Measurement of saturation induced optical nonreciprocity in a ring laser plasma.
Saturation induced optical nonreciprocity in He-Ne ring laser plasma, eliminating frequency locking by using Faraday effect
GAS LASER↗
SEARCH · Engineering Papers
Results for “Plasma optics”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Development of lasers for plasma diagnostics
Optical heterodyne system used to measure electron density of plasma
PLASMA DYNAMICS↗
Electrical and Spectroscopic Diagnostics as Real‐Time Metallization Indicators During Hydrogen Plasma Smelting Reduction
This study investigates the hydrogen (H 2 ) plasma reduction process of direct-reduced-iron-grade hematite ore at different arc currents (100–200 A) in an Ar–5% H 2 atmosphere at 0.9 bar. Iron ore samples (10 g) were exposed to a plasma arc, and the reduction/metallization kinetics were analyzed over fixed time intervals. Electrical diagnostics revealed that the arc voltage exhibited takeover-mode oscillations which were suppressed at higher currents due to stronger electromagnetic coupling. The voltage dropped significantly as metallization approached ∼95%, linked to increased electrical conductivity of the metallic iron (Fe) in the ore as well as Fe evaporation into the arc, lowering the arc resistance. A simplified Elenbaas–Heller model supported this explanation and confirmed that Fe vapor concentration enhances plasma conductivity. Optical emission spectroscopy focused on the plasma–metal interface revealed the plasma's optically thick nature, as the primary Fe I 526.95 nm line experienced self-absorption. However, weaker Fe I lines (404.58, 438.35 nm) normalized to Ar I 696.5 nm provided a reliable proxy for metallization. These diagnostics, electrical and spectroscopic, effectively track metallization in real-time during H 2 plasma smelting reduction.
08 HYDROGEN↗
High-resolution spectroscopy of uranium laser-produced plasma using saturated absorption spectroscopy
High-resolution spectroscopy of laser ablation plumes or laser-produced plasmas (LPPs) is valuable for various applications, including measuring crowded spectral features, determining spectroscopic constants, characterizing plasmas, and performing isotopic analysis. However, various line broadening mechanisms in plasmas limit its use for several applications. Here, in this study, we present the use of saturated absorption spectroscopy (SAS) for Doppler-free linewidth analysis in a uranium LPP. We demonstrate that SAS is effective in obtaining Doppler-free Lamb dip profiles with linewidths on the order of ≤ 20 MHz. The effects of saturation on the Doppler-broadened absorption and Lamb dip profiles at different pressures and probe intensities are quantified, and their impact on measurements of plasma properties is discussed. Finally, we show that the linewidths of the Lamb dips can be used for quantitative estimates of pressure and natural broadening in the plasma.
Absorption spectroscopy↗
Thomson Scattering with Gain
Thomson-scattering signals can be significantly modified by convective gains associated with the stimulated Raman scattering and stimulated Brillouin scattering instabilities as the scattered light traverses the probe beam. Gain results in amplification and narrowing of the red-shifted (i.e., Stokes) scattered light, whereas blue-shifted (anti-Stokes) features are depleted and broadened, making the relative prominence of these features a key signature of gain. Not accounting for instability growth has been a ubiquitous source of error in previous Thomson-scattering measurements.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
A technique for obtaining plasma-sheath configurations and ion optics for an electron- bombardment ion thrustor
Plasma boundaries and ion trajectories for accelerator system of electron bombardment ion thrustor
ELECTRON BOMBARDMENT↗
Spectral line intensities in a nonequilibrium nitrogen plasma.
Nonequilibrium nitrogen plasma spectral line intensities calculated assuming optically thin plasma
Park, C.↗
Atomic processes in plasmas.
Measuring atomic radiation and collision cross section coefficients of plasmas
FIBER OPTICS↗
Electron cyclotron emission measurements and modeling in optically semi-transparent plasma on the HSX stellarator
On the Helically Symmetric Experiment (HSX), electron cyclotron emission (ECE) at the second harmonic of the electron gyrofrequency is measured with a 16-channel heterodyne receiver. An ECE radiometer diagnostic has been calibrated with a broadband frequency source, allowing independent measurements of the electron temperature. The antenna pattern has a significant impact on the measurements, and modeling its effect is necessary to produce an ECE radiation temperature spectrum. Measurements, calibration results, and modeling of the ECE data are presented in this paper. At a relatively high plasma density, HSX plasmas are thermal, and the radiation temperature measured by the radiometer is in good agreement with the electron temperature measured by a Thomson scattering diagnostic. At a relatively low plasma density, the deviation from a Maxwellian distribution is large, and asymmetry in the radiation temperature profile is measured. These measurements are supported by single-pass and multi-pass ray tracing calculations of the electron cyclotron emission using the TRAVIS ray tracing code. Thermal and nonthermal electron populations exist in HSX, and the effect of these populations on the asymmetry in the measured emission is presented.
