Showing 1–34 of 34 results for author: Choi, B

Unveiling charge dynamics on the generation of high extinction wide pulse generation on thin-film lithium tantalate

Authors: Ayed Al Sayem, Shiekh Zia Uddin, Ting-Chen Hu, Tam Huynh, Bongjun Choi, Alaric Tate, Mark Cappuzzo, Rose Kopf, Mark Earnshaw

Abstract: We experimentally demonstrate high-extinction optical pulse generation in thin-film lithium tantalate (TFLT), achieving a wide range of pulse widths with sharp rise and fall edges, without measurable distortion or long temporal tails. We further provide a direct one-to-one comparison with thin-film lithium niobate (TFLN) modulators under identical measurement conditions. Our results reveal that th… ▽ More We experimentally demonstrate high-extinction optical pulse generation in thin-film lithium tantalate (TFLT), achieving a wide range of pulse widths with sharp rise and fall edges, without measurable distortion or long temporal tails. We further provide a direct one-to-one comparison with thin-film lithium niobate (TFLN) modulators under identical measurement conditions. Our results reveal that the distorted pulse response observed in TFLN originates from charge activation and transport, whereas the distortion-free response in TFLT is enabled by the substantially larger activation energy of defect-related charge carriers. This larger activation barrier suppresses leakage-current-induced charging dynamics, thereby enabling stable and distortion-free pulse generation. The successful generation of high-extinction, distortion-free optical pulses in TFLT can play a significant role in integrated quantum photonic technologies, particularly for qubit preparation, measurement, and fast feedback circuits. △ Less

Submitted 7 August, 2026; originally announced August 2026.

Comments: 8 pages, 4 figures

Ultraviolet Exciton-Polaritons in Silver Phenylthiolate

Authors: Bongjun Choi, Bonnie Chen, Thuc T. Mai, Rahul Rao, Adam D. Alfieri, Du Chen, Peijun Guo, Ha-Reem Kim, Michael A. Altvater, Nicholas A. Glavin, Deep Jariwala

Abstract: Ultraviolet (UV) exciton-polaritons (EPs) enable nonlinear optics, polaritonic lasing, and polariton-mediated photochemistry in the short-wavelength regime, yet progress has been limited due to the scarcity of materials that combine large oscillator strength with stable and narrow UV excitons. Here, we demonstrate UV EPs in silver phenylthiolate (Thiorene, AgSPh), a van der Waals (vdW) layered met… ▽ More Ultraviolet (UV) exciton-polaritons (EPs) enable nonlinear optics, polaritonic lasing, and polariton-mediated photochemistry in the short-wavelength regime, yet progress has been limited due to the scarcity of materials that combine large oscillator strength with stable and narrow UV excitons. Here, we demonstrate UV EPs in silver phenylthiolate (Thiorene, AgSPh), a van der Waals (vdW) layered metal-organic chalcogenolate (MOC) that forms a natural multi-quantum-well (MQW) architecture showing strong excitonic features. Imaging spectroscopic ellipsometry reveals a pronounced in-plane excitonic resonance at 3.46 eV with a narrow linewidth of ~ 60 meV, strong UV birefringence (Δn ~ 0.3), and a high refractive index (n ~ 2.1). Temperature-dependent photoluminescence (PL) shows excitonic emission with a large Stokes shift and substantial exciton-phonon coupling. In both open (self-cavity) and closed cavities, thickness-dependent and angle-resolved reflectance spectra exhibit clear anticrossing, yielding large Rabi splittings of approximately 500 meV. These values are among the largest reported in the UV, positioning thiorene as a promising platform for UV polariton lasers and polariton-enabled photochemistry. △ Less

Submitted 4 May, 2026; originally announced May 2026.

Physics-informed data-driven inference of an interpretable equivariant LES model of incompressible fluid turbulence

Authors: Matteo Ugliotti, Brandon Choi, Mateo Reynoso, Daniel R. Gurevich, Roman O. Grigoriev

Abstract: Restrictive phenomenological assumptions represent a major roadblock for the development of accurate subgrid-scale models of fluid turbulence. Specifically, these assumptions limit a model's ability to describe key quantities of interest, such as local fluxes of energy and enstrophy, in the presence of diverse coherent structures. This paper introduces a symbolic data-driven subgrid-scale model th… ▽ More Restrictive phenomenological assumptions represent a major roadblock for the development of accurate subgrid-scale models of fluid turbulence. Specifically, these assumptions limit a model's ability to describe key quantities of interest, such as local fluxes of energy and enstrophy, in the presence of diverse coherent structures. This paper introduces a symbolic data-driven subgrid-scale model that requires no phenomenological assumptions and has no adjustable parameters, yet it outperforms leading LES models. A combination of a priori and a posteriori benchmarks shows that the model produces accurate predictions of various quantities including local fluxes across a broad range of two-dimensional turbulent flows. While the model is inferred using LES-style spatial coarse-graining, its structure is more similar to RANS models, as it employs an additional field to describe subgrid scales. We find that this field must have a rank-two tensor structure in order to correctly represent both the components of the subgrid-scale stress tensor and the various fluxes. △ Less

Submitted 17 February, 2026; originally announced February 2026.

Controlled non-volatile modulation of optical dispersion in monolayer tungsten disulfide via ferroelectric polarization patterning

Authors: Yuhong Cao, Zekun Hu, Jason Lynch, Bongjun Choi, Kyung Min Yang, Hyunmin Cho, Chloe Leblanc, Chen Chen, Joan M. Redwing, Deep Jariwala

Abstract: The manipulation of optical properties, including reflection, refraction, polarization, phase, and frequency, has long been central to advancing photonic and optoelectronic technologies. However, existing electro-optical approaches rely on volatile mechanisms that require continuous power consumption. Here, we demonstrate strong, nonvolatile modulation of optical dispersion in monolayer tungsten d… ▽ More The manipulation of optical properties, including reflection, refraction, polarization, phase, and frequency, has long been central to advancing photonic and optoelectronic technologies. However, existing electro-optical approaches rely on volatile mechanisms that require continuous power consumption. Here, we demonstrate strong, nonvolatile modulation of optical dispersion in monolayer tungsten disulfide (ML WS2) using patterned ferroelectric domains in aluminum scandium nitride (AlScN). By locally poling ferroelectric domains into opposite states, we achieve substantial manipulation of the complex refractive index (Delta n > 0.7, Delta k > 0.4) and excitonic energy shifts (~50 meV) in ML WS2, comparable to previous gate-tuning approaches while eliminating continuous power consumption. We introduce an asymmetric screening model that reveals how ferroelectric polarization induces carrier-density-dependent Coulomb screening, leading to distinct excitonic behaviors between electron- and hole-doped regions. Furthermore, we demonstrate a gate-free lateral p-n homojunction with a rectification ratio of 6e10^3, formed through spatial carrier redistribution. These findings establish ferroelectric/2D heterostructures as a powerful platform for nonvolatile optical dispersion engineering, enabling energy-efficient, reconfigurable photonic and optoelectronic devices. △ Less

Submitted 15 February, 2026; originally announced February 2026.

