Showing papers on "Laser published in 2017"
TL;DR: A new material NH4B4O6F is reported, which exhibits a wide deep-ultraviolet transparent range and suitable birefringence that enables frequency doubling below 200 nm and possesses large nonlinear coefficients about 2.5 times that of KBBF.
Abstract: Nonlinear optical materials are essential for the development of solid-state lasers. KBe2BO3F2 (KBBF) is a unique nonlinear optical material for generation of deep-ultraviolet coherent light; however, its industrial application is limited. Here, we report a new material NH4B4O6F, which exhibits a wide deep-ultraviolet transparent range and suitable birefringence that enables frequency doubling below 200 nm. NH4B4O6F possesses large nonlinear coefficients about 2.5 times that of KBBF. In addition, it is easy to grow bulk crystals and does not contain toxic elements.
752 citations
TL;DR: These engineered nanocrystals offer saturation intensity two orders of magnitude lower than those of fluorescent probes currently employed in stimulated emission depletion microscopy, suggesting a new way of alleviating the square-root law that typically limits the resolution that can be practically achieved by such techniques.
Abstract: Super-resolution optical microscopy based on stimulated emission depletion effects can now be performed at much lower light intensities than before by using bright upconversion emission from thulium-doped nanoparticles. Improvements in super-resolution optical microscopy based on stimulated emission depletion (STED) effects have a problem: they are typically limited by a 'square-root law' regarding the number of photons required to achieve a gain in resolution. Yujia Liu and colleagues have found a way to bypass this troublesome law. As others have done before them, they adopt lanthanide-doped upconversion nanoparticles as the emitting species used to achieve high-resolution imaging. The difference this time is that the laser-like absorption and emission properties of these nanoparticles are engineered to facilitate STED-like microscopy at much lower light intensities. Lanthanide-doped glasses and crystals are attractive for laser applications because the metastable energy levels of the trivalent lanthanide ions facilitate the establishment of population inversion and amplified stimulated emission at relatively low pump power1,2,3. At the nanometre scale, lanthanide-doped upconversion nanoparticles (UCNPs) can now be made with precisely controlled phase, dimension and doping level4,5. When excited in the near-infrared, these UCNPs emit stable, bright visible luminescence at a variety of selectable wavelengths6,7,8,9, with single-nanoparticle sensitivity10,11,12,13, which makes them suitable for advanced luminescence microscopy applications. Here we show that UCNPs doped with high concentrations of thulium ions (Tm3+), excited at a wavelength of 980 nanometres, can readily establish a population inversion on their intermediate metastable 3H4 level: the reduced inter-emitter distance at high Tm3+ doping concentration leads to intense cross-relaxation, inducing a photon-avalanche-like effect that rapidly populates the metastable 3H4 level, resulting in population inversion relative to the 3H6 ground level within a single nanoparticle. As a result, illumination by a laser at 808 nanometres, matching the upconversion band of the 3H4 → 3H6 transition, can trigger amplified stimulated emission to discharge the 3H4 intermediate level, so that the upconversion pathway to generate blue luminescence can be optically inhibited. We harness these properties to realize low-power super-resolution stimulated emission depletion (STED) microscopy and achieve nanometre-scale optical resolution (nanoscopy), imaging single UCNPs; the resolution is 28 nanometres, that is, 1/36th of the wavelength. These engineered nanocrystals offer saturation intensity two orders of magnitude lower than those of fluorescent probes currently employed in stimulated emission depletion microscopy, suggesting a new way of alleviating the square-root law that typically limits the resolution that can be practically achieved by such techniques.
595 citations
TL;DR: This study provides a feasible way to break down the DUV wall for NLO materials by introducing the (BO3 F)4- , (BO2 F2 )3- , and (BOF3 )2- groups in borates to break through the fixed 3D B-O network that would produce a larger birefringence without layering and simultaneously keep a short cutoff edge down to DUV.
