arXiv subjects

L. Hao

Publications and source records attributed to L. Hao.

At least 19 recordsLinked to original sources

arXiv2026

Laser-intensity-spike-dominated hot electron generation from two-plasmon decay instability driven by moderate-bandwidth pulses

Our direct-drive-relevant experiments on the low-coherence Kunwu laser facility identify two-plasmon decay (TPD) as the primary source of hot electrons, and demonstrate for the first time that broadband laser pulses enhance TPD. Using particle-in-cell simulations, we attribute this TPD enhancement and the consequent hot electron production to stochastic intensity spikes inherent in broadband laser fields, robust in both weakly- and strongly-driven regimes. These findings suggest that mitigating hot electron generation requires suppressing these intensity spikes.

physics.plasm-ph↗

arXiv2025

Resonance density range of absolute two-plasmon decay instability

We present a new insight into absolute two-plasmon decay (TPD) instability in nonuniform plasmas by identifying the resonance density range as the key parameter governing the growth of the resonant absolute modes. This range is defined as the density interval within which these resonant modes still exhibit growth in homogeneous plasmas. This range properly characterizes the spatial growth region of the resonant absolute modes in a series of linear fluid simulations across broad parameter spaces. Building on this insight, we investigate the absolute growth of TPD modes driven by laser pulses with intensity modulations, a common feature in broadband lasers used to suppress laser plasma instabilities. We establish the relationship between the resonance density range and the threshold time interval between intensity peaks, beyond which absolute growth is suppressed.

physics.plasm-ph↗

arXiv2025

Resonance density range governs two-plasmon decay saturation and enables hot-electron prediction in inertial confinement fusion

The saturation level of parametric instabilities critically determines their impact on fusion plasmas. We identify the resonance density range of two-plasmon decay as the critical parameter governing nonlinear saturation of ion density fluctuations and Langmuir waves, which drive hot-electron generation. Using this insight, we develop a predictive scaling model for the hot-electron energy fraction f_{hot} that depends only on the laser intensity I, with plasma conditions encoded via plasma ablation theory. The model can work for various experimental configurations-requiring only two (I, f_{hot}) data points to calibrate coefficients-and successfully reproduces results from prior OMEGA and OMEGA-EP experiments.

physics.plasm-ph↗

arXiv2025

QSHS: An Axion Dark Matter Resonant Search Apparatus

We describe a resonant cavity search apparatus for axion dark matter constructed by the Quantum Sensors for the Hidden Sector (QSHS) collaboration. The apparatus is configured to search for QCD axion dark matter, though also has the capability to detect axion-like particles (ALPs), dark photons, and some other forms of wave-like dark matter. Initially, a tuneable cylindrical oxygen-free copper cavity is read out using a low noise microwave amplifier feeding a heterodyne receiver. The cavity is housed in a dilution refrigerator and threaded by a solenoidal magnetic field, nominally 8T. The apparatus also houses a magnetic field shield for housing superconducting electronics, and several other fixed-frequency resonators for use in testing and commissioning various prototype quantum electronic devices sensitive at a range of axion masses in the range 2.0 to 40 micro-eV/c2. The apparatus as currently configured is intended as a test stand for electronics over the relatively wide frequency band attainable with the TM010 cavity mode used for axion searches. We present performance data for the resonator, dilution refrigerator, and magnet, and plans for the first science run.

physics.ins-det↗

arXiv2024

Determining Absolute Neutrino Mass using Quantum Technologies

Next generation tritium decay experiments to determine the absolute neutrino mass require high-precision measurements of $\beta$-decay electron energies close to the kinematic end point. To achieve this, the development of high phase-space density sources of atomic tritium is required, along with the implementation of methods to control the motion of these atoms to allow extended observation times. A promising approach to efficiently and accurately measure the kinetic energies of individual $\beta$-decay electrons generated in these dilute atomic gases, is to determine the frequency of the cyclotron radiation they emit in a precisely characterised magnetic field. This cyclotron radiation emission spectroscopy technique can benefit from recent developments in quantum technologies. Absolute static-field magnetometry and electrometry, which is essential for the precise determination of the electron kinetic energies from the frequency of their emitted cyclotron radiation, can be performed using atoms in superpositions of circular Rydberg states. Quantum-limited microwave amplifiers will allow precise cyclotron frequency measurements to be made with maximal signal-to-noise ratios and minimal observation times. Exploiting the opportunities offered by quantum technologies in these key areas, represents the core activity of the Quantum Technologies for Neutrino Mass project. Its goal is to develop a new experimental apparatus that can enable a determination of the absolute neutrino mass with a sensitivity on the order of 10~meV/$c^2$.

