Brightness Laser Research Articles

Whispering Gallery Mode Micro/Nanolasers for Intracellular Probing at Single Cell Resolution.

Intracellular probing at single cell resolution is key to revealing the heterogeneity of cells, learning new cell subtypes and functions, understanding the pathophysiology of disease, and ensuring precise diagnosis and treatment. Despite the best efforts, an enormous challenge remains due to the very small size, extremely low content, and dynamic microenvironment of a single cell. Whispering gallery mode (WGM) micro/nanolasers (active WGM) offer unique advantages of small mode volume, high quality factors, bright and low threshold laser emission, and narrow line width, particularly suitable for integration within a single cell. In this review, we provide a focused overview of WGM micro/nanolasers for intracellular probing. We deliver information on WGM micro/nanolaser concepts, sensing mechanism, and biocompatibility, as well as recent progress in intracellular probing applications mainly covering cellular-level sensing, molecular-level detection, and feasibility for cellular imaging. At the end, challenges and prospects of WGM micro/nanolasers for intracellular applications are discussed.

A novel application of laser speckle imaging technique for prediction of hypoxic stress of apples

BackgroundFruit storage methods such as dynamic controlled atmosphere (DCA) technology enable adjusting the level of oxygen in the storage room, according to the physiological state of the product to slow down the ripening process. However, the successful application of DCA requires precise and reliable sensors of the oxidative stress of the fruit. In this study, respiration rate and chlorophyll fluorescence (CF) signals were evaluated after introducing a novel predictors of apples' hypoxic stress based on laser speckle imaging technique (LSI).ResultsBoth chlorophyll fluorescence and LSI signals were equally good for stress detection in principle. However, in an application with automatic detection based on machine learning models, the LSI signal proved to be superior, due to its stability and measurement repeatability. Moreover, the shortcomings of the CF signal appear to be its inability to indicate oxygen stress in tissues with low chlorophyll content but this does not apply to LSI. A comparison of different LSI signal processing methods showed that method based on the dynamics of changes in image content was better indicators of stress than methods based on measurements of changes in pixel brightness (inertia moment or laser speckle contrast analysis). Data obtained using the near-infrared laser provided better prediction capabilities, compared to the laser with red light.ConclusionsThe study showed that the signal from the scattered laser light phenomenon is a good predictor for the oxidative stress of apples. Results showed that effective prediction using LSI was possible and did not require additional signals. The proposed method has great potential as an alternative indicator of fruit oxidative stress, which can be applied in modern storage systems with a dynamically controlled atmosphere.

Realizing a kilowatt-level fiber amplifier with a 42 μm core diameter fiber for improved multi-mode performance towards single mode operation output through adaptive spatial mode control utilizing a 3×1 photonic lantern

The photonic lantern, a coherent beam combiner capable of controlling the phase, amplitude, and polarization of input light, has been utilized to enhance the brightness of fiber lasers by managing the output beam’s mode. In this work, a 3×1 photonic lantern-based adaptive spatial mode control system is employed to realize kilowatt-level operation in a 42 μm core fiber laser amplifier. Both simulation and experimental outcomes affirm the ability of this approach to manage modes within large-mode-area fiber laser systems through the use of 3 input arms. The experiment not only streamlines the overall system design but also has the potential to reduce production costs and complexities. Additionally, the spectrum width has been optimized to 10 GHz, striking a balance between the SBS threshold and the coherence of the photonic lantern’s input arms. By implementing this system, we have successfully achieved a stable, improved multi-mode performance towards single mode operation output of 1.08 kW, with a beam quality factor M2 of 2.20. This research furthers our understanding of how photonic lanterns can stabilize and enhance beam quality in high-power fiber lasers, paving the way for potential improvements in their performance and applications.

Performance improvement of reflective phosphor film via adjusting the thickness realizing bright and efficient laser lighting.