Abstract: Deep-ultraviolet nonlinear optical (DUV NLO) crystals are the key materials to extend the output range of solid-state lasers to below 200 nm. The only practical material KBe2BO3F2 suffers high toxicity through beryllium and strong layered growth. Herein, we propose a beryllium-free material design and synthesis strategy for DUV NLO materials. Introducing the (BO3F)(4-),(BO2F2)(3-), and (BOF3)(2-) groups in borates could break through the fixed 3DB-O network that would produce a larger birefringence without layering and simultaneously keep a short cutoff edge down to DUV. The theoretical and experimental studies on a series of fluorooxoborates confirm this strategy. Li2B6O9F2 is identified as aDUV NLO material with a large second harmonic generation efficiency (0.9 x KDP) and a large predicted birefringence (0.07) without layering. This study provides a feasible way to break down the DUV wall for NLO materials.
581 citations
TL;DR: The results open the possibility of diamond lasers based on NV− centres, tuneable over the phonon sideband, which broadens the applications of NV− magnetometers from single centre nanoscale sensors to a new generation of ultra-precise ensemble laser sensors, which exploit the contrast and signal amplification of a lasing system.
Abstract: Stimulated emission is the process fundamental to laser operation, thereby producing coherent photon output. Despite negatively charged nitrogen-vacancy (NV−) centres being discussed as a potential laser medium since the 1980s, there have been no definitive observations of stimulated emission from ensembles of NV− to date. Here we show both theoretical and experimental evidence for stimulated emission from NV− using light in the phonon sidebands around 700 nm. Furthermore, we show the transition from stimulated emission to photoionization as the stimulating laser wavelength is reduced from 700 to 620 nm. While lasing at the zero-phonon line is suppressed by ionization, our results open the possibility of diamond lasers based on NV− centres, tuneable over the phonon sideband. This broadens the applications of NV− magnetometers from single centre nanoscale sensors to a new generation of ultra-precise ensemble laser sensors, which exploit the contrast and signal amplification of a lasing system. Here Jeskeet al. show both theoretical and experimental evidence for stimulated emission from negatively charged nitrogen vacancy centres using light in the phonon sidebands around 700 nm, demonstrating its suitability as a laser medium.
508 citations
TL;DR: The observation of up to ninth-order harmonics in graphene excited by mid-infrared laser pulses at room temperature opens up the possibility of investigating strong-field and ultrafast dynamics and nonlinear behavior of massless Dirac fermions.
Abstract: The electronic properties of graphene can give rise to a range of nonlinear optical responses. One of the most desirable nonlinear optical processes is high-harmonic generation (HHG) originating from coherent electron motion induced by an intense light field. Here, we report on the observation of up to ninth-order harmonics in graphene excited by mid-infrared laser pulses at room temperature. The HHG in graphene is enhanced by an elliptically polarized laser excitation, and the resultant harmonic radiation has a particular polarization. The observed ellipticity dependence is reproduced by a fully quantum mechanical treatment of HHG in solids. The zero-gap nature causes the unique properties of HHG in graphene, and our findings open up the possibility of investigating strong-field and ultrafast dynamics and nonlinear behavior of massless Dirac fermions.
498 citations
TL;DR: It is demonstrated here that Ti3 CN, one of MXene compounds, can serve as an excellent mode-locker that can produce femtosecond laser pulses from fiber cavities.
Abstract: 2D transition metal carbides, nitrides, and carbonitides called MXenes have attracted much attention due to their outstanding properties. However, MXene's potential in laser technology is not explored. It is demonstrated here that Ti3 CN, one of MXene compounds, can serve as an excellent mode-locker that can produce femtosecond laser pulses from fiber cavities. Stable laser pulses with a duration as short as 660 fs are readily obtained at a repetition rate of 15.4 MHz and a wavelength of 1557 nm. Density functional theory calculations show that Ti3 CN is metallic, in contrast to other 2D saturable absorber materials reported so far to be operative for mode-locking. 2D structural and electronic characteristics are well conserved in their stacked form, possibly due to the unique interlayer coupling formed by MXene surface termination groups. Noticeably, the calculations suggest a promise of MXenes in broadband saturable absorber applications due to metallic characteristics, which agrees well with the experiments of passively Q-switched lasers using Ti3 CN at wavelengths of 1558 and 1875 nm. This study provides a valuable strategy and intuition for the development of nanomaterial-based saturable absorbers opening new avenues toward advanced photonic devices based on MXenes.
