Showing papers on "Laser published in 2020"

X-Rays and Extreme Ultraviolet Radiation: Principles and Applications

Abstract: This self-contained, comprehensive book describes the fundamental properties of soft x-rays and extreme ultraviolet (EUV) radiation and discusses their applications in a wide variety of fields, including EUV lithography for semiconductor chip manufacture and soft x-ray biomicroscopy. The author begins by presenting the relevant basic principles such as radiation and scattering, wave propagation, diffraction, and coherence. He then goes on to examine a broad range of phenomena and applications. The topics covered include EUV lithography, biomicroscopy, spectromicroscopy, EUV astronomy, synchrotron radiation, and soft x-ray lasers. He also provides a great deal of useful reference material such as electron binding energies, characteristic emission lines and photo-absorption cross-sections. The book will be of great interest to graduate students and researchers in engineering, physics, chemistry, and the life sciences. It will also appeal to practicing engineers involved in semiconductor fabrication and materials science.

Laser-induced plasmas and applications

Abstract: This book discusses optical science, engineering, and technology Topics covered include the laser and its many commercial and industrial applications, the new optical materials, gradient index optics, electro- and acousto-optics, fiber optics and communications, optical computing and pattern recognition, optical data reading, recording and storage, biomedical instrumentation, industrial robotics, integrated optics, infrared and ultraviolet systems

Electrically pumped topological laser with valley edge modes.

Abstract: Quantum cascade lasers are compact, electrically pumped light sources in the technologically important mid-infrared and terahertz region of the electromagnetic spectrum1,2. Recently, the concept of topology3 has been expanded from condensed matter physics into photonics4, giving rise to a new type of lasing5-8 using topologically protected photonic modes that can efficiently bypass corners and defects4. Previous demonstrations of topological lasers have required an external laser source for optical pumping and have operated in the conventional optical frequency regime5-8. Here we demonstrate an electrically pumped terahertz quantum cascade laser based on topologically protected valley edge states9-11. Unlike topological lasers that rely on large-scale features to impart topological protection, our compact design makes use of the valley degree of freedom in photonic crystals10,11, analogous to two-dimensional gapped valleytronic materials12. Lasing with regularly spaced emission peaks occurs in a sharp-cornered triangular cavity, even if perturbations are introduced into the underlying structure, owing to the existence of topologically protected valley edge states that circulate around the cavity without experiencing localization. We probe the properties of the topological lasing modes by adding different outcouplers to the topological cavity. The laser based on valley edge states may open routes to the practical use of topological protection in electrically driven laser sources.

Massively parallel coherent laser ranging using a soliton microcomb

Abstract: Coherent ranging, also known as frequency-modulated continuous-wave (FMCW) laser-based light detection and ranging (lidar)1 is used for long-range three-dimensional distance and velocimetry in autonomous driving2,3. FMCW lidar maps distance to frequency4,5 using frequency-chirped waveforms and simultaneously measures the Doppler shift of the reflected laser light, similar to sonar or radar6,7 and coherent detection prevents interference from sunlight and other lidar systems. However, coherent ranging has a lower acquisition speed and requires precisely chirped8 and highly coherent5 laser sources, hindering widespread use of the lidar system and impeding parallelization, compared to modern time-of-flight ranging systems that use arrays of individual lasers. Here we demonstrate a massively parallel coherent lidar scheme using an ultra-low-loss photonic chip-based soliton microcomb9. By fast chirping of the pump laser in the soliton existence range10 of a microcomb with amplitudes of up to several gigahertz and a sweep rate of up to ten megahertz, a rapid frequency change occurs in the underlying carrier waveform of the soliton pulse stream, but the pulse-to-pulse repetition rate of the soliton pulse stream is retained. As a result, the chirp from a single narrow-linewidth pump laser is transferred to all spectral comb teeth of the soliton at once, thus enabling parallelism in the FMCW lidar. Using this approach we generate 30 distinct channels, demonstrating both parallel distance and velocity measurements at an equivalent rate of three megapixels per second, with the potential to improve sampling rates beyond 150 megapixels per second and to increase the image refresh rate of the FMCW lidar by up to two orders of magnitude without deterioration of eye safety. This approach, when combined with photonic phase arrays11 based on nanophotonic gratings12, provides a technological basis for compact, massively parallel and ultrahigh-frame-rate coherent lidar systems. A massively parallel coherent light detection and ranging (lidar) scheme using a soliton microcomb—a light source that emits a wide spectrum of sharp lines with equally spaced frequencies—is described.