hep-ex↗

arXiv2024

Efficient generation of divergent and collimated hot electrons via a novel multi-beam two-plasmon decay and stimulated Raman scattering mechanism

In inertial confinement fusion (ICF) implosions, the preheating risks associated with hot electrons generated by laser plasma instabilities (LPI) are contingent upon the angular characteristics of these hot electrons for a given total energy. Using particle-in-cell simulations, we reveal a novel multi-beam collaborative mechanism of two-plasmon decay (TPD) and stimulated Raman scattering (SRS), and investigate the angular variations of hot electrons generated from this shared TPD-SRS (STS) instability driven collectively by dual laser beams with varying incident angles $\theta_{in}$ ($24^\circ$ to $55^\circ$ at the incident plane) for typical ICF conditions. In the simulations with $\theta_{in}\gtrsim44^\circ$, STS emerges as the dominant mechanism responsible for hot electron generation, leading to a wide angular distribution of hot electrons that exhibit both pronounced divergent and collimated components. The common Langmuir wave associated with STS plays a crucial role in accelerating both components.By properly modeling the STS common wave gains, we establish scaling relations between these gains and the energies of collimated and divergent hot electrons. These relations reveal that the divergent hot electrons are more sensitive to variations in gain compared to the collimated electrons. Additionally, the calculated gains qualitatively predict the asymmetry in hot electron angular distributions when the density gradients deviate from the bisector of the laser beams. Our findings offers insights for hot electron generation with multiple beams, potentially complementing previous experiments that underscore the critical role of overlapped intensity from symmetric beams within the same cone and the dominance of dual-beam coupling.

physics.plasm-ph↗

arXiv2023

Anomalous hot electron generation from two-plasmon decay instability driven by broadband laser pulses with intensity modulations

We investigate the hot electrons generated from two-plasmon decay (TPD) instability driven by laser pulses with intensity modulated by a frequency $Δω_m$. Our primary focus lies on scenarios where $Δω_m$ is on the same order of the TPD growth rate $ γ_0$ ( $Δω_m \sim γ_0$), corresponding to moderate laser frequency bandwidths for TPD mitigation. With $Δω_m$ conveniently modeled by a basic two-color scheme of the laser wave fields in fully-kinetic particle-in-cell simulations, we demonstrate that the energies of TPD modes and hot electrons exhibit intermittent evolution at the frequency $Δω_m$, particularly when $Δω_m \sim γ_0$. With the dynamic TPD behavior, the overall ratio of hot electron energy to the incident laser energy, $f_{hot}$, changes significantly with $Δω_m$. While $f_{hot}$ drops notably with increasing $Δω_m$ at large $Δω_m$ limit as expected, it goes anomalously beyond the hot electron energy ratio for a single-frequency incident laser pulse with the same average intensity when $Δω_m$ falls below a specific threshold frequency $Δω_c$. We find this threshold frequency primarily depends on $γ_0$ and the collisional damping rate of plasma waves, with relatively lower sensitivity to the density scale length. We develop a scaling model characterizing the relation of $Δω_c$ and laser plasma conditions, enabling the potential extention of our findings to more complex and realistic scenarios.

physics.plasm-ph↗

arXiv2022

Evidence for mechanical softening-hardening dual anomaly in transition metals from shock compressed vanadium

Solid usually becomes harder and tougher under compression, and turns softer at elevated temperature. Recently, compression-induced softening and heating-induced hardening (CISHIH) dual anomaly was predicted in group VB elements such as vanadium. Here, the evidence for this counterintuitive phenomenon is reported. By using accurate high-temperature high-pressure sound velocities measured at Hugoniot states generated by shock-waves, together with first-principles calculations, we observe not only the prominent compression-induced sound velocity reduction, but also strong heating-induced sound velocity enhancement, in shocked vanadium. The former corresponds to the softening in shear modulus by compression, whereas the latter reflects the reverse hardening by heat. These experiments also unveil another anomaly in Young's modulus that wasn't reported before. Based on the experimental and theoretical data, we infer that vanadium might transition from BCC into two different rhombohedral (RH1 and RH2) phases at about 79GPa and 116GPa along the Hugoniot, respectively, which implies a dramatic difference in static and dynamic loading, as well as the significance of deviatoric stress and rate-relevant effects in high-pressure phase transition dynamics.