441 citations
20 Jun 2017
TL;DR: In this article, surface roughness was exploited to achieve high quality factor (Q) and high confinement in Si3N4 ring resonators, achieving Q of 37 million for a ring of 2.5μm width and 67 million for an inner ring of 10μm.
Abstract: On-chip optical resonators have the promise of revolutionizing numerous fields, including metrology and sensing; however, their optical losses have always lagged behind those of their larger discrete resonator counterparts based on crystalline materials and silica microtoroids. Silicon nitride (Si3N4) ring resonators open up capabilities for frequency comb generation, optical clocks, and high-precision sensing on an integrated platform. However, simultaneously achieving a high quality factor (Q) and high confinement in Si3N4 (critical for nonlinear processes, for example) remains a challenge. Here we show that addressing surface roughness enables overcoming the loss limitations and achieving high-confinement on-chip ring resonators with Q of 37 million for a ring of 2.5 μm width and 67 million for a ring of 10 μm width. We show a clear systematic path for achieving these high Qs, and these techniques can also be used to reduce losses in other material platforms independent of geometry. Furthermore, we demonstrate optical parametric oscillation using the 2.5 μm wide ring with sub-milliwatt pump powers and extract the loss limited by the material absorption in our films to be 0.13±0.05 dB/m, which corresponds to an absorption-limited Q of at least 170 million by comparing two resonators with different degrees of confinement. Our work provides a chip-scale platform for applications such as ultralow-power frequency comb generation, laser stabilization, and sideband-resolved optomechanics.
411 citations
TL;DR: In this paper, topological edge states of a one-dimensional lattice of polariton micropillars that implements an orbital version of the Su-Schrieffer-Heeger Hamiltonian were shown to persist under local deformations of the lattice.
Abstract: Topology describes properties that remain unaffected by smooth distortions. Its main hallmark is the emergence of edge states localized at the boundary between regions characterized by distinct topological invariants. This feature offers new opportunities for robust trapping of light in nano- and micro-meter scale systems subject to fabrication imperfections and to environmentally induced deformations. Here we show lasing in such topological edge states of a one-dimensional lattice of polariton micropillars that implements an orbital version of the Su-Schrieffer-Heeger Hamiltonian. We further demonstrate that lasing in these states persists under local deformations of the lattice. These results open the way to the implementation of chiral lasers in systems with broken time-reversal symmetry and, when combined with polariton interactions, to the study of nonlinear topological photonics.
408 citations
TL;DR: The Pohang Accelerator Laboratory X-ray Free Electron Laser (PAL-XFEL) in South Korea has now entered operation with a timing jitter of just 20 fs.
Abstract: The hard X-ray free-electron laser at the Pohang Accelerator Laboratory (PAL-XFEL) in the Republic of Korea achieved saturation of a 0.144 nm free-electron laser beam on 27 November 2016, making it the third hard X-ray free-electron laser in the world, following the demonstrations of the Linac Coherent Light Source (LCLS) and the SPring-8 Angstrom Compact Free Electron Laser (SACLA). The use of electron-beam-based alignment incorporating undulator radiation spectrum analysis has allowed reliable operation of PAL-XFEL with unprecedented temporal stability and dispersion-free orbits. In particular, a timing jitter of just 20 fs for the free-electron laser photon beam is consistently achieved due to the use of a state-of-the-art design of the electron linear accelerator and electron-beam-based alignment. The low timing jitter of the electron beam makes it possible to observe Bi(111) phonon dynamics without the need for timing-jitter correction, indicating that PAL-XFEL will be an extremely useful tool for hard X-ray time-resolved experiments. The Pohang Accelerator Laboratory X-ray Free Electron Laser (PAL-XFEL) in South Korea has now entered operation with a timing jitter of just 20 fs.
379 citations
TL;DR: In this paper, a geometry-based simulation is used to predict porosity caused by insufficient overlap of melt pools (lack of fusion) in powder bed fusion, and the simulation correctly predicts process conditions at which lack-of-fusion porosity becomes apparent, as well as the rate at which porosity increases with changes in process conditions such as beam speed, layer thickness and hatch spacing.