Phosphor-in-glass-film (PiG-F) has been extensively investigated, showing great potential for use in laser lighting technique. Thickness is apparently a key parameter for PiG-F, affecting the heat dissipation, absorption, and reabsorption, thus determining the luminous efficacy and luminescence saturation threshold (LST). Conventional studies suggest that thinner films often have lower thermal load than that of the thicker ones. Unexpectedly, we found that the Lu3Al5O12:Ce (LuAG:Ce)-based PiG-F with a moderate thickness (78 μm) yielded the optimal LST of 31.9 W (14.2 W·mm-2, rather than 28.0 W (12.3 W·mm-2) for the thinnest one (56 μm). This unexpected result was further verified by thermal simulations. With the high saturation threshold together with a high luminous efficacy (∼296 lm·W-1), an ultrahigh luminous flux of 7178 lm with a luminous exitance of 2930 lm·mm-2 was thus attained. We believe the new, to the best of our knowledge, findings in this study will substantially impact the design principles of phosphors for laser lighting.

Improvement of beam quality of high-power edge-emitting lasers using inhomogeneous waveguides.

Inhomogeneous waveguides with corrugations have the potential to increase the fundamental mode brightness of edge-emitting lasers as compared to straight waveguides. The corrugations partly suppress the high-order lateral modes of the lasers. The impact of the shape and size of rectangular and triangular types of corrugations on the lasing performance is compared for the first time, and an optimized design is presented. This concept of introducing corrugations is investigated for conventional edge-emitting lasers, as well as high-brightness vertical broad-area edge-emitting (HiBBEE) lasers. The corrugated HiBBEE lasers provide an almost two times larger brightness than the reference lasers.

High luminous efficiency and excellent thermal performance in rod-shaped YAG:Ce phosphor ceramics for laser lighting.

High power and high brightness laser lighting puts forward new requirements for phosphor converters such as high luminous efficiency, high thermal conductivity and high saturation threshold due to the severe thermal effect. The structure design of phosphor converters is proposed as what we believe to be a novel strategy for less heat production and more heat conduction. In this work, the rod-shaped YAG:Ce phosphor ceramics (PCs) and disc-shaped YAG:Ce PCs as control group were fabricated by the gel casting and vacuum sintering, to comparatively study the luminescence performance for LD lighting, on the premise that the total number of transverse Ce3+ ions and the volume of samples from two comparison groups were same. All rod YAG:Ce PCs with low Ce3+ concentration exhibited the high luminous efficiency and better thermal stability than YAG:Ce discs with high Ce3+ concentration. Under the laser power density of 47.8 W/mm2, the luminous saturation was never observed in all rod-shaped YAG:Ce PCs. The high luminous efficacy of 245∼274 lm/W, CRI of 56.3∼59.5 and CCT of 4509∼4478 K were achieved. More importantly, due to the extremely low Ce3+ doping concentration (0.01 at%), rod-shaped ceramics based LDs devices showed the excellent thermal performance and their surface temperatures were even below 30.5 °C surprisingly under the laser power density of 20.3 W·mm-2 (2 W). These results indicate that the rod shape of phosphor converter is a promising structure engineering for high power laser lighting.

Brightness enhancement on a narrow-linewidth fiber Bragg grating-based master oscillator power amplification fiber laser

Abstract In this paper, we have experimentally demonstrated a high-power and high-brightness narrow-linewidth fiber amplifier seeded by an optimized fiber oscillator. In order to improve the temporal stability, the fiber oscillator consists of a composite fiber Bragg grating-based cavity with an external feedback structure. By optimizing the forward and backward pumping ratio, the nonlinear effects and stimulated Raman scattering-induced mode distortion of the fiber amplifier are suppressed comprehensively, accompanied with the simultaneous improvement of beam quality and output power. The laser brightness is enhanced further by raising the threshold of transverse mode instability by approximately 1.0 kW by coiling the gain fiber with a novel curvature shape. Finally, a 6 kW narrow-linewidth laser is achieved with beam quality (M2) of approximately 1.4. The laser brightness doubled compared to the results before optimization. To the best of our knowledge, it is the highest brightness narrow-linewidth fiber laser based on a one-stage master oscillator power amplification structure.

Small-size LD-based automobile headlamp design with long illumination distance and wide illumination range.

