Incident Monochromatic Light Research Articles

The Raman Laser Spectrometer for the ExoMars Rover Mission to Mars

Abstract The Raman Laser Spectrometer (RLS) on board the ESA/Roscosmos ExoMars 2020 mission will provide precise identification of the mineral phases and the possibility to detect organics on the Red Planet. The RLS will work on the powdered samples prepared inside the Pasteur analytical suite and collected on the surface and subsurface by a drill system. Raman spectroscopy is a well-known analytical technique based on the inelastic scattering by matter of incident monochromatic light (the Raman effect) that has many applications in laboratory and industry, yet to be used in space applications. Raman spectrometers will be included in two Mars rovers scheduled to be launched in 2020. The Raman instrument for ExoMars 2020 consists of three main units: (1) a transmission spectrograph coupled to a CCD detector; (2) an electronics box, including the excitation laser that controls the instrument functions; and (3) an optical head with an autofocus mechanism illuminating and collecting the scattered light from t...

Thermal analysis on multijunction photovoltaic cell under oblique incident laser irradiation

Laser beam irradiation was modeled to investigate the thermal responses of multijunction photovoltaic cell to the irradiation of oblique incident monochromatic light. First, the monochromatic light absorption in multijunction photovoltaic cell is formulated with accounting for multiple reflections as well as interferences. Then, an iterative algorithm was established to calculate the depositions of incident laser energy in every layer. Finally, the temperature characteristics of the photovoltaic cell are analyzed with finite element method.

Use of fluorescence signals generated by elastic scattering under monochromatic incident light for determining the scattering efficiencies of various plasmonic nanoparticles.

We present a route that estimates the scattering/absorption characteristics of plasmonic nanoparticles by using fluorescence and UV-visible spectroscopy. Because elastic scattering of nanoparticles caused by a monochromatic incident light is reflected in fluorescence emission spectra when recording at the excitation wavelength, the scattering intensities at the excitation wavelength during fluorescence emission scans are used to compare the scattering characteristics of various plasmonic nanoparticles under conditions where the extinction values of all of the nanoparticles are kept constant at this wavelength. For the two excitation wavelengths (519 and 560 nm) we investigated, the scattering intensities of spherical gold nanoparticles increase with increasing size (15, 33, 51, 73, and 103 nm in diameter). These results are correlated with the nanoparticles' scattering efficiencies (the ratios of scattering to the extinction cross-sections), which are theoretically calculated in the literature using Mie theory. Then, linear calibration equations at each wavelength are derived to estimate the scattering efficiencies of two Au nanorods, Au nanocages, and spherical Ag nanoparticles (15, 25, 37, and 62 nm). The values are very comparable with literature values. For various purposes such as biomedicine and optoelectronics, the present method could be beneficial to those who wish to easily compare and determine the scattering characteristics of various plasmonic nanoparticles at a certain wavelength by using commercially-available spectroscopic techniques.

Variation of the refractive index by means of sulfate anion incorporation into nanoporous anodic aluminum oxide films

The variation in the refractive index of nanoporous anodic aluminum oxide (AAO) films regarding the sulfur anion incorporation is studied in this work. For this purpose, different samples are grown under potentiostatic conditions at different voltages and concentrations of sulfuric acid in the electrolyte. The samples are analyzed by Rutherford backscattering spectroscopy and infrared spectrometry, confirming the presence of sulfate anions and water embedded into the nanoporous AAO films. The incorporation of sulfate ions into the alumina matrix varies from 6.3 up to 11.7% regarding aluminum content. We have studied Fabry–Pérot optical interferences by shining incident monochromatic light in specular reflectance conditions. The reflected monochromatic light waves interact in internal reflectivity generating constructive and destructive interferences known as Fabry–Pérot optical interferences. An iterative method based on the equation for constructive interferences conditions in thin films and Snell equations is developed in order to calculate the refractive index of the nanoporous AAO films as a function of the wavelength. The calculated refractive indices increase when the sulfur content of the nanoporous AAO films decreases. The variation of the calculated refractive index is 0.08 and remains constant in the wavelength range 400–1200 nm.

Light trapping for silicon photovoltaic cells illuminated by solar-pumped lasersemitting at 1064 nm

We have demonstrated a significant light-trapping effect for a silicon photovoltaic cell using a bandpass filter on the front surface and a diffuse reflector on the back surface, which is coupled with a solar-pumped laser emitting at 1064 nm, as a new approach to highly efficient solar photovoltaics. We carried out Monte-Carlo simulation of the light-trapping process to consider the effects of realistic optical properties of the surface treatments, and clarified the requisites to remarkably improve the absorbance of the cell. A multilayer bandpass filter consisting of TiO2 and SiO2 was employed, in which the thickness of each layer was optimized. A Si surface roughened by acid etching and covered with a Ag layer realized sufficient diffuse reflection properties. The prototype for optical evaluations using a 45-µm-thick Si wafer, which is extremely thin compared with conventional silicon solar cells, almost perfectly absorbed the monochromatic incident light even though the wavelength was very close to the absorption edge.