Abstract: A geometry-based simulation is used to predict porosity caused by insufficient overlap of melt pools (lack of fusion) in powder bed fusion. The inputs into the simulation are hatch spacing, layer thickness, and melt-pool cross-sectional area. Melt-pool areas used in the simulations can be obtained from experiments, or estimated with the analytical Rosenthal equation. The necessary material constants, including absorptivity for laser-based melting, have been collated for alloy steels, aluminum alloys and titanium alloys. Comparison with several data sets from the literature shows that the simulations correctly predict process conditions at which lack-of-fusion porosity becomes apparent, as well as the rate at which porosity increases with changes in process conditions such as beam speed, layer thickness and hatch spacing.
368 citations
TL;DR: Two ultrastable lasers stabilized to single-crystal silicon Fabry-Pérot cavities at 124 K show unprecedented thermal noise-limited frequency instabilities of 4×10 and linewidths below 10 mHz.
Abstract: We report on two ultrastable lasers each stabilized to independent silicon Fabry-Perot cavities operated at 124 K. The fractional frequency instability of each laser is completely determined by the fundamental thermal Brownian noise of the mirror coatings with a flicker noise floor of 4×10^{-17} for integration times between 0.8 s and a few tens of seconds. We rigorously treat the notorious divergences encountered with the associated flicker frequency noise and derive methods to relate this noise to observable and practically relevant linewidths and coherence times. The individual laser linewidth obtained from the phase noise spectrum or the direct beat note between the two lasers can be as small as 5 mHz at 194 THz. From the measured phase evolution between the two laser fields we derive usable phase coherence times for different applications of 11 to 55 s.
TL;DR: In this article, the effective absorptivity of continuous wave 1070nm laser light has been studied for bare and metal powder-coated discs of 316L stainless steel as well as for aluminum alloy 1100 and tungsten by use of direct calorimetric measurements.
TL;DR: The Göttingen UTEM employs nano-localized linear photoemission from a Schottky emitter, which enables operation with freely tunable temporal structure, from continuous wave to femtosecond pulsed mode and achieves record pulse properties in ultrafast electron microscopy.
TL;DR: In this paper, a zero-dead-time optical clock based on interleaved interrogation of two cold-atom ensembles has been proposed to overcome the Dick effect, which results in an aliasing of frequency noise from the laser interrogating the atomic transition.
Abstract: Optical clocks with a record low zero-dead-time instability of 6 × 10–17 at 1 second are demonstrated in two cold-ytterbium systems. The two systems are interrogated by a shared optical local oscillator to nearly eliminate the Dick effect. Atomic clocks based on optical transitions are the most stable, and therefore precise, timekeepers available. These clocks operate by alternating intervals of atomic interrogation with the ‘dead’ time required for quantum state preparation and readout. This non-continuous interrogation of the atom system results in the Dick effect, an aliasing of frequency noise from the laser interrogating the atomic transition1,2. Despite recent advances in optical clock stability that have been achieved by improving laser coherence, the Dick effect has continually limited the performance of optical clocks. Here we implement a robust solution to overcome this limitation: a zero-dead-time optical clock that is based on the interleaved interrogation of two cold-atom ensembles3. This clock exhibits vanishingly small Dick noise, thereby achieving an unprecedented fractional frequency instability assessed to be for an averaging time τ in seconds. We also consider alternate dual-atom-ensemble schemes to extend laser coherence and reduce the standard quantum limit of clock stability, achieving a spectroscopy line quality factor of Q > 4 × 1015.
TL;DR: Graphene is a promising platform with which to achieve light-field-driven control of electrons in a conducting material, because of its broadband and ultrafast optical response, weak screening and high damage threshold, and it is shown that a current induced in monolayer graphene by two-cycle laser pulses is sensitive to the electric-field waveform.
