Deep Ultraviolet Regime Research Articles

Fractional quantum mechanics meets quantum gravity phenomenology

This letter extends previous findings on the modified Schrödinger evolution inspired by quantum gravity phenomenology. By establishing a connection between this approach and fractional quantum mechanics, we provide insights into a potential deep infrared regime of quantum gravity, characterized by the emergence of fractal dimensions, similar to behaviors observed in the deep ultraviolet regime. Additionally, we explore the experimental investigations of this regime using Bose-Einstein condensates. Notably, our analysis reveals a direct implication of this analogy: general experiments probing fractional quantum mechanics may serve as equivalent models of quantum gravity. We identify instances of nonlocal behavior in such systems, suggesting an analogous phenomenon of nonlocality in quantum gravity.

Deep-ultraviolet transparent conducting SrSnO3 via heterostructure design.

Exploration and advancements in ultrawide bandgap (UWBG) semiconductors are pivotal for next-generation high-power electronics and deep-ultraviolet (DUV) optoelectronics. Here, we used a thin heterostructure design to facilitate high conductivity due to the low electron mass and relatively weak electron-phonon coupling, while the atomically thin films ensured high transparency. We used a heterostructure comprising SrSnO3/La:SrSnO3/GdScO3 (110), and applied electrostatic gating, which allow us to effectively separate charge carriers in SrSnO3 from dopants and achieve phonon-limited transport behavior in strain-stabilized tetragonal SrSnO3. This led to a modulation of carrier density from 1018 to 1020 cm-3, with room temperature mobilities ranging from 40 to 140 cm2 V-1 s-1. The phonon-limited mobility, calculated from first principles, closely matched experimental results, suggesting that room temperature mobility could be further increased with higher electron density. In addition, the sample exhibited 85% optical transparency at a 300-nm wavelength. These findings highlight the potential of heterostructure design for transparent UWBG semiconductor applications, especially in DUV regime.

Prospect of Hexagonal CsMg(I1–xBrx)3 Alloys for Deep-Ultraviolet Light Emission

Abstract Materials for deep-ultraviolet (DUV) light emission are extremely rare, significantly limiting the development of efficient DUV light-emitting diodes. Here we report CsMg(I1−x Br x )3 alloys as potential DUV light emitters. Based on rigorous first-principles hybrid functional calculations, we find that CsMgI3 has an indirect bandgap, while CsMgBr3 has a direct bandgap. Further, we employ a band unfolding technique for alloy supercell calculations to investigate the critical Br concentration in CsMg(I1−x Br x )3 associated with the crossover from an indirect to a direct bandgap, which is found to be ∼ 0.36. Thus, CsMg(I1−x Br x )3 alloys with 0.36 ⩽ x ⩽ 1 cover a wide range of direct bandgap (4.38–5.37 eV; 284–231 nm), falling well into the DUV regime. Our study will guide the development of efficient DUV light emitters.

Low-threshold AlGaN-based deep ultraviolet laser enabled by a nanoporous cladding layer.

We demonstrated an AlGaN-based multiple-quantum-well (MQW) deep ultraviolet (DUV) laser at 278 nm using a nanoporous (NP) n-AlGaN as the bottom cladding layer grown on the sapphire substrate. The laser has a very-low-threshold optically pumped power density of 79 kW/cm2 at room temperature and a transverse electric (TE)-polarization-dominant emission. The high optical confinement factor of 9.12% benefiting from the low refractive index of the nanoporous n-AlGaN is the key to enable a low-threshold lasing. The I-V electrical measurement demonstrates that an ohmic contact can be still achieved in the NP n-AlGaN with a larger but acceptable resistance, which indicates it is compatible with electrically driven laser devices. Our work provides insights into the design and fabrication of low-threshold lasers emitting in the DUV regime.

Modal Phase-Matched Bound States in the Continuum for Enhancing Third Harmonic Generation of Deep Ultraviolet Emission.