Optimal design of bandpass filters to reduce emission from photovoltaic cells under monochromatic illumination

We have theoretically investigated photovoltaic cells used under the illumination condition of monochromatic light incident from a particular direction, which is very different from that for solar cells under natural sunlight, using detailed balance modeling. A multilayer bandpass filter formed on the surface of the cell has been found to trap the light generated by radiative recombination inside the cell, reduce emission from the cell, and consequently improve conversion efficiency. The light trapping mechanism is interpreted in terms of a one-dimensional photonic crystal, and the design guide to optimize the multilayer structure has been clarified. For obliquely incident illumination, as well as normal incidence, a significant light trapping effect has been achieved, although the emission patterns are extremely different from each other depending on the incident directions.

Thermal radiation from optically driven Kerr (χ(3)) photonic cavities

We describe thermal radiation from nonlinear (χ(3)) photonic cavities coupled to external channels and subject to incident monochromatic light. Our work extends related work on nonlinear mechanical oscillators to the problem of thermal radiation, demonstrating that bistability can enhance thermal radiation by orders of magnitude and result in strong lineshape alternations, including “super-narrow spectral peaks” occurring at the onset of kinetic phase transitions. We show that when the cavities are designed to exhibit perfect linear emissivity (rate matching), such thermally activated transitions can be exploited to dramatically tune the output power and radiative properties of the cavity, leading to a kind of Kerr-mediated thermo-optic effect. Finally, we demonstrate that in certain parameter regimes, the output radiation exhibits Stokes and anti-Stokes side peaks whose relative magnitudes can be altered by tuning the internal temperature of the cavity relative to its surroundings, a consequence of strong correlations and interference between the emitted and reflected radiation.

Photospectroscopically observed pore-space correlations of a wetting fluid during the drying process in nanoporous Vycor glass.

We use light scattering to study spatial correlations in the pore space of Vycor glass upon draining a wetting fluid. We analyze the transmission spectrum of forward-scattered light on the basis of the theory of dielectric constant fluctuation, whereas conventional light scattering analyzes the scattered light at small angles of monochromatic incident light. Assuming that the drained pores, which are surrounded by filled pores, exhibit long-range correlations of a fractal dimension of 2.5, we analytically derive the corresponding turbidity. The slight deviation from the λ(-4) Rayleigh wavelength dependence directly provides the correlation length of the interconnected network of drained pores. The estimated length, ranging from 0.5 to 18 nm at most, is almost the same order as that indirectly estimated from our previous simple effective Rayleigh scatterer model.

Nanostructured graphene-based hyperbolic metamaterial performing as a wide-angle near infrared electro-optical switch.

We propose a nanostructured hyperbolic metamaterial (HMM) that can make the transition between elliptic and hyperbolic regimes in the near infrared (IR) frequency range. This switchable HMM is a slab made of a periodic stack of metal/Al(2)O(3)/graphene/Al(2)O(3)/metal nano-layers. By tuning the graphene conductivity via tuning its chemical potential, through a variable external bias, the response of this highly anisotropic medium to a monochromatic TM incident light can be switched between a positive/negative refraction regime and a negative refraction/no-transmission regime. The proposed structure is suitable for applications such as beam splitters, modulators, four-port devices, and optical gates.

Pentacene-Based Photodetector in Visible Region With Vertical Field-Effect Transistor Configuration

Electrical and detection performances of pentacene-based photodetector with vertical field-effect transistor (VFET) configuration were investigated in full visible region. By comparing with planar FET-based photodetector ITO/ PMMA(520 nm)/Pentacene(35 nm)/Au, the VFET-based photodetector ITO/Pentacene(80 nm)/Al(15 nm)/Pentacene(80 nm)/ Au exhibits better performance. At an output current of ca. -8 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-7</sup> A, the threshold voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> ) was -0.61 V for the VFET-based device at V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DS</sub> = -2 V, but V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> = -7.1 V for the planar one at V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DS</sub> = -12 V. The performance of photodetectors depends on incident monochromatic light, and the VFET-based photodetector showed a maximum responsivity of 188 mA/W and a photosensitivity peak of 588 under 350-nm light, which were ~11.75 and 2.83 times as that of the planar one, respectively. Therefore, it provides an easy way to get the VFET-based organic photodetectors in full visible region with excellent photosensitivity, responsivity, and light selectivity, showing its promising application in all-organic image sensors working at low voltages.

