High-power Light Research Articles

Shedding New Lights Into STED Microscopy: Emerging Nanoprobes for Imaging.

First reported in 1994, stimulated emission depletion (STED) microscopy has long been regarded as a powerful tool for real-time superresolved bioimaging . However, high STED light power (101∼3 MW/cm2) is often required to achieve significant resolution improvement, which inevitably introduces phototoxicity and severe photobleaching, damaging the imaging quality, especially for long-term cases. Recently, the employment of nanoprobes (quantum dots, upconversion nanoparticles, carbon dots, polymer dots, AIE dots, etc.) in STED imaging has brought opportunities to overcoming such long-existing issues. These nanomaterials designed for STED imaging show not only lower STED power requirements but also more efficient photoluminescence (PL) and enhanced photostability than organic molecular probes. Herein, we review the recent progress in the development of nanoprobes for STED imaging, to highlight their potential in improving the long-term imaging quality of STED microscopy and broadening its application scope. We also discuss the pros and cons for specific classes of nanoprobes for STED bioimaging in detail to provide practical references for biological researchers seeking suitable imaging kits, promoting the development of relative research field.

Heat transfer performance of the rectangular heat sinks with non-uniform height thermosyphons for high power LED lamps cooling

The rectangular heat sinks with non-uniform height thermosyphons are proposed for high power light emitting diode (LED) lamps cooling in this study. The combined thermal resistance network and finite volume method is developed to reveal the heat transfer mechanism. The simulated results show good agreement with experimental data with relative errors of 2.14–2.69% at heating powers of 12–20 W. In comparison with type-a thermosyphon heat sink, the thermal resistance of type-b thermosyphon heat sink offers 8.47–9.91% higher due to thicker thermal boundary layer between air and thermosyphon fins in the intermediary region, whereas the thermal resistance of type-c thermosyphon heat sink offers 7.26–9.07% lower because of better free stream among thermosyphon fins in the intermediary region. The maximum heat transfer rate of type-a, type-b and type-c thermosyphon heat sinks are 19 W, 17 W and 22 W in regard to the temperature threshold of 85 °C, respectively. This paper provides guidelines for the design of high power LED lamps cooling.

Infrared neurostimulation in ex-vivo rat sciatic nerve using 1470 nm wavelength

Objective. To design and implement a setup for ex-vivo optical stimulation for exploring the effect of several key parameters (optical power and pulse duration), activation features (threshold, spatial selectivity) and recovery characteristics (repeated stimuli) in peripheral nerves. Approach. A nerve chamber allowing ex-vivo electrical and optical stimulation was designed and built. A 1470 nm light source was chosen to stimulate the nerve. A photodiode module was implemented for synchronization of the electrical and optical channels. Main results. Compound neural action potentials (CNAPs) were successfully generated with infrared light pulses of 200–2000 µs duration and power in the range of 3–10 W. These parameters determine a radiant exposure for stimulation in the range 1.59–4.78 J cm−2. Recruitment curves were obtained by increasing durations at a constant power level. Neural activation threshold is reached at a mean radiant exposure of 3.16 ± 0.68 J cm−2 and mean pulse energy of 3.79 ± 0.72 mJ. Repetition rates of 2–10 Hz have been explored. In eight out of ten sciatic nerves (SNs), repeated light stimuli induced a sensitization effect in that the CNAP amplitude progressively grows, representing an increasing number of recruited fibres. In two out of ten SNs, CNAPs were composed of a succession of peaks corresponding to different conduction velocities. Significance. The reported sensitization effect could shed light on the mechanism underlying infrared neurostimulation. Our results suggest that, in sharp contrast with electrical stimuli, optical pulses could recruit slow fibres early on. This more physiological order of recruitment opens the perspective for specific neuromodulation of fibre population who remained poorly accessible until now. Short high-power light pulses at wavelengths below 1.5 µm offer interesting perspectives for neurostimulation.

