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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Towards the design of a wideband reflective long period grating distributed sensor

Abstract In this paper, we computationally investigate the effects of metal coating length and coating coverage on the reflected spectrum of a long period grating (LPG) over a broad bandwidth. Simulation results indicate that coating the tail end of the fiber between the LPG and the end facet of the fiber provides a reflected spectrum that mimics the LPG transmission spectrum shape over a 400 nm bandwidth. Based on single LPG simulation results, we present the design of a distributed LPG structure containing a multiple number ( n ) of LPGs in reflection mode for the first time. Simulation results for n = 1, 2, and 3 are presented here to demonstrate the concept of a distributed reflective LPG design. It is expected that such a sensor will open a new window for distributed sensing using reflective LPGs.

Rana, Sohel (ORCID:0000000262813555)↗
DOE OSTI2025

Passive radiative thermal management using phase-change metasurfaces

Abstract Realizing innovative composite materials with passive thermal management capabilities and minimal ecological footprints is a challenging but much sought-after goal that would have a transformative effect on renewable energy sciences. We demonstrate an environmentally friendly metasurface utilizing vanadium dioxide (VO 2 ) that offers responsiveness to ambient temperature and potentially long-term stability. The metasurface enables passive thermal management by self-adjusting its absorptivity and emissivity response over a broad bandwidth ranging from visible to mid-infrared (IR) wavelengths. Above the VO 2 phase transition the metasurface exhibits increased mid-IR emissivity and reduced visible/near-IR absorptivity, creating an efficient radiative emission channel in the first atmospheric transparency window with reduced absorption of solar radiation. In contrast, below VO 2 ’s transition temperature, the metasurface increasingly absorbs sun light while minimizing mid-IR radiative heat losses. Moreover, a functional silicon layer eliminates the need for an additional capping layer commonly employed to protect VO 2 from environmental degradation. The additional protective layer often impedes the use and performance of VO 2 based devices in terrestrial as well as spacecraft applications. Therefore, the proposed durable and eco-friendly metasurface will be an excellent candidate for essential passive thermal regulation systems across residential and terrestrial applications.

42 ENGINEERING↗
DOE OSTI2021

Imaging ring-current wave packets in the helium atom

We study the reconstruction of a wave packet and the corresponding electron dynamics in an atom via photoelectron angular distributions (PADs) in a pump-probe scheme as a function of time delay. The method is applied to the superposition of ground and one or two excited states in helium atom representing field-free charge migrations on the attosecond timescale in form of ring currents around the core. It is based on the interference between one- and two-photon transitions from ground and excited states into the continuum. In the reconstruction predictions of first- and second-order perturbation theory are used to determine the unknown phases and amplitudes from the PADs, which we simulate via solutions of the time-dependent Schrödinger equation in single-active-electron approximation. Results of calculations show that the reconstruction technique works well for peak laser intensities less than 10 13 W/cm 2 . Knowledge of the electric field of the probe pulse is required with shot-to-shot variations of carrier-to-envelope phase and peak intensity of up to 10% and 20%, respectively. The relevance of different one- and two-photon pathways for the reconstruction as a function of peak intensity and pulse duration is analyzed—specifically their role for ultrashort probe pulses with broad bandwidths.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2020

Electronic Population Transfer via Impulsive Stimulated X-Ray Raman Scattering with Attosecond Soft-X-Ray Pulses

Free electron lasers provide a source of X-ray pulses short enough and intense enough to drive nonlinearities in molecular systems. Impulsive interactions driven by these X-ray pulses provide a way to create and probe valence electron motions with high temporal and spatial resolution. Observing these electronic motions is crucial to understand the role of electronic coherence in chemical processes. A simple nonlinear technique for probing electronic motion, impulsive stimulated X-ray Raman scattering (ISXRS), involves a single impulsive interaction to produce a coherent superposition of electronic states. In this work, we demonstrate electronic population transfer via ISXRS using broad bandwidth (5.5 eV full width at half maximum) attosecond X-ray pulses produced by the Linac Coherent Light Source (LCLS). The impulsive excitation is resonantly enhanced by the oxygen 1s → 2π* resonance of nitric oxide (NO), and excited state neutral molecules are probed with a time-delayed UV laser pulse.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2024