Self-Hybridized Exciton-Polariton Photodetectors From Layered Metal-Organic Chalcogenolates

Authors: Bongjun Choi, Adam D. Alfieri, Wangleong Chen, Deep Jariwala

Abstract: Exciton-polaritons (EPs) arising from strong light-matter coupling offer new pathways for controlling optoelectronic properties. While typically requiring closed optical cavities for strong coupling, we demonstrate that 2D metal-organic chalcogenolates (MOCs), mithrene (AgSePh), with a high refractive index (~2.5) and strong excitons enable self-hybridized polaritons photodetectors (PDs) without t… ▽ More Exciton-polaritons (EPs) arising from strong light-matter coupling offer new pathways for controlling optoelectronic properties. While typically requiring closed optical cavities for strong coupling, we demonstrate that 2D metal-organic chalcogenolates (MOCs), mithrene (AgSePh), with a high refractive index (~2.5) and strong excitons enable self-hybridized polaritons photodetectors (PDs) without top mirrors, simplifying device architecture. Through thickness-tuned multimode polariton engineering, we achieve photodetection of sub-bandgap photons via lower polariton states, validated through reflectance, photoluminescence (PL), and photocurrent spectroscopy with quantitative theoretical agreement. Trap-assisted two-photon absorption enables sustained strong coupling even under sub-bandgap excitation. The polariton dispersion yields ultrafast group velocities (~65 μm/ps), extending exciton diffusion lengths from hundreds of nanometers to several micrometers. Strong-coupling devices demonstrate a 2.38-fold enhancement in photo-to-dark current ratio compared to weak-coupling counterparts, establishing a practical route to polariton-enhanced photodetection and light harvesting. △ Less

Submitted 10 December, 2025; originally announced December 2025.

Data-driven modeling of multiscale phenomena with applications to fluid turbulence

Authors: Brandon Choi, Matteo Ugliotti, Mateo Reynoso, Daniel R. Gurevich, Roman O. Grigoriev

Abstract: This paper introduces a novel data driven framework for constructing accurate and general equivariant models of multiscale phenomena which does not rely on specific assumptions about the underlying physics. This framework is illustrated using incompressible fluid turbulence as an example that is representative, practically important, reasonably simple, and exceedingly well studied. We use direct n… ▽ More This paper introduces a novel data driven framework for constructing accurate and general equivariant models of multiscale phenomena which does not rely on specific assumptions about the underlying physics. This framework is illustrated using incompressible fluid turbulence as an example that is representative, practically important, reasonably simple, and exceedingly well studied. We use direct numerical simulations of freely decaying turbulence in two spatial dimensions to infer an effective field theory comprising explicit, interpretable evolution equations for both the large (resolved) and small (modeled) scales. The resulting closed system of equations is capable of accurately describing the effect of small scales, including backscatter -- the flow of energy from small to large scales, which is particularly pronounced in two dimensions -- which is an outstanding challenge that, to our knowledge, no existing alternative successfully tackles. △ Less

Submitted 14 April, 2026; v1 submitted 12 November, 2025; originally announced November 2025.

Reconfigurable, non-volatile control of optical anisotropy in ReS2 via ferroelectric gating

Authors: Mahfujur Rahaman, Seunguk Song, Aaliyah C. Khan, Bongjun Choi, Aaron M. Schankler, Kwan-Ho Kim, Wonchan Lee, Jason Lynch, Hyeon Suk Shin, Andrew M. Rappe, Deep Jariwala

Abstract: Electrically tunable linear dichroism (LD) with non-volatile properties represents a critical yet elusive feature for next-generation integrated photonic elements in practical device architectures. Here, we demonstrate record-breaking, non-volatile control of optical anisotropy in two-dimensional ReS2 via ferroelectric gating with aluminum scandium nitride (AlScN). Our ferroelectric field-effect t… ▽ More Electrically tunable linear dichroism (LD) with non-volatile properties represents a critical yet elusive feature for next-generation integrated photonic elements in practical device architectures. Here, we demonstrate record-breaking, non-volatile control of optical anisotropy in two-dimensional ReS2 via ferroelectric gating with aluminum scandium nitride (AlScN). Our ferroelectric field-effect transistors achieve near-unity (~95%) LD tunability of differential reflectance at room temperature--the highest reported for any electrically controlled 2D optical system. Crucially, the programmed optical states exhibit exceptional retention exceeding 12,000 seconds without applied bias, enabling true non-volatile optical memory. Through combined experimental characterization and ab initio calculations, we reveal that ferroelectric polarization switching induces substantial asymmetric charge transfer to ReS2, selectively populating conduction band states and triggering structural distortions that dramatically enhance optical anisotropy in the "up" polarization state while leaving the "down" state unperturbed. This ferroelectric-semiconductor coupling provides a universal platform for voltage-programmable, energy-efficient photonic devices with dynamic polarization control, addressing critical needs in integrated photonics as well as programmable far-field optics and telecommunications infrastructure. △ Less

Submitted 15 September, 2025; originally announced September 2025.

Comments: 5 main figures

Natural Hyperbolicity of Hexagonal Boron Nitride in the Deep Ultraviolet

Authors: Bongjun Choi, Jason Lynch, Wangleong Chen, Seong-Joon Jeon, Hyungseob Cho, Kyungmin Yang, Jonghwan Kim, Nader Engheta, Deep Jariwala

Abstract: Hyperbolic media enable unique optical phenomena including hyperlensing, negative refraction, enhanced photonic density of states (PDOS), and highly confined polaritons. While most hyperbolic media are artificially engineered metamaterials, certain natural materials with extreme anisotropy can exhibit hyperbolic dispersion. Here, we report the first observation of natural hyperbolic dispersion in… ▽ More Hyperbolic media enable unique optical phenomena including hyperlensing, negative refraction, enhanced photonic density of states (PDOS), and highly confined polaritons. While most hyperbolic media are artificially engineered metamaterials, certain natural materials with extreme anisotropy can exhibit hyperbolic dispersion. Here, we report the first observation of natural hyperbolic dispersion in hexagonal boron nitride (hBN) in the deep-ultraviolet (DUV) regime, induced by strong, anisotropic exciton resonances. Using imaging spectroscopic ellipsometry (ISE), we characterize the complex dielectric function along in-plane and out-of-plane directions down to 190 nm (6.53 eV), revealing a type-II hyperbolic window in the DUV regime. This hyperbolicity supports hyperbolic exciton polaritons (HEP) with high directionality and slow group velocity. Our findings establish hBN as a promising platform for nanophotonic applications in the technologically significant DUV spectral range. △ Less

Submitted 17 July, 2025; originally announced July 2025.

Comments: 16 pages, 4 figures (main manuscript)

Latent Representation Learning of Multi-scale Thermophysics: Application to Dynamics in Shocked Porous Energetic Material

Authors: Shahab Azarfar, Joseph B. Choi, Phong CH. Nguyen, Yen T. Nguyen, Pradeep Seshadri, H. S. Udaykumar, Stephen Baek

Abstract: Coupling of physics across length and time scales plays an important role in the response of microstructured materials to external loads. In a multi-scale framework, unresolved (subgrid) meso-scale dynamics is upscaled to the homogenized (macro-scale) representation of the heterogeneous material through closure models. Deep learning models trained using meso-scale simulation data are now a popular… ▽ More Coupling of physics across length and time scales plays an important role in the response of microstructured materials to external loads. In a multi-scale framework, unresolved (subgrid) meso-scale dynamics is upscaled to the homogenized (macro-scale) representation of the heterogeneous material through closure models. Deep learning models trained using meso-scale simulation data are now a popular route to assimilate such closure laws. However, meso-scale simulations are computationally taxing, posing practical challenges in training deep learning-based surrogate models from scratch. In this work, we investigate an alternative meta-learning approach motivated by the idea of tokenization in natural language processing. We show that one can learn a reduced representation of the micro-scale physics to accelerate the meso-scale learning process by tokenizing the meso-scale evolution of the physical fields involved in an archetypal, albeit complex, reactive dynamics problem, \textit{viz.}, shock-induced energy localization in a porous energetic material. A probabilistic latent representation of \textit{micro}-scale dynamics is learned as building blocks for \textit{meso}-scale dynamics. The \textit{meso-}scale latent dynamics model learns the correlation between neighboring building blocks by training over a small dataset of meso-scale simulations. We compare the performance of our model with a physics-aware recurrent convolutional neural network (PARC) trained only on the full meso-scale dataset. We demonstrate that our model can outperform PARC with scarce meso-scale data. The proposed approach accelerates the development of closure models by leveraging inexpensive micro-scale simulations and fast training over a small meso-scale dataset, and can be applied to a range of multi-scale modeling problems. △ Less

Submitted 23 September, 2025; v1 submitted 15 June, 2025; originally announced June 2025.