Continuous Gas–Liquid–Solid Slug Flow for Sustainable Heterogeneously Catalyzed PET-RAFT Polymerization

Gas-liquid-solid (G-L-S) three-phase slug flow provides an efficient pathway to utilize solid catalysts in continuous flow and was adopted in the mesoporous graphite carbon nitride (mpg-C3N4)-catalyzed photoinduced electron/energy transfer reversible addition-fragmentation chain transfer (PET-RAFT) polymerization of methyl methacrylate (MMA) in this work. Kinetic studies and chain extension experiments illustrated the realization of reversible deactivation radical polymerization (RDRP) and the to scale upadvantage of a continuous-flow reactor as compared to its batch counterpart. The light intensity played an important role on the PET-RAFT polymerization. An increasing amount of photocatalyst favored the monomer conversion within a limited range due to higher light blockage, and the monomer conversion reached a stable level at a lower catalyst concentration when higher light power was applied. When compared with fully continuous flow, the G-L-S slug flow was beneficial to the PET-RAFT polymerization due to the intensified swirling strength and narrower velocity field. Decreasing the gas-To-slurry ratio also led to narrower velocity distribution, which favored the polymerization as well. Moreover, the polymerization rates remained stable in multiple recycles, demonstrating that the present G-L-S slug flow was a reliable and easy processing approach for utilizing the solid catalyst.

Compressed Air Energy Storage Experimental Platform with off-grid Operation

The compressed air energy storage(CAES) experimental platform can play a role in research and training. Due to the large changes in experimental working conditions and many sudden abnormal situations, it is easy to disturb the safe operation of the power grid when it is integrated into the power grid. By constructing a three-layer compressed air energy storage experimental platform, equipped with a complete test and operation monitoring system, using multiple sets of high-power light bulbs as loads, the experimental platform can be operated off-grid. It has the advantages of simple structure, low cost, wide adaptable voltage range, easy observation of experimental results, etc., and has broad application value.

High color rendering index composite phosphor-in-glass for high-power white laser lighting

The aim of this study is to investigate a thermally robust white color converter for high-power solid-state lighting, especially laser lighting. Lu3Al5O12:Ce3+/CaAlSiN3:Eu2+ phosphor-in-glass samples (LuAG&CASN-PiGs) were synthesized via a low temperature co-sintering technique. The prepared LuAG&CASN-PiGs exhibited remarkably high internal quantum efficiency of 87 %. Tunable warm white light-emitting diodes (wLED) were acquired by tailoring the sample thicknesses and phosphor contents. The optimized sample showed a high luminous flux of 183.68 lm under a blue laser diodes (LDs). In addition, the chromaticity of white LDs based on the LuAG&CASN-PiGs shifted from cool to warm white by changing the sample thicknesses. High quality white light in wLDs was achieved (Ra＝95). More importantly, the constructed LuAG&CASN-PiG converted LDs with a heat sink exhibited the luminous efficiency of 216.79 lm W−1. The results revealed that the prepared LuAG&CASN-PiG had great potential for application in solid-state laser light sources.

Glass crystallization making red phosphor for high-power warm white lighting

Rapid development of solid-state lighting technology requires new materials with highly efficient and stable luminescence, and especially relies on blue light pumped red phosphors for improved light quality. Herein, we discovered an unprecedented red-emitting Mg2Al4Si5O18:Eu2+ composite phosphor (λex = 450 nm, λem = 620 nm) via the crystallization of MgO–Al2O3–SiO2 aluminosilicate glass. Combined experimental measurement and first-principles calculations verify that Eu2+ dopants insert at the vacant channel of Mg2Al4Si5O18 crystal with six-fold coordination responsible for the peculiar red emission. Importantly, the resulting phosphor exhibits high internal/external quantum efficiency of 94.5/70.6%, and stable emission against thermal quenching, which reaches industry production. The maximum luminous flux and luminous efficiency of the constructed laser driven red emitting device reaches as high as 274 lm and 54 lm W−1, respectively. The combinations of extraordinary optical properties coupled with economically favorable and innovative preparation method indicate, that the Mg2Al4Si5O18:Eu2+ composite phosphor will provide a significant step towards the development of high-power solid-state lighting.

Broadband emission Gd3Sc2Al3O12:Ce3+ transparent ceramics with a high color rendering index for high-power white LEDs/LDs.