Broadband coplanar-waveguide-based impedance-transformed Josephson parametric amplifier

Quantum-limited Josephson parametric amplifiers play a pivotal role in advancing the field of circuit quantum electrodynamics by enabling the fast and high-fidelity measurement of weak microwave signals. Therefore, it is necessary to develop robust parametric amplifiers with low noise, broad bandwidth, and reduced design complexity for microwave detection. However, current broadband parametric amplifiers either have degraded noise performance or rely on complex designs. Here, we present a device based on the broadband impedance-transformed Josephson parametric amplifier that integrates a hornlike coplanar waveguide transmission line, which significantly decreases the design and fabrication complexity while keeping comparable performance. The device shows an instantaneous bandwidth of 700 (200) MHz for 15 (20) dB gain with an average input saturation power of − 110 dBm and near quantum-limited added noise. The operating frequency can be tuned over 1.4 GHz using an external flux bias. We further demonstrate the negligible backaction from our device on a transmon qubit. The amplification performance and simplicity of our device promise its wide adaptation in quantum metrology, quantum communication, and quantum information processing. Published by the American Physical Society 2024

Qing, Bingcheng (ORCID:0000000345227017)↗
DOE OSTI2021

Broadband X-ray ptychography using multi-wavelength algorithm

Ptychography is a rapidly developing scanning microscopy which is able to view the internal structures of samples at a high resolution beyond the illumination size. The achieved spatial resolution is theoretically dose-limited. A broadband source can provide much higher flux compared with a monochromatic source; however, it conflicts with the necessary coherence requirements of this coherent diffraction imaging technique. In this paper, a multi-wavelength reconstruction algorithm has been developed to deal with the broad bandwidth in ptychography. Compared with the latest development of mixed-state reconstruction approach, this multi-wavelength approach is more accurate in the physical model, and also considers the spot size variation as a function of energy due to the chromatic focusing optics. Therefore, this method has been proved in both simulation and experiment to significantly improve the reconstruction when the source bandwidth, illumination size and scan step size increase. It is worth mentioning that the accurate and detailed information of the energy spectrum for the incident beam is not required in advance for the proposed method. Further, we combine multi-wavelength and mixed-state approaches to jointly solve temporal and spatial partial coherence in ptychography so that it can handle various disadvantageous experimental effects. The significant relaxation in coherence requirements by our approaches allows the use of high-flux broadband X-ray sources for high-efficient and high-resolution ptychographic imaging.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Miniaturized integrated spectrometer using a silicon ring-grating design

We introduce and experimentally demonstrate a miniaturized integrated spectrometer operating over a broad bandwidth in the short-wavelength infrared (SWIR) spectrum that combines an add-drop ring resonator narrow band filter with a distributed Bragg reflector (DBR) based broadband filter realized in a silicon photonic platform. The contra-directional coupling DBR filter in this design consists of a pair of waveguide sidewall gratings that act as a broadband filter (i.e., 3.9 nm). The re-directed beam is then fed into the ring resonator which functions as a narrowband filter (i.e., 0.121 nm). In this scheme the free spectral range (FSR) limitation of the ring resonator is overcome by using the DBR as a filter to isolate a single ring resonance line. The overall design of the spectrometer is further simplified by simultaneously tuning both components through the thermo-optic effect. Moreover, several ring-grating spectrometer cells with different central wavelengths can be stacked in cascade in order to cover a broader spectrum bandwidth. This can be done by centering each unit cell on a different center wavelength such that the maximum range of one-unit cell corresponds to the minimum range of the next unit cell. This configuration enables high spectral resolution over a large spectral bandwidth and high extinction ratio (ER), making it suitable for a wide variety of applications.