Comments: 32 pages, 19 figures, complementary results added, restructured Introduction section

ACM Class: I.2.6

High-Temperature-Resilient Hyperbolicity in a Mixed-Dimensional Superlattice

Authors: Jason Lynch, Tzu-Yu Peng, Jing-Wei Yang, Ben R. Conran, Bongjun Choi, Cindy Yueli Chen, Zahra Fakhraai, Clifford McAleese, Yu-Jung Lu, Deep Jariwala

Abstract: Hyperbolic superlattices are used for sub-wavelength focusing, cloaking, and optical thermal management. Typically, these superlattices are constructed of layers of noble metals and insulators. Despite these systems displaying excellent optical performance, the poor thermal stability of noble metals prevents their application in high-temperature environments. Instead, CMOS-compatible transition-me… ▽ More Hyperbolic superlattices are used for sub-wavelength focusing, cloaking, and optical thermal management. Typically, these superlattices are constructed of layers of noble metals and insulators. Despite these systems displaying excellent optical performance, the poor thermal stability of noble metals prevents their application in high-temperature environments. Instead, CMOS-compatible transition-metal nitrides are often substituted for noble metals in plasmonic systems since they have high thermal stability at the expense of optical properties. Here, we fabricate hyperbolic titanium nitride (TiN)/hexagonal boron nitride (hBN) superlattices with 3D-2D interfaces. The mixed-dimensional nature of the interfaces prevents atoms from diffusing across the interface at high temperatures. The hyperbolicity of the superlattice is found to be unaffected by annealing at high temperature (800 oC for 10 hrs), and TiN/hBN is found to have a larger hyperbolic figure of merit than similar superlattices. △ Less

Submitted 20 March, 2025; originally announced March 2025.

Inferring contact network characteristics from epidemic data via compact mean-field models

Authors: Andrés Guzmán, Federico Malizia, Gyeong Ho Park, Boseung Choi, Diana Cole, István Z. Kiss

Abstract: Modelling epidemics using contact networks provides a significant improvement over classical compartmental models by explicitly incorporating the network of contacts. However, while network-based models describe disease spread on a given contact structure, their potential for inferring the underlying network from epidemic data remains largely unexplored. In this work, we consider the edge-based co… ▽ More Modelling epidemics using contact networks provides a significant improvement over classical compartmental models by explicitly incorporating the network of contacts. However, while network-based models describe disease spread on a given contact structure, their potential for inferring the underlying network from epidemic data remains largely unexplored. In this work, we consider the edge-based compartmental model (EBCM), a compact and analytically tractable framework, and we integrate it within dynamical survival analysis (DSA) to infer key network properties along with parameters of the epidemic itself. Despite correlations between structural and epidemic parameters, our framework demonstrates robustness in accurately inferring contact network properties from synthetic epidemic simulations. Additionally, we apply the framework to real-world outbreaks, namely the 2001 UK foot-and-mouth disease outbreak and the COVID-19 epidemic in Seoul, to estimate both disease parameters and network characteristics. Our results show that our framework achieves good fits to real-world epidemic data and reliable short-term forecasts. These findings highlight the potential of network-based inference approaches to uncover hidden contact structures, providing insights that can inform the design of targeted interventions and public health strategies. △ Less

Submitted 17 February, 2025; originally announced February 2025.

FLRNet: A Deep Learning Method for Regressive Reconstruction of Flow Field From Limited Sensor Measurements

Authors: Phong C. H. Nguyen, Joseph B. Choi, Quang-Trung Luu

Abstract: Many applications in computational and experimental fluid mechanics require effective methods for reconstructing the flow fields from limited sensor data. However, this task remains a significant challenge because the measurement operator, which provides the punctual sensor measurement for a given state of the flow field, is often ill-conditioned and non-invertible. This issue impedes the feasibil… ▽ More Many applications in computational and experimental fluid mechanics require effective methods for reconstructing the flow fields from limited sensor data. However, this task remains a significant challenge because the measurement operator, which provides the punctual sensor measurement for a given state of the flow field, is often ill-conditioned and non-invertible. This issue impedes the feasibility of identifying the forward map, theoretically the inverse of the measurement operator, for field reconstruction purposes. While data-driven methods are available, their generalizability across different flow conditions (\textit{e.g.,} different Reynold numbers) remains questioned. Moreover, they frequently face the problem of spectral bias, which leads to smooth and blurry reconstructed fields, thereby decreasing the accuracy of reconstruction. We introduce FLRNet, a deep learning method for flow field reconstruction from sparse sensor measurements. FLRNet employs an variational autoencoder with Fourier feature layers and incorporates an extra perceptual loss term during training to learn a rich, low-dimensional latent representation of the flow field. The learned latent representation is then correlated to the sensor measurement using a fully connected (dense) network. We validated the reconstruction capability and the generalizability of FLRNet under various fluid flow conditions and sensor configurations, including different sensor counts and sensor layouts. Numerical experiments show that in all tested scenarios, FLRNet consistently outperformed other baselines, delivering the most accurate reconstructed flow field and being the most robust to noise. △ Less

Submitted 20 November, 2024; originally announced November 2024.

Characterization of a graphene-hBN superlattice field effect transistor

Authors: Won Beom Choi, Youngoh Son, Hangyeol Park, Yungi Jeong, Junhyeok Oh, K. Watanabe, T. Taniguchi, Joonho Jang

Abstract: Graphene provides a unique platform for hosting high quality 2D electron systems. Encapsulating graphene with hexagonal boron nitride (hBN) to shield it from noisy environments offers the potential to achieve ultrahigh performance nanodevices, such as photodiodes and transistors. However, the absence of a bandgap at the Dirac point presents challenges for using this system as a useful transistor.… ▽ More Graphene provides a unique platform for hosting high quality 2D electron systems. Encapsulating graphene with hexagonal boron nitride (hBN) to shield it from noisy environments offers the potential to achieve ultrahigh performance nanodevices, such as photodiodes and transistors. However, the absence of a bandgap at the Dirac point presents challenges for using this system as a useful transistor. In this study, we investigated the functionality of hBN-aligned monolayer graphene as a field effect transistor (FET). By precisely aligning the hBN and graphene, bandgaps open at the first Dirac point and at the hole-doped induced Dirac point via an interfacial moiré potential. To characterize this as a submicrometer scale FET, we fabricated a global bottom gate to tune the density of a conducting channel and a local top gate to switch off this channel. This demonstrated that the system could be tuned to an optimal on/off ratio regime by separately controlling the gates. These findings provide a valuable reference point for the further development of FETs based on graphene heterostructures. △ Less

Submitted 12 July, 2024; v1 submitted 10 May, 2024; originally announced May 2024.