cond-mat.mtrl-sci↗

arXiv2021

Anomalous Magnetoresistance by Breaking Ice Rule in Bi2Ir2O7/Dy2Ti2O7 Heterostructure

While geometrically frustrated quantum magnets are known for a variety of exotic spin states that are of great interests of understanding emergent phenomena as well as enabling revolutionary quantum technologies, most of them are necessarily good insulators which are difficult to be integrated with modern electrical circuit that relies on moving charge carriers. The grand challenge of converting fluctuations and excitations of frustrated moments into electronic responses is finding ways to introduce charge carriers that interact with the localized spins without destroying the spin states. Here, we show that, by designing a Bi2Ir2O7/Dy2Ti2O7 heterostructure, the breaking of the spin ice rule in insulating Dy2Ti2O7 can lead to a charge response in the Bi2Ir2O7 conducting layer that can be detected as anomalous magnetoresistance. These results demonstrate a novel and feasible interfacial approach for electronically probing exotic spin states in insulating magnets, laying out a blueprint for the metallization of frustrated quantum magnets.

cond-mat.str-el↗

arXiv2020

Comprehensive Control of Metamagnetic Transition of Antiferromagnetic Mott Insulator Sr2IrO4 by in-situ Anisotropic Strain

Metamagnetism in antiferromagnets exhibits distinct critical behaviors and dynamics when invoking spin reversal and rotation. Here we show a 0.05% anisotropic strain suffices to in-situ modulate the metamagnetic critical field of the Mott insulator Sr2IrO4 by over 50%, enabling electrical switching of the transition. Resonant x-ray scattering and model simulation reveal that the transition is completely tuned from the spin-flop to spin-flip type as the strain introduces C4-symmetry-breaking magnetic anisotropy. Simultaneous transport study indicates the metamagnetic responses are reflected in the large elasto- and magnetoconductance, highlighting the active charge degree of freedom in the spin-orbit-coupled Mott state and its potential for spin-electronics.

cond-mat.str-el↗

arXiv2019

Growth rate and gain of stimulated Brillouin scattering considering nonlinear Landau damping due to particle trapping

Growth rate and gain of SBS considering the reduced Landau damping due to particle trapping has been proposed to predict the growth and average level of SBS reflectivity. Due to particle trapping, the reduced Landau damping has been taken used of to calculate the gain of SBS, which will make the simulation data of SBS average reflectivity be consistent to the Tang model better. This work will solve the pending questions in laser-plasma interaction and have wide applications in parametric instabilities.

physics.plasm-ph↗

arXiv2018

Enhancing the H2O Megamaser Detection Rate Using Optical and Mid-infrared Photometry

Water megamasers from circumnuclear disks in galaxy centers provide the most accurate measurements of supermassive black hole masses and uniquely probe the sub-parsec accretion processes. At the same time, these systems offer independent crucial constraints of the Hubble Constant in the nearby universe, and thus, the arguably best single constraint on the nature of dark energy. The chances of finding these golden standards are however abysmally low, at an overall =< 3% for any level of water maser emission detected at 22 GHz, and =< 1% for those exhibiting the disk-like configuration. We provide here a thorough summary of the current state of the detection of water megamaser disks, along with a novel investigation of the likelihood of increasing their detection rates based on a multivariate parameter analysis of optical and mid-infrared photometric properties of the largest database of galaxies surveyed for the 22 GHz emission. We find that galaxies with water megamaser emission tend to associate with strong emission in all WISE mid-infrared wavelengths, with the strongest enhancement in the W4 band, at 22 micron, as well as with previously proposed and newly found indicators of AGN strength in the mid-infrared, such as red W1-W2 and W1-W4 colors, and the integrated mid-infrared luminosity of the host galaxy. These trends offer a potential boost of the megamaser detection rates to 6 - 15%, or a factor of 2-8 relative to the current rates, depending on the chosen sample selection criteria, while fostering real chances for discovering >= 20 new megamaser disks.

