High-power Diode Research Articles

Titanium boride coating by high power diode laser alloying of amorphous boron with titanium and its surface property investigations

Present work deals with fabrication of superhard titanium boride coating on titanium surface with preplaced amorphous boron layer using high power diode laser alloying. Amorphous boron instantaneously converts into crystalline boron by the effect of high-power laser interaction, which rapidly drives the boron species into titanium liquid pool and form titanium boride precipitates by its convective flow. Negative Gibbs free energy (ΔG) and enthalpy (ΔH) of amorphous boron crystallization reaction introduces the concept of laser induced self-propagation synthesis. Gibbs free energy (ΔG) for the chemical reactions between Ti and B was calculated to confirm the spontaneous formation of titanium boride compound phases. The diffusion coefficient and activation energy were estimated to understand the phase formation and microstructural evolution. The structural phase, microstructure, microhardness and wear resistance of the laser borided titanium was investigated by XRD, optical and scanning electron microscopy, EDAX, Vickers microhardness analysis and linear reciprocating wear testing. The laser alloyed coating across the cross section shows formation of dendrites and whisker like microstructures. Average microhardness of 800–1600 HV0.2 was measured at different cross-sectional depths and an extreme hardness of about 3800–4700 HV0.2 was obtained in some regions of boron precipitates. The results showed a high negative value of Gibbs free energy of about −250 kJ/mol and −170 kJ/mol at ∼2000 °C respectively which confirms the spontaneity of TiB2 and TiB phase formation. The activation energy of the titanium boride is estimated to be 140 kJ/mol. The laser borided coating with the formation of TiB and TiB2 phases could be useful for surface engineering applications.

In-Situ early anomaly detection and remaining useful lifetime prediction for high-power white LEDs with distance and entropy-based long short-term memory recurrent neural networks

High-power white light-emitting diodes (LEDs) have demonstrated superior efficiency and reliability compared to traditional white light sources. However, ensuring maximum performance for a prolonged lifetime use presents a significant challenge for manufacturers and end users, especially in safety–critical applications. Thus, identifying functional anomalies and predicting the remaining useful lifetime (RUL) is of enormous importance in the operational longevity of the device. To address such challenges, this study proposes a combination of distance-based Mahalanobis distance (MD), entropy generation rate (EGR), and deep learning models for improved anomaly detection and RUL prediction accuracy. Unlike conventional health indicators based on luminous flux data that are challenging to monitor relevant optical performance, the MD and EGR methods are employed to extract in-situ monitored thermal and electrical data as new health indicators. Long short-term memory recurrent neural networks (LSTM-RNN) and convolutional neural networks (CNN) are established to detect anomalies and predict the RUL. The accelerated degradation tests of 3 W high-power white LED have been conducted, and the online and offline collected experimental data are deployed for model development and performance evaluation. The performance of the proposed methods is compared against the Illuminating Engineering Society of North America (IESNA) TM-21 method. The results indicate that LSTM-RNN, when combined with either MD or EGR, can detect anomalies with significantly fewer data (70 %) than is typically required. Furthermore, a significant improvement in prediction accuracy in RUL prediction based on MD and EGR-constructed time series health indicators and employed with the LSTM-RNN model demonstrates the effectiveness of the proposed methods.

Spatial uniformity of the spectral radiance by white LED-based K<sub>2</sub>CaP<sub>2</sub>O<sub>7</sub>:Ce<sup>3+</sup>, Tb<sup>3+</sup> phosphor

The K2CaP2O7:Ce3+, Tb3+ (Ce/Tb-KCPO) phosphor with blue-to-green emission is introduced in this study. The synthesis of the phosphor is carried out with the solid-state approach. The phosphor characteristics, including X-ray diffraction, luminescence lifespan, and thermal stability are measured and examined. The data show that Ce/Tb-KCPO phosphor displays a broadband emission from blue to green when excited by ultraviolet source. Besides, the ion Ce3+ strengthen the emission of Tb3+ ion through an efficient energy-transfer mechanism, which is estimated about 82.51%. The main electric interaction responsible for this Ce/Tb energy transfer is the dipole-quadrupole one. The phosphor also benefits the luminous intensity and color uniformity of the light-emitting diodes (LED) white-light output. Therefore, the Ce/Tb-KCPO phosphor can be a potential material for high-power white light-emitting diodes (WLED).

