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At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Refractive index matching base resin for extremely fine three-dimensional ceramic structures

An optically clear resin for additive manufacturing includes an optically clear ceramic precursor having a pre-defined refractive index. Each molecule of the ceramic precursor has at least two photopolymerizable functional groups, at least one of the photopolymerizable functional groups being functionalized with a refractive index-tuning group thereby causing the ceramic precursor to have the pre-defined refractive index.

Mettry, Magi↗
DOE OSTI2013

Study of nonlinear refraction of organic dye by Z-scan technique using He-Ne laser

Laser induced third-order nonlinear optical responses of Brilliant Green solution has been investigated by utilizing single beam Z-scan technique with a continuous-wave He-Ne laser radiation at 632.8 nm. It was observed that the material exhibits self-defocusing type optical nonlinearity. The measurements of nonlinear refraction were carried out at different dye concentrations and found that the increase in solution concentration leads to the linear increase of the nonlinear refractive index. The experimental results confirm great potential of the Brilliant Green for the application in nonlinear optical devices.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Superlensing effect for surface acoustic waves in a pillar-based phononic crystal with negative refractive index

We demonstrate super resolution imaging for surface acoustic waves using a phononic structure displaying negative refractive index. This phononic structure is made of a monolithic square lattice of cylindrical pillars standing on a semi-infinite medium. The pillars act as acoustic resonator and induce a surface propagating wave with unusual dispersion. We found, under specific geometrical parameters, one propagating mode that exhibits negative refraction effect with negative effective index close to −1. Furthermore, a flat lens with finite number of pillars is designed to allow the focusing of an acoustic point source into an image with a resolution of (λ)/3 , overcoming the Rayleigh diffraction limit.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Phase-dependent high refractive index without absorption in a four-level inverted-Y atomic system

We consider a closed four-level inverted-Y system in the presence and the absence of a microwave field. It is found that due to the quantum coherence between the two lower levels, either induced by the spontaneous decay or by the microwave field, the refraction – absorption properties of the system can be modulated by controlling the relative phase of the applied fields in both driven ways. In particular, by properly setting the values of the relative phase, the desirable high index of refraction without absorption can be achieved. (nonlinear optical phenomena)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Radiation-induced refraction artifacts in the optical CT readout of polymer gel dosimeters

Purpose: The objective of this work is to demonstrate imaging artifacts that can occur during the optical computed tomography (CT) scanning of polymer gel dosimeters due to radiation-induced refractive index (RI) changes in polyacrylamide gels. Methods: A 1 L cylindrical polyacrylamide gel dosimeter was irradiated with 3 × 3 cm{sup 2} square beams of 6 MV photons. A prototype fan-beam optical CT scanner was used to image the dosimeter. Investigative optical CT scans were performed to examine two types of rayline bending: (i) bending within the plane of the fan-beam and (ii) bending out the plane of the fan-beam. To address structured errors, an iterative Savitzky–Golay (ISG) filtering routine was designed to filter 2D projections in sinogram space. For comparison, 2D projections were alternatively filtered using an adaptive-mean (AM) filter. Results: In-plane rayline bending was most notably observed in optical CT projections where rays of the fan-beam confronted a sustained dose gradient that was perpendicular to their trajectory but within the fan-beam plane. These errors caused distinct streaking artifacts in image reconstructions due to the refraction of higher intensity rays toward more opaque regions of the dosimeter. Out-of-plane rayline bending was observed in slices of the dosimeter that featured dose gradients perpendicular to the plane of the fan-beam. These errors caused widespread, severe overestimations of dose in image reconstructions due to the higher-than-actual opacity that is perceived by the scanner when light is bent off of the detector array. The ISG filtering routine outperformed AM filtering for both in-plane and out-of-plane rayline errors caused by radiation-induced RI changes. For in-plane rayline errors, streaks in an irradiated region (>7 Gy) were as high as 49% for unfiltered data, 14% for AM, and 6% for ISG. For out-of-plane rayline errors, overestimations of dose in a low-dose region (∼50 cGy) were as high as 13 Gy for unfiltered data, 10 Gy for AM, and 3.1 Gy for ISG. The ISG routine also addressed unrelated artifacts that previously needed to be manually removed in sinogram space. However, the ISG routine blurred reconstructions, causing losses in spatial resolution of ∼5 mm in the plane of the fan-beam and ∼8 mm perpendicular to the fan-beam. Conclusions: This paper reveals a new category of imaging artifacts that can affect the optical CT readout of polyacrylamide gel dosimeters. Investigative scans show that radiation-induced RI changes can cause significant rayline errors when rays confront a prolonged dose gradient that runs perpendicular to their trajectory. In fan-beam optical CT, these errors manifested in two ways: (1) distinct streaking artifacts caused by in-plane rayline bending and (2) severe overestimations of opacity caused by rays bending out of the fan-beam plane and missing the detector array. Although the ISG filtering routine mitigated these errors better than an adaptive-mean filtering routine, it caused unacceptable losses in spatial resolution.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2018

