Propagation Of Incident Light Research Articles

49‐1: Invited Paper: Novel Brightness Enhancement Technology for Reflective LCDs

Reflective LCDs have a great advantage of low power consumption, but the brightness is not consistently sufficient because ambient light is used as a light source. To increase light efficiency, we combined reflective LCDs and the Pancharatnam‐Berry deflector (PBD), a diffractive optical element that controls the propagation of incident light. We confirmed that on‐axis brightness is increased by 2.2 times against the incident collimated light from a polar angle of 30° when compared to a reflective LCD without PBD.

Terahertz reflective imaging systems with improved angle compatibility realized by the designed quasi-scattering screen

Active imaging can provide significantly larger signal margins in the terahertz (THz) spectral region than passive imaging. However, the imaging effect of THz active imaging is severely constrained by the orientation requirement of target reflection, which limits the application scenarios of this technique. In view of the shortcomings of existing THz reflective imaging systems, this paper proposes a new system optimization scheme from the aspect of hardware - a compact quasi-scattering screen (QSS) is proposed and designed as a beam-shaping element to eliminate the need for the best direction of specular reflection to the greatest extent. The corresponding relationship between the divergent Gaussian beam and target light field is directly established by using the equal-energy mapping method in non-imaging optics, which rejects the collimation process of the THz source. By customizing the optimization function in ZEMAX® to automatically optimize the surface of the QSS, the direction of incident light propagation can be adjusted. A non-coaxial reflective THz imaging system using a 0.1 THz continuous wave source demonstrates the ability of the QSS to improve the angle compatibility of the traditional THz reflective imaging system. The results show that the imaging angle compatibility range of the system can be increased to more than 5 times without changing the original imaging optical path and its resolution. In addition, it can also improve the imaging quality of the original imaging optical path for the object with a smooth surface or certain structure.

Enhanced Deconvolution and Denoise Method for Scattering Image Restoration

Light scattering is a common physical phenomenon in nature. The scattering medium will randomly change the direction of incident light propagation, making it difficult for traditional optical imaging methods to detect objects behind the scattering body. Wiener filtering deconvolution technology based on the optical memory effect has broad application prospects by virtue of its advantages, such as fast calculation speed and low cost. However, this method requires manual parameter adjustment, which is inefficient and cannot deal with the impact of real-scene noise. This paper proposes an improved Wiener filtering deconvolution method that improves the exposure dose during the speckle collection, can quickly obtain the optimal parameter during the calculation phase, and can be completed within 41.5 ms (for a 2448 × 2048 image). In addition, a neural network denoising model was proposed to address the noise issue in the deconvolution recovery results, resulting in an average improvement of 27.3% and 186.7% in PSNR and SSIM of the images, respectively. The work of this paper will play a role in achieving real-time high-quality imaging of scattering media and be helpful in studying the physical mechanisms of scattering imaging.

Applications of single laser pulse from Nd:doped lasers for cleaning of small diameter carious lesions. Modelling and analytical study

We report on an analytical study with physical modelling, some additional experimental studies and computer programming of the cleaning of initial carious lesions (1 - 3 mm in diameter) with a single laser pulse from Nd:doped (Nd:YAG and Nd:Glass) lasers (wavelength 1.06 μm). The analysis is based on experimental data from our preliminary study and aims to develop a method to predetermine the necessary laser pulse parameters for reasonable cleaning. To obtain such laser pulse parameters, we considered the conversion of light energy into heat, the propagation of incident light and the resulting heating of the dental tissue, the induced ablation processes associated with lesion cleaning, and the formation of the necessary hole in combination with acceptable heating of the pulp chamber and prevention of enamel crack formation. Cleaning is naturally associated with the bactericidal effect. The study, except for the estimation, confirms that the use of single light pulses of the considered lasers with energies from 1.3 to 4.5 J, densities from 40 to 120 J/cm2, pulse duration from a few hundred microseconds to ~2 ms (i.e., in the simplest, natural, free mode of operation of the noted lasers) can be considered as a promising method to start caries treatment.

Coherent control of the incident light propagation in a defect one-dimensional photonic crystal

In this paper, we have discussed the transmission and reflection properties of the infrared laser pulse propagated through one-dimensional photonic crystal (1DPC) with single layer of graphene nanotrusses. The single layer graphene system interacts with a probe laser field and two coupling lights. We analytically solve the optical susceptibility of the single layer graphene system for adapting the dielectric function of the 1DPC. After that we discuss the transmission and reflection properties of the incident laser pulse on 1DPC by controlling the intensity for the coupling lights and relative phase between applied lights. We have also found that the absorption and population spectrums of the medium can be controlled by the relative phase between applied lights. Our results show that the gain without population inversion can be obtained for the simultaneous slow light propagation in the transmission and reflection pulses. Our results may have potential application in the future of the all-optical devices in quantum technologies.

