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DOE OSTI2023

The 2023 terahertz science and technology roadmap

Abstract Terahertz (THz) radiation encompasses a wide spectral range within the electromagnetic spectrum that extends from microwaves to the far infrared (100 GHz–∼30 THz). Within its frequency boundaries exist a broad variety of scientific disciplines that have presented, and continue to present, technical challenges to researchers. During the past 50 years, for instance, the demands of the scientific community have substantially evolved and with a need for advanced instrumentation to support radio astronomy, Earth observation, weather forecasting, security imaging, telecommunications, non-destructive device testing and much more. Furthermore, applications have required an emergence of technology from the laboratory environment to production-scale supply and in-the-field deployments ranging from harsh ground-based locations to deep space. In addressing these requirements, the research and development community has advanced related technology and bridged the transition between electronics and photonics that high frequency operation demands. The multidisciplinary nature of THz work was our stimulus for creating the 2017 THz Science and Technology Roadmap (Dhillon et al 2017 J. Phys. D: Appl. Phys. 50 043001). As one might envisage, though, there remains much to explore both scientifically and technically and the field has continued to develop and expand rapidly. It is timely, therefore, to revise our previous roadmap and in this 2023 version we both provide an update on key developments in established technical areas that have important scientific and public benefit, and highlight new and emerging areas that show particular promise. The developments that we describe thus span from fundamental scientific research, such as THz astronomy and the emergent area of THz quantum optics, to highly applied and commercially and societally impactful subjects that include 6G THz communications, medical imaging, and climate monitoring and prediction. Our Roadmap vision draws upon the expertise and perspective of multiple international specialists that together provide an overview of past developments and the likely challenges facing the field of THz science and technology in future decades. The document is written in a form that is accessible to policy makers who wish to gain an overview of the current state of the THz art, and for the non-specialist and curious who wish to understand available technology and challenges. A such, our experts deliver a ‘snapshot’ introduction to the current status of the field and provide suggestions for exciting future technical development directions. Ultimately, we intend the Roadmap to portray the advantages and benefits of the THz domain and to stimulate further exploration of the field in support of scientific research and commercial realisation.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2025

Measuring σ 8 using DESI Legacy Imaging Surveys Emission-Line galaxies and Planck CMB lensing, and the impact of dust on parameter inference

Measuring the growth of structure is a powerful probe for studying the dark sector, especially in light of the σ 8 tension between primary CMB anisotropy and low-redshift surveys. This paper provides a new measurement of the amplitude of the matter power spectrum, σ 8 , using galaxy-galaxy and galaxy-CMB lensing power spectra of Dark Energy Spectroscopic Instrument Legacy Imaging Surveys Emission-Line Galaxies and the Planck 2018 CMB lensing map. We create an ELG catalog composed of 24 million galaxies and with a purity of 85%, covering a redshift range 0 < z < 3, with z mean = 1.09. We implement several novel systematic corrections, such as jointly modeling the contribution of imaging systematics and photometric redshift uncertainties to the covariance matrix. We also study the impacts of various dust maps on cosmological parameter inference. We measure the cross-power spectra over f sky = 0.25 with a signal-to-background ratio of up to 30σ. We find that the choice of dust maps to account for imaging systematics in estimating the ELG overdensity field has a significant impact on the final estimated values of σ 8 and Ω M , with far-infrared emission-based dust maps preferring σ 8 to be as low as 0.702 ± 0.030, and stellar-reddening-based dust maps preferring as high as 0.719 ± 0.030. The highest preferred value is at ∼ 3 σ tension with the Planck primary anisotropy results. These findings indicate a need for tomographic analyses at high redshifts and joint modeling of systematics.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2022

