Diffuse Reflectance Measurements Research Articles

The SPECTRAL Perfusion Arm Clamping dAtaset (SPECTRALPACA) for video-rate functional imaging of the skin

Spectral imaging has the potential to become a key technique in interventional medicine as it unveils much richer optical information compared to conventional RBG (red, green, and blue)-based imaging. Thus allowing for high-resolution functional tissue analysis in real time. Its higher information density particularly shows promise for the development of powerful perfusion monitoring methods for clinical use. However, even though in vivo validation of such methods is crucial for their clinical translation, the biomedical field suffers from a lack of publicly available datasets for this purpose. Closing this gap, we generated the SPECTRAL Perfusion Arm Clamping dAtaset (SPECTRALPACA). It comprises ten spectral videos (∼20 Hz, approx. 20,000 frames each) systematically recorded of the hands of ten healthy human participants in different functional states. We paired each spectral video with concisely tracked regions of interest, and corresponding diffuse reflectance measurements recorded with a spectrometer. Providing the first openly accessible in human spectral video dataset for perfusion monitoring, our work facilitates the development and validation of new functional imaging methods.

Fabrication and adapting the optical, and dielectric performance of PVC/ MnFe2O4/ZnMn2O4 nanocomposite films for optoelectronic applications

The current study focuses on the fabrication of hybrid flexible polymers composed of MnFe2O4/ZnMn2O4 nanocomposites doped polyvinyl chloride (PVC). The doped polymers show great potential for utilization in a wide range of optoelectronics applications. PVC/(1-x)MnFe2O4/xZnMn2O4 were made using the casting and sol gel processes. The effect of (1-x)MnFe2O4/xZnMn2O4 nanocomposite samples on the optical parameters of PVC polymer has been explored using ultraviolet–visible diffused reflectance measurements. Doped polymers might be useful as protective barriers against ultraviolet radiation of various wavelengths (UVA, UVB, UVC) and as excellent absorber materials for solar cells. The direct and indirect bandgaps (Eg) of PVC are 4.26 and 4.08 eV. The direct/indirect optical band gap lowered to their lowest 3.97/3.45 eV as the PVC doped with nanofillers contained 50 %/80 % ZnMn2O4, respectively. Different models were used to extracted the refractive index (n) of different polymers based on the obtained optical band gaps (direct/indirect). Doped polymers containing 50 and 80 % ZnMn2O4 had the highest n values using direct and indirect Eg values, respectively. The n value (obtained from the direct optical bandgap energy) of PVC increased from 2.209 to the maximum value (2.262) as x = 0.5. The n value (obtained from the indirect optical bandgap energy) of PVC increased from 2.349 to the maximum value (2.367) as x = 0.8. All linear and nonlinear optical parameters of PVC polymer were improved as it doped with the nanocomposite fillers. The fluorescence (FL) intensity of PVC was reduced as it was doped with (1-x)MnFe2O4/xZnMn2O4 and this intensity reduced as the content of ZnMn2O4. The standard (CIE) color space chromaticity diagram was used to analysis the FL spectra for different samples. The effect of nanocomposite samples on the AC conductivity, dielectric constants and electric modulus of the PVC was studied. At 1 kHz, the dielectric constant of PVC was increased from 11.745 to 12.906 and 12.096 for polymers with x = 0 and x = 0.2, respectively. The enhanced optical and dielectric properties of the PVC/(1-x)MnFe2O4/xZnMn2O4 polymers nanocomposites suggest that these materials are suitable for smart electronic devices.

Fabrication and evaluation of a spatially resolved fiber-optic probe for diffuse reflectance measurement for noninvasive diabetic foot ulcer diagnosis perspective

Fabrication and evaluation of a spatially resolved fiber-optic probe for diffuse reflectance measurement for noninvasive diabetic foot ulcer diagnosis perspective