Journal ref: Appl. Phys. Lett. 125, 033503 (2024)

Giant Optical Anisotropy in 2D Metal-Organic Chalcogenates

Authors: Bongjun Choi, Kiyoung Jo, Mahfujur Rahaman, Adam Alfieri, Jason Lynch, Greg K. Pribil, Hyeongjun Koh, Eric A. Stach, Deep Jariwala

Abstract: Optical anisotropy is a fundamental attribute of some crystalline materials and is quantified via birefringence. A birefringent crystal not only gives rise to asymmetrical light propagation but also attenuation along two distinct polarizations, a phenomenon called linear dichroism (LD). Two-dimensional (2D) layered materials with high in- and out-of-plane anisotropy have garnered interest in this… ▽ More Optical anisotropy is a fundamental attribute of some crystalline materials and is quantified via birefringence. A birefringent crystal not only gives rise to asymmetrical light propagation but also attenuation along two distinct polarizations, a phenomenon called linear dichroism (LD). Two-dimensional (2D) layered materials with high in- and out-of-plane anisotropy have garnered interest in this regard. Mithrene, a 2D metal-organic chalcogenate (MOCHA) compound, exhibits strong excitonic resonances due to its naturally occurring multi-quantum well (MQW) structure and in-plane anisotropic response in the blue wavelength (~400-500 nm) regime. The MQW structure and the large refractive indices of mithrene allow the hybridization of the excitons with photons to form self-hybridized exciton-polaritons in mithrene crystals with appropriate thicknesses. Here, we report the giant birefringence (~1.01) and tunable in-plane anisotropic response of mithrene, which stem from its low symmetry crystal structure and unique excitonic properties. We show that the LD in mithrene can be tuned by leveraging the anisotropic exciton-polariton formation via the cavity coupling effect exhibiting giant in-plane LD (~77.1%) at room temperature. Our results indicate that mithrene is an ideal polaritonic birefringent material for polarization-sensitive nanophotonic applications in the short wavelength regime. △ Less

Submitted 3 April, 2024; v1 submitted 31 December, 2023; originally announced January 2024.

Ultrastrong Light-Matter Coupling in 2D Metal-Chalcogenates

Authors: Surendra B. Anantharaman, Jason Lynch, Mariya Aleksich, Christopher E. Stevens, Christopher Munley, Bongjun Choi, Sridhar Shenoy, Thomas Darlington, Arka Majumdar, P. James Shuck, Joshua Hendrickson, J. Nathan Hohman, Deep Jariwala

Abstract: Hybridization of excitons with photons to form hybrid quasiparticles, exciton-polaritons (EPs), has been widely investigated in a range of semiconductor material systems coupled to photonic cavities. Self-hybridization occurs when the semiconductor itself can serve as the photonic cavity medium resulting in strongly-coupled EPs with Rabi splitting energies > 200 meV at room temperatures which rece… ▽ More Hybridization of excitons with photons to form hybrid quasiparticles, exciton-polaritons (EPs), has been widely investigated in a range of semiconductor material systems coupled to photonic cavities. Self-hybridization occurs when the semiconductor itself can serve as the photonic cavity medium resulting in strongly-coupled EPs with Rabi splitting energies > 200 meV at room temperatures which recently were observed in layered two-dimensional (2D) excitonic materials. Here, we report an extreme version of this phenomenon, an ultrastrong EP coupling, in a nascent, 2D excitonic system, the metal organic chalcogenate (MOCHA) compound named mithrene. The resulting self-hybridized EPs in mithrene crystals placed on Au substrates show Rabi Splitting in the ultrastrong coupling range (> 600 meV) due to the strong oscillator strength of the excitons concurrent with the large refractive indices of mithrene. We further show bright EP emission at room temperature as well as EP dispersions at low-temperatures. Importantly, we find lower EP emission linewidth narrowing to ~1 nm when mithrene crystals are placed in closed Fabry-Perot cavities. Our results suggest that MOCHA materials are ideal for polaritonics in the deep green-blue part of the spectrum where strong excitonic materials with large optical constants are notably scarce. △ Less

Submitted 21 August, 2023; originally announced August 2023.

A realizable second-order advection method with variable flux limiters for moment transport equations

Authors: Byeongyeob Choi, Jehyun Baek, Donghyun You

Abstract: A second-order total variation diminishing (TVD) method with variable flux limiters is proposed to overcome the non-realizability issue, which has been one of major obstacles in applying the conventional second-order TVD schemes to the moment transport equations. In the present method, a realizable moment set at a cell face is reconstructed by allowing the flexible selection of the flux limiter va… ▽ More A second-order total variation diminishing (TVD) method with variable flux limiters is proposed to overcome the non-realizability issue, which has been one of major obstacles in applying the conventional second-order TVD schemes to the moment transport equations. In the present method, a realizable moment set at a cell face is reconstructed by allowing the flexible selection of the flux limiter values within the second-order TVD region. Necessary conditions for the variable flux limiter scheme to simultaneously satisfy the realizability and the second-order TVD property for the third-order moment set are proposed. The strategy for satisfying the second-order TVD property is conditionally extended to the fourth- and fifth-order moments. The proposed method is verified and compared with other high-order realizable schemes in one- and two-dimensional configurations, and is found to preserve the realizability of moments while satisfying the high-order TVD property for the third-order moment set and conditionally for the fourth- and fifth-order moments. △ Less

Submitted 22 May, 2022; originally announced May 2022.

Abdominal synthetic CT reconstruction with intensity projection prior for MRI-only adaptive radiotherapy

Authors: Sven Olberg, Jaehee Chun, Byong Su Choi, Inkyung Park, Hyun Kim, Taeho Kim, Jin Sung Kim, Olga Green, Justin C. Park

Abstract: An MRI-only adaptive radiotherapy (ART) workflow is desirable for managing interfractional changes in anatomy, but producing synthetic CT (sCT) data through paired data-driven deep learning (DL) for abdominal dose calculations remains a challenge due to the highly variable presence of intestinal gas. We present the preliminary dosimetric evaluation of our novel approach to sCT reconstruction that… ▽ More An MRI-only adaptive radiotherapy (ART) workflow is desirable for managing interfractional changes in anatomy, but producing synthetic CT (sCT) data through paired data-driven deep learning (DL) for abdominal dose calculations remains a challenge due to the highly variable presence of intestinal gas. We present the preliminary dosimetric evaluation of our novel approach to sCT reconstruction that is well suited to handling intestinal gas in abdominal MRI-only ART. We utilize a paired data DL approach enabled by the intensity projection prior, in which well-matching training pairs are created by propagating air from MRI to corresponding CT scans. Evaluations focus on two classes: patients with (1) little involvement of intestinal gas, and (2) notable differences in intestinal gas presence between corresponding scans. Comparisons between sCT-based plans and CT-based clinical plans for both classes are made at the first treatment fraction to highlight the dosimetric impact of the variable presence of intestinal gas. Class 1 patients ($n=13$) demonstrate differences in prescribed dose coverage of the PTV of $1.3 \pm 2.1\%$ between clinical plans and sCT-based plans. Mean DVH differences in all structures for Class 1 patients are found to be statistically insignificant. In Class 2 ($n=20$), target coverage is $13.3 \pm 11.0\%$ higher in the clinical plans and mean DVH differences are found to be statistically significant. Significant deviations in calculated doses arising from the variable presence of intestinal gas in corresponding CT and MRI scans may limit the effectiveness of adaptive dose escalation efforts. We have proposed a paired data-driven DL approach to sCT reconstruction for accurate dose calculations in abdominal ART enabled by the creation of a clinically unavailable training data set with well-matching representations of intestinal gas. △ Less

Submitted 2 July, 2021; originally announced July 2021.

