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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Continuous recoil-driven lasing and cavity frequency pinning with laser-cooled atoms

Abstract Laser-cooled gases of atoms interacting with the field of an optical cavity are a versatile tool for quantum sensing and the simulation of quantum systems. These systems can exhibit phenomena such as self-organization phase transitions, lasing mechanisms, squeezed states and protection of quantum coherence. However, investigations of these phenomena typically occur in a discontinuous manner due to the need to reload atomic ensembles. Here we demonstrate hours-long continuous lasing from laser-cooled 88 Sr atoms loaded into a ring cavity. The required inversion to produce lasing arises from inversion in the atomic-momentum degrees of freedom, which is linked to the self-organization phase transitions and collective atomic recoil lasing observed previously only in a cyclic fashion. We find that over a broad parameter range, the sensitivity of the lasing frequency to changes in cavity frequency is significantly reduced due to an atomic loss mechanism, suggesting a potential approach for mitigating low-frequency cavity noise. Our findings open opportunities for continuous cavity quantum electrodynamics experiments and robust and continuous super-radiant lasers.

Schäfer, Vera M. (ORCID:0000000210003737)↗
DOE OSTI2023

Spectral shaping of an ultrafast ytterbium fiber laser via a passive intracavity optical filter: a simple and reliable route to sub-45 fs pulses

We investigate the use of passive intracavity optical filters for controlling the laser output spectrum of a polarization-mode-locked, ultrafast ytterbium fiber laser. The overall lasing bandwidth is increased or extended by strategic choice of the filter cutoff frequency. Overall laser performance, including pulse compression and intensity noise, is investigated for both shortpass and longpass filters with a range of cutoff frequencies. The intracavity filter not only shapes the output spectra, but also provides a route for overall broader bandwidths and shorter pulses in ytterbium fiber lasers. These results demonstrate that spectral shaping with a passive filter is a useful tool to routinely achieve sub-45 fs pulse durations in ytterbium fiber lasers.

Cooper, Nicholas D.↗
DOE OSTI2022

Effects of laser-annealing on fixed-frequency superconducting qubits

As superconducting quantum processors increase in complexity, techniques to overcome constraints on frequency crowding are needed. The recently developed method of laser-annealing provides an effective post-fabrication method to adjust the frequency of superconducting qubits. In this work, we present an automated laser-annealing apparatus based on conventional microscopy components and demonstrate preservation of highly coherent transmons. In addition, we perform noise spectroscopy to investigate the change in defect features, in particular, two-level system defects, after laser-annealing. Finally, we present a local heating model as well as demonstrate aging stability for laser-annealing on the wafer scale. Our work constitutes an important step toward both understanding the underlying physical mechanism and scaling up laser-annealing of superconducting qubits.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

In situ x-ray imaging to understand subsurface behavior during continuous wave laser drilling

A limited understanding regarding the underlying dynamics and mechanisms of material removal during continuous wave laser drilling has presented significant challenges in achieving precision and process control. Here, to address this, we employed high-fidelity, in situ synchrotron x-ray imaging to reveal previously unknown material behaviors during continuous wave laser drilling with power modulation. Our findings highlight that high-aspect ratio drill holes are achieved when the laser modulation frequency falls within the range of 8–12 kHz, provided that the laser average power and modulation amplitude levels meet the specified limits. Under these conditions, we identified a material removal mechanism driven by incremental accumulation of recoil pressure that gradually pushes material upward from deep within the substrate to the surface. This mechanism manifested as a low-frequency fluctuation in the vapor depression depth, resulting in periodic instances of material ejection. Furthermore, our study underscores that rapid expansion of the melt pool and the widening of the drill hole opening can impede effective material removal by redirecting energy from material ejection to increasing the melt pool size. This investigation contributes essential insights into the subsurface dynamics involved in the drilling of high-aspect ratio holes, furthering our fundamental understanding of this intricate process.