Low-voltage pentacene photodetector based on a vertical transistor configuration

Due to the excellent characteristics of field-effect transistor and its high absorption coefficient in the visible region, pentacene has been widely used in phototransistors. The channel length of the vertical transistor could be designed to be very short (on the order of nanometers). In this way, the device performances and its working frequency can be effectively improved, and the energy consumption can be reduced simultaneously. In this paper, we fabricate a kind of low-voltage pentacene photodetector ITO(S)/Pentacene/Al(G)/Pentacene/Au(D), based on the vertical transistor configuration. The threshold voltage and “on/off” current ratio are -0.9 V and 104 at a low working-voltage of -3 V, respectively. The pentacene photodetector ITO/Pentacene(80 nm)/Al(15 nm)/Pentacene (80 nm)/Au exhibits a good p-type transistor behavior and low-voltage-controlling performance. The photosensitivity and responsivity vary with incident monochromatic light from 350 nm to 750 nm, and the photosensitivity peak of 308 is obtained at 350 nm with a responsivity of 219 mA·W-1, which is even higher than that of the standard Si-based photodetector under 350 nm incident light. Therefore, this work provides an easy way to fabricate a high sensitivity all-organic photodetector working at low voltages.

Influence of the Dielectric PMMA Layer on the Detectivity of Pentacene-Based Photodetector With Field-Effect Transistor Configuration in Visible Region

In this paper, the influence of dielectric polymethylmethacrylate (PMMA) layer on the detectivity of pentacene-based photodetectors with field-effect transistor (FET) configuration were investigated in a visible region. By changing the thickness of the PMMA layer, from 230 nm to 520 nm and 800 nm, electrical parameters, such as the capacitance, “on/off” current ratio, and carrier mobility, of the pentacene-based photodetector decrease with increasing the thickness of the PMMA layer, which influences its detectivity directly. The photosensitivity and responsivity of the FET-based pentacene photodetector with 520-nm PMMA varied with incident monochromatic light from 350 nm to 750 nm, and it showed a maximum responsivity of 149 mA/W with a photosensitivity peak of 1.7 ×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> at 450 nm, which is of the same order as that of the standard Si-based photodetector. Therefore, it is an applicable way to get such kind of FET-based full-organic photodetectors in a full visible region with excellent photosensitivity, responsivity, and selectivity.

Optical transfer function of three-dimensional photonic crystals by volume holographic recording

We investigate optical transformations by three-dimensional photonic crystals fabricated via holographic lithography. Large-area three-dimensional photonic crystal structures are created by multiple-beam interference in photosensitive materials. We perform calculations of the optical transfer function for monochromatic incident light. Our approach is based on three-dimensional vector rigorous coupled-wave approach, which allows modeling the dynamic interaction of light waves generated by diffraction inside a crystal grating. We analyze the Bragg-conditioned energy transfer for different crystal structures and address the influence of the refractive index contrast. Diffractive-optical properties of the fabricated crystals are investigated by laser scanning and monitoring the transmitted light in three-dimensional angular space. The scan results agree well with the modeling predictions for different crystals and recording photopolymers.

P.82: Entire Spectrum Measurement of Kerr Constant and Birefringence Dispersion in a Polymer‐Stabilized Blue‐Phase Liquid Crystal Composite

AbstractA new method is proposed and implemented experimentally for measuring the electric‐field induced birefringence together with the Kerr constant of a polymer‐stabilized blue‐phase liquid crystal (PSBPLC) composite. The conventional Senarmont compensation method is only suitable for the single wavelength measurement limited by the achromatic zero order quarter wavelength plate (QWP). In our new method, the QWP is removed so that a broad band light source can be used instead of monochromatic incident light. Herein planar ITO electrodes are employed, producing a uniformly distributed vertical electric field. Thus the fitting data is accurate and convincing prior to that from the IPS cell measurement. By rotating the sample to an oblique angle and using the spectrometer to scan the voltage dependent optical transmission, the induced birefringence and the Kerr constant for the entire visible spectrum can be carried out using the single band model. Quantitative experimental results have been obtained and presented in this paper to support this proposed scheme.

Scattering signals of monochromatic light incident on a rectangular microchannel

In this paper, the transition process of scattering signals is investigated as an incident monochromatic light irradiates rectangular channels with sizes from micrometers to submicrometers. Monochromatic light scattering from open groove cavities is important in many design analyses for such fields as optical communications, display, storage, sensing, MENS and nano-technology. The distribution of scattering signals for light incident on the groove starts to change due to the diffraction as the opening width of the groove is close to the wavelength of monochromatic light. This study revealed the transition process of scattering signals of monochromatic light irradiating rectangular microchannels with sizes from micrometers to submicrometers. The results showed that the profile for the intensity of scattering signals changes from concave to convex shape in the direction of width and from irregular to regular wave in the direction of depth if the opening width of the rectangular microchannel reduces from micrometer to submicrometer.