A poloidal high- k scattering system for NSTX-U

A previous 5-channel tangential high-k scattering system is being replaced by an 8-channel, poloidal high-k scattering system on the National Spherical Torus eXperiment Upgrade (NSTX-U) device located in Princeton, NJ, USA. The 693 GHz poloidal scattering system replaces a 280 GHz tangential scattering system to study high-k electron density fluctuations on NSTX-U, thereby considerably enhancing planned turbulence physics studies by providing a measurement of the k θ -spectrum of both electron temperature gradient (ETG) and ion temperature gradient (ITG) modes. Two approaches to generating the 693 GHz probe beam are under development: an optically-pumped far-infrared (FIR) laser that generates ~50 mW, and a compact gyrotron that can potentially generate in excess of 5 W. Large aperture optics collect radiation scattered from density fluctuations in the plasma core at 8 simultaneous scattering angles ranging from 2 to 15° corresponding to poloidal wavenumbers that extend to >40 cm -1 . Finally, steerable launch optics coupled with receiver optics mounted on a 5-axis receiver carriage allow the scattering volume to be placed radially from r/a = 0.3 out to the pedestal region (r/a ~ 0.99) and translated horizontally as needed to satisfy wavenumber matching.

47 OTHER INSTRUMENTATION↗

DOE OSTI2020

Extended He ii 4686 emission in Markarian 387

ABSTRACT In order to explore the effect of an active galactic nucleus (AGN) on the interstellar medium of its host galaxy, we selected a promising case for study, Markarian 387 (Mrk 387), based on the strength of its extended He ii 4686 emission, a high-ionization line that can be excited by a hard source of radiation. We use area-resolved spectroscopy from the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey and the availability of additional multiwavelength data. Besides harbouring an obscured AGN and the extended He ii 4686 emission, Mrk 387 has a number of other unusual properties, including a high far-infrared luminosity, a low neutral hydrogen mass compared to the stellar mass, a high Hα luminosity and high Hα equivalent width throughout the disc, and strong He i 5876 in the exterior regions. He ii 4686 and [O iii] 5008 extend with a bilateral morphology beyond 6 kpc from the nucleus. We interpret this emission as due to photoionization from the central source, where the interstellar medium must be sufficiently porous to allow the ionizing flux to reach these relatively distant regions.

Wang, QiQi↗

DOE OSTI2021

The radio loudness of SDSS quasars from the LOFAR Two-metre Sky Survey: ubiquitous jet activity and constraints on star formation

ABSTRACT We examine the distribution of radio emission from ∼42 000 quasars from the Sloan Digital Sky Survey, as measured in the LOFAR Two-metre Sky Survey (LoTSS). We present a model of the radio luminosity distribution of the quasars that assumes that every quasar displays a superposition of two sources of radio emission: active galactic nuclei (jets) and star formation. Our two-component model provides an excellent match to the observed radio flux density distributions across a wide range of redshifts and quasar optical luminosities; this suggests that the jet-launching mechanism operates in all quasars but with different powering efficiency. The wide distribution of jet powers allows for a smooth transition between the ‘radio-quiet’ and ‘radio-loud’ quasar regimes, without need for any explicit bimodality. The best-fitting model parameters indicate that the star formation rate of quasar host galaxies correlates strongly with quasar luminosity and also increases with redshift at least out to z ∼ 2. For a model where star formation rate scales as $L_{\rm bol}^{\alpha } (1+z)^{\beta }$, we find α = 0.47 ± 0.01 and β = 1.61 ± 0.05, in agreement with far-infrared studies. Quasars contribute ≈0.15 per cent of the cosmic star formation rate density at z = 0.5, rising to 0.4 per cent by z ∼ 2. The typical radio jet power is seen to increase with both increasing optical luminosity and black hole mass independently, but does not vary with redshift, suggesting intrinsic properties govern the production of the radio jets. We discuss the implications of these results for the triggering of quasar activity and the launching of jets.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2022

