Incoherent Reflections Research Articles

Spatially incoherent common-path off-axis color digital holography.

We describe a new method for recording spatially incoherent common-path off-axis color digital holograms. We present the theoretical and experimental evidence to demonstrate an incoherent common-path off-axis color digital holographic (ICOCH) system capable of capturing information from three-dimensional color objects under incoherent illumination, both in transmission and reflection modes. Fresnel incoherent correlation holography (FINCH), a common-path system, is a frequently used incoherent holography technique. Our proposed system is conceptually similar to an advanced form of FINCH; moreover, it has three advantages over this advanced form of FINCH. First, removal of the spatial light modulator makes our system simpler and more cost-effective. Second, removal of the polarizer or analyzer allows for greater light throughput. Third, the off-axis optical configuration enables separation of zero-order and twin images with only a single exposure per color rather than requiring three exposures per color for in-line holography FINCH. Therefore, we believe that this simple and cost-effective system with high light throughput can acquire incoherent holograms for different colors involving single exposure for each color, which makes the ICOCH system suitable for many applications.

Time-resolved spectral density of interacting fermions following a quench to a superconducting critical point

Results are presented for the time evolution of fermions initially in a non-zero temperature normal phase, following the switch on of an attractive interaction. The dynamics are studied in the disordered phase close to the critical point, where the superfluid fluctuations are large. The analysis is conducted within a two-particle irreducible, large $N$ approximation. The system is considered from the perspective of critical quenches where it is shown that the fluctuations follow universal model A dynamics. A signature of this universality is found in a singular correction to the fermion lifetime, given by a scaling form $t^{(3-d)/2}S_d(\varepsilon^2 t)$, where $d$ is the spatial dimension, $t$ is the time since the quench, and $\varepsilon$ is the fermion energy. The singular behavior of the spectral density is interpreted as arising due to incoherent Andreev reflections off superfluid fluctuations.

Double cone of eigendirections in optically active ethylenediammonium selenate crystals.

Circular birefringence (CB) is generally responsible for only a small perturbation to the state of light polarization in crystals that also exhibit linear birefringence (LB). As such, the magnetoelectric tensor of gyration, which gives rise to CB and optical activity, is less well determined than the electric permittivity tensor in optical models of the Mueller matrix. To visualize the effect of the magnetoelectric tensor on polarimetric measurements, reported here are experimental mappings of the Mueller matrix and of the CB in a new chiral crystal with accidental null LB at an accessible optical frequency. Single crystals of ethylenediammonium selenate (EDSeO4) were synthesized and characterized by X-ray diffraction and Mueller matrix measurements in transmission and reflection. The crystals are isomorphous with the corresponding sulfate salt. They are tetragonal, space group P41(3)212. The constitutive relations of EDSeO4 were recovered using a partial wave summation of incoherent reflections. The extraordinary and ordinary refractive indices cross at 364 nm (3.41 eV), a scenario commonly called the 'isotropic point' or 'iso-index point'. At this wavelength, the magnetoelectric tensor fully describes the polarization transformation, giving rise to a double cone of eigendirections.

Coherent and incoherent seismic noise attenuation using parabolic radon transform and its application in environmental geophysics

The Radon transform is a mathematical tool that has been widely used in seismic data processing and image analysis. Three types of Radon transforms have been used as noise attenuation techniques in seismic data processing: the slant-stack or τ-p transform; the hyperbolic Radon transform; and the parabolic Radon transform. Ground-roll is a main type of strong noises in environmental geophysics. Attenuation of these types of noises is vital for improving the signal-to-noise ratio of seismic data. In the time–offset (t–x) domain, the ground-roll noise and other noisy waves just like; random noises, direct waves and airwaves overlap each other by the terms of time, which makes it difficult to attenuate coherent and incoherent noises in environmental geophysics. Nevertheless, significant different features shown in the time–slowness (τ–p) domain make it possible to separate coherent and incoherent noise and reflection waves effectively. A new method is proposed to separate these waves, using parabolic Radon transform (PRT). Amplitude and phase information is preserved during the proposed transformation. The reversibility and curvature of PRT provide a foundation for ground-roll noise suppression in the time-slowness domain. Synthetic datasets field and data examples have been implemented to illustrate coherent and incoherent noises attenuation can be achieved with a very little distortion of the effective signals. When compared with the linear radon ground-roll attenuation method, the field example results show the superiority of our method in suppressing the ground-roll noise and preserving the amplitude and phase information of effective waves.

