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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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At least 703 records · Page 39
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Fluorene- and benzofluorene-cored oligomers as low threshold and high gain amplifying media

Deliberate control of intermolecular interactions in fluorene- and benzofluorene-cored oligomers was attempted via introduction of different-length alkyl moieties to attain high emission amplification and low amplified spontaneous emission (ASE) threshold at high oligomer concentrations. Containing fluorenyl peripheral groups decorated with different-length alkyl moieties, the oligomers were found to express weak concentration quenching of emission, yet excellent carrier drift mobilities (close to 10{sup −2} cm{sup 2}/V/s) in the amorphous films. Owing to the larger radiative decay rates (>1.0 × 10{sup 9 }s{sup −1}) and smaller concentration quenching, fluorene-cored oligomers exhibited down to one order of magnitude lower ASE thresholds at higher concentrations as compared to those of benzofluorene counterparts. The lowest threshold (300 W/cm{sup 2}) obtained for the fluorene-cored oligomers at the concentration of 50 wt % in polymer matrix is among the lowest reported for solution-processed amorphous films in ambient conditions, what makes the oligomers promising for lasing application. Great potential in emission amplification was confirmed by high maximum net gain (77 cm{sup −1}) revealed for these compounds. Although the photostability of the oligomers was affected by photo-oxidation, it was found to be comparable to that of various organic lasing materials including some commercial laser dyes evaluated under similar excitation conditions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Spontaneous lateral phase separation of AlInP during thin film growth and its effect on luminescence

The occurrence of spontaneous lateral phase separation during thin film growth of Al{sub x}In{sub 1−x}P by metal-organic chemical vapor deposition was investigated using a combination of transmission electron microscopy and atom probe tomography to obtain a quantitative view of this phenomenon. An anisotropic and coherent composition modulation was observed in the nearly lattice-matched films deposited below 750 °C with a quasi-linear amplification with thickness that was inversely proportional to the growth temperature. The periodicity of the modulation increased exponentially with the growth temperature. A comparison of photoluminescence from phase separated and homogenous direct band gap Al{sub x}In{sub 1−x}P deposited on metamorphic In{sub y}Ga{sub 1−y}As graded buffers showed a lowering of peak-emission energy in accordance with the atom probe compositional characterization without any degradation in luminous intensity. Additionally, indications of carrier trapping in the low band gap regions were observed even at room-temperature. While some of these results are in qualitative agreement with theoretical models of kinetic instability in unstrained alloy growth in the literature, significant discrepancies remain.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

All-optical transistors and logic gates using a parity-time-symmetric Y-junction: Design and simulation

Classical nonlinear or quantum all-optical transistors are dependent on the value of input signal intensity or need extra co-propagating beams. In this paper, we present a kind of all-optical transistors constructed with parity-time (PT)-symmetric Y-junctions, which perform independently on the value of signal intensity in an unsaturated gain case and can also work after introducing saturated gain. Further, we show that control signal can switch the device from amplification of peaks in time to transformation of peaks to amplified troughs. By using these PT-symmetric Y-junctions with currently available materials and technologies, we can implement interesting logic functions such as NOT and XOR (exclusive OR) gates, implying potential applications of such structures in designing optical logic gates, optical switches, and signal transformations or amplifications.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Spectroscopic and energy transfer studies of Er{sup 3+} ions in B{sub 2}O{sub 3}–TeO{sub 2}–MgO–ZnO glasses

Composition dependent spectroscopic behavior of Er{sup 3+} doped telluroborate glasses were prepared and the energy transfer mechanism in Er{sup 3+} ions were investigated for 1.532 µm amplification. The emission cross-section and gain coefficient for {sup 4}I{sub 13/2}→{sup 4}I{sub 15/2} level of Er{sup 3+} ions have been analysed through the Judd-Ofelt and McCumber theory. The excited state decay curves were measured and the effect of TeO{sub 2} on the lifetime for {sup 4}I{sub 13/2}→{sup 4}I{sub 15/2} level of Er{sup 3+} ions has been associated with the various energy transfer mechanism. Further the interaction between Er{sup 3+} and OH{sup −} were investigated and it was confirmed that the OH free radicals in the prepared glasses are dominant quenching center through the non-radiative relaxation that causes the quenching of 1.532 µm amplification. The non-radiative rate through the OH content were calculated and compared with the reported Er{sup 3+} doped glasses.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Photonic-band-gap gyrotron amplifier with picosecond pulses

