Angle Of Total Internal Reflection Research Articles

Fresnel filtering of Gaussian beams in microcavities

We study the output from the modes described by the superposition of Gaussian beams confined in the quasi-stadium microcavities. We experimentally observe the deviation from Snell's law in the output when the incident angle of the Gaussian beam at the cavity interface is near the critical angle for total internal reflection, providing direct experimental evidence on the Fresnel filtering. The theory of the Fresnel filtering for a planar interface qualitatively reproduces experimental data, and a discussion is given on small deviation between the measured data and the theory.

Excitation of guided-mode resonances in thin film silicon solar cells

ABSTRACTThin film silicon solar cells are attractive for photovoltaics; however, the poor charge transport in this material requires that the devices are thinner than the absorption length. Adequate absorption can nevertheless be achieved by light scattering at textured interfaces because light can get trapped inside the absorber layer if it is scattered into angles above the critical angle of total internal reflection. This situation can be identified with the propagation of a guided mode in a waveguide where silicon plays the role of the high index guiding medium and the interface texture serves to couple the incident light to modes via grating coupling. We present an experimental realization of a solar cell structure on a line grating where the enhanced photocurrent can be clearly related to resonant excitation of waveguide modes.

纳米分辨率的非扫描非相干三维光学形貌测量仪

A non-scanning, non-interferometric, three-dimensional (3D) optical profilometer based on geometric optics, critical angle principle, and the use of a charge-coupled device (CCD) camera is presented. The surface profile of the test specimen can be transferred into the reflectance profile. The reflectance profile, obtained from a CCD, is the ratio of the intensity at the critical angle to the intensity obtained at the total internal reflection angle. The optical profilometer provides a sub-micron measuring range with nanometer resolution and can be used to measure roughness or surface defects in real time.

Nanometer Axial Resolution by Three-Dimensional Supercritical Angle Fluorescence Microscopy

We report a noninvasive fluorescence microscopy method and demonstrate nanometer resolution along the optical axis. The technique is based on the influence of the microscope slide on the angular intensity distribution of fluorescence. Axial positions are determined by measuring the proportion of light emitted below the critical angle of total internal reflection, which behaves in a classical way, and light emitted above the critical angle, which is exponentially dependent on the distance of the fluorophore from the microscope slide.

MgO nano-pyramids structure for enhancement of light extraction efficiency in vertical light-emitting diodes

We demonstrate novel method for improving light extraction efficiency for n-side-up vertical InGaN/GaN light-emitting diodes (V-LEDs) using MgO nano-pyramids and ZnO refractive-index modulation layer. The MgO nano-pyramids structure is successfully fabricated on n-GaN/ZnO surface using electron-beam evaporation. The light output power of n-GaN/ZnO/MgO V-LEDs is enhanced by 49% compare to that of n-GaN V-LEDs. The angular-dependent far-field emission shows the significant increase of side emission for the n-GaN/ZnO/MgO V-LEDs due to the increase of critical angle for total internal reflection as well as the roughened surface by MgO pyramids structure. These experimental results indicate the critical role of surface texturing in improving the light extraction efficiency of the V-LEDs for solid-state lighting.

Reflection and refraction of acoustic waves at the insulator-ferromagnetic heusler alloy boundary

Reflection and refraction of longitudinal and transverse acoustic waves on a flat boundary between an insulator and a ferromagnetic crystal of a Heusler alloy Ni2 + x + y Mn1 − x Ga1 − y have been considered in the region of premartensitic and martensitic phase transitions. The possibility is shown of using temperature to effectively controlling the angles of wave refraction and the coefficients of transformation of wave modes by changing strong acoustic crystalline anisotropy induced with approaching the point of the phase transition. The conditions of the appearance of critical angles and the angles of total internal reflection, as well as the effect of temperature on them, have been considered. The possibility has been analyzed of emission, in the vicinity of the phase transition, of a wave that propagates along the boundary into the bulk of the material. Based on the experimental data obtained by Trivisonno for the temperature dependences of the sound velocity in the Ni2 + x + y Mn1 − x Ga1 − y crystal, the conclusions of the theory developed are illustrated by numerical calculations for a concrete structure, namely, Ni2MnGa-quartz.

Optical Photoacoustic Detection of Circulating Melanoma Cells In Vitro.