Chemically Responsive Elastomers Exhibiting Unity-Order Refractive Index Modulation

Chameleons are masters of light, expertly changing their color, pattern, and reflectivity in response to their environment. Engineered materials that share this tunability can be transformative, enabling active camouflage, tunable holograms, and novel colorimetric medical sensors. Although progress has been made in creating artificial chameleon skin, existing schemes often require external power, are not continuously tunable, and may prove too stiff or bulky for applications. In this work, a chemically tunable, large-area metamaterial is demonstrated that accesses a wide range of colors and refractive indices. An ordered monolayer of nanoresonators is fabricated, then its optical response is dynamically tuned by infiltrating its polymer substrate with solvents. The material shows a strong magnetic response with a dependence on resonator spacing that leads to a highly tunable effective permittivity, permeability, and refractive index spanning negative and positive values. The unity-order index tuning exceeds that of traditional electro-optic and photochromic materials and is robust to cycling, providing a path toward programmable optical elements and responsive light routing.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Refractive Index and Abbe Number Tuning via 3D Printable Optical Quality Silica–Titania–Germania Glasses

The development of optical quality GeO 2 –TiO 2 –SiO 2 glasses compatible with direct ink writing (DIW) 3D printing is reported in this study. Colloidal GeO 2 and TiO 2 –SiO 2 core–shell feedstocks are prepared by a sol–gel method and converted to printable inks for DIW. Printed inks are subsequently densified to glass using heat treatment at temperatures up to 1100 °C in air. A series of print‐compatible glass compositions are prepared, yielding transparent glass with the highest refractive index n = 1.576. Herein, it is shown that more TiO 2 can be incorporated into the glass without haziness or scattering through the addition of GeO 2 . The mechanisms for this are discussed, and it is shown that crystallization persists in these glasses despite the lack of visible light scattering. Finally, the combination of both TiO 2 and GeO 2 into a ternary glass also is used to independently tune the dispersion properties of the glass, as demonstrated by measured refractive indices and Abbe numbers, which has potential implications for 3D‐printed optics.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Planar optical waveguide for refractive index determining with high sensitivity and dual-band characteristic for Nano-sensor application

In this paper, we develop an optical waveguide based on metal–insulator-metal as a refractive index sensor with dual-band feature and a high figure of merit (FOM) and sensitivity. In this model, we utilize a Z-shape slot based on two stubs model in both metal layers and this structure is placed over a dielectric layer of SiO{sub 2} as a substrate for planar application in the optical systems. In addition, the parametric studies are used to clarifying the elements influence on controlling the transmission and working frequency to achieve a dual-band characteristic at 1550 and 3100 nm which is suitable for optical fiber application. In fact, the compound stubs technique is suggested to modify the resonances of the waveguide for dual-band attributes based on the transmission line model. We simulate this waveguide using the Finite Integrated Technique (FIT) method. It is supposed that the waveguide is filled by various materials with the different refractive indexes in the range of 1 to 1.5. We obtain the FOM for these materials while the Fano response provides high FOM about the 3800 RIU{sup −1} and the sensitivity is 1790 nm/RIU. Therefore, the compound stubs strategy help to improve the FOM factor in the optical waveguide.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Gold grating assisted SPR based D-shaped single mode fiber for detection of liquid refractive index