Laser cladding of stainless-steel ball valves by a high-power diode laser source with a rectangular beam spot

In this paper, the laser cladding of Ni60 + WC powder on the stainless-steel ball valves is investigated to improve the corrosion resistance and the wear resistance of industrial ball valves. A 2-kW high-power diode laser source based on beam multiplexing is used as the processing source to clad the ball valves. To make this diode laser source more reliable for laser cladding, a homogenizing optical system is designed and optimized to transform a circular beam spot output from the optical fiber to a rectangular spot with a flat-top distribution. Employing this diode laser source, the laser cladding of the stainless-steel ball valve is successfully achieved by use of the pre-set powder feeding. The hardness testing experiments are then performed on the ball valves of different diameters, followed by the evaluation of the thickness and hardness of the cladding coating. It is experimentally demonstrated that the microhardness of the ball valves is improved by 2.7 times and the cladding layer has no cracks, which proves the superior performance of the stainless-steel ball valves by use of the proposed method.

Training and validation of a novel non-invasive imaging system for ruling out malignancy in canine subcutaneous and cutaneous masses using machine learning in 664 masses.

To train and validate the use of a novel artificial intelligence-based thermal imaging system as a screening tool to rule out malignancy in cutaneous and subcutaneous masses in dogs. Training study: 147 client-owned dogs with 233 masses. Validation Study: 299 client-owned dogs with 525 masses. Cytology was non-diagnostic in 94 masses, resulting in 431 masses from 248 dogs with diagnostic samples. The prospective studies were conducted between June 2020 and July 2022. During the scan, each mass and its adjacent healthy tissue was heated by a high-power Light-Emitting Diode. The tissue temperature was recorded by the device and consequently analyzed using a supervised machine learning algorithm to determine whether the mass required further investigation. The first study was performed to collect data to train the algorithm. The second study validated the algorithm, as the real-time device predictions were compared to the cytology and/or biopsy results. The results for the validation study were that the device correctly classified 45 out of 53 malignant masses and 253 out of 378 benign masses (sensitivity = 85% and specificity = 67%). The negative predictive value of the system (i.e., percent of benign masses identified as benign) was 97%. The results demonstrate that this novel system could be used as a decision-support tool at the point of care, enabling clinicians to differentiate between benign lesions and those requiring further diagnostics.

Highly crystalline Y3Al5O12:Ce3+ phosphor-in-silica glass ceramics for high-power solid-state lighting

The pursuit of high-brightness solid-state lighting (SSL) stimulates the development of all-inorganic color converters with high robustness. It is required that the fluorescent material is able to cope with the extreme condition generated from the irradiation of high-power-density excitation light. As such, in this work, we developed a new composite color converter, i.e., Y3Al5O12:Ce3+ phosphor-in-silica glass ceramic (YAG:Ce3+ PiSGC). Remarkably, the amorphous SiO2 matrix spontaneously transforms into tetragonal SiO2 crystallites during co-sintering with crystallization fraction reaching up to >90% (almost full ceramization). The activation energy for crystallization Ec and Avrami index n of amorphous silica oxide are 298.5 kJ/mol and 1.71, indicating the diffusion-controlled glass crystallization mechanism. The fabricated prototype high-power phosphor-converted white light-emitting diode (pc-wLED) and phosphor-converted white laser diode (pc-wLD) based on YAG:Ce3+ PiSGC show satisfactory photometric/colorimetric parameters. The developed color converters have combined merits of environmental protection property, cost-effective manufacturing, good luminescent performance, and easy scalability. This study highlights a new kind of opto-functional composite material and its application as an efficient color converter in high-power solid-state lightings.

Room-Temperature, Multigram-Scale Synthesis and Conversion Mechanism of Highly Luminescent Lead Sulfide Quantum Dots.

PbS quantum dots (QDs) are attractive near-infrared (NIR) materials, but traditional synthetic methods require inert atmosphere and/or high temperature. Herein we develop a facile, room-temperature synthetic route for in situ halide passivated PbS QDs through controllable reactions between lead halide, N,N'-diphenyl thiourea, and oleyamine (OLA) in toluene. Contrast experiments and theoretical calculations reveal that the OLA plays a bifunctional role as a mild base to initiate the formation of PbS monomers and as a dynamic ligand to control the crystallization of PbS QDs and further ligand exchange. The oleic acid-capped PbS QDs exhibit high photoluminescence quantum yields up to 45%. The scaled-up synthesis on multigram scales shows great batch-to-batch consistency. We further demonstrate high-power NIR light-emitting diodes using the PbS QDs as color converters, delivering NIR optical power of 9.2 mW at 160 mA. This work provides a simple and versatile synthetic route for high-quality PbS QDs and boosts the applications of NIR materials.