42 ENGINEERING↗
DOE OSTI2023

Broadband spectral combining of three pulse-shaped fiber amplifiers with 42fs compressed pulse duration

We demonstrate ultra-broadband spectral combining of ultrashort pulses from Yb-doped fiber amplifiers, with coherently spectrally synthesized pulse shaping, to achieve tens-of-fs pulses. This method can fully compensate for gain narrowing and high order dispersion over broad bandwidth. We produce 42fs pulses by spectrally synthesizing three chirped-pulse fiber amplifiers and two programmable pulse shapers across an 80nm overall bandwidth. To the best of our knowledge, this is the shortest pulse duration achieved from a spectrally combined fiber system at one-micron wavelength. This work provides a path toward high-energy, tens-of-fs fiber chirped-pulse amplification systems.

43 PARTICLE ACCELERATORS↗
DOE OSTI2023

Amplification of mid-IR continuum for broadband 2D IR spectroscopy

We report the generation and characterization of microjoule level, broad bandwidth femtosecond pulses in the mid-infrared (MIR) using optical parametric amplification of continuum MIR seed pulses in GaSe. The signal (3 μm) and idler (6 μm) pulses have energies of 6 μJ and 3 μJ with bandwidths of ∼950 cm −1 and 650 cm −1 FWHM and pulse lengths of 34 fs and 80 fs. Broadband 2D IR spectra of O-H and N-H transitions are acquired with the signal beam demonstrating the capabilities of this source for cross peak and line shape measurements.

Optics↗
DOE OSTI2024

Broadband Frequency Conversion of Spectrally Incoherent Pulses and Initial Laser-Plasma Instabilities Mitigation Experiments

There is a need for efficient broadband frequency conversion schemes from the infrared, where optical pulses are efficiently amplified by solid-state laser materials, to the ultraviolet, a wavelength range more suitable for inertial confinement fusion (ICF). The current schemes are inadequate for broadband, spectrally incoherent optical pulses composed of a large number of frequency components distributed over a large frequency range. Implementing novel technologies that generate optical pulses with a large number of spectral components improves the laser-target interaction. In particular, it has long been believed that broad bandwidth mitigates the electron-plasma-wave instabilities that generate suprathermal electrons, which degrade ICF performance by increasing the fuel adiabat and reducing the shell areal density. It is important to develop a platform to demonstrate hot electron suppression caused by the larger available bandwidth, which has not previously been feasible in the laboratory. Experimentally measuring and theoretically assessing these effects with adequately benchmarked simulation codes are paramount to the design and development of novel laser facilities aiming at producing energy via laser fusion. The Laboratory for Laser Energetics is building a new laser facility, the Fourth-generation Laser for Ultrabroadband eXperiments (FLUX), to generate high-energy nanosecond laser pulses with fractional bandwidth larger than 1% in the ultraviolet and perform combined experiments with the 60-beam Omega facility. This large increase in bandwidth from the ~ 0.1% currently available on high-energy laser systems, is achieved by combining amplification in nonlinear optical parametric amplifiers (OPAs) around 1053 nm (1w) with nonlinear frequency conversion to the ultraviolet (around 351 nm, 3w). The novel scheme for frequency conversion is based on the noncollinear sum-frequency generation (SFG) of the angularly dispersed amplified 1w output with a narrowband 2w pulse, which is also used to pump the OPA system. The proposal funded scientific and engineering studies necessary to implement this novel laser facility, accelerated the SFG deployment by funding additional project team resources (shop time, engineers, and technicians), and funded preliminary experiments on the Omega Laser.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Reflective metasurfaces for broadband terahertz linear-to-circular polarization conversion and circular dichroism spectroscopy

Metasurface polarization convertors permit conversion of an input linear polarization to right- or left-handed circular polarization based on the orientation of the input linear polarization, over a broad bandwidth and with high efficiency. The reflected circular polarizations can be used to evaluate samples for circular dichroism. A THz time-domain detection provides a time domain terahertz signal that is Fourier transformed to produce a THz circular dichroism spectrum.