In this paper, a surface plasmon resonance based D-shaped single mode fiber sensor with a gold grating over the polished fiber surface, is analyzed by finite element method for refractive index sensing. Benefitted from the localized surface plasmon resonance effect of gold grating, the proposed sensor achieves a reasonably good wavelength sensitivity of 7590 nm/RIU for the refractive index range varying from 1.34 to 1.38 and the corresponding resolution is 1.31 × 10{sup −5} RIU. Furthermore, the maximum amplitude sensitivity of the sensor is calculated to be 676.08 RIU{sup −1}. The good sensing performance, low cost and simple structure makes this sensor a potential candidate for application in the areas of food processing, environmental monitoring and biochemical analysis.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Sensitivity analysis of ring-shaped slotted photonic crystal waveguides for mid-infrared refractive index sensing

In this paper, the sensitivity of slotted photonic crystal waveguides (SPCW) with triangular lattice pattern of ring-shaped holes is analyzed in order to realize highly refractive index (RI) sensor devices at mid-infrared wavelengths. The sensing principle is based on the shift of the transmission spectrum edge of these specific ring hole SPCW waveguides giving rise to reinforced light–matter interaction. The 3D simulation results applied to silicon waveguides on membrane show that this guide geometry leads to a very high sensitivity to variations in the ambient environment index, with very dependent trends on the opto-geometric factors of the waveguides. As a matter of example, a 720 nm wavelength position band edge shift is predicted, corresponding to a sensitivity of more than 1450 nm per refractive index unit with a device insertion loss level of − 3 dB.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Aquaporin 0 plays a pivotal role in refractive index gradient development in mammalian eye lens to prevent spherical aberration

Highlights: • Intact AQP0 functions as fiber cell-to-fiber cell adhesion protein. • AQP0 facilitates reduction in extracellular space and lens water content. • AQP0 adhesion function aids in lens refractive index gradient (RING) formation. • AQP0 prevents lens spherical aberration by establishing RING. • AQP0 is critical for lens transparency and homeostasis. - Abstract: Aquaporin 0 (AQP0) is a transmembrane channel that constitutes ∼45% of the total membrane protein of the fiber cells in mammalian lens. It is critical for lens transparency and homeostasis as mutations and knockout cause autosomal dominant lens cataract. AQP0 functions as a water channel and as a cell-to-cell adhesion (CTCA) molecule in the lens. Our recent in vitro studies showed that the CTCA function of AQP0 could be crucial to establish lens refractive index gradient (RING). However, there is a lack of in vivo data to corroborate the role of AQP0 as a fiber CTCA molecule which is critical for creating lens RING. The present investigation is undertaken to gather in vivo evidence for the involvement of AQP0 in developing lens RING. Lenses of wild type (WT) mouse, AQP0 knockout (heterozygous, AQP0{sup +/−}) and AQP0 knockout lens transgenically expressing AQP1 (heterozygous AQP0{sup +/−}/AQP1{sup +/−}) mouse models were used for the study. Data on AQP0 protein profile of intact and N- and/or C-terminal cleaved AQP0 in the lens by MALDI-TOF mass spectrometry and SDS–PAGE revealed that outer cortex fiber cells have only intact AQP0 of ∼28 kDa, inner cortical and outer nuclear fiber cells have both intact and cleaved forms, and inner nuclear fiber cells have only cleaved forms (∼26–24 kDa). Knocking out of 50% of AQP0 protein caused light scattering, spherical aberration (SA) and cataract. Restoring the lost fiber cell membrane water permeability (P{sub f}) by transgene AQP1 did not reinstate complete lens transparency and the mouse lenses showed light scattering and SA. Transmission and scanning electron micrographs of lenses of both mouse models showed increased extracellular space between fiber cells. Water content determination study showed increase in water in the lenses of these mouse models. In summary, lens transparency, CTCA and compact packing of fiber cells were affected due to the loss of 50% AQP0 leading to larger extracellular space, more water content and SA, possibly due to alteration in RING. To our knowledge, this is the first report identifying the role of AQP0 in RING development to ward off lens SA during focusing.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2019