Implementation of energy barrier layers for 1550 nm high-power laser diodes

The influence of a thin AlInAs energy barrier on the efficiency of 1550 nm high-power semiconductor lasers efficiency has been experimentally studied. It was shown that the position and number of barriers in an asymmetric laser heterostructure based on a 1.8–1.9 μm thick waveguide has a significant effect on the output optical power. It is shown that in a barrierless structure, the main reason for radiative efficiency decrease is internal quantum yield drop due to the absence of an energy barrier for the type-II heterojunction at the waveguide-p-cladding interface and electron leakage to the p-emitter layer. It is demonstrated that the implementation of single AlInAs energy barrier layer on waveguide-p-cladding heterojunction allows significantly increase laser diode maximum output power. 2 W maximum CW optical power has been achieved from 40 μm aperture laser diode at heatsink temperature 25 °C.

Reducing thermal resistance of high-power semiconductor diode lasers with coupled waveguides

Reducing thermal resistance of high-power semiconductor diode lasers with coupled waveguides

High-Power Laser Diodes Based on InGaAs(P)/Al(In)GaAs(P)/GaAs Heterostructures with Low Internal Optical Loss

High-Power Laser Diodes Based on InGaAs(P)/Al(In)GaAs(P)/GaAs Heterostructures with Low Internal Optical Loss

Preparation and photoluminescence properties of high thermal stability Sr3Ga2Sn1.5Si2.5O14:Eu3+ red phosphors for high-power light-emitting diodes application

A series of Sr3Ga2Sn1·5Si2·5O14:xEu3+ (SGSSO:xEu3+) phosphors with excellent thermal stability were prepared by the solid-state reaction method. The phase and luminescence properties of the sample were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), diffuse reflectance spectroscopy, and photoluminescence (PL) spectra. Under the excitation of 395 nm, the SGSSO:Eu3+ phosphor exhibits strong red emission at 618 nm, which is attributed to the 5D0 → 7F2 transition of the Eu3+ ions. When monitoring the 618 nm emission peak, the excitation spectrum contains several excitation peaks with a maximum value of 395 nm, which is well matched with the commercial violet LED chips. In addition, the emission spectra of SGSSO:Eu3+ at different temperatures have also been studied. Pleasantly, the luminous intensity of the SGSSO:Eu3+ sample at 150 °C still maintains 80.2% of that at room temperature, demonstrating its good thermal stability and application potential in high-power LEDs. The mechanism for the high thermal stability of the as-prepared phosphor was also discussed. Moreover, the photoluminescence quantum yield of the optimized SGSSO:0.06Eu3+ phosphor can reach 62.7%. Finally, a warm white LED device with high color rendering index and low color temperature was prepared using the prepared SGSSO:Eu3+ phosphor as a red component, verifying the application potential of SGSSO:0.06Eu3+ in LEDs.

Mode analysis and measurement of single-emitter blue diode lasers.

Recent developments in blue diode lasers have been hindered by the challenge of balancing high power with beam quality. Typically, high-power blue diode lasers exhibit low beam quality due to the output of multiple longitudinal and lateral modes. A promising solution to this problem is to control and shape the blue beam mode output from a single emitter. To achieve this, it is key to have full knowledge of the properties of the output mode under various conditions. In this paper, we explore the mode characteristics of an InGaN single-emitter laser diode that has a typical wavelength of 447nm (wavelength range: 440-455nm). We measure and analyze the near-field mode using the box model, finding that the near-field mode excited by the blue diode laser overlapped near the threshold current of 0.32A. The p=2 order lateral mode of longitudinal mode groups 3 and 4 overlapped with the p=4 order mode of adjacent longitudinal mode groups. Through a Fourier transform of the near-field mode, we obtain the far-field mode and reveal a spatial law of mode distribution that is similar to the near-field mode. As the current is gradually increased and approaches the rated current of the laser diode, the near-field mode continuously has new longitudinal mode groups added to the long-wavelength side of the starting group. We observe an increase in the number of longitudinal mode groups and high-order lateral modes, leading to more mode overlaps. Additionally, we observe a gradual shift in the peak energy of the modes to the long-wavelength side. This study reveals the mode characteristics of broad-area blue diode lasers, providing crucial information to achieve high-quality laser beams in such systems.