Here, we report the amplification of 250 GHz pulses as short as 260 ps without observation of pulse broadening using a photonic-band-gap circuit gyrotron traveling-wave-amplifier. The gyrotron amplifier operates with a device gain of 38 dB and an instantaneous bandwidth of 8 GHz. The operational bandwidth of the amplifier can be tuned over 16 GHz by adjusting the operating voltage of the electron beam and the magnetic field. The amplifier uses a 30 cm long photonic-band-gap interaction circuit to confine the desired TE 03 -like operating mode while suppressing lower order modes which can result in undesired oscillations. The circuit gain is >55 dB for a beam voltage of 23 kV and a current of 700 mA. These results demonstrate the wide bandwidths and a high gain achievable with gyrotron amplifiers. The amplification of picosecond pulses of variable lengths, 260–800 ps, shows good agreement with the theory using the coupled dispersion relation and the gain-spectrum of the amplifier as measured with quasi-CW input pulses.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2018

Progress toward a self-consistent set of 1D ignition capsule metrics in ICF

One-dimensional metrics can be considered an upper bound on the performance that can be achieved given an implosion with an imploding mass Mimp and a given adiabat α, driven to an implosion velocity V by a specified ablation pressure Pa for single shell capsules with low-opacity ablators. The quantitative value of an ignition metric depends on the definition of ignition. We review the choices that have been made by various authors before settling on a definition based on yield amplification of 30 where yield amplification is the ratio of the yield from an implosion that includes the alpha particle and neutron deposition relative to the yield obtained from PdV work alone. We then derive improved 1D ignition metrics for radiation-driven inertial confinement fusion targets that span a wide range of drive pressures, adiabats, and scales. This includes emphasizing the importance of the total imploding mass and kinetic energy inside the ablation front, including the remaining ablator mass and kinetic energy, on the 1D ignition metrics. We have also explicitly included the sensitivity to ablation pressure driving the implosion, as well as the sensitivity to the coupling efficiency between the total incoming kinetic energy and the hot spot. For implosions in which the remaining ablator mass contributes to the total stagnated mass, we have developed an approach based on defining an effective implosion adiabat which incorporates the properties and the mass of the stagnated ablator as well as the cold DT fuel. We have added a dependence on total ρr to account for the fact that the time available for self-heating increases as the total ρr increases. This extends previous work in that the value of the product of stagnation pressure times burn width required for ignition depends on the total ρr as well as on the fuel ion temperature. Additionally, we show that ignition metrics derived from a requirement on the product of the hotspot ρr and the hot spot temperature are equivalent to ignition metrics derived from a requirement on the product of stagnation pressure and burn width. Further, we discuss those ignition metrics, developed as metrics for the underlying hydrodynamics in the absence of alpha heating, which can be used when alpha heating is present.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Phase modulation failsafe system for multi-kJ lasers based on optical heterodyne detection

Amplification of the transverse scattered component of stimulated Brillouin scattering (SBS) can contribute to optical damage in the large aperture optics of multi-kJ lasers. Because increased laser bandwidth from optical phase modulation (PM) can suppress SBS, high energy laser amplifiers are injected with PM light. Phase modulation distributes the single-frequency spectrum of a master oscillator laser among individual PM sidebands, so a sufficiently high modulation index β can maintain the fluence for all spectral components below the SBS threshold. To avoid injection of single frequency light in the event of a PM failure, a high-speed PM failsafe system (PMFS) must be employed. Because PM is easily converted to AM, essentially all PM failsafes detect AM, with the one described here employing a novel configuration where optical heterodyne detection converts PM to AM, followed by passive AM power detection. Although the PMFS is currently configured for continuous monitoring, it can also detect PM for pulse durations ≥2 ns and could be modified to accommodate shorter pulses. This PMFS was deployed on the Z-Beamlet Laser (ZBL) at Sandia National Laboratories, as required by an energy upgrade to support programs at Sandia’s Z Facility such as magnetized liner inertial fusion. Depending on the origin of a PM failure, the PMFS responds in as little as 7 ns. In the event of an instantaneous failure during initiation of a laser shot, this response time translates to a 30–50 ns margin of safety by blocking a pulse from leaving ZBL’s regenerative amplifier, which prevents injection of single frequency light into the main amplification chain. In conclusion, the performance of the PMFS, without the need for operator interaction, conforms to the principles of engineered safety.