Implications of real-gas behavior on refractive index calculations for optical diagnostics of fuel–air mixing at high pressures

Three models to compute the refractive index of gaseous mixtures at real gas conditions are presented with the purpose to improve the accuracy of state relationships between refractive index and thermodynamic properties. Models are compared with experimental data to determine one that is applicable to high pressure mixtures with non-ideal thermodynamic behavior near or above a fluids’ critical point. The optimal model is applied to analyze adiabatic thermal mixing of fuel and air at typical diesel engine conditions. Our results show that the ideal gas mixture law is appropriate in the vapor region, assuming it is known, for example, from experimental measurements. Finally, the model is applied for binary fuel-air mixing at supercritical conditions to demonstrate its full potential.

02 PETROLEUM↗
DOE OSTI2015

Physicochemical and catalytic properties of Au nanorods micro-assembled in solvents of varying dipole moment and refractive index

Highlights: • Physicochemical activities of Au nanorods in water largely differ from organic solvents. • Au nanorods agglomeration increased with dipole moments of different polar solvents. • Refractive indexes of Au nanorods dispersion in various polar solvents are enhanced. • Electrokinetics significantly altered depending on agglomerated size of Au nanorods. • Catalysis or co-catalysis activity is varied as per the extent of Au nanorods coagulation. - Abstract: This paper deals with the impact of dipole moment (1.66–3.96 D) and refractive index (1.333–1.422) of the dispersion solvent on the plasmon absorption, surface charge, zeta potential, and adsorption properties of Au nanorods (AuNRs). AuNRs (length ≈ 53 nm and width ≈ 20 nm) undergo agglomeration (size 50–180 nm) with increase in the dipole moment of solvent (iPrOH < MeOH < DMF < DMSO). Whereas, no such coagulation occurs in H{sub 2}O and CCl{sub 4} suspension as confirmed by DLS and TEM size distribution. The electrostatic interaction of AuNRs with its surface adsorbed solvent dipoles leads to alteration of the their ionic state, absolute electronic charge and zeta potential (+49.79 mV in H{sub 2}O, +8.99 mV in DMF and −4.65 mV in MeOH dispersion) to a greater extent. This interaction distinctly modifies the adsorption behavior of polar molecules like p-nitrophenol and salicylic acid on AuNRs surface, as evidenced by the measured changes in their electro-kinetic parameters. As a result, we observe a substantial difference in catalytic and co-catalytic activities of AuNRs dispersed in various solvents as mentioned above because the catalytic properties of AuNRs are strongly dependent on the type of solvent in which they are dispersed.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Refractive index and compressibility of LiAlSi{sub 3}O{sub 8} glass in the pressure range up to 6.0 GPa

Highlights: • Refractive index and the compressibility of LiAlSi{sub 3}O{sub 8} glass are obtained. • Among Li(Na,K)AlSi{sub 3}O{sub 8} glasses LiAlSi{sub 3}O{sub 8} glass has the lowest compressibility. • Degree of depolymerization (NBO/T = 0.31) for LiAlSi{sub 3}O{sub 8} glass was calculated. • NBO/T = 0.31 indicates a high content of NBOs atoms and Al in LiAlSi{sub 3}O{sub 8} glass. • Proposed reaction corresponds to the condition of the existence of ∼9% Al. - Abstract: The refractive index and the relative changes in the density for LiAlSi{sub 3}O{sub 8} glass in the pressure range up to 6.0 GPa were obtained using a polarization-interference microscope and an apparatus with diamond anvils. The results were compared with the previous data for the NaAlSi{sub 3}O{sub 8} and KAlSi{sub 3}O{sub 8} glasses. The compressibility of glasses increases in a series of alkali metal cations Li{sup +}, Na{sup +}, K{sup +}. From the previously found dependence of the compressibility (at P = 4.0 GPa) on the degree of depolymerization the value of NBO/T = 0.31 for LiAlSi{sub 3}O{sub 8} glass was calculated. A high degree of depolymerization of the LiAlSi{sub 3}O{sub 8} glass indicates not only a high content of NBOs atoms in the structural network, but also the presence of highly coordinated aluminum (according to the literature data ∼9%). The proposed schematic reaction for the formation of different structural groups corresponds to the condition of the existence of 9% highly coordinated aluminum.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Ultrafast Wavefront Shaping via Space-Time Refraction