Due to the large size of an automobile headlamp that has a laser as the light source, it is difficult to reflect the advantages of high laser brightness into the effect of automobile illumination, so it has not been promoted. We propose a laser headlamp system that integrates low-beam and high-beam structures with superior illumination effects (longer illumination distance and wider illumination range) by designing freeform optical components and optical structure. The small-volume headlamp can meet the requirements of the Economic Commission for Europe regulation (ECE) R112. The structure volume of the headlamp proposed in this study is only 100∗70∗70m m 3, and the maximum luminance is 120lx (simulation result) and 78.5lx (test result). The view angle of the low beam is 13.6°, and the high beam is 15.6°, indicating that the solution is suitable for automotive illumination.

High-brightness green laser diode that uses a multi-order half-wave plate to realize twice-combined polarized beams

In this paper, we describe a method for realizing twice-combined polarized beams by selectively changing the polarization state of lasers with different wavelengths. This improves the output power and brightness of a green laser diode system. A multi-order half-wave plate plays a significant part in combining the polarization states of the first-combined polarized beam by changing the polarization state from orthogonal to approximately parallel. We obtained a maximum output power of 2.85 W and a laser brightness of 25.36 MW/cm2·sr with an optical–optical conversion efficiency of 82.85% and a spectral width of 15.48 nm. Compared with traditional methods for combining polarized beams, the output power is improved by 22.85% and the brightness by 8.65%. This structure provides a new technology for achieving high output power and high brightness from a green laser diode system, and it breaks through the limit of the number of laser units that can be used in combining polarized beams.

Extended BODIPYs as Red-NIR Laser Radiation Sources with Emission from 610 nm to 750 nm.

Herein, we report the synthetic access to a set of π-extended BODIPYs featuring a penta-arylated (phenyl and/or thiophene) dipyrrin framework. We take advantage of the full chemoselective control of 8-methylthio-2,3,5,6-tetrabromoBODIPY when we conduct the Liebeskind-Srogl cross-coupling (LSCC) to functionalize exclusively the meso-position, followed by the tetra-Suzuki reaction to arylate the halogenated sites. All these laser dyes display absorption and emission bands in the red edge of the visible spectrum reaching the near-infrared with thiophene functionalization. The emission efficiency, both fluorescence and laser, of the polyphenylBODIPYs can be enhanced upon decoration of the peripheral phenyls with electron donor/acceptor groups at para positions. Alternatively, the polythiopheneBODIPYs show an astonishing laser performance despite the charge transfer character of the emitting state. Therefore, these BODIPYs are suitable as a palette of stable and bright laser sources covering the spectral region from 610 nm to 750 nm.

A design of laser pyrotechnic device based on fiber laser detonation

In order to meet the application requirements of high performance, high safety and high reliability of laser explosives in future weapons and equipment, this paper tries to solve the problem of interaction reliability between laser and energetic materials, and studies the interaction law between fiber laser and energetic materials with high beam quality. The principle prototype of all-fiber laser ignition with high beam quality is developed. The interaction between high beam quality pulsed laser and energetic materials was studied. Fast and efficient ignition of pulsed fiber laser based on high beam quality is realized. Compared with semiconductor laser, the output brightness of fiber laser is high and the light energy is concentrated under the condition of the same output power, which is conducive to the instantaneous generation of high temperature hot spot when interacting with the agent, which can effectively improve the ignition efficiency. And the photoelectric conversion efficiency is high, can effectively reduce the energy supply. It is an ideal pyrotechnic device which can improve the safety of weapons and equipment in modern war.

Transmission Matrix-Inspired Optimization for Mode Control in a 6 × 1 Photonic Lantern-Based Fiber Laser

A photonic lantern is a coherent beam combination device that can increase the fiber laser brightness by adaptively controlling the input light properties, such as phase, intensity, and polarization. However, the control effect is closely related to the initial optical field, which affects the convergence speed to obtain the optimum solutions. In this work, we propose a novel control strategy using the prior structural information of the photonic lantern. Taking a 6 × 1 photonic lantern as an example, we calculate the transmission matrix of the photonic lantern. The initial optical field conditions, fed as the control inputs, for various mode outputs can be obtained. Compared with the random and equal amplitude control methods, the preset method from the transmission matrix presents a significant improvement of the desired mode content. Our optimization method is generally useful for adaptive control systems to improve their performance, taking advantage of their own structural information.