Cyclotron radiation↗
Fiber-optic bolometers with high-temperature tolerance and reduced time constants for fusion plasma diagnostics
Fiber-optic bolometers (FOBs) designed for plasma radiation measurement in magnetically confined fusion environments have been previously developed and tested at the DIII-D tokamak. These FOBs utilize a silicon Fabry–Perot interferometer at the fiber tip for temperature measurement and a gold disk as a radiation absorber. This paper presents recent advancements in the development of FOBs with reduced cooling time constants and enhanced temperature tolerance. We also demonstrate high-temperature operation and report findings from irradiation tests. By incorporating a copper sensor holder as a thermal sink and integrating two closely packed sensor heads into a compact design, the cooling time constants were reduced to ∼100 ms in vacuum, while minimizing uncertainties caused by temperature gradients. The FOBs were subjected to heating at 400 °C for five hours, with no observed degradation in noise performance post-heating. High-temperature operation tests were conducted at ∼220 °C using a 404 nm square-wave modulated laser to simulate the plasma radiation. In addition, four FOBs constructed from copper-coated pure-silica fibers were fabricated and underwent irradiation testing, enduring a total γ-radiation dose of 15.2 MGy and a neutron fluence of 1.6 × 10 18 n/cm 2 . As a result, the FOBs maintained their physical integrity and the optical signal shows high visibility throughout the test.
42 ENGINEERING↗
Laboratory Demonstration of Collisionless Blob Formation via Laser-Produced Plasma Self-Focusing
Strongly localized, propagating plasma density structures that are capable of crossing magnetic field lines are known as “blobs.” Here we demonstrate a novel mechanism for the formation and propagation of an ion gyroradius-scale blob-cavity structure at the interface between a super-Alfvénic laser-produced plasma (LPP) and an ambient magnetized plasma. The LPP self-focuses along the edge of the diamagnetic cavity which results in a dense, jetlike structure as compared to ballistic motion. This collimated flow couples momentum to the ambient plasma through a collisionless process known as Larmor coupling. The Larmor electric fields locally displace the ambient ions forming a blob above the LPP flow. In the region between a gyrating blob and collimated LPP flow, a secondary cavity of expelled magnetic field forms. In conclusion, these findings are supported by particle-in-cell simulations that replicate the blob formation mechanism and provide insight to similar processes in space, astrophysical, and laboratory settings characterized by ion kinetic scales.
Fluorescence spectroscopy↗
Spatiotemporal control of laser intensity using differentiable programming
Optical techniques for spatiotemporal control can produce laser pulses with custom amplitude, phase, or polarization structure. In nonlinear optics and plasma physics, the use of structured pulses typically follows a forward design approach, in which the efficacy of a known structure is analyzed for a particular application. Inverse approaches, in contrast, enable the discovery of new structures with the potential for superior performance. Here, an implementation of the unidirectional pulse propagation equation that supports automatic differentiation is combined with gradient-based optimization to design structured pulses with features that are advantageous for a range of nonlinear optical and plasma-based applications: (1) a longitudinally uniform intensity over an extended region, (2) a superluminal intensity peak that travels many Rayleigh ranges with constant duration, spot size, and amplitude, and (3) a laser pulse that ionizes a gas to form a uniform column of plasma. In the final case, optimizing the full spatiotemporal structure improves the performance by a factor of 15 compared to optimizing only spatial or only temporal structure, highlighting the advantage of spatiotemporal control.
automatic differentiation↗
Longitudinal shaping of plasma waveguides using diffractive axicons for laser wakefield acceleration
New techniques for the optical generation of plasma waveguides—optical fibers for ultra-intense light pulses—have become vital to the advancement of multi-GeV laser wakefield acceleration. Here, we demonstrate the fabrication and characterization of a transmissive 8-level logarithmic diffractive axicon (LDA) for the generation of meter-scale plasma waveguides. These LDAs enable the formation of a Bessel-like beam with controllable start and end locations of the focal line and near-constant intensity on axis. We present measurements of the Bessel-like focal profile produced by the LDA and of the leading end of the plasma column generated by it. One important feature is the formation of a funnel-mouthed plasma channel entrance that can act as waveguide coupler. We also compare the diffraction efficiency of our 8-level LDA to 4-level and binary versions, with measurements comparing well to theory.