Coherent deep ultraviolet (DUV) light sources are crucial for various applications such as nanolithography, biomedical imaging, and spectroscopy. DUV light sources can be generated by using conventional nonlinear optical crystals (NLOs). However, NLOs are limited by their bulky size, inadequate transparency at the DUV regime, and stringent phase-matching requirements for harmonic generation. Recently, dielectric metasurfaces support high Q-factor resonances and offer a promising approach for efficient harmonic generation at short wavelengths. In this study, we demonstrated a crystalline silicon (c-Si) metasurface simultaneously exciting modal phase-matched bound states in the continuum (BIC) resonance at the fundamental wavelength of 840 nm with a higher degree of freedom for precise control of the BIC resonance and a plasmonic resonance at the wavelength of 280 nm in the DUV to enhance third harmonic generation (THG). We experimentally achieved a Q-factor of ∼180 owing to the relatively large refractive index of the c-Si and the geometric symmetry breaking of the structure. We realized THG at a wavelength of 280 nm with a power of 14.5 nW by using a peak power density of 15 GW/cm2 excitation. The measured THG power is 14 times higher than the state-of-the-art THG dielectric metasurfaces using the same peak power density in the DUV regime, and the maximum obtained THG power enhancement factor is up to 48. This approach relies on the significant third-order nonlinear susceptibility of c-Si, the interband plasmonic nature of the c-Si in the DUV, and the strong field confinement of BIC resonance to boost overall nonlinear conversion efficiency to 5.2 × 10-6% in the DUV regime. Our work shows the potential of c-Si BIC metasurfaces for developing efficient and ultracompact DUV light sources using high-efficacy nonlinear optical devices.

Ultraviolet dimensional reduction of spacetime with zero-point length

Among the many disparate approaches towards quantum gravity, the reduction of spacetime dimension in the ultraviolet regime is expected to be a common thread. The spectral dimension of spacetime is defined in the context of diffusion processes on a manifold. We show that a spacetime with zero-point length has spectral dimension 3.5 when the characteristic diffusion time has the size of the zero-point length. The spectral dimension (negatively) diverges for an even shorter diffusion time, thus preventing reliable physical interpretation in the deep ultraviolet regime. The thermodynamic dimension is defined by realizing that the free energy F(beta ) of a free field or ideal gas at finite temperature (beta ^{-1}) in D dimensions scales as Fsim beta ^{-D}. Using Schwinger’s proper time formalism, we show that for spacetime incorporating a zero-point length, the thermodynamic dimension reduces to 1.5 near the Planck scale and then to 1 in the deep ultraviolet regime. This signifies a “phase-transition” in which a (massless) bosonic ideal gas in four dimensions essentially behaves like radiation (w=1/3) at low energies, whereas near the Planck scale, it behaves equivalently to having an equation of state parameter w=2. Furthermore, dimension can be deduced from the potential V_D(r) of interaction between two point-like sources separated at a distance r as its scaling depends on D. Comparing with the scaling behavior of conventional Yukawa-like potentials at short distances, we show that the ultraviolet dimension appears to be either 2 or 3 depending on the use of massive or massless force carriers as probes.

Deep ultra-violet plasmonics: exploiting momentum-resolved electron energy loss spectroscopy to probe germanium.

Germanium is typically used for solid-state electronics, fiber-optics, and infrared applications, due to its semiconducting behavior at optical and infrared wavelengths. In contrast, here we show that the germanium displays metallic nature and supports propagating surface plasmons in the deep ultraviolet (DUV) wavelengths, that is typically not possible to achieve with conventional plasmonic metals such as gold, silver, and aluminum. We measure the photonic band spectrum and distinguish the plasmonic excitation modes: bulk plasmons, surface plasmons, and Cherenkov radiation using a momentum-resolved electron energy loss spectroscopy. The observed spectrum is validated through the macroscopic electrodynamic electron energy loss theory and first-principles density functional theory calculations. In the DUV regime, intraband transitions of valence electrons dominate over the interband transitions, resulting in the observed highly dispersive surface plasmons. We further employ these surface plasmons in germanium to design a DUV radiation source based on the Smith-Purcell effect. Our work opens a new frontier of DUV plasmonics to enable the development of DUV devices such as metasurfaces, detectors, and light sources based on plasmonic germanium thin films.