The distribution of dust in edge-on galaxies: I. The global structure

ABSTRACT In this first paper in a series we present a study of the global dust emission distribution in nearby edge-on spiral galaxies. Our sample consists of 16 angularly large and 13 less spatially resolved galaxies selected from the DustPedia sample. To explore the dust emission distribution, we exploit the Herschel photometry in the range 100–500 $\mu $m. We employ Sérsic and 3D disc models to fit the observed 2D profiles of the galaxies. Both approaches give similar results. Our analysis unequivocally states the case for the presence of extraplanar dust in between 6 and 10 large galaxies. The results reveal that both the disc scale length and height increase as a function of wavelength between 100 and 500 $\mu $m. The dust disc scale height positively correlates with the dust disc scale length, similar to what is observed for the stellar discs. We also find correlations between the scale lengths and scale heights in the near- and far-infrared which suggest that the stellar discs and their dust counterparts are tightly connected. Furthermore, the intrinsic flattening of the dust disc is inversely proportional to the maximum rotation velocity and the dust mass of the galaxy: more massive spiral galaxies host, on average, relatively thinner dust discs. Also, there is a tendency for the dust-to-stellar scale height ratio to decrease with the dust mass and rotation velocity. We conclude that low-mass spiral galaxies host a diffuse, puffed-up dust disc with a thickness similar to that of the stellar disc.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2022

Actinide opacities for modelling the spectra and light curves of kilonovae

ABSTRACT We extend previous ab initio calculations of lanthanide opacities to include a complete set of actinide opacities for use in the modelling of kilonova (KN) light curves and spectra. Detailed, fine-structure line features are generated using the configuration-interaction approach. These actinide opacities display similar trends to those observed for lanthanide opacities, such as the lighter actinides producing higher opacity than the heavier ones for relevant conditions in the dynamical ejecta. A line-binned treatment is employed to pre-compute opacity tables for 14 actinide elements (89 ≤ Z ≤ 102) over a grid of relevant temperatures and densities. These tabular opacities will be made publicly available for general usage in KN modelling. We demonstrate the usefulness of these opacities in KN simulations by exploring the sensitivity of light curves and spectra to different actinide abundance distributions that are predicted by different nuclear theories, as well as to different choices of ejecta mass and velocity. We find very little sensitivity to the two considered distributions, indicating that opacities for actinides with Z ≥ 99 do not contribute strongly. On the other hand, a single actinide element, protactinium, is found to produce faint spectral features in the far-infrared at late times (5–7 d post merger). More generally, we find that the choice of ejecta mass and velocity have the most significant effect on KN emission for this study.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2024

Superconducting quasiparticle-amplifying transmon: A qubit-based sensor for meV-scale phonons and single terahertz photons

With great interest from the quantum computing community, an immense amount of R&D effort has been invested into improving superconducting qubits. The technologies developed for the design and fabrication of these qubits can be directly applied to applications for ultralow-threshold particle detectors, e.g., low-mass dark matter and far-infrared photon sensing. We propose a novel energy-resolving sensor based on the transmon qubit architecture combined with a signal-enhancing superconducting quasiparticle amplification stage. We refer to these sensors as SQUATs: superconducting quasiparticle-amplifying transmons. We detail the operating principle and design of this new sensor and predict that, with minimal R&D effort, solid-state-based detectors patterned with these sensors can achieve sensitivity to single terahertz photons, and sensitivity to 1 meV phonons in the detector absorber substrate on the microsecond timescale. Published by the American Physical Society 2024

47 OTHER INSTRUMENTATION↗

DOE OSTI2023

Kerr, Faraday, and magnetoelectric effects in MnBi 2 Te 4 thin films

The topological magnetoelectric effect (TME) is a characteristic property of topological insulators. In this paper, we use a simplified coupled-Dirac-cone electronic structure model to theoretically evaluate the THz and far infrared Kerr and Faraday responses of thin films of MnBi 2 ⁢Te 4 with up to N = 10 septuple layers with the goal of clarifying the relationship between these convenient magnetooptical observables and the TME. Here we find that for even N, the linear Kerr and Faraday responses to an electric field vanish in the low-frequency limit, even though the magnetoelectric response is large and approximately quantized.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2025