The purpose of this research was to investigate the sensitivity of a system for the detection of circulating melanoma cells based on the thermoelastic properties of melanoma. The method employs photoacoustic (PA) excitation coupled with an optical transducer capable of determining the presence of cells within the circulating system in vitro. The transducer is based on stress wave-induced changes of the optical reflectance of a glass-water interface, probed with a continuous laser beam that is incident at an angle close to the critical angle of total internal reflection. A frequency tripled Nd:YAG laser pumping an optical parametric oscillator was employed to provide 532 nm and 620 nm laser light with a pulse duration of 10 ns. A custom-made flow chamber was used as an excitation and acoustic wave collection device. The targets were a human melanoma cell line HS 936 with an average diameter of about 15 μm. Melanoma cells were suspended in 10 mL of two types of media. The first one was Tyrode's buffer in concentrations ranging from 10 to 50 cells per μL, and the second one included 10(6) healthy white blood cells per mL of Tyrode's buffer. PA pressure waves were detected by an optical stress transducer. Detection trials resulted in a detection threshold of the order of one individual cell, indicating the effectiveness of the proposed mechanism. Results imply the potential to assay simple blood samples, from healthy and metastatic patients, to test the presence of cancerous melanoma providing an unprecedented method for screening metastatic disease.

Development of a scanning angle total internal reflection Raman spectrometer

A scanning angle total internal reflection (SATIR) Raman spectrometer has been developed for measuring interfacial phenomena with chemical specificity and high axial resolution perpendicular to the interface. The instrument platform is an inverted optical microscope with added automated variable angle optics to control the angle of an incident laser on a prism/sample interface. These optics include two motorized translation stages, the first containing a focusing lens and the second a variable angle galvanometer mirror. The movement of all instrument components is coordinated to ensure that the same sample location and area are probed at each angle. At angles greater than the critical angle, an evanescent wave capable of producing Raman scatter is generated in the sample. The Raman scatter is collected by a microscope objective and directed to a dispersive spectrometer and charge-coupled device detector. In addition to the collected Raman scatter, light reflected from the prism/sample interface is collected to provide calibration parameters that enable modeling the distance over which the Raman scatter is collected for depth profiling measurements. The developed instrument has an incident angle range of 25.5 degrees-75.5 degrees, with a 0.05 degrees angle resolution. Raman scatter can be collected from a ZnSe/organic interface over a range of roughly 35-180 nm. Far from the critical angle, the achieved axial resolution perpendicular to the focal plane is approximately 34 nm. This is roughly a 30-fold improvement relative to confocal Raman microscopy.

Unusual transmission through usual one-dimensional photonic crystal in the presence of evanescent wave

Basing on the condition that the incident angle is larger than the total internal reflection angle, we present a systematic study of transmission properties of one-dimensional photonic crystal with all dielectric materials by the transfer matrix method and the Bloch’s theorem. Due to the existence of the evanescent field within the structure, the transmission bands consist of some discrete symmetry peaks. For light with these peak frequencies, the structure is either transparent or opaque depending on the number of the structure periods. The unusual transmission properties are attributed to the field distribution and Bloch wave vector.

Luminescent solar concentrators: the road to low-cost energy from the sun

Photovoltaics (PVs) enable conversion of solar light into electricity without detrimentally affecting the environment. Unfortunately, solar cells require high-cost semiconductors, which makes them expensive. Concentrator systems help to minimize the coverage needed, but normal concentrators only work for a narrow angular range of solar radiation. Moreover, they need tracking devices and are poorly suited to capturing diffuse radiation. Luminescent solar concentrators (LSCs) avoid these disadvantages.1, 2 An LSC consists of a glass or plastic plate containing or coated with luminophores (dyes or phosphors) that absorb sunlight and emit light at longer wavelengths (see Figure 1). A substantial part of the longer-wavelength light is trapped by total internal reflection and guided to the edges of the LSC plate, where it is absorbed by small-area PV cells. The idea of using LSCs already dates back 30 years,3, 4 and much research has been carried out in this area.5–8 However, up to now, the technology has not delivered on its promise. Although theoretically concentration could be huge,1, 9 the best LSC-based PV system to date10 has a conversion efficiency of 7.1% and saves a factor 2.5 of PV-cell area. The reason for these low numbers is primarily losses of various kinds. For example, light is absorbed by the luminophore, but no luminescent light is emitted because of limited quantum efficiency (QE), i.e., the ratio of absorbed to emitted number of photons. Another important means of loss is escaping luminescent light from the concentrator at angles larger than the critical angle for total internal reflection (see Figure 1). One effective way to prevent this is by applying a wavelength-selective filter on top of the light guide,1, 11, 12 which keeps the luminescent light inside. However, Figure 1. (left) Luminescent solar concentrator with luminophores (dots) absorbing sunlight (dashed) and emitting longer-wavelength light (solid line) that is absorbed by a photovoltaic (PV) cell. (right) Luminescent plates with light guided towards the edges. (Photo courtesy of P. P. C. Verbunt.)