AlGaN-based deep ultraviolet micro-LED emitting at 275 nm.

The investigation of electrical and optical properties of micro-scale AlGaN deep ultraviolet (DUV) light-emitting diodes (LEDs) emitting at ∼275nm was carried out, with an emphasis on fabricated devices having a diameter of 300, 200, 100, 50, and 20 µm, respectively. It was revealed that the LED chips with smaller mesa areas deliver considerably higher light output power density; meanwhile, they can sustain a higher current density, which is mainly attributed to the enhanced current spreading uniformity in micro-scale chips. Importantly, when the diameter of LED chips decreases from 300 µm to 20 µm, the peak external quantum efficiency (EQE) increases by 20%, and the EQE peak current density can be boosted from 8.85A/cm2 and 99.52A/cm2. Moreover, we observed a longer wavelength emission with enlarged full-width at half-maximum (FWHM) in the LEDs with smaller chip sizes because of the self-heating effect at high current injection. These experimental observations provide insights into the design and fabrication of high-efficiency micro-LEDs emitting in the DUV regime with different device geometries for various future applications.

Diamond step-index nanowaveguide to structure light efficiently in near and deep ultraviolet regimes

Two-dimensional metamaterials, consisting of an array of ultrathin building blocks, offer a versatile and compact platform for tailoring the properties of the electromagnetic waves. Such flat metasurfaces provide a unique solution to circumvent the limitations imposed by their three-dimensional counterparts. Albeit several successful demonstrations of metasurfaces have been presented in the visible, infrared, and terahertz regimes, etc., there is hardly any demonstration for ultraviolet wavelengths due to the unavailability of the appropriate lossless materials. Here, we present diamond as an ultra-low loss material for the near and deep ultraviolet (UV) light and engineer diamond step-index nanowaveguides (DSINs) to achieve full control over the phase and amplitude of the incident wave. A comprehensive analytical solution of step-index nanowaveguides (supported by the numerical study) is provided to describe the underlying mechanism of such controlled wavefront shaping. Due to the ultra-low loss nature of diamond in near and deep UV regimes, our DSINs and metasurfaces designed (from them) exhibit a decent efficiency of ≈ 84% over the entire spectrum of interest. To verify this high efficiency and absolute control over wavefront, we have designed polarization-insensitive meta-holograms through optimized DSINs for operational wavelength λ = 250 nm.

Femto- and nanosecond pulse duration dependence of the single-shot ablation threshold and multiple-shot morphology change of poly L-lactic acid in deep ultraviolet regime

Laser processing is a common method used to shape various structures of biodegradable polymers. In this study, we demonstrate PLLA processing with intense deep ultraviolet (DUV) pulses at 266 nm and compare the processing properties using a nanosecond DUV laser. Results allow comparison of the single-shot ablation thresholds and multiple-shot morphology of both the femtosecond and nanosecond DUV laser. For sing-shot experiments, the ablation threshold of femtosecond laser is, at least, one order of magnitude lower than that of nanosecond laser. For multiple-shot experiments, the result provides superior quality of the crater morphology in the DUV femtosecond regime.

Random Tensors and Quantum Gravity

We provide an informal introduction to tensor field theories and to their associated renormalization group. We focus more on the general motivations coming from quantum gravity than on the technical details. In particular we discuss how asymptotic freedom of such tensor field theories gives a concrete example of a natural "quantum relativity" postulate: physics in the deep ultraviolet regime becomes asymptotically more and more independent of any particular choice of Hilbert basis in the space of states of the universe.