47 OTHER INSTRUMENTATION↗
DOE OSTI2021

Suppression of power losses during laser pulse propagation in underdense plasma slab

For current state-of-the-art terawatt lasers, the primary laser scattering mechanisms in plasma include Forward Raman Scattering (FRS), excitation of plasma waves, and the self-modulational instability (SMI). Using 2D PIC simulations, we demonstrate the dominance of the FRS in the regime with medium-to-low density plasma and non-relativistic laser fields. However, the use of multi-colored lasers with frequency detuning exceeding the plasma frequency, Δω > ω pe , suppresses the FRS. Finally, the laser power can then be transmitted efficiently.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Enhanced collisionless laser absorption in strongly magnetized plasmas

We report that strongly magnetizing a plasma adds a range of waves that do not exist in unmagnetized plasmas and enlarges the laser-plasma interaction (LPI) landscape. In this paper, we use particle-in-cell simulations to investigate strongly magnetized LPI in one dimension under conditions relevant for magneto-inertial fusion experiments, focusing on a regime where the electron-cyclotron frequency is greater than the plasma frequency and the magnetic field is at an oblique angle with respect to the wave vectors. We show that when electron-cyclotron-like hybrid wave frequency is about half the laser frequency, the laser light resonantly decays to magnetized plasma waves via primary and secondary instabilities with large growth rates. These distinct magnetic-field-controlled instabilities, which we collectively call two-magnon decays, are analogous to two-plasmon decays in unmagnetized plasmas. Since additional phase mixing mechanisms are introduced by the oblique magnetic field, collisionless damping of large-amplitude magnetized waves substantially broadens the electron distribution function, especially along the direction of the magnetic field. During this process, energy is transferred efficiently from the laser to plasma waves and then to electrons, leading to a large overall absorptivity when strong resonances are present. The enhanced laser energy absorption may explain hotter-than-expected temperatures observed in magnetized laser implosion experiments and may also be exploited to develop more efficient laser-driven x-ray sources.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Strong mutual increase in the efficiency of isotope-selective laser IR dissociation of molecules under nonequilibrium thermodynamic conditions of the compression shock under irradiation in a bimolecular mixture

We have revealed a strong (by a factor of 2 to 5) mutual increase in the yield of IR molecular dissociation (by the example of CF{sub 2}HCl and CF{sub 3}Br) and a significant (by a factor of 1.5 to 3) lowering of dissociation thresholds in the nonequilibrium thermodynamic conditions of compression shock in the irradiation of the molecules by resonance IR laser radiation in the bimolecular mixture in comparison with their individual irradiation. This opens up the possibility to perform efficient isotope-selective IR dissociation of molecules at lower excitation energy densities (Φ ⩽ 1.5 – 2.0 J cm{sup −2}) and thereby to improve the dissociation selectivity. This was demonstrated by the example of chlorine- and bromine-isotope selective dissociation of the specified molecules, which are characterised by quite small (less than 0.25 cm{sup −1}) isotope shifts in the IR vibrational absorption spectra excited by laser radiation. The enrichment coefficients K {sub enr}({sup 35}Cl / {sup 37}Cl) = 0.90 ± 0.05 in the residual CF{sub 2}HCl gas and K {sub enr}({sup 79}Br / {sup 81}Br) in the resultant Br{sub 2} product are obtained when the CF{sub 2}HCl : CF{sub 3}Br = 1 : 1 molecular mixture and CF{sub 3}Br molecules, respectively, are irradiated by the 9R(30) CO{sub 2} laser line (frequency, 1084.635 cm{sup −1}) at an energy density Φ ≈ 1.3 J cm{sup −2}. (laser isotope separation)

36 MATERIALS SCIENCE↗
DOE OSTI2025

Enhanced energy gain through higher-order resonances during direct laser acceleration with superluminal phase velocity

