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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Simulated refraction-enhanced X-ray radiography of laser-driven shocks

Refraction-enhanced x-ray radiography (REXR) is used to infer shock-wave positions of more than one shock wave, launched by a multiple-picket pulse in a planar plastic foil. This includes locating shock waves before the shocks merge, during the early time and the main drive of the laser pulse that is not possible with the velocity interferometer system for any reflector. Simulations presented in this paper of REXR show that it is necessary to incorporate refraction and attenuation of x rays along with the appropriate opacity and refractive-index tables to interpret experimental images. Simulated REXR shows good agreement with an experiment done on the OMEGA laser facility to image a shock wave. REXR can be applied to design multiple-picket pulses with a better understanding of the shock locations. Finally, this will be beneficial to obtain the required adiabats for inertial confinement fusion implosions.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Anisotropic index of refraction and structural properties of hexagonal boron nitride epilayers probed by spectroscopic ellipsometry

The anisotropic index of refraction of 200 μm thick boron-10 enriched hexagonal boron nitride (h-BN) freestanding epilayers grown by metalorganic chemical vapor deposition has been measured using spectroscopic ellipsometry in the UV (4.0–5.1 eV) spectral range. It was found that the index of refraction for the polarization mode with an electric field perpendicular to the c-axis (ordinary, n o ) is much higher than that with an electric field parallel to the c-axis (extraordinary, n e ). By inclusion of turbostratic- (t-) phase layers within h-BN having an average inclination angle (θ) with respect to the ideal c-plane, a simple method for quantifying θ has been deduced. Our results revealed that the presence of t-phase layers decreases the optical anisotropy of h-BN and that a signature of improved crystalline quality is an increase in the ordinary index of refraction (n o ) as a result of the average incline angle θ approaching 0° and predicted that n o = 2.7 and n e = 1.5 at 280 nm for single crystalline h-BN epilayers. More importantly, our results demonstrated that spectroscopic ellipsometry is an effective technique for characterizing the crystalline quality of h-BN epilayers with the advantages of being noninvasive and highly sensitive.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

All-angle negative refraction of highly squeezed plasmon and phonon polaritons in graphene–boron nitride heterostructures

A fundamental building block for nanophotonics is the ability to achieve negative refraction of polaritons, because this could enable the demonstration of many unique nanoscale applications such as deep-subwavelength imaging, superlens, and novel guiding. However, to achieve negative refraction of highly squeezed polaritons, such as plasmon polaritons in graphene and phonon polaritons in boron nitride (BN) with their wavelengths squeezed by a factor over 100, requires the ability to flip the sign of their group velocity at will, which is challenging. Here we reveal that the strong coupling between plasmon and phonon polaritons in graphene–BN heterostructures can be used to flip the sign of the group velocity of the resulting hybrid (plasmon–phonon–polariton) modes. We predict all-angle negative refraction between plasmon and phonon polaritons and, even more surprisingly, between hybrid graphene plasmons and between hybrid phonon polaritons. Graphene–BN heterostructures thus provide a versatile platform for the design of nanometasurfaces and nanoimaging elements.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Reflection and refraction of directrons at the interface

Reflection and refraction are ubiquitous phenomena with extensive applications, yet minimizing energy loss and information distortion during these processes remains a significant challenge. This study examines the behavior of structurally stable solitons, known as directrons, in nematic liquid crystals interacting with an interface where the director field orientation changes, despite identical physical properties, external potentials, and boundary anchoring in the two regions. During reflection and refraction, the directrons maintain nearly constant structure and velocity, ensuring energy conservation and information integrity. Microscopic analyses of the director field and macroscopic evaluations of effective potential are employed to elucidate the dependence of reflection and refraction probabilities on the directron’s incident angle and the orientation difference across the interface. The findings provide valuable insights into the dynamics of solitary waves in structured liquid crystal systems, offering significant implications for the development of tunable photonic devices, reconfigurable optical systems, and nanoscale material engineering.