The discovery of single structure Ce3+ doped garnet transparent ceramics (TCs) with a broad full width at half maximum (FWHM) is essential to realize a high CRI for high-power white light emitting diodes (LEDs) and laser diodes (LDs). In this work, by utilizing the ion substitution engineering strategy, pure phase Gd3Sc2Al3O12:Ce3+ (GSAG:Ce) TC with a broad FWHM of 132.4 nm and a high CRI value of 80.7 was fabricated through the vacuum sintering technique for the first time. The optimized in-line transmittance of TCs was 58.4% @ 800 nm. Notably, the GSAG:Ce TCs exhibited a remarkable red shift from 546 nm to 582 nm, with a high internal quantum efficiency (IQE) of 46.91%. The degraded thermal stability in Ce:GSAG TCs was observed compared with that of Ce:YAG TC, owing to the narrowed band gap of GSAG. Additionally, remote excitation white LEDs/LDs were constructed by combining GSAG:Ce TCs with blue LED chips or laser sources. A tunable color hue from yellow to shinning white was achieved in white LEDs, whereas the acquired CRI and CCT of the white LDs were 69.5 and 7766 K, respectively. This work provides a new perspective to develop TCs with high CRI for their real applications in high-power white LEDs/LDs.

Robust YAG:Ce single crystal for ultra-high efficiency laser lighting

At present, solid-state laser-driven lighting fabricated with blue laser diode (LD) and phosphor has been greatly developed in high-power lighting applications. The major obstacle is the luminescence saturation threshold of the fluorescence conversion material (YAG:Ce). In this work, we successfully prepared a series of high-quality and robust YAG:Ce single crystals. With high quantum efficiency (QE = 92%), regular crystal structure and high thermal conductivity, the single-crystal has excellent ability to deal with high radiation flux and thermal accumulation generated by high power. Matching the single-crystal with the laser, the luminous efficiency up to 274 lm/W and saturation threshold of 12 W/mm2 were obtained. In addition, the influence of Ce doping concentration and sample processing conditions on the indicators in laser-driven white lighting was systematically studied. The results are of great significance and are believed to promote the development of solid-state laser-driven lighting.

Characteristics of double-cascade photodiodes based on p-i-n AlGaAs/GaAs diodes connected by n++-GaAs/i-GaAs/i-AlGaAs/p++-AlGaAs tunnel diodes

Characteristics of double-cascade nonmonolithic p-i-n AlGaAs/GaAs photovoltaic converters of high-power laser radiation, electrically combined with n++-GaAs/i-GaAs/i-AlGaAs/p++-AlGaAs tunnel diodes, have been studied. The AlGaAs/GaAs p-i-n structures of the photovoltaic converters and n++-GaAs/i-GaAs/i-AlGaAs/p++-AlGaAs tunnel diodes were grown by molecular-beam epitaxy. The photoelectric characteristics of the double-cascade AlGaAs/GaAs photovoltaic converters were examined in the temperature range from 103 to 298 K under excitation with a laser light wavelength of 809 nm and a power density ⩽92 W/cm2. The double-cascade p-i-n AlGaAs/GaAs nonmonolithic photovoltaic converters of planar design had a fill factor of 0.88 and efficiency of 58.2% at a temperature of 103 K. It was shown experimentally that the current-voltage characteristics of the connecting n++-GaAs/i-GaAs/i-AlGaAs/p++-AlGaAs tunnel diodes affect the photoelectric parameters of the double-cascade photovoltaic converters of high-power laser light.

Etendue maintained white solid-state light generation by light emitting diodes pumped green aluminate green-yellow phosphor

We propose a technique to generate etendue maintained white light. The proposed technique uses three high-power blue light emitting diodes (LEDs) with identical characteristics to pump green aluminate (GAL) green-yellow phosphor coated on the inner channel of a waveguide. The technique offers two methods of generation of white light. Standalone partial conversion of blue to green and yellow light by GAL phosphor, combined with unconverted blue light, produces white light homogenized within the light guide. Complete conversion of blue to green and yellow light with the further addition of blue and red wavelengths from additional LED sources multiplexed with the output is also possible to further increase total white light output. Following design and optical modeling to prove the concept, the proposed technique is demonstrated, which shows white light emissions from the waveguide with no increase in aperture size while the original LED etendue is maintained. The proposed technique offers an alternative to low-lifetime, low-efficiency xenon lamps for light sources in etendue critical applications such as endoscopy.

Solar-Driven Soft Robots.