Surface plasmon resonance in nanostructured metal films under the Kretschmann configuration

We systematically investigated the surface plasmon resonance in one-dimensional (1D) subwavelength nanostructured metal films under the Kretschmann configuration. We calculated the reflectance, transmittance, and absorption for varying the dielectric fill factor, the period of the 1D nanostructure, and the metal film thickness. We have found that the small dielectric slits in the metal films reduce the surface plasmon resonance angle and move it toward the critical angle for total internal reflection. The reduction in surface plasmon resonance angle in nanostructured metal films is due to the increased intrinsic free electron oscillation frequency in metal nanostructures. Also we have found that the increasing the spatial frequency of the 1D nanograting reduces the surface plasmon resonance angle, which indicates that less momentum is needed to match the momentum of the surface plasmon-polariton. The variation in the nanostructured metal film thickness changes the resonance angle slightly, but mainly remains as a mean to adjust the coupling between the incident optical wave and the surface plasmon-polariton wave.

Calculation of the reflection coefficient of metal-dielectric structures in frustrated total internal reflection

Analytical formulas for calculating the reflection coefficient of a thin-film metal-dielectric structure at light incidence angles greater than the critical angle of total internal reflection were obtained using a conducting surface model for a thin absorbing layer. It is shown that an asymmetric interference pattern of the spectral dependence of the reflection coefficient has higher sensitivity to changes in the refractive index of the medium.

Dynamics at the air-water interface revealed by evanescent wave light scattering

A new tool to study surface phenomena by evanescent wave light scattering is employed for an investigation of an aqueous surface through the water phase. When the angle of incidence passes the critical angle of total internal reflection, a high and narrow scattering peak is observed. It is discussed as an enhancement of scattering at critical angle illumination. Peak width and height are affected by the interfacial profile and the focusing of the beam. In addition, the propagation of capillary waves was studied at the surface of pure water and in the presence of latex particles and amphiphilic diblock copolymers. The range of the scattering vectors where propagating surface waves were detected is by far wider than standard surface quasi-elastic light scattering (SQELS) and comparable with those of X-ray photon correlation spectroscopy (XPCS).

The perfect absorber

We demonstrate that films of very lossy metal or dielectric, with a thickness of only a few nanometers, can absorb almost all incident radiation when illuminated from the substrate side at the critical angle for total internal reflection. The absorption for s-polarized light approaches 100%, while the absorption for p-polarized light vanishes. We demonstrate this effect by measuring the absorption as a function of the angle of incidence at a wavelength of 775 nm in a 4.5 nm thick NbN film with a dielectric constant ϵNbN=−8.2+31.4i. The measured absorption in this film reaches a maximum of 94%. We discuss the design of a near-unity efficiency single-photon detector for s-polarized light that has a broadband absorption coefficient of >90% for wavelengths from 700 to 1600 nm.

광학 박막을 채용한 CMOS 이미지 센서 픽셀의 수광 효율

We consider introducing an optical thin film to the light guiding wall of a pixel in order to enhance the light guiding efficiency of a CMOS image sensor. Simulating the reflectance as a function of the incidence angle using the Essential Macleod program, we find that the range of total internal reflection is greatly increased for several materials. Particularly when air is chosen as the thin film material, the critical angle of total internal reflection could be shifted to about 50 degrees.

Parametric reflection upon cascade interaction of focused optical beams

The parametric reflection of a signal beam in the waist of the reference pump beam upon mismatched three-frequency interaction in a quadratically nonlinear medium is discussed. The critical angle of total internal reflection from the induced defocusing channel is found as a function of the beam waist parameters. It is shown that when the reference beam is focused, this angle increases and some distortions are introduced into the reflected wave due to a finite length of the waist. The modification of the cross section of a wave reflected from a convex parametric mirror is analysed. The optimal beam focusing geometry is found at which the distortions of the shape and divergence of the reflected wave are minimal. Under certain conditions, the signal wave also flows around a cylindrical inhomogeneity produced by the axially symmetric pump beam. The results of theoretical analysis and numerical simulation are in good agreement.