Abstract: The ability to steer electrons using the strong electromagnetic field of light has opened up the possibility of controlling electron dynamics on the sub-femtosecond (less than 10-15 seconds) timescale. In dielectrics and semiconductors, various light-field-driven effects have been explored, including high-harmonic generation, sub-optical-cycle interband population transfer and the non-perturbative change of the transient polarizability. In contrast, much less is known about light-field-driven electron dynamics in narrow-bandgap systems or in conductors, in which screening due to free carriers or light absorption hinders the application of strong optical fields. Graphene is a promising platform with which to achieve light-field-driven control of electrons in a conducting material, because of its broadband and ultrafast optical response, weak screening and high damage threshold. Here we show that a current induced in monolayer graphene by two-cycle laser pulses is sensitive to the electric-field waveform, that is, to the exact shape of the optical carrier field of the pulse, which is controlled by the carrier-envelope phase, with a precision on the attosecond (10-18 seconds) timescale. Such a current, dependent on the carrier-envelope phase, shows a striking reversal of the direction of the current as a function of the driving field amplitude at about two volts per nanometre. This reversal indicates a transition of light-matter interaction from the weak-field (photon-driven) regime to the strong-field (light-field-driven) regime, where the intraband dynamics influence interband transitions. We show that in this strong-field regime the electron dynamics are governed by sub-optical-cycle Landau-Zener-Stuckelberg interference, composed of coherent repeated Landau-Zener transitions on the femtosecond timescale. Furthermore, the influence of this sub-optical-cycle interference can be controlled with the laser polarization state. These coherent electron dynamics in graphene take place on a hitherto unexplored timescale, faster than electron-electron scattering (tens of femtoseconds) and electron-phonon scattering (hundreds of femtoseconds). We expect these results to have direct ramifications for band-structure tomography and light-field-driven petahertz electronics.
TL;DR: Maxima in the isothermal compressibility and correlation length point to the existence of a Widom line, defined as the locus of maximum correlation length emanating from a critical point at positive pressures in the deeply supercooled regime, and the difference in the maximum value of the is thermal compressibility between the two isotopes shows the importance of nuclear quantum effects.
Abstract: Femtosecond x-ray laser pulses were used to probe micrometer-sized water droplets that were cooled down to 227 kelvin in vacuum. Isothermal compressibility and correlation length were extracted from x-ray scattering at the low–momentum transfer region. The temperature dependence of these thermodynamic response and correlation functions shows maxima at 229 kelvin for water and 233 kelvin for heavy water. In addition, we observed that the liquids undergo the fastest growth of tetrahedral structures at similar temperatures. These observations point to the existence of a Widom line, defined as the locus of maximum correlation length emanating from a critical point at positive pressures in the deeply supercooled regime. The difference in the maximum value of the isothermal compressibility between the two isotopes shows the importance of nuclear quantum effects.
TL;DR: The saturable absorption of these emerging LD materials including two-dimensional semiconductors as well as colloidal TI nanoparticles has recently been utilized for Q-switching and mode-locking ultra-short pulse generation across the visible, near infrared and middle infrared wavelength regions.
Abstract: Low-dimensional (LD) materials demonstrate intriguing optical properties, which lead to applications in diverse fields, such as photonics, biomedicine and energy. Due to modulation of electronic structure by the reduced structural dimensionality, LD versions of metal, semiconductor and topological insulators (TIs) at the same time bear distinct nonlinear optical (NLO) properties as compared with their bulk counterparts. Their interaction with short pulse laser excitation exhibits a strong nonlinear character manifested by NLO absorption, giving rise to optical limiting or saturated absorption associated with excited state absorption and Pauli blocking in different materials. In particular, the saturable absorption of these emerging LD materials including two-dimensional semiconductors as well as colloidal TI nanoparticles has recently been utilized for Q-switching and mode-locking ultra-short pulse generation across the visible, near infrared and middle infrared wavelength regions. Beside the large operation bandwidth, these ultrafast photonics applications are especially benefit from the high recovery rate as well as the facile processibility of these LD materials. The prominent NLO response of these LD materials have also provided new avenues for the development of novel NLO and photonics devices for all-optical control as well as optical circuits beyond ultrafast lasers.
TL;DR: This work describes ultrafast all-optical photo-magnetic recording in transparent films of the dielectric cobalt-substituted garnet, which outperforms existing alternatives in terms of the speed of the write–read magnetic recording event and the unprecedentedly low heat load.