Chen, Hou-Tong↗
DOE OSTI2023

Programmable delay device enabling large delay in small package

A programmable delay device that provides delays of more than 100 ns over a broad bandwidth is disclosed. The device includes an input stage that employs M sampling switched capacitor elements such that each sampling switched capacitor element samples at a rate of only 1/M of the fundamental sampling rate. The device includes a programmable delay stage with M programmable switched capacitor banks, each programmable switched capacitor bank having N delay switched capacitor storage elements. Thus, the programmable delay stage includes a total of M×N delay switched capacitor storage elements, thereby reducing the sampling rate by a factor of M×N. This reduced sampling rate permits much smaller sampling switches, resulting in reduced leakage current and enabling far longer programmable delay times. Lastly, the device includes an output reconstruction stage that reconstructs a delayed version of the input RF signal by combining signals from the programmable delay stage.

Forbes, Travis↗
DOE OSTI2023

Large two-photon cross sections and low-threshold multiphoton lasing of CdS/CdSe/CdS quantum shells

Colloidal quantum shells are spherical semiconductor quantum wells, which have shown strong promise as optical materials, particularly in classes of experiments requiring multiple excitons. The two-photon properties of CdS/CdSe/CdS quantum shell samples are studied here to demonstrate large non-linear absorption cross-sections while retaining advantageous multiexciton physics conferred by the geometrical structure. The quantum shells have large two-phonon cross sections (0.4–7.9 × 10 6 GM), which highlights their potential use in upconversion imaging in which large per particle two-photon absorption is critical. Time-resolved measurements confirmed that the quantum shells have long biexciton lifetime (>10 ns in the largest core samples reported here) and large gain bandwidth (>300 meV). The combination of these attributes with large two-photon cross sections makes the CdS/CdSe/CdS quantum shells excellent gain media for two-photon excitation. With a broad gain bandwidth and long gain lifetime, quantum shell solids support multimodal amplified spontaneous emission from excitons, biexcitons, and higher excited states. In conclusion, thresholds for amplified spontaneous emission and lasing, which are as low as 1 mJ cm −2 , are comparable to, or lower than, the thresholds reported for other colloidal materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Reduced bandwidth Compton photons from a laser-plasma accelerator using tailored plasma channels

It has been demonstrated experimentally that laser plasma accelerators can produce multi-100 MeV electron bunches with a few percent energy spread, and from these electrons, multi-MeV quasi-monoenergetic photons have been demonstrated based on Compton up-scattering from a counter-propagating laser. This offers the potential of a high-quality, narrow-bandwidth, compact, photon source with broad application. The bandwidth of the resulting photons depends directly on the distribution of the electron bunch and is limited, in particular, by the bunch divergence (i.e., the spread in transverse velocity angle). At the same time, the ability to decelerate electrons after scattering is important to source deployment. We describe a series of plasma structures that expand and then collimate the electron bunch, reducing its divergence and thus reducing the bandwidth of the scattered photons while enabling both high performance scattering and deceleration. Furthermore, these plasma structures are demonstrated in simulations of the accelerator system, showing the potential to reach few-percent photon spread which is important for applications using nuclear resonance fluorescence.

42 ENGINEERING↗
DOE OSTI2024

Nonreciprocal Dissipation Engineering via Strong Coupling with a Continuum of Modes

Optical nonreciprocity plays a key role in almost every optical system, directing light flow and protecting optical components from backscattered light. Controllable forms of on-chip nonreciprocity are needed for the robust operation of increasingly sophisticated photonic integrated circuits (PICs) in the context of classical and quantum computation, networking, communications, and sensing. However, it has been challenging to achieve wideband, low-loss optical nonreciprocity on-chip. In this paper, we demonstrate strong coupling and Rabi-like energy exchange between photonic bands, possessing a continuum of modes, to unlock nonreciprocity and frequency translation over wide optical bandwidths in silicon. Using a traveling-wave phonon field to drive indirect interband photonic transitions, we demonstrate band hybridization that enables an intriguing form of nonreciprocal dissipation engineering. Using the converted mode to create a nonreciprocal dissipation channel, we demonstrate a frequency-neutral, low-loss (less than 1 dB) isolator with high nonreciprocal contrast (more than 14 dB) and broad operating bandwidth (more than 59 GHz). Additionally, through the implementation of complete interband conversion, we demonstrate a high extinction (more than 55 dB) optical frequency translation operation with near-unity efficiency.

