refractive index of 1.4034. The resulting coated surface is tested in outdoor environments to examine the dust effect on the optical transmittance of the sol-gel coated and oil impregnated glass samples. It is found that deposition of 75 nm size silica particles on the glass surface modifies the texture height of the sol-gel coating, which in turn, improves the surface hydrophobicity. Sol-gel coating results in a web-type fully connected porous structures; in which case, agglomeration of the synthesized particles is responsible for the fully connected porous texture at the coating surface. The optical transmittance remains low for the sol-gel coated glass samples because of scattering and diffusion of the incident optical radiation at the coating surface. Silicon oil impregnation improves the optical transmittance of the sol-gel coated samples. The dust particles immerse into the oil film and reduce the optical transmittance of the oil impregnated samples in outdoor environments.

Efficient broadband energy detection from the visible to near-infrared using a plasmon FET

Plasmon based field effect transistors (FETs) can be used to convert energy induced by incident optical radiation to electrical energy. Plasmonic FETs can efficiently detect incident light and amplify it by coupling to resonant plasmonic modes thus improving selectivity and signal to noise ratio. The spectral responses can be tailored both through optimization of nanostructure geometry as well as constitutive materials. In this paper, we studied various plasmonic nanostructures using gold for a wideband spectral response from visible to near-infrared. We show, using empirical data and simulation results, that detection loss exponentially increases as the volume of metal nanostructure increases and also a limited spectral response is possible using gold nanostructures in a plasmon to electric conversion device. Finally, we demonstrate a plasmon FET that offers a broadband spectral response from visible to telecommunication wavelengths.

Atom localization with double-cascade configuration

We investigate the one-dimensional (1D) and two-dimensional (2D) atom localization of a four-level system in a double-cascade configuration. We demonstrate the possibility of 1D localization in the field of a standing wave, 2D localization in the field of two standing waves and 2D localization only in the field of running waves by using different configurations of driven waves on transitions. In addition, for each configuration we reached a high-precision atom localization in one of the states at scales much smaller than the wavelength of the incident optical radiation.

Influence of dust and mud on the optical, chemical, and mechanical properties of a pv protective glass.

Recent developments in climate change have increased the frequency of dust storms in the Middle East. Dust storms significantly influence the performances of solar energy harvesting systems, particularly (photovoltaic) PV systems. The characteristics of the dust and the mud formed from this dust are examined using various analytical tools, including optical, scanning electron, and atomic force microscopies, X-ray diffraction, energy spectroscopy, and Fourier transform infrared spectroscopy. The adhesion, cohesion and frictional forces present during the removal of dry mud from the glass surface are determined using a microtribometer. Alkali and alkaline earth metal compounds in the dust dissolve in water to form a chemically active solution at the glass surface. This solution modifies the texture of the glass surface, thereby increasing the microhardness and decreasing the transmittance of the incident optical radiation. The force required to remove the dry mud from the glass surface is high due to the cohesive forces that result from the dried mud solution at the interface between the mud and the glass. The ability altering the characteristics of the glass surface could address the dust/mud-related limitations of protective surfaces and has implications for efficiency enhancements in solar energy systems.

Optical amplification using surface plasmon resonance with total internal reflection

The surface plasmon enhanced optical amplification is proposed, designed and simulated in Kretschmann geometry formed by a 500μm thick, 10mm long and 5mm wide BK7 parallel slab and 29nm thin gold layer which is sandwiched between the said parallel slab and 20nm thin GaAs layer. This GaAs layer is pumped by 1319nm higher order Gaussian beam of a Nd:YAG laser, which passes through a cylindrical lens thereby generating a high aspect ratio elliptical cross section to attain intensity dependent negative extinction coefficient on that 3mm long strip of irradiated GaAs. The negative extinction coefficient of GaAs layer facilitates the amplification of the incident optical radiation at 1550nm within the communication window. Here the incident pulsed optical radiation of 5mW is amplified to 274MW through external pumping and surface plasmon resonance phenomenon by total internal reflection with three bounces along the length of said BK7 parallel slab considering the Goos–Hänchen shift at the slab-Au layer interface and slab-air interface.

VO(2) based waveguide-mode plasmonic nano-gratings for optical switching.

In this paper, we present one dimensional plasmonic narrow groove nano-gratings, covered with a thin film of VO(2) (Vanadium Dioxide), as novel optical switches. These narrow groove gratings couple the incident optical radiation to plasmonic waveguide modes leading to high electromagnetic fields in the gaps between the nano-gratings. Since VO(2) changes from its semiconductor to its metallic phase on heating, on exposure to infra-red light, or on application of voltage, the optical properties of the underlying plasmonic grating also get altered during this phase transition, thereby resulting in significant switchability of the reflectance spectra. Moreover, as the phase transition in VO(2) can occur at femto-second time-scales, the VO(2)-coated plasmonic optical switch described in this paper can potentially be employed for ultrafast optical switching. We aim at maximizing this switchability, i.e., maximizing the differential reflectance (DR) between the two states (metallic and semiconductor) of this VO(2) coated nano-grating. Rigorous Coupled Wave Analysis (RCWA) reveals that the switching wavelengths - i.e., the wavelengths at which the values of the differential reflectance between VO(2) (S) and VO(2) (M) phases are maximum - can be tuned over a large spectral regime by varying the nano-grating parameters such as groove width, depth of the narrow groove, grating width, and thickness of the VO(2) layer. A comparison of the proposed ideal nano-gratings with various types of non-ideal nano-gratings - i.e., nano-gratings with non-parallel sidewalls - has also been carried out. It is found that significant switchability is also present for these non-ideal gratings that are easy to fabricate. Thus, we propose highly switchable and wide-spectra VO(2) based narrow groove nano-gratings that do not have a complex structure and can be easily fabricated.

Surface plasmon enhanced ultra-low threshold second harmonic generation in periodically poled whispering gallery resonator

The surface plasmon enhanced ultra-low threshold second harmonic generation is observed, designed and simulated in whispering gallery resonator made of MgO doped periodically poled LiNbO3. Here the electric field associated with incident optical radiation of picowatt level is amplified to milliwatt level through surface plasmon resonance in Kretschmann geometry which is formed by a BK7 prism plane, 29nm thin gold layer and 20nm thin GaAs layer. This enhanced electric field then coupled to a whispering gallery resonator, which facilitated the generation of second harmonic for an incident laser radiation of picowatt level. In this proposed configuration with an incident optical power of 94.6pW, generated second harmonic through whispering gallery resonator is found to be 14.6mW.

High power optics and its new manifestations

The advent of the laser has placed stringent requirements on the fabrication, performance and quality of optical elements employed within systems for most practical applications. Their high power performance is generally governed by three distinct steps, firstly the absorption of incident optical radiation (governed primarily by various absorption mechanisms); secondly, followed by a temperature increase and response governed primarily by thermal properties and finally the elements thermo-optical and thermomechanical response, e.g., distortion, stress birefringenous fracture, etc. All of which needs to be understood in the design as efficient, compact, reliable and useful for many applications high power systems, under a variety of operating conditions, pulsed and continuous wave, rep-rated or burst mode of varying duty cycles.