Ultra-high intensity laser–plasma interactions can produce ultra-relativistic electrons via direct laser acceleration, assisted by quasi-static plasma magnetic and electric fields. These fields transversely confine electron motion and induce betatron oscillations. The net energy gain is strongly influenced by the interplay between two frequencies: the betatron frequency and the frequency of laser field oscillations experienced by the electron. Prior work has shown that energy gain is enabled by a resonance between the betatron oscillations and the oscillations of the laser field. In particular, higher-order resonances occur when the laser field completes multiple cycles during one betatron oscillation, allowing additional regimes of energy transfer beyond the fundamental (betatron) resonance. In this work, we demonstrate that such resonances become particularly effective when the laser's phase velocity is superluminal. Although the two frequencies generally evolve differently with increasing electron energy—leading to detuning—a superluminal phase velocity introduces a non-monotonic frequency ratio with a global minimum. This minimum allows sustained frequency matching over a broad energy range, thereby enabling enhanced energy gain. As the phase velocity increases, the betatron resonance becomes ineffective due to premature frequency detuning. At the same time, higher-order resonances become increasingly effective, emerging as the dominant mechanisms for enhanced energy gain in this regime of direct laser acceleration.

Laser plasma interactions↗
DOE OSTI2022

Sensing depths in frequency domain thermoreflectance

In this work, a method is developed to calculate the length into a sample to which a Frequency Domain Thermoreflectance (FDTR) measurement is sensitive. Sensing depth and sensing radius are defined as limiting cases for the spherically spreading FDTR measurement. A finite element model for FDTR measurements is developed in COMSOL multiphysics and used to calculate sensing depth and sensing radius for silicon and silicon dioxide samples for a variety of frequencies and laser spot sizes. The model is compared to experimental FDTR measurements. Design recommendations for sample thickness are made for experiments where semi-infinite sample depth is desirable. For measurements using a metal transducer layer, the recommended sample thickness is three thermal penetration depths, as calculated from the lowest measurement frequency.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Creating pair plasmas with observable collective effects

Although existing technology cannot yet directly produce fields at the Schwinger level, experimental facilities can already explore strong-field QED phenomena by taking advantage of the Lorentz boost of energetic electron beams. Recent studies show that QED cascades can create electron-positron pairs at sufficiently high density to exhibit collective plasma effects. Signatures of the collective pair plasma effects can appear in exquisite detail through plasmainduced frequency upshifts and chirps in the laser spectrum. Maximizing the magnitude of the QED plasma signature demands high pair density and low pair energy, which suits the configuration of colliding an over 10 18 Jm -3 energy-density electron beam with a 10 22 -10 23 Wcm -2 intensity laser pulse. The collision creates pairs that have a large plasma frequency, made even larger as they slow down or reverse direction due to both the radiation reaction and laser pressure. This paper explains at a tutorial level the key properties of the QED cascades and laser frequency upshift, and at the same time finds the minimum parameters that can be used to produce observable QED plasma.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Standoff Detection of Chemical Plumes Using Swept-ECQCL Remote Detection Technology: Results from EMRTC Complex Terrain Dual Tracer Experiment