TiO2 multi-leg nanotubes for surface-enhanced Raman scattering

Abstract In the recent past, significant research efforts have been put forth to fabricate cost-effective substrates for surface-enhanced Raman scattering (SERS) applications. Here we propose semiconducting TiO2 multi-leg nanotubes and Au nanoparticle-coated TiO2 multi-leg nanotubes (TiO2 MLNTs and Au/TiO2 MLNTs) as SERS substrates. The unique multi-leg architecture of TiO2 nanotubes demonstrated enhanced light-harvesting properties facilitated by an induced photonic absorption edge. Remarkable high SERS sensitivity is observed towards the detection of Methylene blue (MB), up to nM concentration (E.F. ~104) using TiO2 MLNTs. The same is attributed to the resonantly matched photonic absorption edge of TiO2 MLNTs with the wavelength of incident laser probe light. On the other hand, the Au nanoparticle coating further leveraged the light absorption ability of TiO 2 MLNTs with the aid of localized surface plasmon resonance mode (LSPRs). As such, Au/TiO2 MLNTs showed excellent enhancement in SERS sensitivity (E.F. ~105, for nM of MB) facilitated by the synergy between the plasmonic modes of Au and the photonic absorption mode of TiO2 MLNTs. UV-Vis diffuse reflectance and Raman spectroscopy measurements are highlighted to elucidate the light absorption and SERS sensitivity of the TiO2 and Au/TiO2 MLNTs.

In-Line Chemical Composition Monitoring for the Injection Molding Process of Biodegradable Polymer Blends Using Simultaneous Measurement of Near-Infrared Diffuse Reflectance and Transmission Spectra.

In the processing of polymer blends and composites, in-line near-infrared (NIR) spectroscopy enables monitoring of the composition and its composite uniformity and contributes to rapid process development and quality control. However, in the injection molding process, the study of the composition of polymer materials has been delayed due to high-pressure conditions. Our research group developed NIR probes for transmission and diffuse reflectance measurements that can withstand high-pressure and temperature conditions up to 130 MPa and 200 °C. In this research, transmission and diffuse reflectance spectra were measured inline during the injection molding process of polymer blends of poly(lactic acid) and polybutylene succinate adipate. The intensity of each polymer band in the second-derivative spectra exhibited a monotonic increase or decrease in response to changes in the blend ratio. Using transmission and diffuse reflectance spectra as explanatory variables of the partial least squares regression model simultaneously, the model showed high estimation accuracy for the entire region of the blend ratio. Finally, this model was applied to monitor the polymer changeover operation, and the change in the blend ratio in the molded product was successfully estimated in line.

Intensification of organic pollutant degradation under visible light irradiation using ZnO nanostructured photocatalysts doped with praseodymium

Zinc oxide nanostructures doped with praseodymium (ZnO:Pr) at varying Pr content (0.05 % to 1.0 % w/w) were synthesized using the electrospinning-calcination technique. Comprehensive morphological and structural characterizations were conducted through SEM, XRD, and XPS analyses. In addition, diffuse reflectance and photoluminescence spectroscopy measurements were performed to assess the optical properties of materials. The produced photocatalysts (ZnO:Pr) were then employed for the degradation of methylene blue dye and oxytetracycline under visible-light irradiation. ZnO:Pr(0.1 %) demonstrated the best photocatalytic performance against methylene blue showing a pseudo-first-order rate constant of k = 3.630 × 10-2 min−1. Investigation of oxytetracycline photodegradation with ZnO:Pr(0.1 %) revealed a pseudo-second-order rate constant of ks = 1.165 × 10-1 L mg−1 min−1, resulting in a reaction half-life (τ½) of approximately 1 min under optimal conditions. Total organic carbon and mass spectrometry analyses highlighted mineralization and identified the main reaction intermediates, respectively, for the oxytetracycline photodegradation. The photodegradation mechanism of oxytetracycline was proposed by the photocatalytic degradation measurements in the presence of scavengers such as hydroquinone and isopropanol. These nanostructures exhibited robust photocatalytic activity over multiple cycles, demonstrating excellent stability. This study underlines the promising potential of ZnO:Pr(0.1 %) as an efficient photocatalyst able to intensify the photodegradation of organic pollutants.