47 OTHER INSTRUMENTATION↗
DOE OSTI2019

Pulse contrast enhancement via non-collinear sum-frequency generation with the signal and idler of an optical parametric amplifier

We outline an approach for improving the temporal contrast of a high-intensity laser system by >8 orders of magnitude using non-collinear sum-frequency generation with the signal and idler of an optical parametric amplifier. We demonstrate the effectiveness of this technique by cleaning pulses from a millijoule-level chirped-pulse amplification system to provide >10 12 intensity contrast relative to all pre-pulses and amplified spontaneous emission >5 ps prior to the main pulse. The output maintains percent-level energy stability on the time scales of a typical user experiment at our facility, highlighting the method's reliability and operational efficiency. After temporal cleansing, the pulses are stretched in time before seeding two multi-pass, Ti:sapphire-based amplifiers. After re-compression, the 1 J, 40 fs (25 TW) laser pulses maintain a >10^10 intensity contrast >30 ps prior to the main pulse. This technique is both energy-scalable and appropriate for preparing seed pulses for a TW- or PW-level chirped-pulse amplification laser system.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Overdriven-detonation states produced by spherically diverging waves

A series of experiments are currently underway at the Detonation Science and Technology group, within Los Alamos National Laboratory, to study the overdriven-detonation states achievable in energetic materials as a result of detonation-wave interactions. A multi-component, energetic-material array was designed to study the amplification of velocity and pressure states produced by spherically diverging detonation waves in pentaerythritol tetranitrate (PETN) output charges. The unique geometry provides a low-jitter, highly controlled series of interactions between three independent-detonation inputs. Streak-camera imaging was performed on the output face of PETN pellets ranging in thickness from 2.5 – 10 mm to characterize the resulting breakout profile. Additionally, photonic Doppler velocimetry (PDV) measurements were collected at the output-pellet surface to determine simultaneity within the system. Detonation-wave velocities upwards of 16 mm/µs were measured, as compared to a steady-state detonation velocity of 7.9 mm/µs for the PETN pressing density investigated. Finally, additional experiments are being conducted to measure the pressure amplification generated at key areas of interaction.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

A thermodynamic condition for ignition and burn-propagation in cryogenic layer inertially confined fusion implosions

A Lawson-like criterion for ignition (where self-heating dominates over all energy losses) in a dynamic implosion is developed, which accounts for asymmetry and for differences in an implosion x-ray confinement quality. It is shown that the thermodynamic ignition condition is equivalent to yield amplification levels of 16–32. Since negative pdV work of expansion after stagnation increases energy losses above that of x-ray and electron-conduction losses, the Lawson-like ignition criterion is necessary but not sufficient for igniting the hot spot to propagate into the DT fuel with sufficient vigor to generate high gain. Additionally, a higher dimensional generalization of the Lawson-like criterion, which includes the cooling of the implosion upon disassembly, does provide the needed criteria, and it shows that significantly higher temperature is needed for very high levels of yield amplification compared to what traditional ignition metrics imply.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Phase noise limited frequency shift impulsive Raman spectroscopy