Measurement of transmission and reflection from a thick anisotropic crystal modeled by a sum of incoherent partial waves.

Formulas for modeling ellipsometric measurements of bianisotropic crystals assume perfectly coherent plane wave illumination. As such, the finite coherence of typical spectroscopic ellipsometers renders such formulas invalid for crystals thicker than a few micrometers. Reflection measurements of thick crystalline slabs show depolarization. Researchers have proposed strategies for the full accounting for multiply reflected incoherent waves in anisotropic, arbitrarily oriented crystals [Appl. Opt.41, 2521 (2002).APOPAI0003-693510.1364/AO.41.002521], but to the best of our knowledge these methods have not been tested by explicit measurements. It is shown that by a summation of multiply reflected incoherent waves, transmission and reflection measurements of thick quartz slabs can be interpreted in terms of the constitutive material parameters.

An improved thin film approximation to accurately determine the optical conductivity of graphene from infrared transmittance

This work presents an improved thin film approximation to extract the optical conductivity from infrared transmittance in a simple yet accurate way. This approximation takes into account the incoherent reflections from the backside of the substrate. These reflections are shown to have a significant effect on the extracted optical conductivity and hence on derived parameters as carrier mobility and density. By excluding the backside reflections, the error for these parameters for typical chemical vapor deposited (CVD) graphene on a silicon substrate can be as high as 17% and 45% for the carrier mobility and density, respectively. For the mid- and near-infrared, the approximation can be simplified such that the real part of the optical conductivity is extracted without the need for a parameterization of the optical conductivity. This direct extraction is shown for Fourier transform infrared (FTIR) transmittance measurements of CVD graphene on silicon in the photon energy range of 370–7000 cm−1. From the real part of the optical conductivity, the carrier density, mobility, and number of graphene layers are determined but also residue, originating from the graphene transfer, is detected. FTIR transmittance analyzed with the improved thin film approximation is shown to be a non-invasive, easy, and accurate measurement and analysis method for assessing the quality of graphene and can be used for other 2-D materials.

Determination of the In-Plane Optical Conductivity of Multilayer Graphene Supported on a Transparent Substrate of Finite Thickness from Normal-Incidence Transmission Spectra

Normal-incidence transmission measurements are commonly used for determining the real part of the in-plane optical conductivities σ1(ω) of graphene layers. We present an accurate expression for σ1 (ω) in a closed form for a multilayer graphene film supported on a finite-thickness transparent substrate. This form takes into account the coherent and incoherent multiple reflections of the system, whereas the traditional method assumes a semi-infinite substrate. The simulated results for graphene sheets with a layer number N ≤ 10 show that no matter what the transparent substrate is, the accuracy to which σ1(ω) is determined by applying this expression is improved with no systematic error. Moreover, the layer number N can be exactly determined by simply dividing the σ1(ωp) value of N-layer graphene by the corresponding σ1(ωp) of monolayer graphene, where ωp is the peak frequency of the ordinary dielectric function's imaginary part ε2(ω) of graphene.