Electronic, Crystal Chemistry, and Nonlinear Optical Property Relationships in the Dugganite A3B3CD2O14 Family.

A family of six nonlinear optical (NLO) materials, A3B3CD2O14 (A = Sr, Ba, or Pb; B = Mg or Zn; C = Te or W; and D = P or V), has been synthesized and characterized. In addition to the synthesis and crystal structures, comprehensive characterization of these compounds includes second harmonic generation (SHG) measurements, theoretical calculations, infrared and diffuse reflectance spectroscopies, and thermogravimetric measurements. We find that all of the reported materials are SHG-active at 1064 nm, with responses ranging from 2.8 to 13.5 × KDP, and exhibit absorption edges in the mid- to deep-ultraviolet regime. By systematically replacing the A, B, C, and D cations, we are able to tune these properties and investigate the role of different NLO-active structural units in producing the SHG responses. Specifically, our electronic structure calculations reveal that the presence of Pb(2+) on the A-site and Te(6+) on the C-site is critical for generating a large SHG response. The synthesis and structure-property relationships described in this family of materials will enable the design and discovery of new NLO materials.

Confining energy migration in upconversion nanoparticles towards deep ultraviolet lasing.

Manipulating particle size is a powerful means of creating unprecedented optical properties in metals and semiconductors. Here we report an insulator system composed of NaYbF4:Tm in which size effect can be harnessed to enhance multiphoton upconversion. Our mechanistic investigations suggest that the phenomenon stems from spatial confinement of energy migration in nanosized structures. We show that confining energy migration constitutes a general and versatile strategy to manipulating multiphoton upconversion, demonstrating an efficient five-photon upconversion emission of Tm3+ in a stoichiometric Yb lattice without suffering from concentration quenching. The high emission intensity is unambiguously substantiated by realizing room-temperature lasing emission at around 311 nm after 980-nm pumping, recording an optical gain two orders of magnitude larger than that of a conventional Yb/Tm-based system operating at 650 nm. Our findings thus highlight the viability of realizing diode-pumped lasing in deep ultraviolet regime for various practical applications.

Optical properties of transition metal atom adsorbed graphene: A density functional theoretical calculation

Electronic and optical properties of 3d-transition metal adsorbed graphene system, theoretically studied in the framework of density functional theory, reveals significant modification compared to the pristine system. Due to adsorption of transition metal, the emergence of closely separated electronic bands leads to substantial amount of low energy optical absorption below 2.0eV photon energy. Very significant enhancement of static dielectric constant and large value of reflectivity in the low optical energy regime has been identified for different adsorbed systems. In the different 3d-transition metal adsorbed systems, particularly up to the half filled d-shell transition metal atom, pronounced emergence of optical absorption line in the deep ultraviolet regime beyond 30.0eV photon energy is observed.

Broadband plasmonic response of self-organized aluminium nanowire arrays

We investigated the plasmonic response of arrays of Al nanowires fabricated in high-vacuum and embedded within a transparent protective medium. The nanostructures exhibited a strongly-birefringent plasmonic response which, depending on the mutual orientation of the incident-field polarization and the nanowire axis, allowed the plasmon resonance to span the whole spectral range from the visible to the deep-ultraviolet regime. Comparing the experimental data with theoretical calculations allowed to rationalize the optical response in terms of non-ideal nanowire morphologies arising from the bottom-up character of the nanofabrication method. The broadband plasmonic response suggests the potential application of these systems in plasmon-enhanced photovoltaics, exploiting the great advantage of the low-cost of aluminium.