As part of the Complex Terrain Dual Tracer Experiments performed in support of the LYNM program, a swept-wavelength external cavity quantum cascade laser (swept-ECQCL) remote detection system was deployed to measure chemical plume propagation with high temporal resolution. The swept-ECQCL remote detection technology was initially developed at PNNL, and is now under further development at Opticslah, LLC under SBIR funding from DOE (DOE SBIR Phase I Project DE-SC0019855, Remote Detection Technologies, Program Manager Chris Ramos). The swept-ECQCL technology provides a single-frequency infrared laser source which is rapidly scanned over a large wavelength range to measure the infrared absorption of gases, liquids, or solids. Analysis of the measured infrared absorption spectrum is used to detect, identify, and quantify the chemical species which are present. While most previous laser-based techniques used small wavelength tuning ranges to measure only a few isolated spectral lines of a few species, the swept-ECQCL provides the large tuning range needed to measure multiple species simultaneously, and to detect broad absorption features from large molecules or condensed phase materials. In addition, the swept-ECQCL systems have high enough spectral resolution and sensitivity to measure narrow lines of small molecules and determine isotope ratios. The remote detection system for gas plumes is based on the swept-ECQCL technology, and consists of a swept-ECQCL source, infrared detector, control electronics, and beam transmitting and alignment optics. The remote detection system directs the infrared output of the swept-ECQCL to a target retro reflector typically located at ~10-10,000 m distance. The swept-ECQCL wavelength is varied continuously over a large wavelength range (>1000 nm) at rates up to 1000 Hz. The swept ECQCL light reflected from the remote target is collected and focused onto an infrared photodetector. By measuring the detector signal continuously as the swept-ECQCL wavelength is varied, a time-series of absorption spectra are measured for the gases along the beam line of-sight. Based on analysis and fitting of the measured absorption spectra, the time-dependent chemical concentrations of species are determined. Multiple species and mixtures can be detected simultaneously, for all species with absorption features above the sensor noise floor. The sensor output is thus a continuous, high-speed record of identified chemicals along with their concentrations and isotope ratios of interest. The high-speed operation enables low-noise operation in conditions of atmospheric turbulence and allows tracking of fluctuating concentrations in transient chemical plumes as needed for reliable remote detection applications. All components operate with minimal cooling requirements and no cryogens are needed. In addition, the output infrared light is invisible with an intensity below the maximum permissible exposure (MPE) threshold of 100 mW/cm2 for these infrared wavelengths and thus eye safe. The measurement concept for plume detection using the swept-ECQCL remote detection system is as follows. The ECQCL beam is directed toward a remote retro-reflector, which reflects the beam back to the ECQCL system where it is focused onto an infrared photodetector. The line-of-sight from the ECQCL system to the retro-reflector defines the measurement path. The detected infrared signal is recorded continuously and detects the absorption of molecular species along the measurement path. Before a plume release, the system measures absorption from atmospheric constituents, which in this LWIR band consist primarily of lines from H 2 O and CO 2 , with additional weaker absorption from N 2 O, NH 3 , and O 3 possibly contributing. The system then measures any changes in absorption due to the tracer compounds when they enter the measurement path. The shape of absorption features is used to distinguish and identify the different tracer compounds, and the strength of the absorption is used to determine the path-integrated concentration – also called the column density.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Backscatter-Immune Injection-Locked Brillouin Laser in Silicon

As self-sustained oscillators, lasers possess the unusual ability to spontaneously synchronize. These nonlinear dynamics are the basis for a simple yet powerful stabilization technique known as injection locking, in which a laser’s frequency and phase can be controlled by an injected signal. Because of its inherent simplicity and favorable noise characteristics, injection locking has become a workhorse for coherent amplification and high-fidelity signal synthesis in applications ranging from precision atomic spectroscopy to distributed sensing. Within integrated photonics, however, these injection-locking dynamics remain relatively untapped—despite significant potential for technological and scientific impact. In this work, we demonstrate injection locking in a silicon photonic Brillouin laser. Injection locking of this monolithic device is remarkably robust, allowing us to tune the laser emission by a significant fraction of the Brillouin gain bandwidth. Harnessing these dynamics, we demonstrate amplification of small signals by more than 23 dB. Moreover, we demonstrate that the injection-locking dynamics of this system are inherently nonreciprocal, yielding unidirectional control and backscatter immunity in an all-silicon system. This device physics opens the door to strategies for phase-noise reduction, low-noise amplification, and backscatter immunity in silicon photonics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Frequency Comb-Based Remote Methane Observation Network (Final Scientific/Technical Report)

ARPA-E investment in long-range, frequency comb-based methane detection has resulted in the first scalable, cost-effective continuous methane emissions system. At the onset of this ARPA-E MONITOR award, the dual-frequency comb spectrometer was a sprawling, expensive, laboratory-confined device which had only recently been demonstrated capable of measuring atmospheric trace gases over open-paths. Bringing the technology to the point of being able to monitor for and characterize methane emissions at oil and natural gas production facilities seemed an almost impossible task. Over the subsequent months and years, our team transitioned the Nobel-prize-winning frequency-comb-laser spectrometer technology to a field-deployed regional methane leak detection system. The spectrometer enables highly sensitive near-infrared absorption measurements of methane along kilometer-scale laser beam paths. The measurements are coupled with an atmospheric modeling and inversion framework to triangulate the location of emission sources and quantify the emission rates.