Enhanced passive thermal stealth properties of VO$_2$ thin films via gradient W doping

Authors: Hyuk Jin Kim, Young Hwan Choi, Dong Kyu Lee, In Hak Lee, Byoung Ki Choi, Soo-Hyun Phark, Young Jun Chang

Abstract: Thermal stealth and camouflage have been intensively studied for blending objects with their surroundings against remote thermal image detection. Adaptive control of infrared emissivity has been explored extensively as a promising way of thermal stealth, but it still requires an additional feedback control. Passive modulation of emissivity, however, has been remained as a great challenge which req… ▽ More Thermal stealth and camouflage have been intensively studied for blending objects with their surroundings against remote thermal image detection. Adaptive control of infrared emissivity has been explored extensively as a promising way of thermal stealth, but it still requires an additional feedback control. Passive modulation of emissivity, however, has been remained as a great challenge which requires a precise engineering of emissivity over wide temperature range. Here, we report a drastic improvement of passive camouflage thin films capable of concealing thermal objects at near room temperature without any feedback control, which consists of a vanadium dioxide (VO2) layer with gradient tungsten (W) concentration. The gradient W-doping widens the metal-insulator transition width, accomplishing self-adaptive thermal stealth with a smooth change of emissivity. Our simple approach, applicable to other similar thermal camouflage materials for improving their passive cloaking, will find wide applications, such as passive thermal camouflage, urban energy-saving smart windows, and improved infrared sensors. △ Less

Submitted 12 May, 2021; originally announced May 2021.

Comments: 20 pages, 4 figures

A Novel Approach for Semiconductor Etching Process with Inductive Biases

Authors: Sanghoon Myung, Hyunjae Jang, Byungseon Choi, Jisu Ryu, Hyuk Kim, Sang Wuk Park, Changwook Jeong, Dae Sin Kim

Abstract: The etching process is one of the most important processes in semiconductor manufacturing. We have introduced the state-of-the-art deep learning model to predict the etching profiles. However, the significant problems violating physics have been found through various techniques such as explainable artificial intelligence and representation of prediction uncertainty. To address this problem, this p… ▽ More The etching process is one of the most important processes in semiconductor manufacturing. We have introduced the state-of-the-art deep learning model to predict the etching profiles. However, the significant problems violating physics have been found through various techniques such as explainable artificial intelligence and representation of prediction uncertainty. To address this problem, this paper presents a novel approach to apply the inductive biases for etching process. We demonstrate that our approach fits the measurement faster than physical simulator while following the physical behavior. Our approach would bring a new opportunity for better etching process with higher accuracy and lower cost. △ Less

Submitted 6 April, 2021; originally announced April 2021.

Comments: 5 pages; accepted to NeurIPS 2020 Workshop on Interpretable Inductive Biases and Physically Structured Learning

Evaluation of the clinical usefulness of modulated Arc treatment

Authors: Young Kyu Lee, Hong Seok Jang, Yeon Sil Kim, Byung Ock Choi, Sang Hee Nam, Hyeong Wook Park, Shin Wook Kim, Hun Joo Shin, Jae Choon Lee, Ji Na Kim, Sung Kwang Park, Jin Young Kim, Young-Nam Kang

Abstract: The purpose of this study is to evaluate the clinical usefulness of modulated arc (mARC) treatment techniques. The mARC treatment plans of the non-small cell lung cancer (NSCLC) patients were performed in order to verify the clinical usefulness of mARC. A pre study was conducted to find the most competent plan condition of mARC treatment and the usefulness of mARC treatment plan was evaluated by c… ▽ More The purpose of this study is to evaluate the clinical usefulness of modulated arc (mARC) treatment techniques. The mARC treatment plans of the non-small cell lung cancer (NSCLC) patients were performed in order to verify the clinical usefulness of mARC. A pre study was conducted to find the most competent plan condition of mARC treatment and the usefulness of mARC treatment plan was evaluated by comparing it with the other Arc treatment plans such as Tomotherapy and RapidArc. In the case of mARC, the optimal condition for the mARC plan was determined by comparing the dosimetric performance of the mARC plans with the use of various parameters. The various parameters includes the photon energies (6 MV, 10 MV), optimization point angle (6°-10° intervals), and total segment number (36-59 segment). The best dosimetric performance of mARC was observed at 10 MV photon energy and the point angle 6 degree, and 59 segments. The each treatment plans of three different techniques were compared with the following parameters: conformity index (CI), homogeneity index (HI), target coverage, dose in the OARs, monitor units (MU), beam on time and the normal tissue complication probability (NTCP). As a result, all three different treatment techniques show the similar target coverage. The mARC results the lowest V20 and MU per fraction compared with both RapidArc and Tomotherapy plan. The mARC plan reduces the beam on time as well. Therefore, the results of this study provided a satisfactory result which mARC technique is considered as a useful clinical technique for radiation treatment. △ Less

Submitted 11 March, 2015; originally announced March 2015.

Comments: 11 pages, 4 figures

Report number: KJMP201414-0062

First Operation of an Ungated Diamond Field-Emission Array Cathode in a L-Band Radiofrequency Electron Source

Authors: P. Piot, C. A. Brau, B. K. Choi, B. Blomberg, W. E. Gabella, B. Ivanov, J. Jarvis, M. H. Mendenhall, D. Mihalcea, S. Panuganti, P. Prieto, J. Reid

Abstract: We report on the first successful operation of a field-emitter-array cathode in a conventional L-band radio-frequency electron source. The cathode consisted of an array of $\sim 10^6$ diamond diamond tips on pyramids. Maximum current on the order of 15~mA were reached and the cathode did not show appreciable signs of fatigue after weeks of operation. The measured Fowler-Nordheim characteristics, t… ▽ More We report on the first successful operation of a field-emitter-array cathode in a conventional L-band radio-frequency electron source. The cathode consisted of an array of $\sim 10^6$ diamond diamond tips on pyramids. Maximum current on the order of 15~mA were reached and the cathode did not show appreciable signs of fatigue after weeks of operation. The measured Fowler-Nordheim characteristics, transverse beam density, and current stability are discussed. Numerical simulations of the beam dynamics are also presented. △ Less

Submitted 27 February, 2014; originally announced February 2014.