Abstract: Discovering ways to control the magnetic state of media with the lowest possible production of heat and at the fastest possible speeds is important in the study of fundamental magnetism, with clear practical potential. In metals, it is possible to switch the magnetization between two stable states (and thus to record magnetic bits) using femtosecond circularly polarized laser pulses. However, the switching mechanisms in these materials are directly related to laser-induced heating close to the Curie temperature. Although several possible routes for achieving all-optical switching in magnetic dielectrics have been discussed, no recording has hitherto been demonstrated. Here we describe ultrafast all-optical photo-magnetic recording in transparent films of the dielectric cobalt-substituted garnet. A single linearly polarized femtosecond laser pulse resonantly pumps specific d-d transitions in the cobalt ions, breaking the degeneracy between metastable magnetic states. By changing the polarization of the laser pulse, we deterministically steer the net magnetization in the garnet, thus writing '0' and '1' magnetic bits at will. This mechanism outperforms existing alternatives in terms of the speed of the write-read magnetic recording event (less than 20 picoseconds) and the unprecedentedly low heat load (less than 6 joules per cubic centimetre).
TL;DR: TMDs are established as practical materials for integrated TMD-silicon nanolasers suitable for silicon-based nanophotonic applications in silicon-transparent wavelengths with the largest value reported for a TMD laser.
Abstract: Monolayer transition-metal dichalcogenides (TMDs) have the potential to become efficient optical-gain materials for low-energy-consumption nanolasers with the smallest gain media because of strong excitonic emission. However, until now TMD-based lasing has been realized only at low temperatures. Here we demonstrate for the first time a room-temperature laser operation in the infrared region from a monolayer of molybdenum ditelluride on a silicon photonic-crystal cavity. The observation is enabled by the unique combination of a TMD monolayer with an emission wavelength transparent to silicon, and a high-Q cavity of the silicon nanobeam. The laser is pumped by a continuous-wave excitation, with a threshold density of 6.6 W cm-2. Its linewidth is as narrow as 0.202 nm with a corresponding Q of 5,603, the largest value reported for a TMD laser. This demonstration establishes TMDs as practical materials for integrated TMD-silicon nanolasers suitable for silicon-based nanophotonic applications in silicon-transparent wavelengths.
TL;DR: This comprehensive review paper charts advances in the development and applications of laser Doppler vibrometry (LDV) since those first pioneering experiments, and considers the challenges that continue to be posed by laser speckle.
TL;DR: It is shown that the formation/annihilation of iodine vacancies (VI) in MAPbI3 films, driven by electric fields and light illumination, can induce pronounced resistive switching effects and provide guidance toward improved stability and performance of perovskite-based optoelectronic systems.
Abstract: Organic–inorganic halide perovskite (OHP) materials, for example, CH3NH3PbI3 (MAPbI3), have attracted significant interest for applications such as solar cells, photodectors, light-emitting diodes, and lasers. Previous studies have shown that charged defects can migrate in perovskites under an electric field and/or light illumination, potentially preventing these devices from practical applications. Understanding and control of the defect generation and movement will not only lead to more stable devices but also new device concepts. Here, it is shown that the formation/annihilation of iodine vacancies (VI's) in MAPbI3 films, driven by electric fields and light illumination, can induce pronounced resistive switching effects. Due to a low diffusion energy barrier (≈0.17 eV), the VI's can readily drift under an electric field, and spontaneously diffuse with a concentration gradient. It is shown that the VI diffusion process can be suppressed by controlling the affinity of the contact electrode material to I− ions, or by light illumination. An electrical-write and optical-erase memory element is further demonstrated by coupling ion migration with electric fields and light illumination. These results provide guidance toward improved stability and performance of perovskite-based optoelectronic systems, and can lead to the development of solid-state devices that couple ionics, electronics, and optics.
TL;DR: In this paper, the discovery of superior mid-IR NLO metal chalcogenides is still a big challenge mainly due to the difficulty of achieving a good balance between the NLO effect and laser damage threshold (LDT).
Abstract: Mid-infrared (IR) nonlinear optical (NLO) materials with high performance are vital to expanding the laser wavelengths into the mid-IR region and have important technological applications in many civil and military fields. For the last two decades metal chalcogenides have attracted great attention since many of them possess a large NLO effect, wide transparent range, moderate birefringence, and high resistance to laser damage. However, the discovery of superior mid-IR NLO metal chalcogenides is still a big challenge mainly due to the difficulty of achieving a good balance between the NLO effect and laser damage threshold (LDT). In this review, metal chalcogenides are catalogued according to the different types of microscopic building blocks. These groups include triangle planar units, tetrahedral metal-centered units, polyhedra with second-order John-Teller cations, and polyhedra with stereochemically active lone electron pairs cations, rare-earth cations, and/or halogen anions. The determinations of thes...