Tripathi, N.↗
Pulsed contact glow discharge electrification for online material quantification
Real-time elemental analysis of liquids in extreme environments remains a significant challenge for sensor development, particularly in applications such as advanced nuclear reactors. Plasma-based optical emission spectroscopy offers a promising solution. In this study, we investigate pulsed contact glow discharge electrolysis (CGDE) as an alternative plasma generation method for emission-based material quantification. Using aqueous NaCl solutions, we examine the role of discharge polarity on plasma behavior, emission characteristics, and spectral output. Our results demonstrate that cathodic discharges generate more energetic plasmas, enabling the detection of ionic species such as cerium, while anodic discharges favor atomic emission. These findings reveal a potential dual-mode sensing capability controlled by circuit configuration rather than hardware changes. Through synchronized measurements of emission, current, bubble, and spectral dynamics, we present a model in which electron emission and ohmic heating drive plasma formation. This model enhances our understanding of pulsed-CGDE and supports its potential as a versatile, adaptable platform for future deployment in high-temperature liquids such as molten salts.
98 - NUCLEAR DISARMAMENT, SAFEGUARDS, AND PHYSICAL↗
Molecular beam epitaxy growth of IrO 2 using plasma-only oxidation
Growth of IrO 2 films via molecular beam epitaxy (MBE) using an oxygen plasma as the sole oxidant is demonstrated for the first time. We investigate the oxidizing conditions required for IrO 2 by characterizing the species present in the plasma using optical emission spectroscopy and comparing the thermodynamic equilibrium between Ir/IrO 2 under atomic and molecular oxygen. Across the pressure range accessible, monatomic oxygen was the primary reactive species present in the plasma. IrO 2 films were grown under varying Ir flux, oxygen pressure, and substrate temperature to understand growth thermodynamics and kinetics. Structural characterization assessed film phase and composition, crystallinity, strain, and surface morphology. The optimized films from this study validate plasma-only reactive growth by MBE as a successful method for growing IrO 2 .
36 MATERIALS SCIENCE↗
An ICP-OES method for the precise and accurate quantification of rare earth elements in natural water: A comparative study from mine waste sites in New Mexico, USA
Inductively coupled plasma techniques such as ICP-OES and ICP-MS are routinely used to determine the concentrations of rare earth elements (REE) in water samples. However, their performance for the determination of REE concentration in mine drainage waters from epithermal vein and porphyry copper mining districts has not been evaluated extensively. In this work, we develop an REE analysis method on an Agilent 5900 ICP-OES instrument and assess the accuracy and precision for the quantification of REE in the natural waters collected from mine adits and an acid seep of mine sites in the Steeple Rock and Hillsboro mining districts, New Mexico, USA. The total REE concentrations in the water samples were measured using the methods we developed for both ICP-OES and ICP-MS. The power of the new ICP-OES method lies in routine analysis of μg/L level concentrations normally analyzed using ICP-MS, including a U.S. Geological Survey standard reference sample, laboratory blank samples spiked with a National Institute of Standards and Technology traceable standard, and surface water samples from mine waste sites. This ICP-OES method achieves low quantification limits ranging from 0.2 to 5 μg/L and excellent analytical accuracy and precision for REE analysis. The precision of light (La-Gd) and heavy (Tb-Lu) REE analysis using this method are better than 5% at average concentrations above 5 ± 4 μg/L and 3 ± 2 μg/L, respectively, and 3% at average concentrations above 10 ± 9 μg/L and 5 ± 4 μg/L, respectively. This method also shows excellent sensitivity and reproducibility for our laboratory and field samples.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Plasma-based prism compressor design for high-intensity laser pulses
A concept for a femtosecond pulse compressor based on underdense plasma prisms is presented. An analytical model is developed to calculate the spectral phase incurred and the expected pulse compression. A 2D particle-in-cell simulation verifies the analytical model. Simulated intensities ( ∼10 16 W/cm 2 ) were orders of magnitude higher than the damage threshold for conventional gratings used in chirped pulse amplification. Theoretical geometries for compact (tens of cm scale) compressors for 1, 10 and 100 PW power levels are proposed.
47 OTHER INSTRUMENTATION↗
Photon phase-space dynamics in a plasma wakefield accelerator
Frequency up-shifting of laser light in a beam-driven plasma wakefield has the potential to provide high-intensity sources of short wavelength radiation. Simulations have demonstrated that a laser pulse can undergo large frequency shifts, limited only by the drive beam energy, when the plasma density is tailored to match the accelerating phase of the wake to the group velocity of the pulse. Here, we study the dynamical evolution of photons in the 1D1P phase-space vicinity of the plasma wake-phase matching condition. Numerical calculations using a photon kinetic model are validated by direct comparison with 1D and quasi-3D particle-in-cell simulations. These calculations form the basis of a linear theory of the photon dynamics which reveals several important results, including scalings for the properties of the witness pulse and a self-similar solution for the photon phase-space dynamics. One prediction of the analytic theory is that the pulse can be compressed indefinitely, though the amount of compression would ultimately be limited by practical constraints. These results suggest that photon acceleration can provide a novel source of sub-femtosecond, short wavelength radiation.
XUV generation↗