In-situ optical diagnostics of boron-doped diamond films growth

Interferometry is desirable method for in-situ measurement of thin, dielectric film growth, as it don't modify conditions of film deposition. Here we present interferometrical measurements of thickness of doped diamond films during Chemical Vapor Deposition (CVD) process. For this purpose we used semiconductor laser with 405 nm wavelength. Additional ex-situ measurement using spectral interferometry and ellipsometry have been performed. We found that doping diamond with boron does not cause degradation of interference of light inside the film. To our knowledge this is first study of optical monitoring of boron doped, polycrystalline diamond films deposition. Full Text: PDF References J. Asmussen, D. Reinhard, Diamond Films Handbook, 1st ed. (CRC Press 2002). CrossRef R. S. Sussmann, CVD diamond for electronic devices and sensors. (Chichester, U.K.: J. Wiley 2009). CrossRef E. Bakker, Y. Qin, "Electrochemical Sensors", Anal. Chem. 78, 12 (2006). CrossRef V. Prajzler et al., "Design and investigation of properties of nanocrystalline diamond optical planar waveguides", Opt. Express 21, 7 (2013) CrossRef N.J. Alberto et al., "Nanodiamond coated Bragg gratings for sensing applications", Proc. SPIE 8421 (2012). CrossRef R. Bogdanowicz et al., "Nucleation and growth of CVD diamond on fused silica optical fibres with titanium dioxide interlayer", Phys. Status Solidi (a) 210, 10 (2013). CrossRef M. Smietana et al., "Application of diamond-like carbon films in optical fibre sensors based on long-period gratings", Diamond Relat. Mater. 16, 4 (2007). CrossRef R. Bogdanowicz et al., "Amperometric sensing of chemical oxygen demand at glassy carbon and silicon electrodes modified with boron-doped diamond", Sens, Actuator B-Chem. 189 (2013) CrossRef C.E. Nebel et al., "Diamond and biology", J. R. Soc. Interface 4, 14 (2007). CrossRef R. Bogdanowicz et al., "Influence of the boron doping level on the electrochemical oxidation of the azo dyes at Si/BDD thin film electrodes", Diamond Relat. Mater. 39, (2013). CrossRef J.J. Gracio et al., "Diamond growth by chemical vapour deposition", J. Phys. D: App. Phys. 43, 37 (2010). CrossRef J. Luo, X. Ying, P. Wang, L. Chen, "Study on the growth of CVD diamond thin films by in situ reflectivity measurement", Diamond Relat. Mater. 11, 11 (2002). CrossRef A.M. Bonnot, R. Schauer, B. Weidner, "HFCVD diamond film nucleation and growth studies by in-situ optical technique and ex-situ AFM observations", Diamond Relat. Mater., 7, 2 (1998). CrossRef C.D. Zuiker, D.M. Gruen, A.R. Krauss, "In situ laser reflectance interferometry measurement of diamond film growth", J. Appl. Phys. 79, 7 (1996). CrossRef M. Bass et al., Handbook of opitcs, Volume IV: Optical Properties of Meterials, Nonlinear Optics, Quantum Optics (McGraw-Hill 2009). E.D. Palik ed., Handbook of Optical Constants of Solids (Elsevier 1998). D.I. Siapkas, C.L. Mitsas, "Generalized matrix method for analysis of coherent and incoherent reflectance and transmittance of multilayer structures with rough surfaces, interfaces, and finite substrates", Appl. Opt. 34, 10 (1995). CrossRef C. Katsidis, D.I. Siapkas, "General Transfer-Matrix Method for Optical Multilayer Systems with Coherent, Partially Coherent, and Incoherent Interference", Appl. Opt. 41, 19 (2002). CrossRef

Fabricating BRDFs at high spatial resolution using wave optics

Recent attempts to fabricate surfaces with custom reflectance functions boast impressive angular resolution, yet their spatial resolution is limited. In this paper we present a method to construct spatially varying reflectance at a high resolution of up to 220dpi, orders of magnitude greater than previous attempts, albeit with a lower angular resolution. The resolution of previous approaches is limited by the machining, but more fundamentally, by the geometric optics model on which they are built. Beyond a certain scale geometric optics models break down and wave effects must be taken into account. We present an analysis of incoherent reflectance based on wave optics and gain important insights into reflectance design. We further suggest and demonstrate a practical method, which takes into account the limitations of existing micro-fabrication techniques such as photolithography to design and fabricate a range of reflection effects, based on wave interference.

Extending the 1-D Hovel Model for Coherent and Incoherent Back Reflections in Homojunction Solar Cells

In this paper we extend the analytical drift-diffusion model, or Hovel model, to model the electrical characteristics of solar cells incorporating a back mirror. We use a compact summation approach to derive modified optical generation functions in Homojunction solar cells, considering both coherent and incoherent reflections from the back reflector. These modified generation functions are then used to derive analytical formulae for the current-voltage characteristics of mirrored solar cells. We simulate the quantum efficiency of a simple GaAs np diode with a planar gold back reflector, and compare the results with the standard Hovel model using a generation function given by the Beer-Lambert law. Finally, we use the model to simulate the performance of a real GaAs solar cell device fabricated using an epitaxial-lift-off procedure, demonstrating excellent agreement between the simulated and measured characteristics.