Effective Laser Fly Control with Modulated UV-A Light Trapping for Mushroom Fungus Gnats (Diptera: Sciaridae)

Fungus gnats (Sciaridae) are one of the most devastating pests on mushroom farms. Generally, they are controlled using relatively inefficient physical means, like sticky or pheromone traps, or with chemical pesticides. Here, we have proposed an integrated fungus gnat control system combining a UV-A LED source at 365 nm and a high-power laser diode at 445 nm. The 365 nm UV-A LED serves a light trap, since previous studies have concluded that fungus gnats show maximum attraction in the range of 365–390 nm. The UV-A LED is also modulated at different frequencies, and the response of the gnats corresponding to these different frequencies was observed. We utilized an Arduino Uno microcontroller to run the integrated device, and a BASLER USB camera was used to capture the images. Our experiments indicated that a frequency of 40 Hz is the optimal choice for attracting the gnats most rapidly. Within 20 s of exposure, the UV-A LED operated at 40 Hz was found to trap approximately 80% of the gnats. In a restricted trapping zone measuring 2.5 × 2.5 × 3 cm3, our integrated module, which includes a 40 Hz modulated UV-A LED and a laser, resulted in a survival rate of only 50% for the total number of gnats. This outcome was accomplished through periodic 200 ms long exposures, amounting to a total duration of 2 min for a group of 100 gnats.

All-solid-state CW Pr3+:YLF green laser at 522 nm end-pumped by a high-power fiber-coupled 444 nm blue LD module

Continuous wave (CW) green lasers have a lot of important applications in many fields, including holography, interferometry, atom cooling and trapping, and quantum optics, and they are usually achieved by frequency-doubling 1 µm lasers based on the Nd3+ gain media. In this paper, we present an all-solid-state CW green laser with an output wavelength of 522 nm, which was directly attained by employing a Pr3+:YLF crystal pumped with a high-power fiber-coupled blue laser diode (LD) module as the gain medium. Due to the negative thermal lens effect of the Pr3+:YLF crystal, the designed laser resonator had to be lengthened with the increase in the incident pump power. As a result, when a 0.5% doped Pr3+:YLF crystal was employed as the gain medium and the incident pump power was 12 W, the length of the resonator was optimized to 311.3 mm and the maximum output power of 522 nm green laser was up to 886 mW. The obtained conversion efficiency and beam quality M2 were 11.25% and 1.15, respectively. The long-term power stability within 4.5 h was better than ±1.5% at an output power of 700 mW. The obtained watt-level green laser can also be used to generate high power CW deep UV laser for laser processing of silicon and organic materials, inspection, etc.

Theoretical and experimental investigation of the molecular depolarization ratio for broadband polarization lidar techniques.

The molecular depolarization ratio (MDR) is of great significance for polarization lidar techniques in terms of validating the measurement accuracy, etc. However, previous studies mainly focused on cases with narrowband laser linewidths, and the transmittance of the Cabannes line in the receiver has been assumed constant. In this work, the narrowband theoretical model of MDR has been re-examined by taking the transmittance of the Cabannes line into account. A large relative deviation of beyond 200% has been found if the wavelength-shift reaches up to 0.5 nm for a receiving bandwidth of 0.5 nm at 532 nm, which is much larger than the case without considering the transmittance of the Cabannes line, i.e., only 15%, reported in previous studies. Besides, a broadband theoretical model has been proposed to evaluate the MDR for polarization lidar using high-power multimode laser diodes as light sources. Simulation studies have revealed that the MDR is highly related to the laser linewidth, the receiving bandwidth, as well as the wavelength-shift between the laser wavelength and the center wavelength of the receiver. The MDR at 520 nm calculated by the broadband theoretical model is about 21% larger than the value evaluated without considering the laser linewidth, when the receiving bandwidth is equivalent to the laser linewidth (e.g., 2 nm). Validation measurements, employing a 520-nm imaging-based polarization lidar with a 3.4-nm laser linewidth and a 10-nm receiving bandwidth, illustrated that the volume depolarization ratio in a clean atmospheric region (0.129±0.0025) was highly consistent with the theoretical MDR (0.132). The good agreement between theoretical and experimental results demonstrated a high measurement accuracy of the imaging-based polarization lidar and excellent feasibility of the broadband theoretical model.

Enhanced Optical–Thermal Performances of High-Power LED by Plated Copper on Thick Film Ceramic Substrate

Thick printed ceramic substrate (TPC) is a promising technique for the packaging of high-power light-emitting diode (LED). Nevertheless, the incorporation of glass phase and voids in the sintered Ag layer decrease the electrical conductivity and heat dissipation of TPC substrate, which contributes to an increase in the junction temperature of LED. This article demonstrates a novel packaging design to plate copper on the sintered Ag layer of TPC substrate, which was applied to enhance the optical–thermal performances of high-power LED. After plating, the copper layers are well bonded with the Ag layer and the sheet resistance decreases rapidly. With the plated copper on thick film (PCTF) substrate package, the total thermal resistance is 17.45% lower than that with TPC package, while the junction temperature change of LED samples is 8.04 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula> C and 9.92 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula> C, respectively. Moreover, the surface temperature of LED sample packaged with PCTF is 11.16% lower than that with TPC at the working current of 1600 mA, and the optical power is 4.79% and 3.2% higher at the working current of 400 and 1200 mA, respectively. The results demonstrate that the optical–thermal performances of LED are enhanced by using the PCTF substrate due to its excellent heat dissipation.

