Use Of Multiple Reflections Research Articles

Design and development of a single-laser 2D Thomson scattering measurement system for TS-6 merging tokamak/magnetic reconnection experiments

Nd:YAG Thomson scattering diagnostics is reliable measurement of electron temperature and density, but its 2D extension conventionally needs as many polychromators as measuring points and as many lasers as measuring paths. To reduce the numbers and costs, we designed and developed a single-laser 2D measurement system by use of multiple reflection and time-of-flight of laser light. A single laser pulse reflects between mirrors on both sides of the vacuum vessel and makes seven round trips, which enables measurement at m × 7 points with only m polychromators and a single laser. Here, we present the design to satisfy the resolution required for TS-6 merging tokamak and magnetic reconnection experiments and the system development, especially the time-separation of scattered light signals from different points with time-of-flight delays. The measured Thomson scattering signals from 7 × 2 points and the measured Raman scattered signals from points in four laser paths indicate the feasibility of Thomson scattering measurement at m × 4 points.

Simultaneous Imaging of Primaries and Multiples Based on Wavelet Estimation and Stereographic Imaging Condition

Multiple reflections contain abundant structural information about the subsurface because of their smaller reflection angles and wider coverage. Multiple imaging has increasingly attracted attention. However, the imaging of multiples first needs to separate the multiples, which is a time-consuming and high-cost job. Therefore, the simultaneous imaging of primaries and multiples, which can make good use of multiple reflections with no need for multiple separation, has increasingly attracted attention. However, there are still some challenges to the conventional method, including wavelet selection and image artifacts suppression. In this paper, an improved method of the simultaneous imaging of primaries and multiples is proposed by introducing two creative strategies. First, considering that the wavelet, which is usually estimated by signal analysis under certain assumptions, is crucial to the simultaneous imaging, we propose to estimate the wavelet by iterative SRME (surface-related multiple elimination) using the original data containing multiples based on wave equation theory instead of signal analysis. Second, the stereographic imaging condition is introduced to suppress the crosstalk artifacts in the image. According to the numerical examples and field data test, the feasibility and effectiveness of our approach is verified.

Enhanced characterization of fracture compliance heterogeneity using multiple reflections and data‐driven Green's function retrieval

AbstractThe spatial heterogeneity along a fracture is a key determinant for fracture‐associated mechanical and hydraulic properties of the subsurface. Laboratory experiments have been performed to test the applicability of the nonwelded interface representation to predict the frequency‐ and angle‐dependent elastic response of a single fracture. The observation that nonwelded interface model can represent quite well the frequency‐ and angle‐dependent reflection response of a fracture has led us to develop a new methodology for estimating the spatially heterogeneous fracture compliance from the reflection response along a fracture surface. A data‐driven approach based on Marchenko equation coupled with inverse scattering to solve the nonwelded interface boundary condition has been formulated. The approach estimates the elastic wavefield along a fracture accurately, including the multiple reflections. As an extension, it offers the possibility to estimate fracture compliance using the multiple reflections. We illustrate the concept by numerically modeling 2‐D SH waves sensing the heterogeneous tangential compliance of a fracture. The stationary phase method is applied to single and double spatial integrals to analyze the effect of source and receiver aperture on the Green's function retrieval. Our results show that the use of multiple reflections allows a better estimation of the heterogeneous fracture compliance than using primary reflections alone, especially for the far offsets on the fracture plane.

High-contrast filtering by multipass diffraction between paired volume Bragg gratings.

High-contrast filtering via multiple reflections between matched volume Bragg gratings (VBGs) is demonstrated. The use of multiple reflections serves to increase the suppression ratio of the out-of-band spectral content such that contributions of grating sidelobes can be mitigated. The result is a device that retains spectral and angular selectivity and diffracts light into a single order with high efficiency but reshapes the spectral/angular response to achieve higher signal-to-noise ratios. We demonstrate that multipass spectral filters can be recorded with extremely high suppression ratios using reflecting Bragg gratings (RBGs) in three different configurations. These filters demonstrate roll-offs of over 150 dB/nm. Similarly, we demonstrate angular filtering by multipass transmitting gratings.

Development of a Two-Dimensional Thomson Scattering Diagnostic System involving Use of Multiple Reflection and the Time-of-Flight of Laser Light

Development of a Two-Dimensional Thomson Scattering Diagnostic System involving Use of Multiple Reflection and the Time-of-Flight of Laser Light

Wide-band x-ray optics with a large angular aperture

Grazing-incidence x-ray optics is briefly reviewed and shown to have several interesting properties. Capillary focusing systems which make use of multiple reflection of x rays are described. This optics is of interest in surface research, medicine, etc.

Ellipsometry and multiple reflection between parallel plates

Improvement in the sensitivity of ellipsometry techniques by the use of multiple reflection between parallel plates is considered, and some experimental work carried out to support the conclusions reached. Useful gain can be obtained by introducing from 2 to 5 reflections, but larger numbers are prohibited by the intensity of the p-component becoming so weak that ellipticity can no longer be measured. With films of greater than a few hundred angstroms the reflectivity minimum in the n-component of light makes observation difficult or impossible. However, the technique can be employed with advantage for films in the 0–100 Å range, using either identical specimens or a single specimen and inert reflector.

Electrophotographic Mirror Contact Printing

An electrophotographic contact printing process is discussed in which amplification of the transmission densities present in an original is achieved by the use of multiple reflections. It is shown that originals on highly opaque substrates are preferred over vellum originals. Experimental results are in reasonable agreement with theoretical predictions.

XXVI. Optical constants of metals in the infra-red—experimental methods

Summary For metals the principal angle of incidence in the infra-red is near 90° and it has been shown that the real and imaginary parts of the dielectric constant are best obtained by measuring ρ and Δ; ρ is the ratio of the reflectivities of the p- and s- components and Δ the relative phase difference. ρ and Δ may be obtained without using birefringent materials by measuring two ratios of intensities, a technique which provides a cross-check. The experimental methods and arrangements developed to measure a number of metals in the spectral range 2μ to 12μ are described ; this range can be extended where necessary. Use of multiple reflections is discussed and errors are examined. Measurements are reported of evaporated aluminium mirrors since these are frequently used.