Combined experimental and first principles look into (Ce, Mo) doped BiVO4

Here we investigated the effects of Ce and Mo doping on hydrothermally synthesized bismuth vanadate BiVO4 nanoparticles (NPs). The existence of monoclinic scheelite and tetragonal zircon phases of NPs was validated from Rietveld refinement of the powdered X-ray diffraction, room temperature Raman, and Fourier-transform infrared spectroscopy. The co-doping of Bi and V sites with respective Ce and Mo dopants in a mixed tetragonal zircon and monoclinic scheelite phases of BiVO4 lattice was corroborated from high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy. The photoluminescence measurements revealed enhancement of photo-generated carrier recombination in (Ce, Mo) co-doped BiVO4 NPs which may have hampered its photocatalytic efficiency in degrading the methylene blue dye. The simulations based on Hubbard U corrected density functional theory (DFT+U) suggest that Mo and Ce co-doping introduced deep impurity states which may have facilitated the photo-generated carrier recombination detrimental to photocatalytic performance. The UV-vis diffuse reflectance measurements provided evidence for the presence of these defect states. In summary, this work may have presented a comprehensive experimental analysis of (Ce, Mo) doped BiVO4 supported by DFT simulations.

Syntheses, Crystal Structures, and Electronic Structures of Quaternary Group IV-Selenide Semiconductors.

Early transition-metal chalcogenides have garnered recent attention for their optoelectronic properties for solar energy conversion. Herein, the first Zr-/Hf-chalcogenides with a main group cation, Ba9Hf3Sn2Se19 (1) and Ba8Zr2SnSe13(Se2) (2), have been synthesized. The structure of 1 is formed from isolated SnSe44- tetrahedra and distorted HfSe6 octahedra. The latter condense via face-sharing trimeric motifs that are further vertex-bridged into chains of 1∞[Hf(1)2Hf(2)Se11]10-. The structure of 2 is comprised of SnSe44- tetrahedra, Se22- dimers, and face-sharing dimers of distorted ZrSe6 octahedra. These represent the first reported examples of Hf-/Zr-chalcogenides exhibiting face-sharing octahedra with relatively short Hf-Hf and Zr-Zr distances. Their preparation in high purity is inhibited by their low thermodynamic stability, with calculations showing small calculated ΔUdec values of +7 and +9 meV atom-1 for 1 and 2, respectively. Diffuse reflectance measurements confirm the semiconducting nature of 1 with an indirect band gap of ∼1.4(1) eV. Electronic structure calculations show that the band gap absorptions arise from transitions between predominantly Se-4p valence bands and mixed Hf-5d/Sn-5p or Zr-4d/Sn-5p conduction bands. Optical absorption coefficients were calculated to be more than ∼105 cm-1 at greater than 1.8 eV. Thus, promising optical properties are demonstrated for solar energy conversion within these synthetically challenging chemical systems.

The Effect of an Er:YAG Laser Combined with a 755 nm Picosecond Laser on Tattoo Removal in a Rat Model

Laser tattoo removal is an effective technique, but multiple rounds of treatment are required to eliminate tattoos, which can be a challenge for patients who do not have the time. Additionally, there is relatively limited research on the mechanisms of laser tattoo removal, necessitating further in-depth studies. This study aimed to investigate the efficacy of an Er:YAG laser combined with a 755-picosecond laser for tattoo removal and the changes in skin diffuse reflection, pigment particle size, macrophage recruitment, and inflammatory factor levels during combined laser treatment. Our experiments used three sets of lasers—an Er:YAG laser, a 755 nm picosecond laser, and an Er:YAG laser combined with a 755 nm picosecond laser—for tattoo removal. The effects of tattoo removal at different time points were evaluated. Moreover, the mechanisms were explored using HE staining, immunohistochemistry, diffuse reflectance measurements, in vitro gel tests, mass spectrometry, and ELISA experiments. The combined treatment was more effective for tattoo removal in rats. The combined laser treatment effectively reduced diffuse reflection from the skin, thereby increasing the effective laser power, reducing the size of the pigment particles, allowing for easier removal of the pigment, and increasing the recruitment of dermal macrophages and the release of inflammatory factors, thus increasing the rate of tattoo removal in vivo.

Advancing energy storage and supercapacitor applications through the development of Li+-doped MgTiO3 perovskite nano-ceramics.