Stimuli‐responsive materials have been lately employed in soft robotics enabling new classes of robots that can emulate biological systems. The untethered operation of soft materials with high power light, magnetic field, and electric field has been previously demonstrated. While electric and magnetic fields can be stimulants for untethered actuation, their rapid decay as a function of distance limits their efficacy for long‐range operations. In contrast, light—in the form of sunlight or collimated from an artificial source (e.g., laser, Xenon lamps)—does not decay rapidly, making it suitable for long‐range excitation of untethered soft robots. In this work, an approach to harnessing sunlight for the untethered operation of soft robots is presented. By employing a selective solar absorber film and a low‐boiling point (34 °C) fluid, light‐operated soft robotic grippers are demonstrated, grasping and lifting objects almost 25 times the mass of the fluid in a controllable fashion. The method addresses one of the salient challenges in the field of untethered soft robotics. It precludes the use of bulky peripheral components (e.g., compressors, valves, or pressurized gas tank) and enables the untethered long‐range operation of soft robots.

Tulip-Shaped Pattern Imprinting for Omni-Phobic Surfaces Using Partially Cured Photopolymer

Functional films with hydrophobic, oleophobic, anti-fouling, anti-icing, anti-bacterial and low reflectance properties can be produced by patterning nano- or micro-structures on films via nano imprint lithography. Here, an omni-phobic surface showing both hydrophobicity and oleophobicity was obtained without chemical surface treatment by increasing the surface roughness and deforming the pattern morphology using only nano imprint lithography and the oxygen-inhibited curing properties of polyurethane acrylate (PUA) resin. A tulip-shaped pattern imprinting process was designed in which microscale patterns were fabricated using a porous polydimethylsiloxane (PDMS) mold with high oxygen transmission. During ultraviolet (UV) curing, a curing inhibiting layer was formed by reaction with oxygen. Next, a PDMS pad was used for the pressurized curing of the curing inhibition layer to modify the micro scale structures. Finally, final curing of the deformed pattern was performed using ultra high-power UV light. The deformation of the pattern into tulip-like shapes with increased surface roughness was confirmed by microscopy, and contact angle measurement was performed to confirm omni-phobicity. The final cured imprinted samples showed water and oil contact angles reaching 169.2° and 115°, respectively; thus, the omni-phobic surface could be demonstrated by a tulip-shaped pattern imprinting process.

CaAlSiN3:Eu/glass composite film in reflective configuration: A thermally robust and efficient red-emitting color converter with high saturation threshold for high-power high color rendering laser lighting

To achieve high color rendering and proper color temperature, a red color converter is essential for phosphor-converted white lighting devices. CaAlSiN3:Eu2+ (CASN) is a highly suitable red phosphor for white light-emitting diodes. However, it can be hardly used in high-power laser lighting due to poor thermal/chemical performance of the phosphor/silicone resin mixture. A series of all-inorganic CASN-based phosphors (e.g., composite ceramic and phosphor-in-glass) were developed to avoid the use of resin. However, new challenges emerged: none of them showed sufficient luminous efficacy (i.e., >50 lm/W) and adequate saturation-threshold (i.e., >30 W or 10 W/mm2). Here, we report a facile fabrication of CASN/glass composite films using a simple and efficient blade-coating method. Upon 450 nm excitation, the resultant composite film presents a high internal quantum efficiency of ~83%, comparable to that of pristine CASN powder (~90%). When irradiated with a blue laser, the composite film shows a record high luminous efficacy of 82 lm/W. Furthermore, its saturation threshold was investigated in high power and high power density mode, respectively. When measured in high power mode, it shows a high saturation threshold over 29.7 W (1.75 W/mm2), thus achieving a high luminous flux of 1576 lm; when measured in high power density mode, it shows a saturation threshold of ~10.2 W/mm2 (1.13 W). With abovementioned excellent properties, the CASN/glass composite film has great potential for use in high-power and high color rendering laser lighting.

Nonlinear amplification based on a tightly phase locked 750 MHz Yb:fiber frequency comb

In this paper, a nonlinear amplification system for a low noise 750 MHz ytterbium-doped fiber frequency comb is developed with a repetition rate stabilized to a continuous wave laser by employing a bulk electro-optic modulator. By managing the dispersion prior to the nonlinear amplifier, the proposed high-power frequency comb light source can deliver over 10 W of <90 fs pulse trains with an integrated relative intensity noise instability of 0.04%. Moreover, the noise characteristics of the proposed amplified comb, where the seed laser is a tightly stabilized 750 MHz fiber frequency comb, are analyzed in several representative states of different launched pump powers and pre-chirping group delay dispersions. The optical fiber frequency combs produced by nonlinear amplification may serve as an alternative for achieving high-power and ultrafast combs with good phase stability.