Science & Technology - Other Topics↗
DOE OSTI2020

Study of turbulence-induced refraction of lower hybrid waves using synthetic scrape-off layer filaments

Here, turbulence-induced refraction effects to lower hybrid (LH) wave propagation and current drive are studied using synthetic scrape-off layer (SOL) blob/filament fields. A synthetic 3D, field-following, blob turbulence model is implemented in the ray-tracing/Fokker-Planck (RTFP) codes GENRAY/CQL3D. In Alcator C-Mod, the blob field is shown to significantly affect LH ray-trajectories, leading to increased on-axis damping and smoother current profiles. This effect depends on the average blob size and amplitude. In addition, the diffusion of ray-trajectories in phase-space caused by turbulence increases the robustness of the RTFP model. A modified $N_{||}$ launch spectrum, acting as a proxy for parametric decay instability (PDI) effects, is included in simulations with the blob model. A synergy between the modified launch spectrum and turbulence-induced refraction results in synthetic hard x-ray profiles that agree with experiment. Lastly, the blob model is used to predict the effect of SOL turbulence on DIII-D high-field side (HFS) LH launch. Assuming low turbulence amplitude in the HFS SOL (~5%), turbulence-induced refraction is predicted to have little effect on current drive efficiency.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

What is the temporal analog of reflection and refraction of optical beams?

It is shown numerically and analytically that when an optical pulse approaches a moving temporal boundary across which the refractive index changes, it undergoes a temporal equivalent of reflection and refraction of optical beams at a spatial boundary. The main difference is that the role of angles is played by changes in the frequency. The frequency dependence of the dispersion of the material in which the pulse is propagating plays a fundamental role in determining the frequency shifts experienced by the reflected and refracted pulses. As a result, our analytic expressions for these frequency shifts allow us to find the condition under which an analog of total internal reflection may occur at the temporal boundary.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Time Refraction of Spin Waves

Here, we present an experimental study of time refraction of spin waves (SWs) propagating in microscopic waveguides under the influence of time-varying magnetic fields. Using space- and time-resolved Brillouin light scattering microscopy, we demonstrate that the broken translational symmetry along the time coordinate results in a loss of energy conservation for SWs and thus allows for a broadband and controllable shift of the SW frequency. With an integrated design of SW waveguide and microscopic current line for the generation of strong, nanosecond-long, magnetic field pulses, a conversion efficiency up to 39% of the carrier SW frequency is achieved, significantly larger compared to photonic systems. Given the strength of the magnetic field pulses and its strong impact on the SW dispersion relation, the effect of time refraction can be quantified on a length scale comparable to the SW wavelength. Furthermore, we utilize time refraction to excite SW bursts with pulse durations in the nanosecond range and a frequency shift depending on the pulse polarity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Retrieval of the complex-valued refractive index of germanium near the M 4,5 absorption edge

The complex-valued index of refraction of germanium in the extreme ultraviolet (XUV) is measured by multiangle reflectance of synchrotron radiation. The resulting index of refraction is higher resolution than previously measured values. It reveals new structures attributed to transitions from the 3d-core orbitals to the $Σ^{c}_{5,2}$ and the $X^{c}_{5,2}$ conduction bands. Additionally, it is shown that the problem of total external reflection, which renders multi-angle reflectance measurements insensitive to the complex-valued refractive index at grazing incidence, can be overcome by employing measurements at angles of incidence away from the critical angle.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Hybrid interferometric diagnostic for the refractive index measurement across nearly discrete shock waves

The measurement of high temperature gas properties is key for characterizing high speed flows. Nearly discrete changes in density across shock waves, in particular, are difficult to resolve through traditional fringe-counting interferometric methods. Existing techniques for estimating large fringe jumps are either resolution limited or require specialized window configurations. In this Letter, we describe a unique hybrid interferometric technique that combines narrowband fringes for high resolution and broadband fringes as an absolute reference to measure changes in refractive index with a resolution of up to 7 × 10 −8 across nearly discrete index changes of up to 1.5 × 10 −4 . By capturing fringes with an ultrahigh-speed camera, the refractive index changes across discrete shock fronts can be estimated inside a shock tube with high accuracy and time resolution. First, a novel hybrid calibration method for tracking finite fringes is discussed. Next, this technique is used to measure the post-initial-shock refractive indices for Mach 2.7 to 4.2 flows (pressures from 90.4 to 228.4 kPa). Results are then compared with theoretical values showing agreement within 2%.