Perovskite oxide materials, specifically MgTiO3 (MT) and Li-doped MgTiO3 (MTxLi), were synthesized via a sol-gel method and calcination at 800°C. This study explores the impact of varying Li doping levels (x = 0, 0.01, 0.05, and 0.1) on the crystalline structure and properties of MgTiO3. X-ray diffraction analysis revealed a well-defined rhombohedral MgTiO3 phase. Optical diffuse reflectance measurements provided insights into energy gap values, refractive index, and dielectric constant. Li+ doping enhanced the electrical properties of MgTiO3, with a notable phase transition observed at 50°C. The study investigated impedance and AC conductivity under varying temperature and frequency conditions (25-120°C, 4 Hz to 8 MHz). Electrochemical analysis through cyclic voltammetry and electrochemical impedance spectroscopy confirmed highly electrocatalytic properties for MTxLi, particularly when modified onto screen-printed electrodes. This work not only advances the understanding of Li-doped MgTiO3 nanostructures but also highlights their significant potential for direct electrochemical applications, particularly in the realm of energy storage.

Study the effect of nano NiCo2O4 doping on the optical and dielectric properties of PMMA/PEO/MWCNTs

In this study, NiCo2O4 nanoparticles were prepared using a hydrothermal process and examined by x-ray diffraction. After that, using the casting technique, blends of polymethyl methacrylate (PMMA)/poly(ethylene oxide) (PEO) were loaded with multi-walled carbon nanotubes (MWCNTs) and different amounts (x) of NiCo2O4 nanoparticles. The obtained blends were characterized using X-ray diffraction and scanning electron microscopy techniques. Utilizing diffuse reflectance measurements, various optical parameters, including energy gap, refractive index, extinction coefficient, optical dielectric constant, optical conductivity, and nonlinear optical parameters, were investigated. Following incorporation of MWCNTs/NiCo2O4 in the blend, the transmittance of the PMMA/PEO blend (90 %) displayed a drop reaching 21 %, the reflectivity and refractive index increased. The direct/indirect optical band gap values of PMMA/PEO (5.07/4.8 eV) decreased attaining 4.96/4.54 eV for the blend with 2.5 wt% NiCo2O4. The optical conductivity greatly enhanced, and the linear and nonlinear optical parameters increased as the amount of NiCo2O4 doping increased. The dispersion parameters for all blends were also calculated. Fluorescence spectra (FL) measurements revealed a reduction in the FL intensity with increasing the NiCo2O4 content (x). Through the dielectric measurements, the impact of increasing NiCo2O4 content on the ac conductivity, dielectric properties, energy density, and electric modulus was analyzed for all blends. Remarkably, a significant increase in AC conductivity was obtained upon loading with 1.5 wt% NiCo2O4. Overall, variation in the dielectric and optical features of the PMMA/PEO/MWCNTs/x wt.% NiCo2O4 blends makes them appropriate for optoelectronic and energy storage applications.

Effect of Ca substitution on crystal structure and band gap of solar cell material BaSi2

To ameliorate the potential of a promising solar cell material BaSi2, the effects of substituting Ba with Ca atoms on the crystal structure and band gap Eg of BaSi2, were investigated both experimentally and computationally. The solid-solution limit of the Ca atoms in BaSi2 was approximately 2.3 at.%. Single-crystal X-ray diffraction analysis of Ba1−xCaxSi2 (0.025 ≤ x ≤ 0.072) revealed that the unit cell volume decreases with Ca content x, and the Ba atoms at the A1 crystallographic site are preferentially substituted by Ca atoms. Diffuse reflectance measurements indicated that Eg decreases with x (1.24 eV at x = 0 and 1.17 eV at x = 0.07). The density functional theory calculations demonstrate that the experimentally observed decrease in Eg by Ca substitution can be explained qualitatively by the combination of the substitution of Ca atoms in the unit cell volume of BaSi2 and the volume reduction.

The pressure-stabilized polymorph of indium triiodide.

A layered rhombohedral polymorph of indium(III) triiodide is synthesized at high pressure and temperature. The unit cell symmetry and approximate dimensions are determined by single crystal X-ray diffraction. Its R3̄ crystal structure, with a = 7.214 Å, and c = 20.47 Å, is refined by the Rietveld method on powder X-ray diffraction data. The crystal structure is based on InI6 octahedra sharing edges to form honeycomb lattice layers, though with considerable stacking defects. Different from ambient pressure InI3, which has a monoclinic molecular structure and a light-yellow color, high pressure InI3 is layered and has an orange color. The band gaps of both the monoclinic and rhombohedral variants of InI3 are estimated from diffuse reflectance measurements.

The luminescent semiconductor Pb7I6(CN2)4.