A MHz-repetition-rate hard X-ray free-electron laser driven by a superconducting linear accelerator

Abstract: The European XFEL is a hard X-ray free-electron laser (FEL) based on a high-electron-energy superconducting linear accelerator. The superconducting technology allows for the acceleration of many electron bunches within one radio-frequency pulse of the accelerating voltage and, in turn, for the generation of a large number of hard X-ray pulses. We report on the performance of the European XFEL accelerator with up to 5,000 electron bunches per second and demonstrating a full energy of 17.5 GeV. Feedback mechanisms enable stabilization of the electron beam delivery at the FEL undulator in space and time. The measured FEL gain curve at 9.3 keV is in good agreement with predictions for saturated FEL radiation. Hard X-ray lasing was achieved between 7 keV and 14 keV with pulse energies of up to 2.0 mJ. Using the high repetition rate, an FEL beam with 6 W average power was created.

Reversible 3D laser printing of perovskite quantum dots inside a transparent medium

Abstract: The three-dimensional (3D) patterning of semiconductors is potentially important for exploring new functionalities and applications in optoelectronics1,2. Here, we show that it is possible to write on demand 3D patterns of perovskite quantum dots (QDs) inside a transparent glass material using a femtosecond laser. By utilizing the inherent ionic nature and low formation energy of perovskite, highly luminescent CsPbBr3 QDs can be reversibly fabricated in situ and decomposed through femtosecond laser irradiation and thermal annealing. This pattern of writing and erasing can be repeated for many cycles, and the luminescent QDs are well protected by the inorganic glass matrix, resulting in stable perovskite QDs with potential applications such as high-capacity optical data storage, information encryption and 3D artwork. Luminescent CsPbBr3 quantum dots can be written into glass using femtosecond laser pulses and thermal annealing, and erased by further femtosecond laser irradiation. The resulting quantum dot patterns could prove useful for data storage, decoration or security purposes.

The role of side-branching in microstructure development in laser powder-bed fusion

Abstract: In-depth understanding of microstructure development is required to fabricate high quality products by additive manufacturing (for example, 3D printing). Here we report the governing role of side-branching in the microstructure development of alloys by laser powder bed fusion. We show that perturbations on the sides of cells (or dendrites) facilitate crystals to change growth direction by side-branching along orthogonal directions in response to changes in local heat flux. While the continuous epitaxial growth is responsible for slender columnar grains confined to the centreline of melt pools, side-branching frequently happening on the sides of melt pools enables crystals to follow drastic changes in thermal gradient across adjacent melt pools, resulting in substantial broadening of grains. The variation of scan pattern can interrupt the vertical columnar microstructure, but promotes both in-layer and out-of-layer side-branching, in particular resulting in the helical growth of microstructure in a chessboard strategy with 67° rotation between layers. Understanding metal component microstructure during 3D printing remains a challenge. Here, the authors use local thermal parameters and the solidification microstructure to better understand how the printed microstructure varies with the laser scan strategy.

Nucleation-controlled growth of superior lead-free perovskite Cs3Bi2I9 single-crystals for high-performance X-ray detection.

Abstract: The organic-inorganic hybrid lead halide perovskites have emerged as a series of star materials for solar cells, lasers and detectors. However, the issues raised by the toxic lead element and marginal stability due to the volatile organic components have severely limited their potential applications. In this work, we develop a nucleation-controlled solution method to grow large size high-quality Cs3Bi2I9 perovskite single crystals (PSCs). Using the technique, we harvest some centimeter-sized single crystals and achieved high device performance. We find that X-ray detectors based on PSCs exhibit high sensitivity of 1652.3 μC Gyair−1 cm−2 and very low detectable dose rate of 130 nGyair s−1, both desired in medical diagnostics. In addition, its outstanding thermal stability inspires us to develop a high temperature X-ray detector with stable response at up to 100 °C. Furthermore, PSCs exhibit high X-ray imaging capability thanks to its negligible signal drifting and extremely high stability. Organic-inorganic hybrid halide perovskites have been emerged as promising candidates for X-ray detectors while toxicity and instability are known issues. Here, Zhang et al. grow large size lead-free single crystals for high performance X-ray detection and imaging devices that can operate at 100 °C.

