Results for “BACKSCATTERING” — Page 80

DOE OSTI2016

Optimization of interaction conditions for efficient short laser pulse amplification by stimulated Brillouin scattering in the strongly coupled regime

Plasma amplification of low energy, a short (∼100–500 fs) laser pulse by an energetic long (∼10 ps) pulse via strong coupling Stimulated Brillouin Backscattering is investigated with an extensive analysis of one-dimensional particle-in-cell simulations. Parameters relevant to nowadays experimental conditions are investigated. The obtained seed pulse spectra are analyzed as a function of the interaction conditions such as plasma profile, pulses delay, and seed or pulse duration. The factors affecting the amount of energy transferred are determined, and the competition between Brillouin-based amplification and parasitic Raman backscattering is analyzed, leading to the optimization of the interaction conditions.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2016

Effect of sample thickness on 511 keV single Compton-scattered gamma rays

Gamma backscattering experiments were performed on metal foils varying some geometric parameters of the assembly. A collimated beam from a {sup 22}Na source impinges on aluminum sheets of dimensions 33.3×20.4×1.0 cm{sup 3} and iron sheets of (33.2×20.4×0.2) cm{sup 3}. The backscattered photons are detected by a 3″×3″ CsI scintillator detector placed at 90° to the incident beam. The experimental results show that thickness of metalic samples can be determined with a very small uncertainty.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2016

Mapping growth windows in quaternary perovskite oxide systems by hybrid molecular beam epitaxy

Requisite to growing stoichiometric perovskite thin films of the solid-solution A ' 1-x A x B O 3 by hybrid molecular beam epitaxy is understanding how the growth conditions interpolate between the end members A'B O 3 and AB O 3 , which can be grown in a self-regulated fashion, but under different conditions. Using the example of La 1-x Sr x VO 3 , the two-dimensional growth parameter space that is spanned by the flux of the metal-organic precursor vanadium oxytriisopropoxide and composition, x , was mapped out. The evolution of the adsorption-controlled growth window was obtained using a combination of X-ray diffraction, atomic force microscopy, reflection high-energy electron-diffraction (RHEED), and Rutherford backscattering spectroscopy. It is found that the stoichiometric growth conditions can be mapped out quickly with a single calibration sample using RHEED. Once stoichiometric conditions have been identified, the out-of-plane lattice parameter can be utilized to precisely determine the composition x . This strategy enables the identification of growth conditions that allow the deposition of stoichiometric perovskite oxide films with random A-site cation mixing, which is relevant to a large number of perovskite materials with interesting properties, e.g., high-temperature superconductivity and colossal magnetoresistance, that emerge in solid solution A ' 1-x A x B O 3 .

36 MATERIALS SCIENCE↗

DOE OSTI2017

Measurements of complex coupling coefficients in a ring resonator of a laser gyroscope

A method is proposed for measuring complex coupling coefficients in a ring optical resonator in the absence of an active gas mixture. A setup is described on which measurements are performed in ring resonators of ring He – Ne lasers with a wavelength of 632.8 nm. A model of backscattering field interference between conservative and dissipative sources is presented. Within the framework of this model, the unusual behaviour of backscattering fields in ring resonators observed in experiments is explained: a significant difference in the moduli of coupling coefficients of counterpropagating waves and variation of the magnitude of the total phase shift in a wide range. It is proposed to use this method as a metrological method when assembling and aligning a ring resonator of a laser gyroscope.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2015