We introduce a method to enable optical amplification of a coherent Raman spectroscopy signal, which we call radio frequency (RF) Doppler Raman spectroscopy. In this article, we consider the perturbation of a probe pulse in a sample due to an excited Raman vibrational coherence as a generalized Doppler shift, which connects a time-varying optical path length (the product of the propagation length and refractive index, OPL = n ℓ) with an optical frequency shift. Amplification of a Raman signal outside of the focused interaction is enabled by converting the Doppler frequency shift experienced by a laser probe pulse into a periodic timing jitter. This transit time perturbation is detected through the phase of a RF electronic signal measured at a harmonic of the probe pulse train with a method adapted from precision metrology techniques used to measure laser pulse train timing jitter. Measurement of a timing jitter allows access to much lower noise floors than other coherent Raman techniques, and by exploiting the new capability to scale the signal of a coherent Raman spectroscopic signal, this method opens the potential to detect very weak Raman signals that are currently not observable due to limits of illumination intensity imposed by laser damage to the specimen and noise.

47 OTHER INSTRUMENTATION↗
DOE OSTI2021

Modulation-slippage trade-off in resonant four-wave upconversion

Following up on a proposal to use four-wave mixing in an underdense plasma at mildly relativistic laser intensities to produce vastly more energetic x-ray pulses [V. M. Malkin and N. J. Fisch, Phys. Rev. E, 101, 023211 (2020)], we perform the first numerical simulations in one dimension to illustrate amplification of a short high frequency seed through four-wave mixing. Here, we illustrate how parasitic processes including phase modulation and spatial pulse slippage limit the amplification efficiency. Although the regimes studied were not where the optimal efficiencies were expected, these regimes do expose the basic physical processes at play, while still yielding not insignificant spectral power upshift.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Geometry and dynamics of passive scalar structures in compressible turbulent mixing

We present a structure-based numerical analysis of passive scalar mixing in decaying homogeneous isotropic turbulence (DHIT) and shock-turbulence interaction canonical configurations. The analysis focuses on the temporal evolution of ensembles of passive scalar structures, initialized as spheres of different sizes relative to the Taylor microscale. An algorithm is introduced to track the evolution of each individual structure and the interactions with other structures in the ensemble, relating changes in the surface geometry and the underlying physical processes (turbulent transport, scalar dissipation, and shock compression). The tracking algorithm is applied to datasets from shock-capturing direct numerical simulations of DHIT, with Taylor microscale Reynolds number Re λ =40 and turbulence Mach number M t =0.2 ⁠, and STI cases in which the turbulence is processed by a shock wave at Mach numbers M = 1.5 and 3.0. Temporal surface convolution increases for initially larger structures, resulting in a higher probability of locally hyperbolic geometries where breakup into smaller structures occurs. Shock-induced deformation of the structures amplifies breakup processes, enhancing mixing, particularly for larger structures. Mixing enhancement by the shock is manifested as an amplification of the surface-averaged scalar gradient, which increases for initially larger structures. The alignment between the scalar gradient and the most extensional strain-rate eigendirection on the scalar isosurfaces also increases across the shock. Larger magnitudes of the scalar gradient and its alignment with the most compressive strain-rate eigendirection correlate with flatter surface regions. Shock-induced structure compression increases the area coverage of flat regions, where the amplification of scalar gradient is localized.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Progress in relativistic laser–plasma interaction with kilotesla-level applied magnetic fields

We report on progress in the understanding of the effects of kilotesla-level applied magnetic fields on relativistic laser–plasma interactions. Ongoing advances in magnetic-field–generation techniques enable new and highly desirable phenomena, including magnetic-field–amplification platforms with reversible sign, focusing ion acceleration, and bulk-relativistic plasma heating. Building on recent advancements in laser–plasma interactions with applied magnetic fields, we introduce simple models for evaluating the effects of applied magnetic fields in magnetic-field amplification, sheath-based ion acceleration, and direct laser acceleration. These models indicate the feasibility of observing beneficial magnetic-field effects under experimentally relevant conditions and offer a starting point for future experimental design.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Femtosecond wavelength-tunable laser system using gain managed nonlinear amplifier