Low Image Contrast Detection in a Bright Light Interference HDR Scene Using Smart CAOS Camera

Proposed and experimentally demonstrated is the linear low contrast detection capability of a smart design Coded Access Optical Sensor (CAOS) camera operating under interfering bright light conditions. This fine contrast imaging capability is delivered by engaging both the silicon CMOS sensor-mode of the constructed smart CAOS camera and deploying spatial filtering within its inherent on/off light routing structure via the Digital Micromirror Device (DMD). The camera uses the CMOS-mode identified non-bright light region of interest to engage the Code-Division Multiple Access (CDMA) CAOS-mode to achieve successful target imaging. Specifically, the low contrast variation (¡ 6 dB dynamic range) test target region of the toy horse target is successfully experimentally imaged within a near 87 dB High Dynamic Range (HDR) scene created by the presence of an external interfering bright visible light source. Applications scenarios that can benefit from the use of the proposed camera include natural bright light conditions surveillance as well as bright laser and LED targeted imaging across medical, industrial and scientific sectors.

Ultrafast 2D-IR spectroscopy of intensely optically scattering pelleted solid catalysts.

Solid, powdered samples are often prepared for infrared (IR) spectroscopy analysis in the form of compressed pellets. The intense scattering of incident light by such samples inhibits applications of more advanced IR spectroscopic techniques, such as two-dimensional (2D)-IR spectroscopy. We describe here an experimental approach that enables the measurement of high-quality 2D-IR spectra from scattering pellets of zeolites, titania, and fumed silica in the OD-stretching region of the spectrum under flowing gas and variable temperature up to ∼500 ◦C. In addition to known scatter suppression techniques, such as phase cycling and polarization control, we demonstrate how a bright probe laser beam comparable in strength with the pump beam provides effective scatter suppression. The possible nonlinear signals arising from this approach are discussed and shown to be limited in consequence. In the intense focus of 2D-IR laser beams, a free-standing solid pellet may become elevated in temperature compared with its surroundings. The effects of steady state and transient laser heating effects on practical applications are discussed.

High Brightness Diode Laser Based on V-Shaped External Cavity and Beam-Waist Splitting Polarization Combining

A beam combining method to improve the brightness of diode lasers is proposed based on a V-shaped external cavity spectral beam and beam-waist splitting polarization combination. This design has the outstanding advantages of improving the beam quality, brightness, and versatility of the diode laser. Specifically, an output power over 16W with M2 factors of 1.79 × 3.92 (Beam Parameter Product BPP = 0.55 × 1.22 mm mrad) at 40 A in the fast and slow axis is demonstrated for a commercial standard cm-bar. Furthermore, the slow axis M2 of the combined laser is improved by 56% compared with that of a single emitter. Additionally, the brightness of 262 MW·cm−2·sr−1, 136% higher than that of spectral beam combining without using beam-waist splitting polarization, was realized.

Optical Field Transmission Analysis of an All-Fiber Signal Combiner With a Dumbbell Shape

In this paper, the optical field transmission characteristics of an all-fiber signal combiner with a dumbbell shape and its application in laser beam combining are analyzed theoretically. Based on the three-layer waveguide model, the mode characteristics of a tapered multi-core fiber and a tapered single core fiber are analyzed respectively. On this basis, the working principle of an all-fiber signal combiner with a dumbbell shape is introduced from the perspective of mode evolution. The finite-difference beam propagation method is used to numerically analyze optical field envolution process in the combiner. Influences of the waist diameter, taper length and geometric arrangement are analyzed in detail. The calculation results show that an all-fiber signal combiner with a dumbbell shape can realize high brightness laser beam combining and the beam quality can reach the theoretical limit.