TL;DR: In this paper, the vertical cavity surface emitting laser (VCSEL) based on the CsPbX3 IPNCs, featuring low threshold (9 µJ cm−2), directional output (beam divergence of ≈3.6°), and favorable stability, are realized for the first time.
Abstract: Recently, newly engineered all-inorganic cesium lead halide perovskite nanocrystals (IPNCs) (CsPbX3, X = Cl, Br, I) are discovered to possess superior optical gain properties appealing for solution-processed cost-effective lasers. Yet, the potential of such materials has not been exploited for practical laser devices, rendering the prospect as laser media elusive. Herein, the challenging but practically desirable vertical cavity surface emitting lasers (VCSELs) based on the CsPbX3 IPNCs, featuring low threshold (9 µJ cm−2), directional output (beam divergence of ≈3.6°), and favorable stability, are realized for the first time. Notably, the lasing wavelength can be tuned across the red, green, and blue region maintaining comparable thresholds, which is promising in developing single-source-pumped full-color visible lasers. It is fully demonstrated that the characteristics of the VCSELs can be versatilely engineered by independent adjustment of the cavity and solution-processable nanocrystals. The results unambiguously reveal the feasibility of the emerging CsPbX3 IPNCs as practical laser media and represent a significant leap toward CsPbX3 IPNC-based laser devices.
TL;DR: High-quality all-inorganic cesium lead halide alloy perovskite micro/nanorods with complete composition tuning by vapor-phase deposition are reported and function as effective Fabry-Perot cavities for nanoscale lasers.
Abstract: Although great efforts have been devoted to the synthesis of halide perovskites nanostructures, vapor growth of high-quality one-dimensional cesium lead halide nanostructures for tunable nanoscale lasers is still a challenge. Here, we report the growth of high-quality all-inorganic cesium lead halide alloy perovskite micro/nanorods with complete composition tuning by vapor-phase deposition. The as-grown micro/nanorods are single-crystalline with a triangular cross section and show strong photoluminescence which can be tuned from 415 to 673 nm by varying the halide composition. Furthermore, these single-crystalline perovskite micro/nanorods themselves function as effective Fabry–Perot cavities for nanoscale lasers. We have realized room-temperature tunable lasing of cesium lead halide perovskite with low lasing thresholds (∼14.1 μJ cm–2) and high Q factors (∼3500).
TL;DR: In this paper, the authors show that modal and chromatic dispersions in fiber laser can be counteracted by strong spatial and spectral filtering, which allows locking of multiple transverse and longitudinal modes to create ultrashort pulses with a variety of spatiotemporal profiles.
Abstract: A laser is based on the electromagnetic modes of its resonator, which provides the feedback required for oscillation Enormous progress has been made toward controlling the interactions of longitudinal modes in lasers with a single transverse mode For example, the field of ultrafast science has been built on lasers that lock many longitudinal modes together to form ultrashort light pulses However, coherent superposition of longitudinal and transverse modes in a laser has received little attention We show that modal and chromatic dispersions in fiber lasers can be counteracted by strong spatial and spectral filtering This allows locking of multiple transverse and longitudinal modes to create ultrashort pulses with a variety of spatiotemporal profiles Multimode fiber lasers thus open new directions in studies of nonlinear wave propagation and capabilities for applications
TL;DR: In this paper, a negatively charged nitrogen-vacancy (NV−) center is created in diamond by laser writing (with pulses with a central wavelength of 790 nm and duration of 300 fs) with an accuracy of 200 nm in the transverse plane.