Modeling incoherent reflections from rough room surfaces with image sources

Reflections at rough surfaces change the temporal structure of the reflected signal. This paper shows how to incorporate this temporal behavior in geometric room acoustics modeling. Specifically, a beam tracer is used for calculating the image sources and reflection paths. The roughness of the surfaces is taken into account in post-processing. A single reflection is assumed to distribute the energy according to an exponential function in time based on Biot's rough surface modeling theory. Multiple reflections are modeled with convolutions of exponential functions which are approximated as gamma functions.

Determination of the complex refractive index of a thick slab material from its spectral reflectance and transmittance at normal incidence

Multiple beam incoherent reflectance, transmittance and absorbance of a homogenous planar slab are derived by ray tracing and transfer matrix approaches. Two different procedures are introduced to retrieve the bulk complex refractive index analytically. The needed experimental measurements are the slab thickness, the spectral reflectance and transmittance at normal incidence. Errors of the deduced refractive indices are calculated to be of about 1×10−7 for imaginary and 0.013 for real refractive indices. Refractive indices of two different thicknesses and compositions glassy slabs are determined across a wide spectral range 0.22–2.2μm.

Noise Correlations in Three-Terminal Diffusive Superconductor–Normal-Metal–Superconductor Nanostructures

We present measurements of current noise and cross correlations in three-terminal superconductor-normal-metal-superconductor (S-N-S) nanostructures that are potential solid-state entanglers thanks to Andreev reflections at the N-S interfaces. The noise-correlation measurements spanned from the regime where electron-electron interactions are relevant to the regime of incoherent multiple Andreev reflection. In the latter regime, negative cross correlations are observed in samples with closely spaced junctions.

Mechanisms of geometrical seismic attenuation

In several recent reports, we have explained the frequency dependence of the apparent seismic quality-factor (Q) observed in many studies according to the effects of geometrical attenuation, which was defined as the zerofrequency limit of the temporal attenuation coefficient. In particular, geometrical attenuation was found to be positive for most waves traveling within the lithosphere. Here, we present three theoretical models that illustrate the origin of this geometrical attenuation, and we investigate the causes of its preferential positive values. In addition, we discuss the physical basis and limitations of both the conventional and new attenuation models. For waves in media with slowly varying properties, geometrical attenuation is caused by variations in the wavefront curvature, which can be both positive (for defocusing) and negative (for focusing). In media with velocity/density contrasts, incoherent reflectivity leads to geometrical-attenuation coefficients which are proportional to the mean squared reflectivity and are always positive. For «coherent» reflectivity, the geometrical attenuation is approximately zero, and the attenuation process can be described according to the concept of «scattering Q». However, the true meaning of this parameter is in describing the mean reflectivity within the medium, and not that of the traditional resonator quality factor known in mechanics. The general conclusion from these models is that non-zero and often positive levels of geometrical attenuation are common in realistic, heterogeneous media, both observationally and theoretically. When transformed into the conventional Q-factor form, this positive geometrical attenuation leads to Q values that quickly increase with frequency. These predictions show that the positive frequency-dependent Q observed in many datasets might represent artifacts of the transformations of the attenuation coefficients into Q.

SOME PHENOMENA THEORETICALLY PREDICTED AND EXPLAINED BY THE TIME ANALYSIS OF THE EXPERIMENTAL DATA ON NUCLEAR PROCESSES

The self-consistent methods in time analysis of nuclear collisions and decays are based on the properties of time as a quantum observable, canonically conjugate to energy, and the appropriate definition of mean durations of quantum collisions, the variances in their distributions, the decay functions, and the surviving functions of the meta-stable states, including radioactive and compound nuclei. Even a simplified application of these methods for the elementary study of the α-decay in the exponential-law-decay approximation resulted in the simple phenomenological method of the determination of the α-particle one-step virtual and real sojourn time inside the parent α-radioactive nucleus between the α-particle successive incoherent multiple internal reflections during the α-decay. And also the direct temporal study of the quasi-monochromatic proton scattering by 12 C and 14 N nuclei at the range of isolated resonances distorted by the nonresonant background, accompanied by the bremsstrahlung, brings to the simple revealing of the possible existence of the delay–advance phenomenon in the proton emission during scattering (in the center-of-mass system). The utilization of the self-consistent methods of time analysis to the study of high-energy nuclear reactions (near and above 0.1 GeV per nucleon in the final compound–fragment formations) resulted in the discovery of the phenomenon of time resonances (or explosions) for such formations. Some perspectives of the further study of the evident temporal phenomena in nuclear processes are also indicated.