Second harmonic generation in topological insulators under quantizing magnetic fields

We theoretically investigate the second harmonic generation (SHG) of topological insulator surface states in a perpendicular magnetic field. Our theory is based on the microscopic expression of the second-order magneto-optical conductivity developed from the density matrix formalism, taking into account hexagonal warping effects on the surface states' band structure. Using numerically exact Landau-level energies and wave functions including hexagonal warping, we calculate the spectrum of SHG conductivities under normal incidence for different values of magnetic field and chemical potential. The imaginary parts of the SHG conductivities show prominent resonant peaks corresponding to one-photon and two-photon inter-Landau-level transitions. Treating the hexagonal warping term perturbatively, these transitions are clarified analytically within a perturbation theory from which approximate selection rules for the allowable optical transitions for SHG are determined. Furthermore, our results show extremely high SHG susceptibility that is easily tunable by magnetic field and doping level for topological surface states in the far-infrared regime, exceeding that of many conventional nonlinear materials. This work highlights the key role of hexagonal warping effects in generating second-order optical responses and provides insights into the nonlinear magneto-optical properties of the topological insulators.

Landau levels↗

DOE OSTI2021

Development of FD-SOI cryogenic amplifier for application to STJ readout in COBAND project

The COBAND is a project of an experimental search for the cosmic background neutrino decay [1] – [9] . The existence of the cosmic background neutrino is predicted as a relic of the big bang in the theoretical cosmology. Since the neutrino is found to have mass generations and mixing between them, a heavier neutrino is possible to decay to a lighter neutrino with a far-infrared photon, even though its lifetime is expected to be much longer than the age of the universe [10] . However, neither the cosmic background neutrino nor the neutrino decay is yet established experimentally. Only a lower limit in the order of 10 12 years is given on the heaviest neutrino lifetime. We, thus, search for photons which come from the cosmic background neutrino decays. The photons from the cosmic background neutrino decays are expected to shape a spectrum of a unique signature with a sharp edge at a wavelength of around 50μm depending on the heaviest neutrino mass. To identify the signature against the overwhelming zodiacal emission foreground as well as the cosmic infrared background, the photodetectors are required to have an ability to measure the FIR spectrum around 50pm with sufficient precision. Thus, we aim at developing a photodetector with capability of FIR photon-by-photon spectrometry. We employ superconducting tunnel junction (STJ) sensors in combination with cryogenic amplifiers for signal readout to maximize the potential of STJ.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2021

Toroidal polar topology in strained ferroelectric polymer

Polar topological texture has become an emerging research field for exotic phenomena and potential applications in reconfigurable electronic devices. Here, we report toroidal topological texture self-organized in a ferroelectric polymer, poly(vinylidene fluoride-ran-trifluoroethylene) [P(VDF-TrFE)], that exhibits concentric topology with anticoupled chiral domains. The interplay among the elastic, electric, and gradient energies results in continuous rotation and toroidal assembly of the polarization perpendicular to polymer chains, whereas relaxor behavior is induced along polymer chains. Such toroidal polar topology gives rise to periodic absorption of polarized far-infrared (FIR) waves, enabling the manipulation of the terahertz wave on a mesoscopic scale. Our observations should inform design principles for flexible ferroic materials toward complex topologies and provide opportunities for multistimuli conversions in flexible electronics.

36 MATERIALS SCIENCE↗

DOE OSTI2023

Moiré photonics and optoelectronics

Moiré superlattices, the artificial quantum materials, have provided a wide range of possibilities for the exploration of completely new physics and device architectures. In this Review, we focus on the recent progress on emerging moiré photonics and optoelectronics, including but not limited to moiré excitons, trions, and polaritons; resonantly hybridized excitons; reconstructed collective excitations; strong mid- and far-infrared photoresponses; terahertz single-photon detection; and symmetry-breaking optoelectronics. We also discuss the future opportunities and research directions in this field, such as developing advanced techniques to probe the emergent photonics and optoelectronics in an individual moiré supercell; exploring new ferroelectric, magnetic, and multiferroic moiré systems; and using external degrees of freedom to engineer moiré properties for exciting physics and potential technological innovations.