Higher particle form factors of branch point twist fields in integrable quantum field theories

In this paper we compute higher particle form factors of branch point twist fields. These fields were first described in the context of massive (1+1)-dimensional integrable quantum field theories and their correlation functions are related to the bi-partite entanglement entropy. We find analytic expressions for some form factors and check those expressions for consistency, mainly by evaluating the conformal dimension of the corresponding twist field in the underlying conformal field theory. We find that solutions to the form factor equations are not unique so various techniques need to be used to identify those corresponding to the branch point twist field we are interested in. The models for which we carry out our study are characterized by staircase patterns of various physical quantities as functions of the energy scale. As the latter is varied, the β-function associated with these theories comes close to vanishing at several points between the deep infrared and deep ultraviolet regimes. In other words, renormalization group flows approach the vicinity of various critical points before ultimately reaching the ultraviolet fixed point. This feature provides an optimal way of checking the consistency of higher particle form factor solutions, as the changes on the conformal dimension of the twist field at various energy scales can only be accounted for by considering higher particle form factor contributions to the expansion of certain correlation functions.

Fractional dynamics and the TeV regime of field theory

Fractional dynamics offers a reliable tool for the study of far-from equilibrium processes that display scale-invariant properties, dissipation and long-range correlations. This is particularly attractive when dealing with the complex dynamics generated in the deep ultraviolet regime of quantum field theory. We analyze a simple scalar field Lagrangian using Caputo derivatives and the approximation of low-level fractionality. Results may be extrapolated to more realistic field models and suggest a series of surprising implications regarding phenomena that are expected to emerge beyond the range of the standard model for particle physics.

High reflectance of reflective-type attenuated-phase-shifting masks for extreme ultraviolet lithography with high inspection contrast in deep ultraviolet regimes

Phase-shifting masks are a vital resolution enhance technique that will be used in extreme ultraviolet (EUV) lithography beyond the 20nm node. In this article, we demonstrate a structure for a reflective-type attenuated phase-shifting mask, which is based on a Fabry–Perot structure with common materials in EUV masks. The mask structure not only performs 180° phase shift with high reflectance at EUV wavelength, but also has high inspection contrast at deep ultraviolet (DUV) wavelength. The top layer of mask structures exhibits good conductivity, which can alleviate the charging effect during electron-beam patterning. The reflectance ratio of the absorber stack could be tuned from 32.6% (TaN∕SiO2∕Mo) to 4.4% (TaN∕SiO2∕TaN) by choosing different bottom layers and thickness. The inspection contrast could be raised to 99% with large thickness-control tolerance.

Design considerations of a MW-scale, high-efficiency, industrial-use, ultraviolet FEL amplifier

Theoretical and experimental work in free electron laser (FEL) physics, and the physics of particle accelerators over the last 10 years has pointed to the possibility of the generation of MW-level optical beams with laser-like characteristics in the ultraviolet (UV) spectral range. The concept is based on generation of the radiation in the master oscillator–power FEL amplifier (MOPA) configuration. The FEL amplifier concept eliminates the need for an optical cavity. As a result, there are no thermal loading limitations to increase the average output power of this device up to the MW-level. The problem of a tunable master oscillator can be solved with available conventional quantum lasers. The use of a superconducting energy-recovery linac could produce a major, cost-effective facility with wall plug power to output optical power efficiency of about 20% that spans wavelengths from the visible to the deep ultraviolet regime. The stringent electron beam qualities required for UV FEL amplifier operation can be met with a conservative injector design (using a conventional thermionic gun and subharmonic bunchers) and the beam compression and linear acceleration technology, recently developed in connection with high-energy linear collider and X-ray FEL programs.

A novel bottom antireflective coating working for both KrF and ArF excimer laser lithography

Hexamethyldisiloxane (HMDSO) is used as coating material in a conventional ECR-PECVD process. By simply adjusting the gas flow rate ratio, the material can be varied to have suitable optical constants for making bottom antireflective coating (BARC) layers working at both 248 nm and 193 nm wavelengths. The measured reflectances lower than 1 % on a silicon crystal substrate at both wavelengths have been achieved. The swing effect in the resist is significantly reduced. We also show that an HMDSO-based multi-layer structure can be used for broadband AR coating in deep ultraviolet regimes.