Wang, Gwendolyn T. (ORCID:000000016271893X)↗
DOE OSTI2025

Time-refraction near the critical angle and angular streaking with attosecond resolution [Invited]

We study the time-refraction of optical waves as they propagate through a time-varying slab and find the frequency shift associated with the abrupt change in the refractive index. We discover a geometrical mechanism responsible for an ultrafast blueshift followed by a redshift, occurring while the refractive index is increased monotonically. Furthermore, we find high sensitivity to incident angles near the traditional critical angle and unravel a new critical angle that varies in time. Finally, we introduce an innovative concept of a streak camera design that utilizes ultrafast nonlinearities in time-varying media and offers attosecond resolution capabilities.

Fruhling, Colton (ORCID:0000000282968802)↗
DOE OSTI2021

Spatiotemporal refraction of light in an epsilon-near-zero indium tin oxide layer: frequency shifting effects arising from interfaces

When light travels through a medium in which the refractive index is rapidly changing with time, the light will undergo a shift in its frequency. Significant frequency shifting effects have recently been reported for transparent conductive oxides. These observations have been interpreted as emerging from temporal changes to the propagation phase in a bulk medium resulting from temporal variations in the refractive index. It is an effect referred to as temporal refraction. Here, we show that the frequency shift in an epsilon-near-zero layer made of indium tin oxide originates not only from this bulk response but includes a significant effect resulting from temporal changes to the spatial boundary conditions. This boundary effect can lead to a dominant, opposing shift to the bulk effect for certain angles. Hence, this process gives rise to a frequency shift that can be tailored through the angle, decoupling the amplitude and phase modulation.

Bohn, Justus (ORCID:0000000214376450)↗
DOE OSTI2024

High Refractive Index Adhesives for Laser Glass Cladding Applications (ABBREVIATED Report)

To eliminate parasitic light oscillations (amplified spontaneous emission (ASE)), high energy laser systems often utilize polymeric materials to adhere optically absorptive cladding materials to laser gain media (glass or crystal). Most of these polymeric optical adhesives are index matched to lower index gain media, and there was no capability to achieve refractive indices (RI) greater than 1.60 with low color, while also maintaining mechanical compliance to serve as adhesives for cladding applications. The completion of LDRD 23-FS-043 shows we can chemically develop novel suitable adhesive candidates with refractive indices above 1.64 at 532 nm while also exhibiting Shore A hardness between 50-90, with high optical clarity, low color, and minimal haze for films ~1-2 mm thick (84 %Transmission at 532 nm). This will enable us to begin mapping a process space to allow future customizable adhesive formulations for building a variety of laser systems with tunable refractive index matching for various gain and cladding media.

36 MATERIALS SCIENCE↗
DOE OSTI2026

PNNL INFRARED REFRACTIVE INDEX (n/k) DATASET FOR SEVEN PAH SOLIDS AT ROOM TEMPERATURE

This dataset is an open-source repository of spectral data measured at Pacific Northwest National Laboratory (PNNL). This database provides quantitative values for the complex index of refraction for seven polycyclic aromatic hydrocarbon (PAH) solids. A list of the chemicals is available in the readme file. These spectra consist of the optical constants, i.e., the real, n(ν), and imaginary, k(ν), refractive indices, over the spectral range from 7,800 to 400 cm-1 (1.28 – 25 μm). The conditions under which the individual data were acquired are described in the associated metadata files, and the user is strongly encouraged to read and understand this information to ensure the data are used appropriately for your application. Recommended Citation for Dataset Jessica M Salcido, Jeremy D. Erickson, Ashley M. Bradley, Russell G. Tonkyn, Timothy J. Johnson and Tanya L. Myers. 2026. PNNL INFRARED REFRACTIVE INDEX (n/k) DATASET FOR SEVEN PAH SOLIDS AT ROOM TEMPERATURE. [Data Set] PNNL DataHub. INSERT DOI License Information This work is marked with CC0 1.0: https://creativecommons.org/publicdomain/zero/1.0/. The authors do request that you appropriately cite the dataset when referencing or using the dataset.