Comments: 4 pages, 7 figures; preprint submitted to Applied Physics Letters

Report number: FERMILAB-PUB-13-323-APC

Journal ref: Appl. Phys. Lett. 104, 263504 (2014)

Observation and applications of single-electron charge signals in the XENON100 experiment

Authors: E. Aprile, M. Alfonsi, K. Arisaka, F. Arneodo, C. Balan, L. Baudis, B. Bauermeister, A. Behrens, P. Beltrame, K. Bokeloh, A. Brown, E. Brown, S. Bruenner, G. Bruno, R. Budnik, J. M. R. Cardoso, W. -T. Chen, B. Choi, A. P. Colijn, H. Contreras, J. P. Cussonneau, M. P. Decowski, E. Duchovni, S. Fattori, A. D. Ferella , et al. (55 additional authors not shown)

Abstract: The XENON100 dark matter experiment uses liquid xenon in a time projection chamber (TPC) to measure xenon nuclear recoils resulting from the scattering of dark matter Weakly Interacting Massive Particles (WIMPs). In this paper, we report the observation of single-electron charge signals which are not related to WIMP interactions. These signals, which show the excellent sensitivity of the detector… ▽ More The XENON100 dark matter experiment uses liquid xenon in a time projection chamber (TPC) to measure xenon nuclear recoils resulting from the scattering of dark matter Weakly Interacting Massive Particles (WIMPs). In this paper, we report the observation of single-electron charge signals which are not related to WIMP interactions. These signals, which show the excellent sensitivity of the detector to small charge signals, are explained as being due to the photoionization of impurities in the liquid xenon and of the metal components inside the TPC. They are used as a unique calibration source to characterize the detector. We explain how we can infer crucial parameters for the XENON100 experiment: the secondary-scintillation gain, the extraction yield from the liquid to the gas phase and the electron drift velocity. △ Less

Submitted 28 January, 2014; v1 submitted 5 November, 2013; originally announced November 2013.

Comments: 16 pages, 8 figures. Accepted for publication in Journal of Physics G: Nuclear and Particle Physics

Journal ref: E Aprile et al. [XENON100 Collaboration], J. Phys. G: Nucl. Part. Phys. 41 (2014) 035201

The neutron background of the XENON100 dark matter experiment

Authors: E. Aprile, M. Alfonsi, K. Arisaka, F. Arneodo, C. Balan, L. Baudis, B. Bauermeister, A. Behrens, P. Beltrame, K. Bokeloh, A. Brown, E. Brown, G. Bruno, R. Budnik, J. M. R. Cardoso, W. -T. Chen, B. Choi, A. P. Colijn, H. Contreras, J. P. Cussonneau, M. P. Decowski, E. Duchovni, S. Fattori, A. D. Ferella, W. Fulgione , et al. (52 additional authors not shown)

Abstract: The XENON100 experiment, installed underground at the Laboratori Nazionali del Gran Sasso (LNGS), aims to directly detect dark matter in the form of Weakly Interacting Massive Particles (WIMPs) via their elastic scattering off xenon nuclei. This paper presents a study on the nuclear recoil background of the experiment, taking into account neutron backgrounds from ($α$,n) and spontaneous fission re… ▽ More The XENON100 experiment, installed underground at the Laboratori Nazionali del Gran Sasso (LNGS), aims to directly detect dark matter in the form of Weakly Interacting Massive Particles (WIMPs) via their elastic scattering off xenon nuclei. This paper presents a study on the nuclear recoil background of the experiment, taking into account neutron backgrounds from ($α$,n) and spontaneous fission reactions due to natural radioactivity in the detector and shield materials, as well as muon-induced neutrons. Based on Monte Carlo simulations and using measured radioactive contaminations of all detector components, we predict the nuclear recoil backgrounds for the WIMP search results published by the XENON100 experiment in 2011 and 2012, 0.11$^{+0.08}_{-0.04}$ events and 0.17$^{+0.12}_{-0.07}$ events, respectively, and conclude that they do not limit the sensitivity of the experiment. △ Less

Submitted 2 September, 2013; v1 submitted 10 June, 2013; originally announced June 2013.

The distributed Slow Control System of the XENON100 Experiment

Authors: E. Aprile, M. Alfonsi, K. Arisaka, F. Arneodo, C. Balan, L. Baudis, A. Behrens, P. Beltrame, K. Bokeloh, E. Brown, G. M. Bruno, R. Budnik, M. Le Calloch, J. M. Cardoso, W. -T. Chen, B. Choi, H. Contreras, J. -P. Cussonneau, M. P. Decowski, E. Duchovni, S. Fattori, A. D. Ferella, W. Fulgione, F. Gao, M. Garbini , et al. (50 additional authors not shown)

Abstract: The XENON100 experiment, in operation at the Laboratori Nazionali del Gran Sasso (LNGS) in Italy, was designed to search for evidence of dark matter interactions inside a volume of liquid xenon using a dual-phase time projection chamber. This paper describes the Slow Control System (SCS) of the experiment with emphasis on the distributed architecture as well as on its modular and expandable nature… ▽ More The XENON100 experiment, in operation at the Laboratori Nazionali del Gran Sasso (LNGS) in Italy, was designed to search for evidence of dark matter interactions inside a volume of liquid xenon using a dual-phase time projection chamber. This paper describes the Slow Control System (SCS) of the experiment with emphasis on the distributed architecture as well as on its modular and expandable nature. The system software was designed according to the rules of Object-Oriented Programming and coded in Java, thus promoting code reusability and maximum flexibility during commissioning of the experiment. The SCS has been continuously monitoring the XENON100 detector since mid 2008, remotely recording hundreds of parameters on a few dozen instruments in real time, and setting emergency alarms for the most important variables. △ Less

Submitted 5 November, 2012; originally announced November 2012.

Comments: 12 pages, 4 figures

Measurement of the Scintillation Yield of Low-Energy Electrons in Liquid Xenon

Authors: E. Aprile, R. Budnik, B. Choi, H. A. Contreras, K. -L. Giboni, L. W. Goetzke, J. E. Koglin, R. F. Lang, K. E. Lim, A. J. Melgarejo Fernandez, R. Persiani, G. Plante, A. Rizzo

Abstract: We have measured the energy dependence of the liquid xenon (LXe) scintillation yield of electrons with energy between 2.1 and 120.2keV, using the Compton coincidence technique. A LXe scintillation detector with a very high light detection efficiency was irradiated with 137Cs γ rays and the energy of the Compton-scattered γ rays was measured with a high-purity germanium (HPGe) detector placed at di… ▽ More We have measured the energy dependence of the liquid xenon (LXe) scintillation yield of electrons with energy between 2.1 and 120.2keV, using the Compton coincidence technique. A LXe scintillation detector with a very high light detection efficiency was irradiated with 137Cs γ rays and the energy of the Compton-scattered γ rays was measured with a high-purity germanium (HPGe) detector placed at different scattering angles. The excellent energy resolution of the HPGe detector allows the selection of events with Compton electrons of known energy in the LXe detector. We find that the scintillation yield initially increases as the electron energy decreases from 120 keV to about 60keV but then decreases by about 30% from 60keV to 2keV. The measured scintillation yield was also measured with conversion electrons from the 32.1 keV and 9.4 keV transitions of the 83mKr isomer, used as an internal calibration source. We find that the scintillation yield of the 32.1 keV transition is compatible with that obtained from the Compton coincidence measurement. On the other hand, the yield for the 9.4keV transition is much higher than that measured for a Compton electron of the same energy. We interpret the enhancement in the scintillation yield as due to the enhanced recombination rate in the presence of Xe ions left from the 32.1 keV transition, which precedes the 9.4 keV one by 220 ns, on average. △ Less

Submitted 17 September, 2012; originally announced September 2012.