Design of a Novel La3Si6N11:Ce3+ Phosphor-in-Glass Film for High Power Laser Lighting: Luminous Efficiency toward 200 lmW–1

Inorganic fluorescent glass films have been widely considered in the field of high power laser lighting because of their excellent comprehensive properties as fluorescent conversion materials. Herein, we adjust the optimum sintering temperature to prepare a series of La3Si6N11:Ce3+ phosphor-in-glass films (LSN PiFs) with excellent optical properties on a single sapphire structure. The prepared LSN PiF has ultrahigh internal quantum efficiency (IQE) (98%) and excellent thermal stability. The thermal conductivity at room temperature can reach 9.8 Wm–1 K–1. When the temperature is 100 °C, the fluorescence intensity can still be maintained. The LSN:Ce phosphor particles did not react with the glass matrix and retained the original luminescence properties. Moreover, by further adjusting the concentration and thickness of LSN PiF, the luminous flux and luminous efficiency of LSN PiF under optimal conditions can reach 1071.73 and 207.58 lmW–1 under the excitation of 460 nm, which is the optimal result reported so far. In addition, the color rendering index (CRI) and low color temperature (CCT) are 64.05 and 5612.6 K, respectively, and the color coordinates are all close to the white light region. All the results show that LSN PiF has great application prospects in the high quality and high brightness laser lighting field.

High Brightness Diode Lasers Based on Beam Splitting and Polarization Combining

A new method to improve the brightness of diode lasers based on beam-waist splitting and polarization combining was proposed and demonstrated. The beam waist was split by a precisely cut prism into two parts and combined with a polarization beam combiner. The advantages of simple setup, high efficiency, brightness, and universality were presented. The slow axis M2 factor of a broad-area diode laser with a ridge beam width of 180 μm was reduced from 18.5 to 9.8, and a brightness of 42.4 MW cm−2 sr−1 was realized; this brightness was a 84.21% improvement of the same emitter at 8 A. The slow axis M2 factor of a commercial broad-area diode laser array combined by spectral beam combining was reduced from 9.08 to 4.78, and 80.6% improvement of brightness was realized on the same commercial broad-area diode laser array. A brightness of 195.8 MW cm−2 sr−1 was realized at 36 A by this diode laser array. This method can be applied in a highly polarized light source to improve the beam quality and brightness.

High-performance and heat-resistant Ce:YAG phosphor in glass for laser lighting

In recent years, the success of laser lighting and display technology depends on the comprehensive properties of light conversion materials such as thermal stability and luminous efficiency. Therefore, fluorescent glass has become the main research object due to its outstanding comprehensive properties such as simple preparation and high quantum efficiency. In this study, a kind of Na2O-K2O-SrO-MgO-CaO-Al2O3-B2O3-SiO2 glass matrix was carefully designed to reduce the damage of Y3Al5O12:Ce3+(Ce:YAG) phosphor in the compounding process. This glass component not only has a low melting point, but also has a high thermal conductivity. More importantly, Ce:YAG phosphor-in-glass (Ce:YAG-PiG) prepared by mixing the optimized glass powder with Ce:YAG phosphors has high thermal conductivity and luminescent properties. Under the excitation of 460 nm blue light, the quantum efficiency of Ce:YAG-PiG can reach 84.8%, which is 91.8% of that of the phosphors (92.4%). When the temperature is below 225 ℃, the thermal conductivity of the sample can be kept above 2.0 Wm−1K−1. Particularly, without any heat dissipation measures, the sample can withstand 3.15 W/mm2 blue laser radiation, and the luminous flux (LF) is 517.83 lm. The results show that this Ce:YAG-PiG composite material can be used for ultra-high brightness laser illumination, which will have a good application prospect.

Smart vector-inspired optical vision guiding method for autonomous underwater vehicle docking and formation.

A smart vector-inspired optical vision guiding (VIOVG) method for autonomous underwater vehicle (AUV) docking and formation is proposed. Unlike traditional optical guiding methods based on LED arrays, the method is inspired by a vector, and uses four laser diodes to form a wing-light pattern to realize smart optical guiding for AUVs. Due to the light scattering effect from water, the four laser diodes can emit four bright and slim laser beams in water, which can be captured by underwater cameras. The intersections of the laser beams form wing-lights as markers for AUV distance and pose estimation. The wing-light pattern is easily tuned and extended by changing the propagation direction and the power of the laser beams beyond the limitation of the physical size of the AUV or docking station. The simulations and experiments show that the proposed method can achieve high precision positioning. A relative distance error of 3.35% is achieved in a positioning experiment at ∼10 m. It has great potential for AUV docking and formation, especially for small AUVs.