Design of Ultra-thin Near-infrared Freestanding Dielectric Meta-optics Devices

Metasurface optics devices feature powerful capability for wavefront manipulation by guiding the propagation of incident light efficiently. We present a classification of freestanding dielectric meta-optics to achieve efficient ultrathin optical elements and guiding light without metals. Specifically, freestanding dielectric metasurfaces provide advanced features solely described by structural design and improve coupling efficiency by removing the substrate. A few freestanding meta-devices operating at near-infrared (near-IR) wavelength (1.55 µm) have been designed and verified numerically.

Raman spectroscopy provides insight into carbonate rock fabric based on calcite and dolomite crystal orientation.

Carbonate rocks record the oldest forms of life on Earth, and their geologic reconstruction requires multiple methods to determine physical and chemical processes before conclusions of ancient biosignatures are made. Since crystal orientation within rock fabric may be used to infer geologic settings, we present here a complementary Raman method to study the orientation of calcite (CaCO3) and dolomite [CaMg (CO3)2] minerals. The relative peak intensity ratio of the carbonate lattice Eg modes T and L reveals the crystallographic orientation of calcite and dolomite with respect to the incident light polarization. Our results for calcite show that when the incident laser light propagates down the crystallographic a/b axis: (1) the L mode is always greater in intensity than the T mode (I T < I L), and (2) the spectra are most intense at 45° and least intense at 90° polarization angles measured from around the c axis. Our results for dolomite show that (1) I T > I L when the incident light propagation is down the crystallographic c axis and (2) I T < I L when the incident light propagation is down the crystallographic a/b axis. This study reveals mineral orientation variation related to deposition and paragenesis within limestone and dolostone samples. The method presented yields information related to growth and deformation during diagenetic and metamorphic alteration and may be used in research seeking to identify the fabric parameters of any calcite or dolomite containing rock. The compositional and structural data obtained from Raman mapping is useful in structural geology, materials science, and biosignature research.

A Calculation Method for Response Spectrum of Mercury Cadmium Telluride Infrared Focal Plane Arrays Detector

The invention discloses a calculation method for a response spectrum of a mercury cadmium telluride infrared focal plane detector, and the method mainly comprises the propagation of incident light in the mercury cadmium telluride infrared focal plane detector, the transportation of carriers in a mercury cadmium telluride absorption layer, and the comprehensive design of the surface state composite model of the mercury cadmium telluride absorption layer and the response spectrum. The designed response spectral curve is consistent with the actual test results in the interference fringes and the decrease in quantum efficiency in the short-wave infrared region. This design method is of great significance for the response spectrum optimization of the mercury cadmium telluride infrared focal plane detector.

Theoretical study on 252 terahertz Gaussian beam shaping based on an off-axis transmissive all-dielectric metasurface

An off-axis transmissive all-dielectric square metasurface with a side length of 55 mm is designed and studied in this paper. It can shape the 2.52 terahertz Gaussian beam into a rigorous plane wave (we define the required field-quality of the rigorous plane wave region: peak-to-peak amplitude ripple less than 1 dB and phase ripple less than 10°). The metasurface is composed of silicon cylindrical resonators whose phase modulation can almost span over the entire 2π range and the poly (4-methyl-1-pentene) substrate. The diameters of the resonators are from 11 to 35 μm and the heights of them are all 60 μm. The working range of the obtained plane wave is calculated by the physical optics integral formula when the off-axis angle is 22°. The results show that when the off-axis propagation distance is 1050 mm, the area satisfying the plane wave condition is 17×20 mm2, and the diffraction efficiency (we define the diffraction efficiency: the ratio of the total light field energy on the target plane to the total energy of light field that is just after the metasurface along the propagation of incident light) of the rigorous plane wave region cross-section is 23.4%. In addition, a random silicon cylinder diameter fabrication error within ± 4.5 μm is taken into account for the actual fabrication condition. The error satisfies the normal distribution with a mean of 0 μm and a standard deviation of 3 μm. The influence of the fabrication error on the shaping result is studied. We anticipate that the whole study will have certain pragmatic applications in some fields, such as enlarging the capture area of terahertz optical tweezers.

Stimulated Raman Scattering Interferometer for Molecular-Selective Tomographic Imaging.