A myriad of metasurfaces have been demonstrated that manipulate light by spatially structuring thin optical layers. Manipulation of the optical properties of such layers in both space and time can unlock new physical phenomena and enable new optical devices. Examples include photon acceleration and frequency conversion, which modifies Snell’s relation to a more general, nonreciprocal form. Here, we combine theory and experiment to realize wavefront shaping and frequency conversion on subpicosecond time-scales by inducing space-time refractive index gradients in epsilon-near-zero (ENZ) films with femtosecond light pulses. Furthermore, we experimentally tune wavefront steering by controlling the incident angle of the beams and the pump–probe delay without the need for nanostructure fabrication. As a demonstration of this approach, we leverage the ultrafast, high-bandwidth optical response of transparent oxides in their ENZ wavelength range to create large refractive index gradients and new types of nonreciprocal, ultrafast two-dimensional (2D) optics, including an ultrathin transient lens.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Steering and collimating ballistic electrons with amphoteric refraction

We show that amphoteric refraction of ballistic electrons, i.e., positive or negative refraction depending on the incidence angle, occurs at an interface between an isotropic and an anisotropic medium and can be employed to steer and collimate electron beams. The steering angle is determined by the materials' parameters, but the degree of collimation can be tuned in a significant range by changing the energy of ballistic electrons.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

Method of time resolved refractive index measurements of x-ray laser heated solids

With the advent of new x-ray light-sources worldwide, the creation of dense, uniformly heated plasma states arising from intense x-ray irradiation of solids has been made possible. In the early stages of x-ray solid heating, before significant hydrodynamic motion occurs, the matter exists in a highly non-equilibrium state. A method based on wavefront sensing is proposed to probe some of the fundamental properties of these states. The deflection and absorption of a high harmonic probe beam propagated through the plasma can be measured with a wavefront sensor, and allow for the determination of the complex refractive index (RI) of the plasma, giving a 2D map of the optical properties as function of time in a pump-probe arrangement. A solid heating model has been used to estimate the expected temperatures of x-ray heated thin foils, and these temperatures are used in three separate models to estimate the changes in the refractive index. The calculations show the changes induced on an extreme ultra-violet (XUV) probe beam by a solid density thin foil plasma are significant, in terms of deflection angle and absorption, to be measured by already existing XUV Hartmann wavefront sensors. The method is applicable to a wide range of photon energies in the XUV (10 s to several 100 s of eV) and plasma parameters, and can add much needed experimental data to the fundamental properties of such dense plasma states.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Shock wave refraction enhancing conditions on an extended interface

We determined the law of shock wave refraction for a class of extended interfaces with continuously variable gradients. When the interface is extended or when the gas parameters vary fast enough, the interface cannot be considered as sharp or smooth and the existing calculation methods cannot be applied. The expressions we derived are general enough to cover all three types of the interface and are valid for any law of continuously varying parameters. We apply the equations to the case of exponentially increasing temperature on the boundary and compare the results for all three types of interfaces. We have demonstrated that the type of interface can increase or inhibit the shock wave refraction. Our findings can be helpful in understanding the results obtained in energy deposition experiments as well as for controlling the shock-plasma interaction in other settings.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