Cross Correlation of Incoherent Multiple Andreev Reflections

We use a semiclassical theory to calculate the current correlations in a multiterminal structure composed of a normal metallic dot connected to all superconducting leads at arbitrary voltage and temperature. This theory holds when the proximity effect is suppressed in the dot. At low voltage, eV<<Delta (Delta is the superconducting gap in the leads), when charge transport is due to incoherent multiple Andreev reflections, the correlations are strongly enhanced compared to those in the normal state. Moreover, we predict that the cross correlation can be positive or negative depending on the properties of the point contacts between the dot and the leads. We also discuss the effect of inelastic scattering in the dot.

Temperature‐dependent spectro‐ellipsometric studies of optical transitions near absorption edge of TlInS2

AbstractThe temperature dependence of the absorption edge of the layered TlInS2 was studied in a region of the incommensurate phase by spectroscopic phase modulated ellipsometry (SPME) on (001) surfaces in incoherent reflection mode that was sensitive to both E⊥C* and E//C* components of the reflected light (C*: the direction bisecting the angle between two optic axes). The energy position of the absorption edge, which was obtained from the measured Ic signal, was found to exhibit an irregular behavior with temperature in a similar way with the obtained earlier temperature dependence of excitons. It is proposed that this behaviour reflects the changes in electronic spectrum due to the temperature phase transition while the peaking anomaly of the measured in‐layer‐plane optical anisotropy is mostly related with the spatial structure of the incommensurate phase. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Optical characteristics of a multilayer photovoltaic cell for oblique incidence of light

Taking into account the contributions of interference and incoherent multiple reflections of light in the substrate, we have determined the distribution of the absorbed energy density Q in layers of a multilayer photovoltaic cell in the general case of oblique incidence of light on the cell. The relations obtained are expressed in terms of the Fresnel reflection and transmission coefficients for interfaces between media, which for oblique incidence are different for s and p polarization of the incident light. The energy absorbed by an active layer of the cell varies very slightly with the angle of incidence if the maximum in the Q distribution is located at a heterojunction. We carried out a numerical analysis for a five-layer cell based on a copper phthalocyanine-fullerene heterojunction.

Refractive indices of layered semiconductor ferroelectrics TlInS2, TlGaS2, and TlGaSe2 from ellipsometric measurements limited to only layer-plane surfaces

The ternary layered Tl-contained semiconductor ferroelectrics TlInS2, TlGaS2, and TlGaSe2, exhibiting an incommensurate phase and a relaxor state with temperature, were approached down to 0.76eV at room temperature by spectroscopic phase modulated ellipsometry in a region below the energy gap of each material. By using both coherent and incoherent reflection modes on only the layer-plane surfaces, the refractive indices in the parallel- and perpendicular-to-the-layers directions of the light propagation were determined. Sellmeier single-oscillator form was used to fit the model data to the experimental intensities. The discrepancy between the model and experimental data was shown to be negligible. Besides, a self-consistent picture of the obtained refraction indices was emerging after the discussion based on the available data for the studied materials. The applied experimental approach was thus found to be quite effective for layered materials, and the obtained refractive indices might be used for database with high degree of confidence.

Modelling gratings on either side of the substrate for light extraction in light-emitting diodes

We present a three-dimensional model based on rigorous coupled wave analysis (RCWA) which allows us to study the influence of periodic structures on light extraction in light-emitting diodes. The gratings can be placed both at the interface between the emitting layers and the substrate, where they coherently interact with the dipole field, or at the interface between the substrate and air, where multiple incoherent reflections in the thick substrate contribute to the overall extraction. Even in the case of a grating at the interface between the substrate and air, these multiple incoherent reflections in the substrate still contribute to the overall extraction for large devices, an effect which has been mostly ignored in literature FDTD simulations.