Tunable isolated attosecond X-ray pulses with gigawatt peak power from a free-electron laser

Abstract: The quantum-mechanical motion of electrons in molecules and solids occurs on the sub-femtosecond timescale. Consequently, the study of ultrafast electronic phenomena requires the generation of laser pulses shorter than 1 fs and of sufficient intensity to interact with their target with high probability. Probing these dynamics with atomic-site specificity requires the extension of sub-femtosecond pulses to the soft X-ray spectral region. Here, we report the generation of isolated soft X-ray attosecond pulses with an X-ray free-electron laser. Our source has a pulse energy that is millions of times larger than any other source of isolated attosecond pulses in the soft X-ray spectral region, with a peak power exceeding 100 GW. This unique combination of high intensity, high photon energy and short pulse duration enables the investigation of electron dynamics with X-ray nonlinear spectroscopy and single-particle imaging, unlocking a path towards a new era of attosecond science. The generation of ultrashort X-ray pulses with a peak power exceeding 100 GW offers new opportunities for studying electron dynamics with nonlinear spectroscopy and single-particle imaging.

Materials chemistry and engineering in metal halide perovskite lasers

Abstract: The invention and development of the laser have revolutionized science, technology, and industry. Metal halide perovskites are an emerging class of semiconductors holding promising potential in further advancing the laser technology. In this Review, we provide a comprehensive overview of metal halide perovskite lasers from the viewpoint of materials chemistry and engineering. After an introduction to the materials chemistry and physics of metal halide perovskites, we present diverse optical cavities for perovskite lasers. We then comprehensively discuss various perovskite lasers with particular functionalities, including tunable lasers, multicolor lasers, continuous-wave lasers, single-mode lasers, subwavelength lasers, random lasers, polariton lasers, and laser arrays. Following this a description of the strategies for improving the stability and reducing the toxicity of metal halide perovskite lasers is provided. Finally, future research directions and challenges toward practical technology applications of perovskite lasers are provided to give an outlook on this emerging field.

Thulium fiber laser: the new player for kidney stone treatment? A comparison with Holmium:YAG laser

Abstract: To compare the operating modes of the Holmium:YAG laser and Thulium fiber laser. Additionally, currently available literature on Thulium fiber laser lithotripsy is reviewed. Medline, Scopus, Embase, and Web of Science databases were searched for articles relating to the operating modes of Holmium:YAG and Thulium fiber lasers, including systematic review of articles on Thulium fiber laser lithotripsy. The laser beam emerging from the Holmium:YAG laser involves fundamental architectural design constraints compared to the Thulium fiber laser. These differences translate into multiple potential advantages in favor of the Thulium fiber laser: four-fold higher absorption coefficient in water, smaller operating laser fibers (50–150 µm core diameter), lower energy per pulse (as low as 0.025 J), and higher maximal pulse repetition rate (up to 2000 Hz). Multiple comparative in vitro studies suggest a 1.5–4 times faster stone ablation rate in favor of the Thulium fiber laser. The Thulium fiber laser overcomes the main limitations reported with the Holmium:YAG laser relating to lithotripsy, based on preliminary in vitro studies. This innovative laser technology seems particularly advantageous for ureteroscopy and may become an important milestone for kidney stone treatment.

A high-performance topological bulk laser based on band-inversion-induced reflection.

Abstract: Topological insulators are materials that behave as insulators in the bulk and as conductors at the edge or surface due to the particular configuration of their bulk band dispersion. However, up to date possible practical applications of this band topology on materials' bulk properties have remained abstract. Here, we propose and experimentally demonstrate a topological bulk laser. We pattern semiconductor nanodisk arrays to form a photonic crystal cavity showing topological band inversion between its interior and cladding area. In-plane light waves are reflected at topological edges forming an effective cavity feedback for lasing. This band-inversion-induced reflection mechanism induces single-mode lasing with directional vertical emission. Our topological bulk laser works at room temperature and reaches the practical requirements in terms of cavity size, threshold, linewidth, side-mode suppression ratio and directionality for most practical applications according to Institute of Electrical and Electronics Engineers and other industry standards. We believe this bulk topological effect will have applications in near-field spectroscopy, solid-state lighting, free-space optical sensing and communication.