Abstract: A negatively charged nitrogen–vacancy centre — a promising quantum light source — is created in diamond by laser writing (with pulses with a central wavelength of 790 nm and duration of 300 fs) with an accuracy of 200 nm in the transverse plane. Optically active point defects in crystals have gained widespread attention as photonic systems that could be applied in quantum information technologies1,2. However, challenges remain in the placing of individual defects at desired locations, an essential element of device fabrication. Here we report the controlled generation of single negatively charged nitrogen–vacancy (NV−) centres in diamond using laser writing3. Aberration correction in the writing optics allows precise positioning of the vacancies within the diamond crystal, and subsequent annealing produces single NV− centres with a probability of success of up to 45 ± 15%, located within about 200 nm of the desired position in the transverse plane. Selected NV− centres display stable, coherent optical transitions at cryogenic temperatures, a prerequisite for the creation of distributed quantum networks of solid-state qubits. The results illustrate the potential of laser writing as a new tool for defect engineering in quantum technologies, and extend laser processing to the single-defect domain.
TL;DR: Theoretical predictions suggest that reducing the laser wavelength can provide the possibility of HR-LIPSS production on principally any metal and makes this laser-writing technology to be flexible, robust and, hence, highly competitive for advanced industrial applications based on surface nanostructuring.
Abstract: Highly regular laser-induced periodic surface structures (HR-LIPSS) have been fabricated on surfaces of Mo, steel alloy and Ti at a record processing speed on large areas and with a record regularity in the obtained sub-wavelength structures. The physical mechanisms governing LIPSS regularity are identified and linked with the decay length (i.e. the mean free path) of the excited surface electromagnetic waves (SEWs). The dispersion of the LIPSS orientation angle well correlates with the SEWs decay length: the shorter this length, the more regular are the LIPSS. A material dependent criterion for obtaining HR-LIPSS is proposed for a large variety of metallic materials. It has been found that decreasing the spot size close to the SEW decay length is a key for covering several cm2 of material surface by HR-LIPSS in a few seconds. Theoretical predictions suggest that reducing the laser wavelength can provide the possibility of HR-LIPSS production on principally any metal. This new achievement in the unprecedented level of control over the laser-induced periodic structure formation makes this laser-writing technology to be flexible, robust and, hence, highly competitive for advanced industrial applications based on surface nanostructuring.
TL;DR: The irradiation of gold nanorod colloids with a femtosecond laser can be tuned to induce controlled nan orod reshaping, yielding colloid clusters with exceptionally narrow localized surface plasmon resonance bands.
Abstract: The irradiation of gold nanorod colloids with a femtosecond laser can be tuned to induce controlled nanorod reshaping, yielding colloids with exceptionally narrow localized surface plasmon resonance bands. The process relies on a regime characterized by a gentle multishot reduction of the aspect ratio, whereas the rod shape and volume are barely affected. Successful reshaping can only occur within a narrow window of the heat dissipation rate: Low cooling rates lead to drastic morphological changes, and fast cooling has nearly no effect. Hence, a delicate balance must be achieved between irradiation fluence and surface density of the surfactant on the nanorods. This perfection process is appealing because it provides a simple, fast, reproducible, and scalable route toward gold nanorods with an optical response of exceptional quality, near the theoretical limit.
TL;DR: Laser-based approaches for graphene synthesis, reduction, modification, cutting and micro-patterning have been developed and applied to the fabrication of various electronic devices as discussed by the authors, such as micro-supercapacitors, flexible electrodes, field effect transistors, and sensors.
TL;DR: In this paper, an ultralow lasing threshold (0.39 μJ/cm2) was obtained for a hybrid vertical cavity surface emitting laser (VCSEL) structure consisting of a CsPbBr3 QD thin film and two highly reflective distributed Bragg reflectors (DBRs).
Abstract: All-inorganic cesium lead bromide (CsPbBr3) perovskite quantum dots (QDs) have recently emerged as highly promising solution-processed materials for next-generation light-emitting applications. They combine the advantages of QD and perovskite materials, which makes them an attractive platform for achieving high optical gain with high stability. Here, we report an ultralow lasing threshold (0.39 μJ/cm2) from a hybrid vertical cavity surface emitting laser (VCSEL) structure consisting of a CsPbBr3 QD thin film and two highly reflective distributed Bragg reflectors (DBRs). Temperature dependence of the lasing threshold and long-term stability of the device were also characterized. Notably, the CsPbBr3 QDs provide superior stability and enable stable device operation over 5 h/1.8 × 107 optical pulse excitations under ambient conditions. This work demonstrates the significant potential of CsPbBr3 perovskite QD VCSELs for highly reliable lasers, capable of operating in the short-pulse (femtosecond) and quasi-co...