03 NATURAL GAS↗
DOE OSTI2021

Photodissociation and Infrared Spectroscopy of Uranium–Nitrogen Cation Complexes

Laser vaporization of uranium in a pulsed supersonic expansion of nitrogen is used to produce complexes of the form U + (N 2 ) n (n = 1–8). These ions are mass selected in a reflectron time-of-flight spectrometer and studied with visible and UV laser fixed-frequency photodissociation and with tunable infrared laser photodissociation spectroscopy. The dissociation patterns and spectroscopy of U + (N 2 ) n indicate that N 2 ligands are intact molecules and that there is no insertion chemistry resulting in UN + or NUN + . Fixed frequency photodissociation at 532 and 355 nm indicate that the U + –N 2 bond dissociation energy varies little with changing coordination. The photon energy and the number of ligands eliminated allow an estimate of the average U + –N 2 dissociation energy of 12 kcal/mol. Infrared bands are observed for these complexes near the N–N stretch vibration via elimination of N 2 molecules. These resonances are observed to be shifted about 130 cm–1 to the red from the free-N 2 frequency for complexes with n = 3–8. Density functional theory indicates that U + is most stable in the sextet state in these complexes and that N 2 molecules bind in end-on configurations. Furthermore, the fully coordinated complex is predicted to be U + (N 2 ) 8 , which has a cubic structure. The vibrational frequencies predicted by theory are consistently lower than those in the experiment, independent of the isomeric structure or spin state of the complexes. Despite its failure to reproduce the infrared spectra, theory provides an average U + –N 2 dissociation energy of 11.8 ± 0.5 kcal/mol, in good agreement with the value from the experiments.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2023

Modeling noise in global Mølmer-Sørensen interactions applied to quantum approximate optimization

Many-qubit Mølmer-Sørensen (MS) interactions applied to trapped ions offer unique capabilities for quantum information processing, with applications including quantum simulation and the quantum approximate optimization algorithm (QAOA). Here, we develop a physical model to describe many-qubit MS interactions under four sources of experimental noise: vibrational mode frequency fluctuations, laser power fluctuations, thermal initial vibrational states, and state preparation and measurement errors. The model parametrizes these errors from simple experimental measurements, without free parameters. Herein, we validate the model in comparison with experiments that implement sequences of MS interactions on two 171 Yb + ions. The model shows reasonable agreement after several MS interactions as quantified by the reduced chi-squared statistic $χ^{2}_{red}$≈2. As an application we examine MaxCut QAOA experiments on three and six ions. The experimental performance is quantified by approximation ratios that are 91% and 83% of the optimal theoretical values. Our model predicts $0.93^{+0.03}_{-0.02}$ and $0.95^{+0.04}_{-0.03}$, respectively, with disagreement in the latter value attributable to secondary noise sources beyond those considered in our analysis. With realistic experimental improvements to reduce measurement error and radial trap frequency variations, the model achieves approximation ratios that are 99% of the optimal. Incorporating these improvements into future experiments is expected to reveal new aspects of noise for future modeling and experimental improvements.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Dual frequency comb spectroscopy of solid fuel pyrolysis and combustion: Quantifying the influence of moisture content in Douglas fir

As the fire research community develops multi-scale models to predict the spread of wildland fires, there is a need for well-controlled, small-scale experiments which provide benchmark data and fundamental understanding of the effects of key parameters on the combustion of wildland fuels. Here, we implement a unique suite of non-intrusive, quantitative diagnostics that simultaneously measure mass loss, surface temperature, in situ gas temperature and water vapor concentration, including the first implementation of dual frequency comb spectroscopy for the study of solid fuels. As a demonstration, we examine the effect of fuel moisture content on the burning of Douglas fir wood samples that are ignited under constant radiative heat flux from a cone calorimeter to provide benchmark data for multi-scale models. Peak flame temperatures 3 mm above the sample surface measured with the dual frequency comb laser spectrometer are in excess of 1200 K. The flame temperature decreases by over 150 K as fuel moisture content increases from 0.7% to 40%. This work demonstrates a platform for simultaneous, quantitative measurements of well-controlled small-scale experiments which provide benchmark data for the development of advanced modeling and simulations capable of capturing the complex physics present in wildland fire systems.

54 ENVIRONMENTAL SCIENCES↗