Zhou, Yishu↗
DOE OSTI2024

Inverse design for waveguide dispersion with a differentiable mode solver

Inverse design of optical components based on adjoint sensitivity analysis has the potential to address the most challenging photonic engineering problems. However, existing inverse design tools based on finite-difference-time-domain (FDTD) models are poorly suited for optimizing waveguide modes for adiabatic transformation or perturbative coupling, which lies at the heart of many important photonic devices. Among these, dispersion engineering of optical waveguides is especially challenging in ultrafast and nonlinear optical applications involving broad optical bandwidths and frequency-dependent anisotropic dielectric material response. In this work, we develop gradient back-propagation through a general-purpose electromagnetic eigenmode solver and use it to demonstrate waveguide dispersion optimization for second harmonic generation with maximized phase-matching bandwidth. This optimization of three design parameters converges in eight steps, reducing the computational cost of optimization by ∼100x compared to exhaustive search and identifying new designs for broadband optical frequency doubling of laser sources in the 1.3–1.4 µm wavelength range. Furthermore, we demonstrate that the computational cost of gradient back-propagation is independent of the number of parameters, as required for optimization of complex geometries. This technique enables practical inverse design for a broad range of previously intractable photonic devices.

Gray, Dodd (ORCID:000000030469599X)↗
DOE OSTI2025

Stacked-mosaic amplifier and diode delivery concept for kJ-class inertial fusion energy laser driver

We report on a laser amplifier architecture designed as a modular element for scaling to multi-megajoule laser facilities intended for inertial fusion energy (IFE) power plants. This kilojoule-class module features a stacked mosaic of gain media integrated with a diode delivery system for efficient optical pumping of the mosaic-structured gain medium, enabling high-repetition-rate operation at high wall plug efficiencies, necessary for an IFE driver. Details of a diode delivery system capable of pumping the mosaic architecture are presented. Comprehensive numerical modeling demonstrates that the stacked-mosaic approach reduces transverse gain by five orders of magnitude compared to a conventional full-aperture Yb:YAG based amplifier, substantially suppressing transverse amplified spontaneous emission (TASE) and enabling enhanced longitudinal energy extraction. Detailed analysis of thermal management and wavefront distortion in a 4 × 4 mosaic array indicates that temperature gradients and thermally induced aberrations are effectively controlled using gas cooling and commercially available phase-plate and deformable mirror technologies. We further discuss the applicability of a stacked-mosaic architecture to direct-drive IFE schemes, where broad spectral bandwidth is critical, and its compatibility with frequency conversion modules for up-conversion to blue wavelengths. Finally, an example point design for a 10 kJ, 10 Hz Yb:YAG module operating at 175 K with wall-plug efficiency exceeding 10 % is presented, underscoring the feasibility of this approach for next-generation high-energy lasers for IFE drivers. The results establish the stacked-mosaic amplifier as a scalable, robust platform not only for IFE but also for a broad range of advanced scientific and industrial laser applications.

Lasers↗
DOE OSTI2023

Long-Lived and Bright Biexcitons in Quantum Dots with Parabolic Band Potentials

Multiple exciton physics in semiconductor nanocrystals play an important role in optoelectronic devices. Here, this work investigates radially alloyed CdZnSe/CdS nanocrystals with suppressed Auger recombination due to the spatial separation of carriers, which also underpins their performance in optical gain and scintillation experiments. Due to suppressed Auger recombination, the biexciton lifetime is greater than 10 ns, much longer than most nanocrystals. The samples show optical gain, amplified spontaneous emission, and lasing at thresholds <2 excitons per particle. They also show broad gain bandwidth (>500 meV) encompassing 4 amplified spontaneous emission bands. Similarly enabled by slowed multiple exciton relaxation, the samples display strong performance in scintillating films under X-ray illumination. The CdZnSe/CdS samples have fast radioluminescence rise (<80 ps) and decay times (<5 ns), light yields up to 6700 photonsMeV -1 , and the demonstrated capacity for incorporation into large area films for scintillation imaging.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