Salcido, Jessica Marie Ortola↗
DOE OSTI2017

Refractive index sensing and surface-enhanced Raman spectroscopy using silver–gold layered bimetallic plasmonic crystals

Herein we describe the fabrication and characterization of Ag and Au bimetallic plasmonic crystals as a system that exhibits improved capabilities for quantitative, bulk refractive index (RI) sensing and surface-enhanced Raman spectroscopy (SERS) as compared to monometallic plasmonic crystals of similar form. The sensing optics, which are bimetallic plasmonic crystals consisting of sequential nanoscale layers of Ag coated by Au, are chemically stable and useful for quantitative, multispectral, refractive index and spectroscopic chemical sensing. Compared to previously reported homometallic devices, the results presented herein illustrate improvements in performance that stem from the distinctive plasmonic features and strong localized electric fields produced by the Ag and Au layers, which are optimized in terms of metal thickness and geometric features. Finite-difference time-domain (FDTD) simulations theoretically verify the nature of the multimode plasmonic resonances generated by the devices and allow for a better understanding of the enhancements in multispectral refractive index and SERS-based sensing. Taken together, these results demonstrate a robust and potentially useful new platform for chemical/spectroscopic sensing.

plasmonics↗
DOE OSTI2019

Sub-band Image Reconstruction Using Differential Chromatic Refraction

Refraction by the atmosphere causes the positions of sources to depend on the airmass through which an observation was taken. This shift is dependent on the underlying spectral energy of the source and the filter or bandpass through which it is observed. Wavelength-dependent refraction within a single passband is often referred to as differential chromatic refraction (DCR). With a new generation of astronomical surveys undertaking repeated observations of the same part of the sky over a range of different airmasses and parallactic angles, DCR should be a detectable and measurable astrometric signal. In this paper we introduce a novel procedure that takes this astrometric signal and uses it to infer the underlying spectral energy distribution of a source; we solve for multiple latent images at specific wavelengths via a generalized deconvolution procedure built on robust statistics. We demonstrate the utility of such an approach for estimating a partially deconvolved image, at higher spectral resolution than the input images, for surveys such as the Large Synoptic Survey Telescope.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1973

Refraction of acoustic duct waveguide modes by exhaust jets.

The refraction of acoustic duct waveguide modes emitted from the open end of a semiinfinite rectangular duct by a jet-like exhaust flow is studied theoretically. The problem is formulated as a Wiener-Hopf problem and is ultimately solved by an approximate method due to Carrier and Koiter. Continuity of transverse acoustic particle displacement and of acoustic pressure is assumed at the jet/still-air interface. The solution exhibits several features of the acoustics of moving media such as a source convection effect, zones of relative silence, and simple refraction. Plots of far-field directivity patterns are presented for several cases and show refraction effects to be important even at modest exhaust Mach numbers of order 0.3. Only subsonic exhaust Mach numbers are considered.

Mani, R.↗
NASA NTRS1974

Determination of astronomical refraction near the horizon in different seasons of the year

The results are presented of astronomical refraction measurements for zenith distances of 80-90 degrees performed in different seasons with a two inch universal instrument. The differences between observed and calculated refraction were found to exhibit seasonal variations, and the results were compared with data of atmospheric aerologic soundings. The great departures in observed refraction from that calculated with the Pulkovo tables were ascribed to temperature gradient changes within the ground kilometer layer of atmosphere.

Vasilenko, N. A.↗
NASA NTRS1975

A seismic refraction technique used for subsurface investigations at Meteor Crater, Arizona

A seismic refraction technique for interpreting the subsurface shape and velocity distribution of an anomalous surface feature such as an impact crater is described. The method requires the existence of a relatively deep refracting horizon and combines data obtained from both standard shallow refraction spreads and distant offset shots by using the deep refractor as a source of initial arrivals. Results obtained from applying the technique to Meteor crater generally agree with the known structure of the crater deduced by other investigators and provide new data on an extensive fractured zone surrounding the crater. The breccia lens is computed to extend roughly 190 m below the crater floor, about 30 m less than the value deduced from early drilling data. Rocks around the crater are fractured as distant as 900 m from the rim crest and to a depth of at least 800 m beneath the crater floor.

Ackermann, H. D.↗