High-purity orbital angular momentum states from a visible metasurface laser

Abstract: Orbital angular momentum (OAM) from lasers holds promise for compact, at-source solutions for applications ranging from imaging to communications. However, conjugate symmetry between circular spin and opposite helicity OAM states (±l) from conventional spin–orbit approaches has meant that complete control of light’s angular momentum from lasers has remained elusive. Here, we report a metasurface-enhanced laser that overcomes this limitation. We demonstrate new high-purity OAM states with quantum numbers reaching l = 100 and non-symmetric vector vortex beams that lase simultaneously on independent OAM states as much as Δl = 90 apart, an extreme violation of previous symmetric spin–orbit lasing devices. Our laser conveniently outputs in the visible, producing new OAM states of light as well as all previously reported OAM modes from lasers, offering a compact and power-scalable source that harnesses intracavity structured matter for the creation of arbitrary chiral states of structured light. A metasurface laser generates orbital angular momentum states with quantum numbers reaching l = 100. Simultaneous output vortex beams, with Δl as great as 90, are demonstrated in the visible regime.

MEMS Mirrors for LiDAR: A review.

Abstract: In recent years, Light Detection and Ranging (LiDAR) has been drawing extensive attention both in academia and industry because of the increasing demand for autonomous vehicles. LiDAR is believed to be the crucial sensor for autonomous driving and flying, as it can provide high-density point clouds with accurate three-dimensional information. This review presents an extensive overview of Microelectronechanical Systems (MEMS) scanning mirrors specifically for applications in LiDAR systems. MEMS mirror-based laser scanners have unrivalled advantages in terms of size, speed and cost over other types of laser scanners, making them ideal for LiDAR in a wide range of applications. A figure of merit (FoM) is defined for MEMS mirrors in LiDAR scanners in terms of aperture size, field of view (FoV) and resonant frequency. Various MEMS mirrors based on different actuation mechanisms are compared using the FoM. Finally, a preliminary assessment of off-the-shelf MEMS scanned LiDAR systems is given.

Photobiomodulation-Underlying Mechanism and Clinical Applications.

Abstract: The purpose of this study is to explore the possibilities for the application of laser therapy in medicine and dentistry by analyzing lasers' underlying mechanism of action on different cells, with a special focus on stem cells and mechanisms of repair. The interest in the application of laser therapy in medicine and dentistry has remarkably increased in the last decade. There are different types of lasers available and their usage is well defined by different parameters, such as: wavelength, energy density, power output, and duration of radiation. Laser irradiation can induce a photobiomodulatory (PBM) effect on cells and tissues, contributing to a directed modulation of cell behaviors, enhancing the processes of tissue repair. Photobiomodulation (PBM), also known as low-level laser therapy (LLLT), can induce cell proliferation and enhance stem cell differentiation. Laser therapy is a non-invasive method that contributes to pain relief and reduces inflammation, parallel to the enhanced healing and tissue repair processes. The application of these properties was employed and observed in the treatment of various diseases and conditions, such as diabetes, brain injury, spinal cord damage, dermatological conditions, oral irritation, and in different areas of dentistry.

2D Material Optoelectronics for Information Functional Device Applications: Status and Challenges

Abstract: Graphene and the following derivative 2D materials have been demonstrated to exhibit rich distinct optoelectronic properties, such as broadband optical response, strong and tunable light-mater interactions, and fast relaxations in the flexible nanoscale. Combining with optical platforms like fibers, waveguides, grating, and resonators, these materials has spurred a variety of active and passive applications recently. Herein, the optical and electrical properties of graphene, transition metal dichalcogenides, black phosphorus, MXene, and their derivative van der Waals heterostructures are comprehensively reviewed, followed by the design and fabrication of these 2D material-based optical structures in implementation. Next, distinct devices, ranging from lasers to light emitters, frequency convertors, modulators, detectors, plasmonic generators, and sensors, are introduced. Finally, the state-of-art investigation progress of 2D material-based optoelectronics offers a promising way to realize new conceptual and high-performance applications for information science and nanotechnology. The outlook on the development trends and important research directions are also put forward.