Sintered Cr/Pt and Ni/Au ohmic contacts to B{sub 12}P{sub 2}

Icosahedral boron phosphide (B{sub 12}P{sub 2}) is a wide-bandgap semiconductor possessing interesting properties such as high hardness, chemical inertness, and the reported ability to self-heal from irradiation by high energy electrons. Here, the authors developed Cr/Pt and Ni/Au ohmic contacts to epitaxially grown B{sub 12}P{sub 2} for materials characterization and electronic device development. Cr/Pt contacts became ohmic after annealing at 700 °C for 30 s with a specific contact resistance of 2 × 10{sup −4} Ω cm{sup 2}, as measured by the linear transfer length method. Ni/Au contacts were ohmic prior to any annealing, and their minimum specific contact resistance was ∼l–4 × 10{sup −4} Ω cm{sup 2} after annealing over the temperature range of 500–800 °C. Rutherford backscattering spectrometry revealed a strong reaction and intermixing between Cr/Pt and B{sub 12}P{sub 2} at 700 °C and a reaction layer between Ni and B{sub 12}P{sub 2} thinner than ∼25 nm at 500 °C.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Atomic layer deposition of 2D and 3D standards for synchrotron-based quantitative composition and structure analysis methods

Atomic layer deposition (ALD) is a scalable deposition technique known for producing uniform, conformal films of a wide range of compounds on nearly any substrate material. These traits make it an ideal deposition method for producing films to replace the National Institute of Standards and Technology (NIST) standards and create Standard Reference Materials (SRMs) on a wide range of relevant two-dimensional and three-dimensional substrates. The use of SRM from NIST for quantitative analysis of chemical composition using synchrotron based x-ray fluorescence (SR-XRF) and scanning transmission x-ray microscopy (STXM) is common. Such standards, however, can suffer from inhomogeneity in chemical composition and thickness and often require further calculations, based on sample mounting and detector geometry, to obtain quantitative results. These inhomogeneities negatively impact the reproducibility of the measurements and the quantitative measure itself. Utilizing Rutherford backscattering, x-ray reflectivity, quartz crystal microbalance, STXM, and SR-XRF, the authors show that ALD is capable of producing high quality standards that are homogenous over scales ranging from nanometers to 100s of micrometers.

Becker, Nicholas G.↗

DOE OSTI2016

SU-F-J-12: Dosimetrical Characteristics of a 2.5 MV Megavoltage Photon Beam

Purpose: To evaluate the accuracy of modeling scatter factor (SF) and primary off-axis ratio (POAR) for 2.5 MV megavoltage photon beams using an empirical model, which can be used as a dose calculation model for low energy EPID imaging. Methods: Scatter photon parameters were calculated for 2.5 MV photon beam from a Varian TrueBeam by fitting the product of depth dose, PDD, and the phantom scatter factor, Sp, for a range of square field sizes between 2 and 40 cm and depths between 0 and 30 cm. The model is then applied to off-axis profiles measured for a slit field (3cm ×35 cm) for 5 depths: 0.6, 5, 10, and 20, 30 cm. Primary off-axis ratio (POAR) values were determined based on the fitting to data using the empirical model. Results: The fitting to PDD*Sp has a maximum error of 14%, mostly near surface, where backscattering of photons dominate and has a standard deviation of 4.7%. The attenuation coefficient and beam-hardening coefficient of the beam is determined to be 0.095 1/cm and 0.0038 1/cm, respectively. POAR for 2.5 MV has a peak in the center, corresponding to a beam without sufficient material to flatten the beam. Conclusion: This work illustrates a deficiency of the current empirical model to fit SF for a 2.5 MV photon beams. Most of the errors are near the surface region and an improved model that incorporate better modeling of backscattering can be developed to improve the model accuracy.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2019

Influence of the Charge State of Xenon Ions on the Depth Distribution Profile Upon Implantation into Silicon

Experimental depth distributions of the concentration of implanted xenon ions depending on their charge state and irradiation energy are presented. Xenon ions in charge states q = 1–20 and energies in the range from 50 to 400 keV are incorporated into single-crystal silicon. Irradiation is performed in the direction not coinciding with the crystallographic axes of the crystal to avoid the channeling effect. The ion fluence varies in the range of 5 × (10{sup 14}–10{sup 15}) ion/cm{sup 2}. The irradiation by singly charged ions and investigation of the samples by Rutherford backscattering spectroscopy is performed using an HVEE acceleration complex at Moscow State University. Multiply charged ions are implanted using a FAMA acceleration complex at the Vinća Institute of Nuclear Sciences. The depth distribution profiles of the incorporated ions are found using Rutherford backscattering spectroscopy. Experimental results are correlated with computer calculations. It is shown that the average projective path of multiply charged ions in most cases is shorter when compared with the average projected path of singly charged ions and the results of computer modeling.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2016