The development of new compounds in the domain of metal dinitridocarbonates is most efficiently performed via solid-state metathesis or simply by addition reactions. Our discovery of Pb7I6(CN2)4 is the result of a solid-state reaction of PbCN2 with PbI2 at 420 °C. Its crystal structure was solved and refined from X-ray diffraction data based on a single crystal with the space group P63/mmc. The crystal structure is based on a network of lead tetrahedra, lead trigonal bipyramids and lead octahedra interconnected by [NCN]2- and iodide. Properties of the material were investigated by diffuse reflection measurement, photoluminescence measurements, and electronic band structure calculations demonstrating that this material is a semiconductor.

Physical Properties Investigation on Sunscreens with Red Dragon Fruit Peel Extract

Red dragon fruit peel extract is reported as an active ingredient in sunscreen because of its ability to protect the skin. UV exposure to the skin can cause reddish skin to develop skin cancer. This study aimed to determine the characteristics of the cream made from ZnO and red dragon fruit peel extracts (Hylocereus costaricensis), such as sun protection factor (SPF), pH, stability, viscosity, spreadability, and adhesion. Red dragon fruit peel extract was obtained by maceration using methanol, and DPPH-scavenging activity resulted in an IC50 of 0.96 μg/mL. Measurement of diffuse UV-vis reflectance shows that ZnO has absorption at λex 385 nm, which correlates with a bandgap energy of 3.22 eV. F1 formulation cream (red dragon fruit peel extract and ZnO ratio of 0:1) has the highest SPF value of 17. The Kruskal-Wallis test shows that there is a significant difference in adhesion between the F1 formulation cream with F2 (p-value = 0.002) and F4 (p-value = 0.03).

Facile microwave synthesis of Zinc Ferrite@NCDs for photocatalytic degradation of fluoroquinolone antibiotics

Zinc ferrite (ZnFe2O4) composites have attracted growing interest in photocatalytic water purification. Herein, the hybrids of zinc ferrite and nitrogen-doped carbon dots (ZnF@x%NCDs) were synthesized via facile microwave synthesis. X-ray diffraction and Raman characterization confirm the formation of the spinel structure, and elemental composition has been analyzed by X-ray photoelectron spectroscopy. The photocatalytic activity of ZnF@x%NCDs was evaluated via the decomposition of ciprofloxacin and norfloxacin under visible light illumination. We noted that 20 % weight loading of NCDs led to the highest (∼79.2 %) ciprofloxacin (CIP) degradation. Diffuse reflectance measurements demonstrate the reduction of the band gap in composites ZnF@20%NCDs (1.91 eV) compared with bare ZnF (2.03 eV); moreover, the hybridization of zinc ferrites with NCDs results in enhanced photocurrent density and surface area. The effect of experimental parameters, including the role of photocatalyst dosage, pH value, and initial concentration of pollutants on the degradation of CIP, have also been investigated.

Photocatalytic Degradation of Ceftriaxone Using TiO2 Coupled with ZnO Micronized by Supercritical Antisolvent Route.

Heterogeneous photocatalysis is a promising technique for removing pollutants from water. In this work, supercritical antisolvent (SAS)-micronized ZnO (ZnOSAS) is coupled with commercial anatase TiO2 (PC50) to study the photocatalytic degradation of ceftriaxone under UV and visible light. Diffuse ultraviolet-visible reflectance (UV-vis DRS) measurement revealed that the presence of ZnO leads to a slight absorption in the visible region. Wide-angle X-ray diffraction (WAXD) analysis showed the presence of both ZnO wurtzite and TiO2 anatase crystalline phases in the composite. Photocatalytic tests proved that the activity of the ZnOSAS/PC50 composite is higher than that of commercial ZnO, SAS-micronized ZnO, and PC50, allowing complete ceftriaxone degradation under UV light after only 2 min of irradiation time. In contrast, about 90% of ceftriaxone degradation is achieved after 180 min of visible-light irradiation. The photocatalytic results for an experiment carried out in the presence of probe scavenger molecules for reactive oxygen species show that hydroxyl radicals and positive holes are both reactive species involved in the ceftriaxone photocatalytic degradation mechanism. Finally, reuse cycles of the ZnOsas/PC50 composite are performed, demonstrating the stability and recyclability of the photocatalyst.