Development of a stimulated Raman scattering (SRS) interferometer is presented. In the apparatus, a SRS signal generated in a sample is collinearly overlapped with a reference beam, and the interference pattern between the signal and reference beams is obtained. From the interference pattern, the phase of the SRS signal can be measured. From the phase of the signal, the spatial distribution of the target molecule can be obtained with high positioning precision. In the present article, the SRS interferometer was developed and the first SRS interference signal was obtained from a polyethylene film. The phase change of the SRS interference pattern caused by scanning the sample position along the direction of the incident light propagation was measured. From the result, the sample position difference for a sub-micron was detected with uncertainties of 15%. The tomographic images of a triple-layered polymer film were successfully obtained. The SRS interferometer would become a core optical technique of a novel molecular-selective tomographic imaging method.

New Acousto-Optic Regime of Interaction in Media Possessing Strong Elastic Anisotropy

We present results on theoretical and rst experimental investigation of a new regime of acousto-optic interaction existing in acoustically anisotropic medium. We de ned the new regime as semi-collinear or mixed interaction since it combined properties of the traditional non-collinear di raction and the pure collinear interaction. The peculiar phenomenon was registered in the tellurium dioxide crystal due to the extremely strong elastic anisotropy of the material. Application of a speci c cut of the crystal provided observation of the e ect in the middle infrared at the optical wavelength 3.39 μm and at the acoustic frequencies limited to 300 MHz. The observed interaction was characterized by a non-collinear propagation of incident light with respect to acoustic energy ow and simultaneously a collinear propagation of di racted radiation along the acoustic energy ow. A brief theoretical analysis of the interaction based on wave vector diagrams and two-dimensional coupled wave equations is included in the presentation. Finally, we describe in the paper, the setup and basic details of the carried out acousto-optic experiment.

Extrinsic 2D chirality: giant circular conversion dichroism from a metal-dielectric-metal square array.

Giant chiroptical responses routinely occur in three dimensional chiral metamaterials (MMs), but their resonance elements with complex subwavelength chiral shapes are challenging to fabricate in the optical region. Here, we propose a new paradigm for obtaining strong circular conversion dichroism (CCD) based on extrinsic 2D chirality in multilayer achiral MMs, showing that giant chiroptical response can be alternatively attained without complex structures. Our structure consists of an array of thin Au squares separated from a continuous Au film by a GaAs dielectric layer, where the Au squares occupy the sites of a rectangular lattice. This structure gives rise to a pronounced extrinsically 2D-chiral effect (CCD) in the mid-infrared (M-IR) region under an oblique incidence, where the 2D-chiral effect is due to the mutual orientation of the Au squares array and the incident light propagation direction; the large magnitude of CCD due to the large difference between left-to-left and right-to-right circularly polarized reflectance conversion efficiencies.

Backward emission angle of microscopic second-harmonic generation from crystallized type I collagen fiber

A theoretical model that deals with SHG from crystallized type I collagen fiber formed by a bundle of fibrils is established. By introducing a density distribution function of dipoles within fibrils assembly into the dipole theory and combining with structural order (m,l) parameters revealed by quasi-phase-matching (QPM) theory, our established theoretical model comprehensively characterizes both biophysical features of collagen dipoles and the crystalline characteristics of collagen fiber. This new model quantitatively reveals the 3-D distribution of second-harmonic generation (SHG) emission angle (θ,ϕ) in accordance with the emission power. Results show that fibrils diameter d(1) and structural order m, which describes the structural characteristics of collagen fiber along the incident light propagation direction has significant influence on backward∕forward SHG emission. The decrease of fibrils diameter d(1) induces an increase of the peak SHG emission angle θ(max). As d(1) decreases to a threshold value, in our case it is around d(1) = 150 nm when (m,l) = (1,0), θ(max) > 90 deg, indicating that backward SHG emission appears. The SHG may have two symmetrical emission distribution lobes or may have only one or two unsymmetrical emission lobes with unequal emission power, depending on the functional area of (m,l) on d(1).

Plasmon-Induced Magneto-Optical Activity in Nanosized Gold Disks

In this Letter we show that nanostructures made out of pure noble metals can exhibit measurable magneto-optic activity at low magnetic fields. This phenomenon occurs when the localized surface plasmon resonance of the nanostructure is excited in the presence of a static magnetic field parallel to the propagation of incident light. The large magneto-optical response observed comes from an increase of the magnetic Lorentz force induced by the large collective movement of the conduction electrons in the nanostructures when the resonance is excited.