Laser Ceilometer CL51 Demonstration Field Campaign Report

Improvements in the measurements of clouds and the ability to support observation systems are critically important to advancing our understanding and improving global climate model performance. The purpose of a demonstration of the Vaisala CL51 ceilometer was to evaluate its high-range capabilities as a possible augmentation to data provided by the CL31 ceilometer that currently is deployed at U.S. Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Climate Research Facility sites. Vaisala performed a no-cost demonstration of the equipment; Pacific Northwest National Laboratory (PNNL) supported the data analysis; and ARM provided logistical support, power, maintenance, etc. The laser ceilometer provided measurements of cloud-base height, vertical visibility, and backscatter profile at a vertical range of 15 km. The ceilometer demonstration was conducted during the Characterization of Cirrus and Aerosol Properties campaign (CCAP) to provide coincident observations of cirrus cloud heights and potential backscatter signals by aerosols. This campaign included deployment of a CL51 ceilometer at the ARM Facility’s Southern Great Plains (SGP) site, co-located with the current CL31, micropulse lidar, and balloon-borne sounding system. Data collected from these sensors were analyzed to compare and contrast the data from the CL51 ceilometer.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2016

NONLINEAR REFLECTION PROCESS OF LINEARLY POLARIZED, BROADBAND ALFVÉN WAVES IN THE FAST SOLAR WIND

Using one-dimensional numerical simulations, we study the elementary process of Alfvén wave reflection in a uniform medium, including nonlinear effects. In the linear regime, Alfvén wave reflection is triggered only by the inhomogeneity of the medium, whereas in the nonlinear regime, it can occur via nonlinear wave–wave interactions. Such nonlinear reflection (backscattering) is typified by decay instability. In most studies of decay instabilities, the initial condition has been a circularly polarized Alfvén wave. In this study we consider a linearly polarized Alfvén wave, which drives density fluctuations by its magnetic pressure force. For generality, we also assume a broadband wave with a red-noise spectrum. In the data analysis, we decompose the fluctuations into characteristic variables using local eigenvectors, thus revealing the behaviors of the individual modes. Different from the circular-polarization case, we find that the wave steepening produces a new energy channel from the parent Alfvén wave to the backscattered one. Such nonlinear reflection explains the observed increasing energy ratio of the sunward to the anti-sunward Alfvénic fluctuations in the solar wind with distance against the dynamical alignment effect.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2014

Radar Wind Profiler (a0)

The radar wind profiler/radio acoustic sounding system (RWP/RASS), available in 915-MHz (for U.S. deployments) and 1290-MHz (for foreign deployments), measures wind profiles and backscattered signal strength between (nominally) 0.1 km and 5 km and virtual temperature profiles between 0.1 km and 2.5 km. However, ARM no longer operates the RASS portion. The RWP transmits electromagnetic energy into the atmosphere in as many as five directions (four tilted in opposing vertical planes and on vertical) and measures the strength and frequency of backscattered energy. Calculation of the Doppler shift of the returned signal allows calculation of the atmospheric wind profile.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2014

Radar Wind Profiler (a0)

The radar wind profiler/radio acoustic sounding system (RWP/RASS), available in 915-MHz (for U.S. deployments) and 1290-MHz (for foreign deployments), measures wind profiles and backscattered signal strength between (nominally) 0.1 km and 5 km and virtual temperature profiles between 0.1 km and 2.5 km. However, ARM no longer operates the RASS portion. The RWP transmits electromagnetic energy into the atmosphere in as many as five directions (four tilted in opposing vertical planes and on vertical) and measures the strength and frequency of backscattered energy. Calculation of the Doppler shift of the returned signal allows calculation of the atmospheric wind profile.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2014