Electrical Conductivity and Water Effects in Phosphoric Acid Solutions for Doping of Membranes in Polymer Electrolyte Fuel Cells

Abstract Fuel cells (FCs) are among the more efficient solutions to limit the emission of greenhouse gases. Based on the conversion of the chemical energy of a fuel (often hydrogen) and an oxidizing agent (often oxygen) into electrical energy, a typical FC produces a voltage of 0.7 V under load. The potential is highly increased by placing the cells in series to obtain a stacked cell. Among the types of FCs, the polymer electrolyte membrane FCs (PEMFCs) are developed mainly for transport applications, because of their low impact on the environment, high power density and light weight compared with other types of FCs. Phosphoric acid (H3PO4) doped polybenzimidazole (PBI) membranes are widely used as efficient electrolytes. The performance of a (high temperature, 130–200 °C) HT-PEMFC depends mainly on the amount of H3PO4 in the solid polymer membrane. The strong autoprotolysis of H3PO4 is responsible for the high proton conductivity also in the anhydrous state. In this study, the H2OH3PO4 system is investigated in the temperature range 60–150 °C with varying water vapour activity at constant atmospheric pressure. Main purpose is to gain more insights into the kinetics of the equilibria in the H2O-H3PO4 system, which influence the fuel cell performance. Density, water content, electrical conductivity and activation energy are determined by exposing H3PO4 solutions for sufficiently long periods to controlled gas atmosphere in order to reach near-equilibrium conditions. The coexistence of ortho- and pyrophosphoric acid is analysed and higher condensed species are also considered. A new setup fully made in quartz is designed and developed to mix the phosphoric acid solutions in a climate chamber. The experimental results are compared to literature data to validate the developed setup and the methodology.

On Effective Usage of Mobile Automatic Light Traps for UV-attracted Lepidoptera Studies in Mountainous Conditions

The usage of automatic light traps based on UV-sources for collecting material is currently a generally accepted trend in field studies of insects with nocturnal activity. Despite the widespread use of light traps, the methods of their use remain poorly developed. The aim of this study is to compare different methods of using light traps with different types of UV-radiation in the field and to develop the most optimal method for their usage. The study was carried out in three localities in Kyrgyzstan, each stage of the experiment included 4 observations (using one powerful light trap, then one powerful and two not powerful light traps with the same UV-radiation wavelength, then one powerful and two not powerful light traps with different UV-radiation wavelengths; up to 5 different light traps were used on the last night). It has been shown that the most efficient, both qualitatively and quantitatively, method of collecting material using light traps is the use of one light trap with a high-power UV-source and light traps with low-power UV-sources and different wavelengths located at the boundaries of its light spot. The smallest effective number of mobile automatic light traps is three, one of which is of high power, the other two are of low power and of different wavelengths. The results obtained in this study allow planning and making more efficient use of light traps in field research.

Time-dependent measurement of high-power laser light reflection by low-Z foam plasma

Abstract Porous materials have many applications for laser–matter interaction experiments related to inertial confinement fusion. Obtaining new knowledge about the properties of the laser-produced plasma of porous media is a challenging task. In this work, we report, for the first time to the best of our knowledge, the time-dependent measurement of the reflected light of a terawatt laser pulse from the laser-produced plasma of low-Z foam material of overcritical density. The experiments have been performed with the ABC laser, with targets constituted by foam of overcritical density and by solid media of the same chemical composition. We implemented in the MULTI-FM code a model for the light reflection to reproduce and interpret the experimental results. Using the simulations together with the experimental results, we indicate a criterion for estimating the homogenization time of the laser-produced plasma, whose measurement is challenging with direct diagnostic techniques and still not achieved.

Novel high-thermal-conductivity composite ceramic phosphors for high-brightness laser-driven lighting

A new MgO–YAG:Ce composite ceramic showed an excellent thermal conductivity and a high luminous saturation threshold, indicating that it is a promising phosphor converter for high-power laser-driven lighting.

Phosphor Ceramics for High-power Solid-state Lighting

Phosphor Ceramics for High-power Solid-state Lighting