High-resolution surface plasmon resonance sensors based on a dove prism

Wavelength interrogation surface plasmon resonance (SPR) spectroscopy using a dove prism combines a simple and inexpensive optical design with high-resolution refractive index monitoring and biosensing. A BK7 dove prism inverts an optical image with a total internal reflection angle of 72.8°, an angle active in SPR. Hence, a unique system can accomplish SPR biosensing using wavelength interrogation and also perform SPR imaging. This optical configuration advantageously uses a single axis optical path between each optical component, simplifying the optical design of SPR instruments without compromise of the analytical performance. Fluidics were also incorporated to the instrument design for efficient sample delivery. The SPR instrument is characterized in terms of refractive index (RI) sensitivity, RI resolution, reproducibility, and application for monitoring low concentration biological events. Data analysis methodologies are compared for improved resolution of the measured response. Raw data analyzed using a minimum hunting procedure results in RI resolution in the 10 −6 range, while pre-treating data with singular value decomposition improves the resolution by one order of magnitude. Depending on the spectrophotometer employed, the RI range accessible can be easily tuned; examples with a 550–850 nm and a 550–1100 nm spectrophotometers are shown and results respectively in RI ranges of 1.32–1.39 RIU and 1.32–1.42 RIU. Monitoring of μM concentration of β-lactamase is performed using the wavelength interrogation configuration of the biosensor. Finally, a SPR image of a surface with a water droplet (volume = 500 nL) was obtained using the dove prism SPR with a band pass filter and a CCD camera. SPR using a dove prism configuration combines advantages of portable SPR instruments, SPR imagers and research-grade SPR instruments in a unique platform.

Cavity Plasmon Resonance Biosensing

Surface plasmon resonance (SPR) spectroscopy has demonstrated unprecedented performance in label-free real-time probing of various biopolymer, ligand, protein, and DNA interactions. Since its inception in the late sixties, the basic physical phenomenon underlying the SPR biosensing remained unchanged, namely, resonant absorption of TM-polarized light incident upon a metallic nanofilm above the critical total internal reflection angle. Since the SPR field is strictly confined to the metal-analyte interface, the measurements are usually limited to molecular adsorbates located in an immediate vicinity of this surface. Herein, we propose a novel biosensing method utilizing cavity plasmon resonance (CPR) excitation in nanofilms. As opposed to the classical TM-polarized SPR, the CPR is applicable for both TE and TM polarizations and does not require complicated evanescent field excitation conditions. It holds a promise for highly sensitive real-time probing of scalable amounts of analytes in a variety of frequency bands.

Visualization of the Molecular Dynamics of Lipopolysaccharide on the Plasma Membrane of Murine Macrophages by Total Internal Reflection Fluorescence Microscopy

The molecular action of Alexa 594-labeled lipopolysaccharide (LPS) from Escherichia coli was examined on living peritoneal macrophages of C57BL/6 mice by total internal reflection fluorescence microscope (TIRFM), and the molecular kinetics of LPS was analyzed. TIRFM visualization of the action of fluorescence-labeled LPS revealed an increase in the mean fluorescence intensity of LPS on the plasma membrane of wild type macrophages at 60 min after administration, indicating the oligomerization of LPS after binding to the macrophages. Additionally, a time-dependent sharp decrease in the mean diffusion coefficient of LPS was observed. On the other hand, both mean fluorescence intensity and diffusion coefficient of LPS in cases of TLR4(-/-), MD2(-/-), MyD88(-/-), and TRIF(-/-) macrophages were significantly different from the corresponding values of wild type macrophage, whereas differences were also noticed among these molecule-deficient macrophages. Furthermore, statistical analysis indicated the major role of receptors (TLR4 and MD2) and intracellular signaling molecules (MyD88 and TRIF) in oligomerization and lowering of the diffusion rate of LPS on the plasma membrane of murine macrophages, respectively.

Surface plasmon resonance applied to DNA-protein complexes.

Surface plasmon resonance (SPR) measures refractive index changes (Δn) at or near a surface and relates these to changes in mass at the surface Fig 1). This relationship is given by the Clausius Mossotti form (Eq. 2) of the Debye equation (Eq. 1): Open image in new window (1) Open image in new window Fig. 1. Schema showing the principle of surface plasmon resonance. Light from a laser source arriving through a prism at a gold surface at the angle of total internal reflection (θ) induces a nonpropagative evanescent wave that penetrates into the flow cell opposite the prism. The intensity of the reflected light is continuously monitored. At a given angle (λ) dependent on the refractive index of the solution in the flow cell, resonance between the evanescent wave and free electrons in the gold layer results in a reduction in the intensity of reflected light. The change in angle of reduced intensity (Δλ) reflects changes in the refractive index (n) of the solution in the flow cell immediately adjacent to the gold layer. A dextran surface coupled to the gold layer allows immobilization of ligands (e.g., DNA) within the evanescent field. where ɛ is the real part of the dielectric constant or permittivity constant related to the refractive index by ɛ = n 2, N is the number density given by N Aρ/Ma (N A is Avogadro’s number, ρ is the density and M a is the molecular mass). It is assumed that Δn/ΔC is a constant.