Radar Wind Profiler (a0)

The radar wind profiler/radio acoustic sounding system (RWP/RASS), available in 915-MHz (for U.S. deployments) and 1290-MHz (for foreign deployments), measures wind profiles and backscattered signal strength between (nominally) 0.1 km and 5 km and virtual temperature profiles between 0.1 km and 2.5 km. However, ARM no longer operates the RASS portion. The RWP transmits electromagnetic energy into the atmosphere in as many as five directions (four tilted in opposing vertical planes and on vertical) and measures the strength and frequency of backscattered energy. Calculation of the Doppler shift of the returned signal allows calculation of the atmospheric wind profile.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2014

Radar Wind Profiler (a0)

The radar wind profiler/radio acoustic sounding system (RWP/RASS), available in 915-MHz (for U.S. deployments) and 1290-MHz (for foreign deployments), measures wind profiles and backscattered signal strength between (nominally) 0.1 km and 5 km and virtual temperature profiles between 0.1 km and 2.5 km. However, ARM no longer operates the RASS portion. The RWP transmits electromagnetic energy into the atmosphere in as many as five directions (four tilted in opposing vertical planes and on vertical) and measures the strength and frequency of backscattered energy. Calculation of the Doppler shift of the returned signal allows calculation of the atmospheric wind profile.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2014

Radar Wind Profiler (a0)

The radar wind profiler/radio acoustic sounding system (RWP/RASS), available in 915-MHz (for U.S. deployments) and 1290-MHz (for foreign deployments), measures wind profiles and backscattered signal strength between (nominally) 0.1 km and 5 km and virtual temperature profiles between 0.1 km and 2.5 km. However, ARM no longer operates the RASS portion. The RWP transmits electromagnetic energy into the atmosphere in as many as five directions (four tilted in opposing vertical planes and on vertical) and measures the strength and frequency of backscattered energy. Calculation of the Doppler shift of the returned signal allows calculation of the atmospheric wind profile.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2014

915rwpprecipmeanlow (a1)

The radar wind profiler/radio acoustic sounding system (RWP/RASS), available in 915-MHz (for U.S. deployments) and 1290-MHz (for foreign deployments), measures wind profiles and backscattered signal strength between (nominally) 0.1 km and 5 km and virtual temperature profiles between 0.1 km and 2.5 km. However, ARM no longer operates the RASS portion. The RWP transmits electromagnetic energy into the atmosphere in as many as five directions (four tilted in opposing vertical planes and on vertical) and measures the strength and frequency of backscattered energy. Calculation of the Doppler shift of the returned signal allows calculation of the atmospheric wind profile.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2014

915rwpprecipmeanhigh (a1)

The radar wind profiler/radio acoustic sounding system (RWP/RASS), available in 915-MHz (for U.S. deployments) and 1290-MHz (for foreign deployments), measures wind profiles and backscattered signal strength between (nominally) 0.1 km and 5 km and virtual temperature profiles between 0.1 km and 2.5 km. However, ARM no longer operates the RASS portion. The RWP transmits electromagnetic energy into the atmosphere in as many as five directions (four tilted in opposing vertical planes and on vertical) and measures the strength and frequency of backscattered energy. Calculation of the Doppler shift of the returned signal allows calculation of the atmospheric wind profile.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2014

915rwpwindmeanlow (a1)

The radar wind profiler/radio acoustic sounding system (RWP/RASS), available in 915-MHz (for U.S. deployments) and 1290-MHz (for foreign deployments), measures wind profiles and backscattered signal strength between (nominally) 0.1 km and 5 km and virtual temperature profiles between 0.1 km and 2.5 km. However, ARM no longer operates the RASS portion. The RWP transmits electromagnetic energy into the atmosphere in as many as five directions (four tilted in opposing vertical planes and on vertical) and measures the strength and frequency of backscattered energy. Calculation of the Doppler shift of the returned signal allows calculation of the atmospheric wind profile.

54 ENVIRONMENTAL SCIENCES↗