Laser‐Driven Strong‐Field Terahertz Sources

Abstract: DOI: 10.1002/adom.201900681 reason for this interest relies on the fact that THz radiation can couple resonantly to numerous fundamental motions of ions, electrons, and electron spins in all phases of matter. For example, in solids, the THz range overlaps with the frequency of lattice vibrations (phonons), the collision rates of conduction electrons, the binding energy of bound electron–hole pairs (excitons), and the precession frequency of spin waves (magnons). Consequently, THz radiation, both continuous-wave and pulsed, has been used for characterization of and gaining insight into elementary processes in complex materials. The majority of these studies used relatively weak THz fields and, thus, probed the linear response of the material, without inducing notable material modifications. Only recently, however, completely new avenues in THz science were opened up by triggering nonlinear THz responses of materials.[3–13] Instead of using weak fields to primarily observe selected THz modes such as phonons or magnons, strong fields allow one to actively drive them to unprecedentedly large amplitudes, potentially thereby resulting in novel states of matter.[6,8,11] For example, simulations suggest that exciting matter with intense THz transients may lead to massive modifications of electrically[14] or magnetically[15] ordered domains and enable the acceleration of free ions to ≈1 MeV,[16] and postacceleration to 50–100 MeV energies.[17] Remarkable experimental results such as switching of magnetic order,[18,19] parametric amplification of optical phonons,[20] novel insights into spin-lattice coupling,[21,22] and acceleration of free electrons in a THz linear accelerator[23] were achieved only recently. This progress has been made possible by the development of laser-driven table-top THz sources routinely providing pulses with unprecedented energies and peak electric and magnetic field strengths throughout the entire THz spectral range. Different laser-based THz pulse generation techniques can be used to access different parts of the spectral range extending from 0.1 to 10 THz. Some of the recently developed technologies enable the generation of radiation with even larger bandwidth or tuning range up to 100 THz and beyond, which lead to an extension of what is called the THz spectral range. An overview of the approximate spectral coverage and the achieved highest pulse energies and peak electric-field strengths of various laserdriven technologies is given in Figure 1.

Low-threshold topological nanolasers based on the second-order corner state.

Abstract: Topological lasers are immune to imperfections and disorder. They have been recently demonstrated based on many kinds of robust edge states, which are mostly at the microscale. The realization of 2D on-chip topological nanolasers with a small footprint, a low threshold and high energy efficiency has yet to be explored. Here, we report the first experimental demonstration of a topological nanolaser with high performance in a 2D photonic crystal slab. A topological nanocavity is formed utilizing the Wannier-type 0D corner state. Lasing behaviour with a low threshold of approximately 1 µW and a high spontaneous emission coupling factor of 0.25 is observed with quantum dots as the active material. Such performance is much better than that of topological edge lasers and comparable to that of conventional photonic crystal nanolasers. Our experimental demonstration of a low-threshold topological nanolaser will be of great significance to the development of topological nanophotonic circuitry for the manipulation of photons in classical and quantum regimes. A high-performance topological laser could pave the way for its use in a wide range of nanophotonic applications. Semiconductor lasers are the most common type of laser, but their performance deteriorates if there are any structural defects in the lasing material. Topological lasers allow light to travel around a cavity of any shape without scattering, promising better performing lasers. However, creating a topological laser with a low threshold for lasing and high efficiency has proved challenging. A team of Chinese researchers led by Xiulai Xu from the Chinese Academy of Sciences have now developed a topological laser made from a two-dimensional photonic crystal nanocavity slab with a lasing threshold of about one micro-watt and high spontaneous emission coupling factor of 0.25 and is comparable to the performance of conventional semiconductor lasers.

Observation of extremely efficient terahertz generation from mid-infrared two-color laser filaments

Abstract: Extreme nonlinear interactions of THz electromagnetic fields with matter are the next frontier in nonlinear optics. However, reaching this frontier in free space is limited by the existing lack of appropriate powerful THz sources. Here, we experimentally demonstrate that two-color filamentation of femtosecond mid-infrared laser pulses at 3.9 μm allows one to generate ultrashort sub-cycle THz pulses with sub-milijoule energy and THz conversion efficiency of 2.36%, resulting in THz field amplitudes above 100 MV cm−1. Our numerical simulations predict that the observed THz yield can be significantly upscaled by further optimizing the experimental setup. Finally, in order to demonstrate the strength of our THz source, we show that the generated THz pulses are powerful enough to induce nonlinear cross-phase modulation in electro-optic crystals. Our work paves the way toward free space extreme nonlinear THz optics using affordable table-top laser systems. Powerful terahertz pulses are generated during the nonlinear propagation of ultrashort laser pulses in gases. Here, the authors demonstrate efficient sub-cycle THz pulse generation by using two-color midinfrared femtosecond laser filaments in ambient air.