Comments: 14 pages, 8 figures

Performance of a cryogenic system prototype for the XENON1T Detector

Authors: Elena Aprile, Ran Budnik, Bin Choi, Hugo Contreras, Karl Giboni, Luke Goetzke, Rafael Lang, Kyungeun Lim, Antonio melgarejo, Petr Shagin

Abstract: We have developed an efficient cryogenic system with heat exchange and associated gas purification system, as a prototype for the XENON1T experiment. The XENON1T detector will use about 3 ton of liquid xenon (LXe) at a temperature of 175K as target and detection medium for a dark matter search. In this paper we report results on the cryogenic system performance focusing on the dynamics of the gas… ▽ More We have developed an efficient cryogenic system with heat exchange and associated gas purification system, as a prototype for the XENON1T experiment. The XENON1T detector will use about 3 ton of liquid xenon (LXe) at a temperature of 175K as target and detection medium for a dark matter search. In this paper we report results on the cryogenic system performance focusing on the dynamics of the gas circulation-purification through a heated getter, at flow rates above 50 Standard Liter per Minute (SLPM). A maximum flow of 114 SLPM has been achieved, and using two heat exchangers in parallel, a heat exchange efficiency better than 96% has been measured. △ Less

Submitted 29 August, 2012; v1 submitted 9 August, 2012; originally announced August 2012.

Dark Matter Results from 225 Live Days of XENON100 Data

Authors: XENON100 Collaboration, E. Aprile, M. Alfonsi, K. Arisaka, F. Arneodo, C. Balan, L. Baudis, B. Bauermeister, A. Behrens, P. Beltrame, K. Bokeloh, E. Brown, G. Bruno, R. Budnik, J. M. R. Cardoso, W. -T. Chen, B. Choi, D. Cline, A. P. Colijn, H. Contreras, J. P. Cussonneau, M. P. Decowski, E. Duchovni, S. Fattori, A. D. Ferella , et al. (53 additional authors not shown)

Abstract: We report on a search for particle dark matter with the XENON100 experiment, operated at the Laboratori Nazionali del Gran Sasso (LNGS) for 13 months during 2011 and 2012. XENON100 features an ultra-low electromagnetic background of (5.3 \pm 0.6) \times 10^-3 events (kg day keVee)^-1 in the energy region of interest. A blind analysis of 224.6 live days \times 34 kg exposure has yielded no evidence… ▽ More We report on a search for particle dark matter with the XENON100 experiment, operated at the Laboratori Nazionali del Gran Sasso (LNGS) for 13 months during 2011 and 2012. XENON100 features an ultra-low electromagnetic background of (5.3 \pm 0.6) \times 10^-3 events (kg day keVee)^-1 in the energy region of interest. A blind analysis of 224.6 live days \times 34 kg exposure has yielded no evidence for dark matter interactions. The two candidate events observed in the pre-defined nuclear recoil energy range of 6.6-30.5 keVnr are consistent with the background expectation of (1.0 \pm 0.2) events. A Profile Likelihood analysis using a 6.6-43.3 keVnr energy range sets the most stringent limit on the spin-independent elastic WIMP-nucleon scattering cross section for WIMP masses above 8 GeV/c^2, with a minimum of 2 \times 10^-45 cm^2 at 55 GeV/c^2 and 90% confidence level. △ Less

Submitted 20 March, 2013; v1 submitted 25 July, 2012; originally announced July 2012.

Comments: 6 pages, 5 figures. Matches version accepted by PRL. Includes limits up to 10 TeV/c^2, published as supplementary material: http://prl.aps.org/supplemental/PRL/v109/i18/e181301 Please cite high mass limits as "Phys. Rev. Lett. 109, 181301 (2012), online supplementary material."

Journal ref: Phys. Rev. Lett. 109, 181301 (2012)

Measurement of the Quantum Efficiency of Hamamatsu R8520 Photomultipliers at Liquid Xenon Temperature

Authors: E. Aprile, M. Beck, K. Bokeloh, R. Budnik, B. Choi, H. A. Contreras, K. -L. Giboni, L. W. Goetzke, R. F. Lang, K. E. Lim, A. J. Melgarejo Fernandez, G. Plante, A. Rizzo, P. Shagin, C. Weinheimer

Abstract: Vacuum ultraviolet light sensitive photomultiplier tubes directly coupled to liquid xenon are being used to efficiently detect the 178 nm scintillation light in a variety of liquid xenon based particle detectors. Good knowledge of the performance of these photomultipliers under cryogenic conditions is needed to properly characterize these detectors. Here, we report on measurements of the quantum e… ▽ More Vacuum ultraviolet light sensitive photomultiplier tubes directly coupled to liquid xenon are being used to efficiently detect the 178 nm scintillation light in a variety of liquid xenon based particle detectors. Good knowledge of the performance of these photomultipliers under cryogenic conditions is needed to properly characterize these detectors. Here, we report on measurements of the quantum efficiency of Hamamatsu R8520 photomultipliers, used in the XENON Dark Matter Experiments. The quantum efficiency measurements at room temperature agree with the values provided by Hamamatsu. At low temperatures, between 160K and 170K, the quantum efficiency increases by $\sim5-11$% relative to the room temperature values. △ Less

Submitted 23 July, 2012; originally announced July 2012.

Analysis of the XENON100 Dark Matter Search Data

Authors: The XENON100 Collaboration, E. Aprile, M. Alfonsi, K. Arisaka, F. Arneodo, C. Balan, L. Baudis, A. Behrens, P. Beltrame, K. Bokeloh, E. Brown, G. Bruno, R. Budnik, J. M. R. Cardoso, W. -T. Chen, B. Choi, D. B. Cline, H. Contreras, J. P. Cussonneau, M. P. Decowski, E. Duchovni, S. Fattori, A. D. Ferella, W. Fulgione, F. Gao , et al. (49 additional authors not shown)

Abstract: The XENON100 experiment, situated in the Laboratori Nazionali del Gran Sasso, aims at the direct detection of dark matter in the form of weakly interacting massive particles (WIMPs), based on their interactions with xenon nuclei in an ultra low background dual-phase time projection chamber. This paper describes the general methods developed for the analysis of the XENON100 data. These methods have… ▽ More The XENON100 experiment, situated in the Laboratori Nazionali del Gran Sasso, aims at the direct detection of dark matter in the form of weakly interacting massive particles (WIMPs), based on their interactions with xenon nuclei in an ultra low background dual-phase time projection chamber. This paper describes the general methods developed for the analysis of the XENON100 data. These methods have been used in the 100.9 and 224.6 live days science runs from which results on spin-independent elastic, spin-dependent elastic and inelastic WIMP-nucleon cross-sections have already been reported. △ Less

Submitted 14 October, 2013; v1 submitted 14 July, 2012; originally announced July 2012.

Comments: 18 pages, 17 figures, information for the 224.6 live days run included

Journal ref: Astropart. Phys. 54 (2014) 11-24

Material screening and selection for XENON100

Authors: XENON100 Collaboration, E. Aprile, K. Arisaka, F. Arneodo, A. Askin, L. Baudis, A. Behrens, K. Bokeloh, E. Brown, J. M. R. Cardoso, B. Choi, D. Cline, S. Fattori, A. D. Ferella, K. L. Giboni, A. Kish, C. W. Lam, J. Lamblin, R. F. Lang, K. E. Lim, J. A. M. Lopes, T. Marrodan Undagoitia, Y. Mei, A. J. Melgarejo Fernandez, K. Ni , et al. (16 additional authors not shown)

Abstract: Results of the extensive radioactivity screening campaign to identify materials for the construction of XENON100 are reported. This Dark Matter search experiment is operated underground at Laboratori Nazionali del Gran Sasso (LNGS), Italy. Several ultra sensitive High Purity Germanium detectors (HPGe) have been used for gamma ray spectrometry. Mass spectrometry has been applied for a few low mass… ▽ More Results of the extensive radioactivity screening campaign to identify materials for the construction of XENON100 are reported. This Dark Matter search experiment is operated underground at Laboratori Nazionali del Gran Sasso (LNGS), Italy. Several ultra sensitive High Purity Germanium detectors (HPGe) have been used for gamma ray spectrometry. Mass spectrometry has been applied for a few low mass plastic samples. Detailed tables with the radioactive contaminations of all screened samples are presented, together with the implications for XENON100. △ Less

Submitted 22 June, 2011; v1 submitted 30 March, 2011; originally announced March 2011.