Photo-assisted Cl-, Br- and I- production in caesium sputter ion source

We have measured the effect of 445 nm, high power diode laser, directed on the cathode of a SNICS ion source on the extracted beam currents of Cl-, Br- and I- ion beams. Beam current enhancement factors up to 9 were observed in Cs-depleted operation mode of the ion source. The photo-assisted enhancement is shown to scale with the laser power and depend strongly on the neutral Cs flux into the ion source. The effect of the laser diminishes with increasing Cs oven temperature. We present a qualitative model, supported by cathode current measurement, arguing that photoelectron emission and Cs coverage of the cathode surface could explain the observations.

Experimental and theoretical studies into longitudinal spatial hole burning as a power limit in high-power diode lasers at 975 nm

Spatial-hole-burning as a limit to the continuous-wave (CW) output power of GaAs-based diode lasers is experimentally studied. For 90 μm stripe lasers with 6 mm resonator length and 0.8% front facet reflectivity, spontaneous emission (SE) intensity data show that the carrier density in the device center rises rapidly at the rear facet with bias and falls at the front, consistent with simulation. At the front, the carrier density at the edge of the laser stripe also rises rapidly with bias (lateral carrier accumulation, LCA), consistent with previous observations of increased local current flow. Devices with 20% front facet reflectivity for a flat longitudinal optical field profile show smaller variation in the local carrier density. Weak variation is seen in the carrier density outside the stripe; hence, current spreading is not a power limit. SE wavelength data show higher temperatures at the front with a twofold higher increase in temperature for 0.8% than for 20% front facet. The increased front temperature likely triggers lateral spatial-hole-burning and LCA in this region, limiting power. Finally, pulsed threshold current is more strongly temperature dependent for devices with 0.8% than 20% front facets, attributed to the higher rear facet carrier density. The temperature dependence of slope in pulsed is comparable for both devices at low bias but is more rapid for 0.8% at 20 A, likely due to non-clamping at the back. The temperature dependence of slope for CW is strong with 0.8% facets, likely due to the high temperature and LCA at the front but reduced for 20% facets.

Management of oral leukoplakia with an 808-nm high-power diode laser: a single-center experience.

High-power diode laser emerges as a promising approach to the treatment of oral leukoplakia (OL); however, its short- and long-term effects have been barely explored. This study evaluated the postoperative endpoints and the recurrence rate of high-power diode laser treatment in a well-defined series of patients with OL. A prospective analysis was performed on 22 individuals comprising 31 OL. The lesions were irradiated using the following protocol: Indium-Gallium-Arsenide diode laser, 808nm, continuous-wave mode, 1.5-2.0 W, 780.0 ± 225.1J, and 477.1 ± 131.8s. Postoperative pain was assessed with a visual analog scale at three endpoints. Clinical follow-up was performed on all patients and the Kaplan-Meier test was used to analyze the probability of recurrence. The series consisted mostly of women (72.7%) with a mean age of 62.8years. A single laser session was performed in 77.4% of cases. The median score on the scale that assessed pain on the 1st, 14th and 42nd postoperative day was 4, 1, and 0, respectively. The mean follow-up period per lesion was 28.6months (range: 2-53months). A complete response was observed in 93.5% of OL cases, while 6.5% had recurrence. The probability of recurrence at 39months was 6.7%. No patient experienced malignant transformation. High-power diode laser for the treatment of OL is safe and effective during the trans- and postoperative period. These findings represent an alternative approach to the management of OL, mainly because a low recurrence rate was observed.

Design and experiment of 10 kW-level laser with high-uniformity distribution and large-size output beam

A 11.5 kW laser irradiation source was established to study the pyrolysis and fire of combustibles. The high-power laser diode array (LDA) is first used in the laser irradiation source. By using the homogenized waveguide and large-aperture reshaper, we obtained the high-uniformity distribution and large-size beam simultaneously. The intensity uniformity and the beam size were 95 % and 102.3 mm respectively, correspondingly the power intensity was 1.4 MW/m2. To the best of our knowledge, this is the first time to realize the large-size high-uniformity and MW/m²-level laser irradiation source, which lays a solid foundation for the experiment of the pyrolysis and fire of combustibles induced by the light irradiation. In addition, by the innovative designs, it is effectively enhanced that the damage threshold and the thermal stability of homogenized waveguide under the high-power CW laser.