Bi2ZnTiO6 thin films for next-generation photovoltaics: Study of material properties characterization and deposition conditions optimization

The perovskite-like oxide Bi2ZnTiO6 (BZT) combines a narrow band gap with significant ferroelectric polarization, key parameters for the development of next-generation photovoltaic devices. Nevertheless, BZT remains a relatively unexplored material due to its difficult synthesis. The present experimental work unfolds and optimizes the deposition of BZT phase thin films by rf-sputtering method on standard Pt(111)/TiO2/SiO2/Si(001) substrates. The series of thin films explores different deposition conditions: Substrate temperature (350º-600ºC), RF power (50–80 W), exposure time (30–120 min), O2:Ar ratio (25–50%) and thermal treatments (air-O2). Thin films deposited between 350 and 475ºC are mainly amorphous. Above 490–550ºC the films show incipient crystallization. Depositions at temperatures above 600ºC and heat treatments resulted in partial recrystallization of spurious Bi- or Zn-rich oxides and aurivillius or pyrochlore-like phases. At 550 ºC, the films are dominated by a polycrystalline BZT phase in P4mm tetragonal structure, and the increase of the O2:Ar ratio contributes to improve the B-site order. Not least, no significant structural changes were observed after ∼3 years ageing. Diffuse reflectance measurements show relatively narrow optical band gaps between 1.4–1.9 eV within expected values for this system. Piezo-force microscopy revealed domains contrast and hysteresis loops correlated with the quality of the film crystallized BZT phase.

Depth-selective method for time-domain diffuse reflectance measurements: validation study of the dual subtraction technique.

Research on the spatial distribution of sensitivity of time-domain near infrared diffuse reflectance measurement is reported in this paper. The main objective of the investigation is to validate theoretically calculated sensitivity profiles for a measurement geometry with two detectors and two sources in which sensitivity profiles of statistical moments of distributions of time of flight of photons (DTOFs) are spatially restricted to a region underneath the detectors. For this dual subtraction method, smaller sensitivities to changes appearing in the superficial layer of the medium were observed compared to the single distance and single subtraction methods. Experimental validation of this approach is based on evaluation of changes in the statistical moments of DTOFs measured on a liquid phantom with local absorption perturbations. The spatial distributions of sensitivities, depth-related sensitivity and depth selectivities were obtained from the dual subtraction method and compared with those from single distance and single subtraction approaches. Also, the contrast to noise ratio (CNR) was calculated for the dual subtraction technique and combined with depth selectivity in order to assess the overall performance (product of CNR and depth selectivity) of the method. Spatial sensitivity profiles from phantom experiments are in a good agreement with the results of theoretical studies and feature more locally restricted sensitivity volume with the point of maximal sensitivity located deeper. The highest value of overall performance was obtained experimentally for the second statistical moment in the dual subtraction method (∼10.8) surpassing that of the single distance method (∼8.7). This confirms the advantage of dual subtraction measurement geometries in the suppression of optical signals originated in the superficial layer of the medium.

Enhanced Diffuse Reflectance of Photons in Molybdenum Back Electrode Films Achieved via Surface Texturing for Thin Film Solar Cells

Molybdenum (Mo) thin film is widely used as the bottom electrode in substrate‐configured thin film solar cells due to its high conductivity and reflectivity. Mo grown onto microtextured substrates increases the diffuse reflection of incident photons via scattering/multiple reflections on the corner/edges, in addition to the contribution from increased surface area. Herein, bilayer Mo is grown using direct current magnetron sputtering onto plain and textured substrates. To texture the glass substrate surface, a periodic array of cross‐linked photoresist structures (SU‐8 2000.5 & SU‐8 2005) is introduced via UV‐lithography process. Characterizations are done using X‐ray diffractometer, optical microscope, scanning electron microscope, and optical profilometer. Angle‐dependent specular reflectance, diffuse reflectance, and electrical measurements done on Mo grown on plain and textured substrates lead to a comprehensive understanding of the advantages of growing Mo films on textured substrates. The electrical resistivity of Mo grown on plain and textured substrates is of the same order, measuring 3.09 × 10−5 Ω cm, 3.25 × 10−5 Ω cm, and 3.87 × 10−5 Ω cm, respectively. A high‐diffuse reflectance of 62.7% is obtained for SU‐8 2005 textured Mo films. Investigations using COMSOL simulations support the optical reflectance analysis.