Comments: 8 pages, 1 figure

Journal ref: Astropart.Phys.35:43-49,2011

Xenon Recirculation-Purification with a Heat Exchanger

Authors: K. L. Giboni, E. Aprile, B. Choi, T. Haruyama, R. F. Lang, K. E. Lim, A. J. Melgarejo, G. Plante

Abstract: Liquid-xenon based particle detectors have been dramatically growing in size during the last years, and are now exceeding the one-ton scale. The required high xenon purity is usually achieved by continuous recirculation of xenon gas through a high-temperature getter. This challenges the traditional way of cooling these large detectors, since in a thermally well insulated detector, most of the cool… ▽ More Liquid-xenon based particle detectors have been dramatically growing in size during the last years, and are now exceeding the one-ton scale. The required high xenon purity is usually achieved by continuous recirculation of xenon gas through a high-temperature getter. This challenges the traditional way of cooling these large detectors, since in a thermally well insulated detector, most of the cooling power is spent to compensate losses from recirculation. The phase change during recondensing requires five times more cooling power than cooling the gas from ambient temperature to -100C (173 K). Thus, to reduce the cooling power requirements for large detectors, we propose to use the heat from the purified incoming gas to evaporate the outgoing xenon gas, by means of a heat exchanger. Generally, a heat exchanger would appear to be only of very limited use, since evaporation and liquefaction occur at zero temperature difference. However, the use of a recirculation pump reduces the pressure of the extracted liquid, forces it to evaporate, and thus cools it down. We show that this temperature difference can be used for an efficient heat exchange process. We investigate the use of a commercial parallel plate heat exchanger with a small liquid xenon detector. Although we expected to be limited by the available cooling power to flow rates of about 2 SLPM, rates in excess of 12 SLPM can easily be sustained, limited only by the pump speed and the impedance of the flow loop. The heat exchanger operates with an efficiency of (96.8 +/- 0.5)%. This opens the possibility for fast xenon gas recirculation in large-scale experiments, while minimizing thermal losses. △ Less

Submitted 4 March, 2011; originally announced March 2011.

Comments: 10 pages, 3 figures

Journal ref: JINST 6 P03002 (2011)

Electric field-induced quantum interference control in a semiconductor: A new manifestation of the Franz-Keldysh effect

Authors: J. K. Wahlstrand, H. Zhang, S. B. Choi, S. Kannan, D. S. Dessau, J. E. Sipe, S. T. Cundiff

Abstract: In (100)-oriented GaAs illuminated at normal incidence by a laser and its second harmonic, interference between one- and two-photon absorption results in ballistic current injection, but not modulation of the overall carrier injection rate. Results from a pump-probe experiment on a transversely biased sample show that a constant electric field enables coherent control of the carrier injection rate… ▽ More In (100)-oriented GaAs illuminated at normal incidence by a laser and its second harmonic, interference between one- and two-photon absorption results in ballistic current injection, but not modulation of the overall carrier injection rate. Results from a pump-probe experiment on a transversely biased sample show that a constant electric field enables coherent control of the carrier injection rate. We ascribe this to the nonlinear optical Franz-Keldysh effect and calculate it for a two-band parabolic model. The mechanism is relevant to centrosymmetric semiconductors as well. △ Less

Submitted 29 March, 2011; v1 submitted 11 August, 2010; originally announced August 2010.

Comments: 4 pages, 2 figures. New data, less theory

New Measurement of the Relative Scintillation Efficiency of Xenon Nuclear Recoils Below 10 keV

Authors: E. Aprile, L. Baudis, B. Choi, K. L. Giboni, K. E. Lim, A. Manalaysay, M. E. Monzani, G. Plante, R. Santorelli, M. Yamashita

Abstract: Liquid xenon is an important detection medium in direct dark matter experiments, which search for low-energy nuclear recoils produced by the elastic scattering of WIMPs with quarks. The two existing measurements of the relative scintillation efficiency of nuclear recoils below 20 keV lead to inconsistent extrapolations at lower energies. This results in a different energy scale and thus sensitiv… ▽ More Liquid xenon is an important detection medium in direct dark matter experiments, which search for low-energy nuclear recoils produced by the elastic scattering of WIMPs with quarks. The two existing measurements of the relative scintillation efficiency of nuclear recoils below 20 keV lead to inconsistent extrapolations at lower energies. This results in a different energy scale and thus sensitivity reach of liquid xenon dark matter detectors. We report a new measurement of the relative scintillation efficiency below 10 keV performed with a liquid xenon scintillation detector, optimized for maximum light collection. Greater than 95% of the interior surface of this detector was instrumented with photomultiplier tubes, giving a scintillation yield of 19.6 photoelectrons/keV electron equivalent for 122 keV gamma rays. We find that the relative scintillation efficiency for nuclear recoils of 5 keV is 0.14, staying constant around this value up to 10 keV. For higher energy recoils we measure a value around 20%, consistent with previously reported data. In light of this new measurement, the XENON10 experiment's results on spin-independent WIMP-nucleon cross section, which were calculated assuming a constant 0.19 relative scintillation efficiency, change from $8.8\times10^{-44}$ cm$^2$ to $9.9\times10^{-44}$ cm$^2$ for WIMPs of mass 100 GeV/c$^2$, and from $4.4\times10^{-44}$ cm$^2$ to $5.6\times10^{-44}$ cm$^2$ for WIMPs of mass 30 GeV/c$^2$. △ Less

Submitted 16 May, 2010; v1 submitted 1 October, 2008; originally announced October 2008.

Comments: 8 pages, 8 figures

Journal ref: Phys.Rev.C79:045807,2009

Development of the Low Energy Accelerator for Komac

Authors: B. H. Choi

Abstract: KAERI (Korea Atomic Energy Research Institute) has been performing the project named KOMAC (Korea Multi-purpose Accelerator Complex) within the frame work of national mid and long term nuclear research plan. The final objectives of KOMAC is to build a 20-MW (1 GeV and 20 mA) cw (100% duty factor) proton linear accelerator. As the first stage, the low energy accelerator up to 20 MeV is being deve… ▽ More KAERI (Korea Atomic Energy Research Institute) has been performing the project named KOMAC (Korea Multi-purpose Accelerator Complex) within the frame work of national mid and long term nuclear research plan. The final objectives of KOMAC is to build a 20-MW (1 GeV and 20 mA) cw (100% duty factor) proton linear accelerator. As the first stage, the low energy accelerator up to 20 MeV is being developed in KTF (KOMAC Test Facility). The low energy accelerator consists of an injector, RFQ, CCDTL, and RF systems. The proton injector with Duoplasmatron ion source has been developed, and the LEBT with solenoid lens is under development. The RFQ linac that will accelerate a 20mA proton beam from 50keV to 3MeV has been designed and is being fabricated. The RF system for RFQ is being developed, and the CCDTL up to 20MeV is being designed. The status of the low energy accelerator will be presented. △ Less

Submitted 18 August, 2000; originally announced August 2000.

Comments: jpg color version of all figures separated listed. Linac 2000 Conference paper ID No. TUD21

Journal ref: eConf C000821:TUD21,2000