Multiplexed NIR-II Probes for Lymph Node-Invaded Cancer Detection and Imaging-Guided Surgery

Abstract: Tumor-lymph node (LN) metastasis is the dominant prognostic factor for tumor staging and therapeutic decision-making. However, concurrently visualizing metastasis and performing imaging-guided lymph node surgery is challenging. Here, a multiplexed-near-infrared-II (NIR-II) in vivo imaging system using nonoverlapping NIR-II probes with markedly suppressed photon scattering and zero-autofluorescence is reported, which enables visualization of the metastatic tumor and the tumor metastatic proximal LNs resection. A bright and tumor-seeking donor-acceptor-donor (D-A-D) dye, IR-FD, is screened for primary/metastatic tumor imaging in the NIR-IIa (1100-1300 nm) window. This optimized D-A-D dye exhibits greatly improved quantum yield of organic D-A-D fluorophores in aqueous solutions (≈6.0%) and good in vivo performance. Ultrabright PbS/CdS core/shell quantum dots (QDs) with dense polymer coating are used to visualize cancer-invaded sentinel LNs in the NIR-IIb (>1500 nm) window. Compared to clinically used indocyanine green, the QDs show superior brightness and photostability (no obvious bleaching even after continuous laser irradiation for 5 h); thus, only a picomolar dose is required for sentinel LNs detection. This combination of dual-NIR-II image-guided surgery can be performed under bright light, adding to its convenience and appeal in clinical use.

On-chip integrated laser-driven particle accelerator.

Abstract: Particle accelerators represent an indispensable tool in science and industry. However, the size and cost of conventional radio-frequency accelerators limit the utility and reach of this technology. Dielectric laser accelerators (DLAs) provide a compact and cost-effective solution to this problem by driving accelerator nanostructures with visible or near-infrared pulsed lasers, resulting in a 104 reduction of scale. Current implementations of DLAs rely on free-space lasers directly incident on the accelerating structures, limiting the scalability and integrability of this technology. We present an experimental demonstration of a waveguide-integrated DLA that was designed using a photonic inverse-design approach. By comparing the measured electron energy spectra with particle-tracking simulations, we infer a maximum energy gain of 0.915 kilo-electron volts over 30 micrometers, corresponding to an acceleration gradient of 30.5 mega-electron volts per meter. On-chip acceleration provides the possibility for a completely integrated mega-electron volt-scale DLA.

Ultra-low-threshold continuous-wave and pulsed lasing in tensile-strained GeSn alloys

Abstract: Strained GeSn alloys are promising for realizing light emitters based entirely on group IV elements. Here, we report GeSn microdisk lasers encapsulated with a SiNx stressor layer to produce tensile strain. A 300 nm-thick GeSn layer with 5.4 at% Sn, which is an indirect-bandgap semiconductor as-grown, is transformed via tensile strain engineering into a direct-bandgap semiconductor that supports lasing. In this approach, the low Sn concentration enables improved defect engineering and the tensile strain delivers a low density of states at the valence band edge, which is the light hole band. We observe ultra-low-threshold continuous-wave and pulsed lasing at temperatures up to 70 K and 100 K, respectively. Lasers operating at a wavelength of 2.5 μm have thresholds of 0.8 kW cm−2 for nanosecond pulsed optical excitation and 1.1 kW cm−2 under continuous-wave optical excitation. The results offer a path towards monolithically integrated group IV laser sources on a Si photonics platform. Continuous-wave lasing in strained GeSn alloys is reported at temperatures of up to 100 K. The approach offers a route towards a group-IV-on-silicon laser.