astro-ph.GA↗

arXiv2018

Spatially resolved star formation and dust attenuation in Mrk848: Comparison of the integral field spectra and the UV-to-IR SED

We investigate the star formation history and the dust attenuation in the galaxy merger Mrk848. Thanks to the multiwavelength photometry from the ultraviolet (UV) to the infrared (IR), and MaNGA's integral field spectroscopy, we are able to study this merger in a detailed way. We divide the whole merger into the core and tail regions, and fit both the optical spectrum and the multi-band spectral energy distribution (SED) to models to obtain the star formation properties for each region respectively. We find that the color excess of stars in the galaxy $E(B-V)_s^{SED}$ measured with the multi-band SED fitting is consistent with that estimated both from the infrared excess (the ratio of IR to UV flux) and from the slope of the UV continuum. Furthermore, the reliability of the $E(B-V)_s^{SED}$ is examined with a set of mock SEDs, showing that the dust attenuation of the stars can be well constrained by the UV-to-IR broadband SED fitting. The dust attenuation obtained from optical continuum $E(B-V)_s^{spec}$ is only about half of $E(B-V)_s^{SED}$. The ratio of the $E(B-V)_s^{spec}$ to the $E(B-V)_g$ obtained from the Balmer decrement is consistent with the local value (around 0.5). The difference between the results from the UV-to-IR data and the optical data is consistent with the picture that younger stellar populations are attenuated by an extra dust component from the birth clouds compared to older stellar populations which are only attenuated by the diffuse dust. Both with the UV-to-IR SED fitting and the spectral fitting, we find that there is a starburst younger than 100~Myr in one of the two core regions, consistent with the scenario that the interaction-induced gas inflow can enhance the star formation in the center of galaxies.

astro-ph.GA↗

arXiv2017

Two-dimensional ${J}_{\rm eff}$ = 1/2 antiferromagnetic insulator unraveled from interlayer exchange coupling in artificial perovskite iridate superlattices

We report an experimental investigation of the two-dimensional ${J}_{\rm eff}$ = 1/2 antiferromagnetic Mott insulator by varying the interlayer exchange coupling in [(SrIrO$_3$)$_1$, (SrTiO$_3$)$_m$] ($m$ = 1, 2 and 3) superlattices. Although all samples exhibited an insulating ground state with long-range magnetic order, temperature-dependent resistivity measurements showed a stronger insulating behavior in the $m$ = 2 and $m$ = 3 samples than the $m$ = 1 sample which displayed a clear kink at the magnetic transition. This difference indicates that the blocking effect of the excessive SrTiO$_3$ layer enhances the effective electron-electron correlation and strengthens the Mott phase. The significant reduction of the Neel temperature from 150 K for $m$ = 1 to 40 K for $m$ = 2 demonstrates that the long-range order stability in the former is boosted by a substantial interlayer exchange coupling. Resonant x-ray magnetic scattering revealed that the interlayer exchange coupling has a switchable sign, depending on the SrTiO$_3$ layer number $m$, for maintaining canting-induced weak ferromagnetism. The nearly unaltered transition temperature between the $m$ = 2 and the $m$ = 3 demonstrated that we have realized a two-dimensional antiferromagnet at finite temperatures with diminishing interlayer exchange coupling.

cond-mat.str-el↗

arXiv2017

Nonlinear Fluid Simulation Study of Stimulated Raman and Brillouin Scatterings in Shock Ignition

We developed a new nonlinear fluid laser-plasma-instability code (FLAME) using a multi-fluid plasma model combined with full electromagnetic wave equations. The completed one-dimensional (1D) version of FLAME was used to study laser-plasma instabilities in shock ignition. The simulations results showed that absolute SRS modes growing near the quarter-critical surface were saturated by Langmuir-wave Decay Instabilities (LDI) and pump depletion. The ion-acoustic waves from LDI acted as seeds of stimulated Brillouin Scattering (SBS), which displayed a bursting pattern and caused strong pump depletion. Re-scattering of SRS at the 1/16th-critical surface was also observed in a high temperature case. These results largely agreed with corresponding Particle-in-Cell simulations.