Multiple scattering of polarized light: comparison of Maxwell theory and radiative transfer theory

For many research areas in biomedical optics, information about scattering of polarized light in turbid media is of increasing importance. Scattering simulations within this field are mainly performed on the basis of radiative transfer theory. In this study a polarization sensitive Monte Carlo solution of radiative transfer theory is compared to exact Maxwell solutions for all elements of the scattering Müller matrix. Different scatterer volume concentrations are modeled as a multitude of monodisperse nonabsorbing spheres randomly positioned in a cubic simulation volume which is irradiated with monochromatic incident light. For all Müller matrix elements effects due to dependent scattering and multiple scattering are analysed. The results are in overall good agreement between the two methods with deviations related to dependent scattering being prominent for high volume concentrations and high scattering angles.

Circular and near-circular polarization states of evanescent monochromatic light fields in total internal reflection

Conditions for the production of near-circular polarization states of the evanescent field present in the rarer medium in total internal reflection of incident monochromatic p-polarized light at a dielectric-dielectric planar interface are determined. Such conditions are satisfied if high-index (>3.2) transparent prism materials (e.g., GaP and Ge) are used at angles of incidence well above the critical angle but sufficiently below grazing incidence. Furthermore, elliptical polarization of incident light with nonzero p and s components can be tailored to cause circular polarization of the resultant tangential electric field in the plane of the interface or circular polarization of the transverse electric field in a plane normal to the direction of propagation of the evanescent wave. Such polarization control of the evanescent field is significant, e.g., in the fluorescent excitation of molecules adsorbed at solid-liquid and solid-gas interfaces by total internal reflection.

Photoelectrochemical switch based on cis-Azobenzene chromophore modified TiO 2 nanowires

Carboxylated-azobenzene chromophore modified TiO 2 nanowire composites were prepared and characterized. Photocurrent measured with monochromatic incident light irradiation results showed that azobenzene modified TiO 2 nanowire electrode had obviously higher photocurrent and broader visible light response covering range of 350–650 nm, and the wavelength position corresponding to the maximum photocurrent was red shift to about 470 nm. After alternate irradiation with UV and visible light, the azobenzene modified TiO 2 nanowire electrode exhibited obvious photoelectrochemical switching properties. Furthermore, the photocurrent under visible light irradiation was much higher than that under UV irradiation due to the cis-to- trans isomerization transformation of azobenzene chromophore.

광학활성 동축 이중 원통을 수직하게 비추는 단색 빛의 산란 : II. 수치 계산 결과

The scattering of a normally incident monochromatic light by optically active concentric double cylinders is studied by using a numerical method. A numerical code is developed on the basis of the analytical solutions, and the angular distributions of the intensity and the polarization of the scattered light are computed for some specific cases. The numerical code can be used to non-invasively determine the size, structure, and composition of a double cylinder with high accuracy by measuring the angular distribution of the scattered light by an experiment.Keywords: Optically active concentric cylinders, Light scatteringOCIS codes: (240.3695) Linear and nonlinear light scattering from surfaces; (160.1585) Chiral media

Spectral kinetic modeling and long‐term behavior assessment of Arthrospira platensis growth in photobioreactor under red (620 nm) light illumination

The ability to cultivate the cyanobacterium Arhtrospira platensis in artificially lightened photobioreactors using high energetic efficiency (quasi-monochromatic) red LED was investigated. To reach the same maximal productivities as with the polychromatic lightening control conditions (red + blue, P/2e(-) = 1.275), the need to work with an optimal range of wavelength around 620 nm was first established on batch and continuous cultures. The long-term physiological and kinetic behavior was then verified in a continuous photobioreactor illuminated only with red (620 nm) LED, showing that the maximum productivities can be maintained over 30 residence times with only minor changes in the pigment content of the cells corresponding to a well-known adaptation mechanism of the photosystems, but without any effect on growth and stoichiometry. For both poly and monochromatic incident light inputs, a predictive spectral knowledge model was proposed and validated for the first time, allowing the calculation of the kinetics and stoichiometry observed in any photobioreactor cultivating A. platensis, or other cyanobacteria if the parameters were updated. It is shown that the photon flux (with a specified wavelength) must be used instead of light energy flux as a relevant control variable for the growth. The experimental and theoretical results obtained in this study demonstrate that it is possible to save the energy consumed by the lightening device of photobioreactors using red LED, the spectral range of which is defined according to the action spectrum of photosynthesis. This appears to be crucial information for applications in which the energy must be rationalized, as it is the case for life support systems in closed environments like a permanent spatial base or a submarine.