Optical parametric amplifiers require a seed energy at the spectral range of interest for amplification. In the case of pulsed laser systems, seed pulse characteristics such as spectral energy density and spectral uniformity influence laser system design and performance. In this letter, we present the design and modeling of a few micro-joules, wavelength-tunable, femtosecond parametric amplifier system. We employ a gain-managed nonlinear fiber amplifier output as the seed pulse. This seed pulse is relatively uniform across its bandwidth from 1010 to 1180 nm. Its spectral energy density averages 600 pJ/nm, 30 times higher than conventional counterparts. The overall amplification gain is 175, and the conversion efficiency is 17.5%. The inherent quasi-linear chirp of the seed pulse is utilized to alter the output wavelength. Our tunable femtosecond laser is an enabling technology for high-demand applications such as time-resolved spectroscopy, nonlinear and advanced material research, and biomedical imaging and microscopy modalities.

47 OTHER INSTRUMENTATION↗
DOE OSTI2026

Modeling of injected current stream-induced 3D perturbations in local helicity injection plasmas

Solenoid-free tokamak startup techniques are essential for spherical tokamaks and offer a pathway to cost reduction and design simplification in fusion energy systems. Local helicity injection (LHI) is one such approach, employing compact edge current sources to drive open field line current that initiates and sustains tokamak plasmas. The recently commissioned Pegasus-III Experiment provides a platform for advancing this and other solenoid-free startup methods. This study investigates the effect of LHI on magnetic topology in Pegasus-III plasmas. A helical filament model represents the injected current, and the linear plasma response to its three-dimensional field is calculated with M3D-C1. Poincaré mapping reveals substantial flux surface degradation in all modeled cases. The onset of overlapping magnetic structures and large-scale surface deformation begins near Ψ N ≈ 0.37, indicating a broad region of perturbed topology extending toward the edge. In rotating plasmas, both single-fluid and two-fluid models exhibit partial screening of the n = 1 perturbation, with two-fluid calculations showing stronger suppression near the edge. In contrast, the absence of rotation leads to strong resonant field amplification in the single-fluid case, while the two-fluid case with zero electron rotation mitigates this amplification and preserves edge screening. Magnetic probe measurements indicate that modeling the stream with spatial spreading—representing distributed current and/or oscillatory motion—better reproduces measured magnetic power profiles than a rigid filament model. The results underscore the role of rotation and two-fluid physics in screening stream perturbations and point to plasma flow measurements and refined stream models as key steps toward improving predictive fidelity.

Schaefer, Carolyn E. [Univ. of Wisconsin, Madison,↗
DOE OSTI2012

Supercontinuum generation in thulium-doped fibres

Supercontinuum generation in thulium-doped fibres under pumping at 1.59 {mu}m is investigated. Amplification of supercontinuum in the range of 1.8--2.0 {mu}m is found for a fibre doped to a level of 2 Multiplication-Sign 10{sup 19} cm{sup -3}. For a fibre with an activator concentration of 2 Multiplication-Sign 10{sup 20} cm{sup -3} amplification is also observed in the (2.1 - 2.45)-{mu}m band, which suggests the occurrence of the {sup 3}H{sub 4} {yields} {sup 3}H{sub 5} optical transition in the fibre. The occupation of the {sup 3}H{sub 4} level can be explained by cooperative effects. (optical fibres, lasers and amplifiers. properties and applications)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Microsecond gain-switched master oscillator power amplifier (1958 nm) with high pulse energy

An all-fibre master oscillator power amplifier (MOPA) emitting high-energy pulses at 1958 nm is presented. The seed laser is a microsecond gain-switched thulium-doped fibre laser (TDFL) pumped with a commercial 1550-nm pulsed fibre laser. The TDFL operates at a repetition rate f in the range of 10 to 100 kHz. The two-stage thulium-doped fibre amplifier is built to scale the energy of the pulses generated by the seed laser. The maximum output pulse energy higher than 0.5 mJ at 10 kHz is achieved which is comparable with the theoretical maximum extractable pulse energy. The slope efficiency of the second stage amplifier with respect to the pump power is 30.4% at f = 10 kHz. The wavelength of the output pulse laser is centred near 1958 nm at a spectral width of 0.25 nm after amplification. Neither nonlinear effects nor significant amplified spontaneous emission (ASE) is observed in the amplification experiments. (lasers)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