Science & Technology - Other Topics↗

DOE OSTI2020

Ground-State In-Plane Light-Holes in GaAs/AlGaAs Structures [Book Chapter]

We have performed low-temperature magnetoluminescence, far-infrared cyclotron resonance, and magneto-transport measurements on narrow (4.5 nm) GaAs/Al 0.25 Ga 0.75 As single quantum-wells. The ground state in-plane valence band was found to be light and very nonparabolic, i.e., at zone center, the valence band mass is m v ≈ 0. 1 and for E f ≈ 10 meV, m v ≈ 0.25.

36 MATERIALS SCIENCE↗

DOE OSTI2022

Deep Learning and Natural Language Processing for Accelerated Inverse Design of Optical Metamaterials

Optical metamaterial device design has enjoyed a long track of success over the past 50 years leading to the manipulation of light over a wide range of wavelengths spanning the ultraviolet to the far infrared. The manipulation of light over such wavelengths has already led to many technological advancements such as the design of selective radiative absorbers for solar energy, daytime passive cooling using deep space, and optical invisibility cloaks for defense applications. Further disruptive advancements in energy, defense, computing, and biomedical fields could be enabled or enhanced by future optical metamaterial devices. These technologies could lead to increased energy efficiency and hence reduced national primary energy consumption, cheap long duration energy storage, and next generation solid-state heat engines. But historically the methods to invent and develop all of these devices have been time- consuming and based mostly on intuition and iteration. Finding an optimal design can take years.

36 MATERIALS SCIENCE↗

DOE OSTI2022

Deep Learning and Natural Language Processing for Accelerated Inverse Design of Optical Metamaterials

36 MATERIALS SCIENCE↗

DOE OSTI2024

Unique optical excitations in topological insulators (Final Technical Report)

The overall objective of this research is to understand how light interacts with topological insulator (TI) films and layered structures. Unlike normal materials, the electrons in TI films are trapped at the top and bottom surfaces of the film. These electrons have unusual properties, including low mass and high velocity. Light shining on these trapped electrons will excite electron density waves, called plasmons, which inherit the unusual properties of the electrons. This project aims to understand how these plasmons interact with each other and how the plasmon properties change as the film dimensions change. By controlling the physical properties of the films, the optical response of the film can also be controlled. In addition to single TI films, the project will also investigate the properties of stacks of TI films layered with normal insulating films. Stacking these materials results in multiple layers of trapped electrons whose plasmons can interact in ever more complex ways. After these interactions are understood, we can begin to engineer complex TI structures to obtain designer optical phenomena in the far-infrared and THz, wavelength ranges of interest for environmental monitoring and chemical sensing. This research directly addresses DOE Grand Challenges, including understanding how properties of matter emerge from complex electronic correlations and learning how to control these properties as well as the mission of the Basic Energy Sciences program to understand and control matter at the electronic/atomic level.

36 MATERIALS SCIENCE↗

DOE OSTI2023

Phonon Anharmonicity and Spin–Phonon Coupling in CrI 3

We report on the far-infrared, temperature-dependent optical properties of a CrI 3 transition metal halide single crystal, a van der Waals ferromagnet (FM) with a Curie temperature of 61 K. In addition to the expected phonon modes determined by the crystalline symmetry, the optical reflectance and transmittance spectra of CrI 3 single crystals show many other excitations as a function of temperature as a consequence of the combination of a strong lattice anharmonicity and spin–phonon coupling. This complex vibrational spectrum highlights the presence of entangled interactions among the different degrees of freedom in CrI 3 .

36 MATERIALS SCIENCE↗