Electro-optic frequency combs

Abstract: Frequency combs are optical spectra composed of a set of discrete equally spaced lines. Such spectra can be generated by diverse sources such as mode-locked lasers, resonators, or electro-optic modulators. This last possibility has shown a growing interest in the recent years for its advantageous features in providing high repetition rates, intrinsic mutual coherence, or high power per comb lines. Moreover, applications of electro-optic modulator-based combs have flourished in fundamental physics, spectroscopy, or instrumental calibrations. In this paper, we present the most recent progresses made on frequency combs generated by electro-optic modulators, along with the applications where these combs have shown a particular interest.

Metallic 1T Phase Enabling MoS2 Nanodots as an Efficient Agent for Photoacoustic Imaging Guided Photothermal Therapy in the Near-Infrared-II Window.

Abstract: Transition metal dichalcogenide (TMD) nanomaterials, specially MoS2 , are proven to be appealing nanoagents for photothermal cancer therapies. However, the impact of the crystal phase of TMDs on their performance in photoacoustic imaging (PAI) and photothermal therapy (PTT) remains unclear. Herein, the preparation of ultrasmall single-layer MoS2 nanodots with different phases (1T and 2H phase) is reported to explore their phase-dependent performances as nanoagents for PAI guided PTT in the second near-infrared (NIR-II) window. Significantly, the 1T-MoS2 nanodots give a much higher extinction coefficient (25.6 L g-1 cm-1 ) at 1064 nm and subsequent photothermal power conversion efficiency (PCE: 43.3%) than that of the 2H-MoS2 nanodots (extinction coefficient: 5.3 L g-1 cm-1 , PCE: 21.3%). Moreover, the 1T-MoS2 nanodots also give strong PAI signals as compared to negligible signals of 2H-MoS2 nanodots in the NIR-II window. After modification with polyvinylpyrrolidone, the 1T-MoS2 nanodots can be used as a highly efficient agent for PAI guided PTT to effectively ablate cancer cells in vitro and tumors in vivo under 1064 nm laser irradiation. This work proves that the crystal phase plays a key role in determining the performance of nanoagents based on TMD nanomaterials for PAI guided PTT.

Experimental observation of the liquid-liquid transition in bulk supercooled water under pressure

Abstract: We prepared bulk samples of supercooled liquid water under pressure by isochoric heating of high-density amorphous ice to temperatures of 205 ± 10 kelvin, using an infrared femtosecond laser. Because the sample density is preserved during the ultrafast heating, we could estimate an initial internal pressure of 2.5 to 3.5 kilobar in the high-density liquid phase. After heating, the sample expanded rapidly, and we captured the resulting decompression process with femtosecond x-ray laser pulses at different pump-probe delay times. A discontinuous structural change occurred in which low-density liquid domains appeared and grew on time scales between 20 nanoseconds to 3 microseconds, whereas crystallization occurs on time scales of 3 to 50 microseconds. The dynamics of the two processes being separated by more than one order of magnitude provides support for a liquid-liquid transition in bulk supercooled water.

Lanthanide-Doped Core@Multishell Nanoarchitectures: Multimodal Excitable Upconverting/Downshifting Luminescence and High-Level Anti-Counterfeiting.

Abstract: The development of luminescent materials with concurrent multimodal emissions is a great challenge to improve security and data storage density. Lanthanide-doped nanocrystals are particularly appropriate for such applications for their abundant intermediate energy states and distinguishable spectroscopic profiles. However, traditional lanthanide luminescent nanoparticles have a limited capacity for information storage or complexity to shield against counterfeiting. Herein, it is demonstrated that the combination of upconverting and downshifting emissions in a particulate designed lanthanide-doped core@multishell nanoarchitecture allows the generation of multicolor dual-modal luminescence over a wide spectral range for complex information storage. Precise control of lanthanide dopants distribution in the core and distinct shells enables simultaneous excitation of 980/808 nm focusing/defocusing laser and 254 nm light and produces complex upconverting emissions from Er, Tm, Eu, and Tb via multiphoton energy transfer processes and downshifting emissions from Eu and Tb via efficient energy transfer from Ce to Eu/Tb in Gd-assisted lattices. It is experimentally proven that multiple visualized anti-counterfeit and information encryption with facile decryption and authentication using screen-printing inks containing the present core@multishell nanocrystals are practically applicable by selecting different excitation modes.