physics.plasm-ph↗

arXiv2016

Simulation of Stimulated Brillouin Scattering and Stimulated Raman Scattering In Shock Ignition

We study stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS) in shock ignition by comparing fluid and PIC simulations. Under typical parameters for the OMEGA experiments [Theobald \emph{et al}., Phys. Plasmas \textbf{19}, 102706 (2012)], a series of 1D fluid simulations with laser intensities ranging between 2$\times$10$^{15}$ and 2$\times$10$^{16}$ W/cm$^2$ finds that SBS is the dominant instability, which increases significantly with the incident intensity. Strong pump depletion caused by SBS and SRS limits the transmitted intensity at the 0.17n$_c$ to be less than 3.5$\times$10$^{15}$ W/cm$^2$. The PIC simulations show similar physics but with higher saturation levels for SBS and SRS convective modes and stronger pump depletion due to higher seed levels for the electromagnetic fields in PIC codes. Plasma flow profiles are found to be important in proper modeling of SBS and limiting its reflectivity in both the fluid and PIC simulations.

physics.plasm-ph↗

arXiv2014

The Properties of Hα Emission-Line Galaxies at z = 2.24

Using deep narrow-band $H_2S1$ and $K_{s}$-band imaging data obtained with CFHT/WIRCam, we identify a sample of 56 H$α$ emission-line galaxies (ELGs) at $z=2.24$ with the 5$σ$ depths of $H_2S1=22.8$ and $K_{s}=24.8$ (AB) over 383 arcmin$^{2}$ area in the ECDFS. A detailed analysis is carried out with existing multi-wavelength data in this field. Three of the 56 H$α$ ELGs are detected in Chandra 4 Ms X-ray observation and two of them are classified as AGNs. The rest-frame UV and optical morphologies revealed by HST/ACS and WFC3 deep images show that nearly half of the H$α$ ELGs are either merging systems or with a close companion, indicating that the merging/interacting processes play a key role in regulating star formation at cosmic epoch z=2-3; About 14% are too faint to be resolved in the rest-frame UV morphology due to high dust extinction. We estimate dust extinction from SEDs. We find that dust extinction is generally correlated with H$α$ luminosity and stellar mass (SM). Our results suggest that H$α$ ELGs are representative of star-forming galaxies (SFGs). Applying extinction correction for individual objects, we examine the intrinsic H$α$ luminosity function (LF) at $z=2.24$, obtaining a best-fit Schechter function characterized by a faint-end slope of $α=-1.3$. This is shallower than the typical slope of $α\sim -1.6$ in previous works based on constant extinction correction. We demonstrate that this difference is mainly due to the different extinction corrections. The proper extinction correction is thus key to recovering the intrinsic LF as the extinction globally increases with H$α$ luminosity. Moreover, we find that our H$α$ LF mirrors the SM function of SFGs at the same cosmic epoch. This finding indeed reflects the tight correlation between SFR and SM for the SFGs, i.e., the so-called main sequence.

astro-ph.CO↗

arXiv2009

A Spitzer high resolution mid-infrared spectral atlas of starburst galaxies

We present an atlas of Spitzer/IRS high resolution (R~600) 10-37um spectra for 24 well known starburst galaxies. The spectra are dominated by fine-structure lines, molecular hydrogen lines, and emission bands of polycyclic aromatic hydrocarbons. Six out of the eight objects with a known AGN component show emission of the high excitation [NeV] line. This line is also seen in one other object (NGC4194) with, a priori, no known AGN component. In addition to strong polycyclic aromatic hydrocarbon emission features in this wavelength range (11.3, 12.7, 16.4um), the spectra reveal other weak hydrocarbon features at 10.6, 13.5, 14.2um, and a previously unreported emission feature at 10.75um. An unidentified absorption feature at 13.7um is detected in many of the starbursts. We use the fine-structure lines to derive the abundance of neon and sulfur for 14 objects where the HI 7-6 line is detected. We further use the molecular hydrogen lines to sample the properties of the warm molecular gas. Several basic diagrams characterizing the properties of the sample are also shown. We have combined the spectra of all the pure starburst objects to create a high S/N template, which is available to the community.

astro-ph.CO↗