Chemical Mapping of Rubbers and Polymers via Confocal Raman Spectroscopic Imaging

Abstract Confocal Raman Spectroscopic Imaging has been demonstrated as a non-destructive technique to determine the spatial and chemical content of rubbers and polymers. Raman spectroscopy is a particularly useful tool for characterizing chemicals and mixtures because each chemically-distinct species has a unique Raman spectrum. The addition of confocal optics to the microscope greatly improves both the lateral and axial spatial resolution of the instrument. The lateral resolution of the instrument is less than one-third of a micron. The axial resolution, the resolution in the direction of incident light propagation, is as good as two microns with an air objective and on the order of a micron for an oil immersion objective. The vast enhancement of resolution provided by the confocal optical arrangement allows rubber and polymer mixtures to be mapped in multiple dimensions with excellent spatial, chemical, and morphological specificity. Confocal Raman microscopy is a rapid technique that should be considered as an alternative, or in addition, to analysis that requires other microscopic techniques such as atomic force microscopy (AFM) or scanning electron microscopy (SEM).

Application of Mie theory to determine the structure of spheroidal scatterers in biological materials

We present here the results of a numerical study on light scattering from nonspherical particles with relevance to detecting precancerous states in epithelial tissues. In previous studies of epithelial cell nuclei, the experimental light scattering data have been analyzed by comparison with Mie theory. However, given the spheroidal shape of many cell nuclei, the validity of this assumption demands a thorough investigation. We investigate this assumption by using the T-matrix method to model light scattered from spheroids with parameters relevant to epithelial cell nuclei. In our previous studies, we have developed a data analysis procedure that extracts the oscillatory component of the angular-scattering distribution for an ensemble of epithelial cell nuclei for comparison with Mie theory. We demonstrate that application of our analysis procedure to the predictions of the T-matrix method for spheroids, oriented such that their axis of symmetry is aligned with the incident light propagation direction, generally yields the spheroid dimension that is transverse to the incident light propagation direction with subwavelength accuracy.

Implementation of a submicrometer patterning technique in azopolymer films towards optimization of photovoltaic solar cells efficiency

The weak absorption of the photoactive layer appears as a one of the main factors limiting organic photovoltaic solar cells performances. In order to increase the interaction of the incident light with the photoactive materials, we investigate the effect of a periodic patterning of the solar cells surface with microstructures in the optical wavelength scale. In this aim, we present an original all optical patterning technique of polymer films. The method is based on a laser controlled mass transport in azopolymer films leading to efficient deformation of the film surface in conjunction with the incoming light interference pattern. The technique is used to pattern one-dimensional gratings on the surface of solar cells. In the work presented here, the cell photoactive material is based on the interpenetrated network of a conjugated donor polymer and a fullerene derivative. The cells investigated are illuminated in a reverse configuration through a semi-transparent top cathode. The effect of the periodic structures onto the incident light propagation has been investigated through optical characterizations. We demonstrate that a part of the incident light can be trapped inside the solar cell layers due to diffraction onto the periodic structures.

Simulation of obliquely incident light propagation through a general twisted nematic liquid crystal cell by the Jones matrix technique

Simulation of obliquely incident light propagation through a general twisted nematic liquid crystal cell by the Jones matrix technique

Active optical thin-film waveguide sensor for ion sensing

In this paper, an active PVC optical thin-film waveguide sensor is proposed which can select a specific ion and measure its concentration. The waveguide was fabricated using the plasticized poly(vinyl chloride) (PVC), bis ethyl hexyl phthalate (BEHP), lipophilic anionic dye (LAD-3), and ionophores (K23E1 for calcium, or C14DD16C5 for sodium) in which the PVC membrane plays important roles for both incident light propagation and selective ion sensing. In order to investigate the applicability of this sensor to Ca 2+ and Na + measurement, the sensor was applied to sample solutions whose CaCl 2 concentration was gradually altered. Also, we applied it to a NaCl solution. In this experiment, we found that this PVC thin-film waveguide possessed good light propagation for argon laser light at 488 nm. Also, the comparison of the experimental responses between the active waveguide sensor and a commonly utilized waveguide sensor (evanescent waveguide spectrometry), indicated that the sensitivity of the active waveguide sensor is obviously higher than that of the conventional waveguide sensor. These findings suggested that the proposed PVC waveguide ion sensor is applicable to the determination of various ions with high sensitivity.

On the critical behavior of circular intensity difference for a nonpolar fluid composed of chiral molecules

The effect of double scattering on circular intensity difference (CID) in a nonpolar fluid composed of chiral molecules is explicitly obtained in the critical region, where the Ornstein–Zernike theory holds, using the stationary phase approximation. The double scattering in the direction of orthogonal to the direction of propagation of incident light makes a minor contribution to CID in the critical region, compared with the single scattering. In the direction of propagation of incident light the double scattering plays the most dominant role in the critical region very close to the critical point and the magnitude of CID is same as that in the direction orthogonal to the propagation of incident light, while its effect on CID may be neglected in the critical region far from the critical point.