Blue Laser Diodes Research Articles

White Light Generation and Stability Analysis of High-Power Blue LDs with Remote YAG Phosphors

This paper presents a comprehensive analysis of white light generation and the associated aging dynamics using high-power blue laser diodes (LDs) combined with transmissive single crystal remote YAG phosphors. By systematically varying input currents (ranging from 0.6 A to 3 A) and phosphor thicknesses (250 μm and 500 μm), this study elucidates the optical and electrical characteristics of LD-phosphor systems under diverse operating conditions. The results highlight the system’s potential for stable and efficient white light generation, making it suitable for high-power lighting applications. Experimental setups included both single LDs and a 4 × 2 LD array. For the single LD, a peak optical output of 4.16 W was achieved at 3 A, corresponding to an initial luminous flux of approximately 700 Lm and a correlated color temperature (CCT) of 4653 K, with minimal color temperature shift observed during a 60 min aging process. The 4 × 2 LD array demonstrated consistent white light output across varying phosphor thicknesses, with maximum luminous fluxes of 1857 Lm at 1.4 A and 2622 Lm at 1.6 A for phosphor thicknesses of 250 μm and 500 μm, respectively. Importantly, the phosphor exhibited excellent thermal stability throughout the aging process, with the CCT maintained within a range of 4600 K to 5500 K. These findings underscore the reliability and applicability of LD-based white light systems in demanding high-power lighting environments, offering a promising alternative to conventional light sources for automotive, industrial, and specialized lighting applications.

High‐Power GaN‐Based Blue Laser Diodes Degradation Investigation and Anti‐aging Solution

High‐Power GaN‐Based Blue Laser Diodes Degradation Investigation and Anti‐aging Solution

679/339.5 nm radiation generation of pr: YLF laser pumped by fiber coupled blue laser diode module

679/339.5 nm radiation generation of pr: YLF laser pumped by fiber coupled blue laser diode module

High-speed formation of pure copper layers via multibeam laser metal deposition with blue lasers

To realize a carbon-neutral society, it is necessary to shift from gasoline-powered vehicles to electric vehicles. Electric vehicles use copper components such as coil motors and batteries for which copper joining technology is important. Additive manufacturing is one of the most essential technologies for the next generation of manufacturing. Therefore, the technology for forming pure copper layer on a pure copper substrate is important. Laser metal deposition (LMD) is one of the additive manufacturing technologies. A blue diode laser is expected to be effective in shaping pure copper parts because light absorptance of pure copper at blue light is higher than that of near-infrared light. Thus, a multibeam LMD system with the blue diode laser in which metal powder was supplied perpendicular to the processing point and multiple lasers were irradiated from the surroundings was developed for additively manufactured pure copper. In our previous study, we succeeded in forming a pure copper layer on a pure copper substrate at a speed of 1.5 mm/s with blue diode lasers. However, an increase in processing speed was necessary for industrial application. It is considered that the improvement of energy density at the processing point and the control of heat input to the powder and the substrate by lasers are essential to improve the processing speed. Therefore, in this study, we designed an optical system with ten times higher energy density and calculated the heat input to the powder to form a pure copper layer at a speed of 10 mm/s or faster.

Degradation mechanism during catastrophic optical damage in 385 nm GaN-based ultraviolet laser diodes

The failure mechanism of 385 nm GaN-based ultraviolet (UV) laser diodes (LDs) has been investigated. The degradation factors were studied by analyzing scanning electron microscopy (SEM), cathodoluminescence, and transmission electron microscopy (TEM) after aging. In degraded UV LD, degradation is easily observed on the anterior cavity facet, with holes found in the epitaxial GaN material, primarily concentrated in the quantum wells and waveguide regions of the LDs. This shows that the degradation may be closely related to the higher photon energy of the UV laser beam emitted by UV LDs. In the aging process of samples, emission of UV lasers leads to deterioration at the interface and in the semiconductor. This degradation leads to continuous heat accumulation and may create a positive feedback loop. Ultimately, this results in the failure of the UV LD. This study presents a possible major factor for the shorter lifetime of UV LD compared to blue LD. Therefore, it is very significant to improve the interface quality for extending the lifetime of UV LDs.

Green pulse regenerative amplification using a Pr3+:LiYF4 crystal pumped by GaN blue laser diodes

Green pulse regenerative amplification using a Pr3+:LiYF4 crystal pumped by GaN blue laser diodes

Improvement of layer fabrication efficiency and dilution rate for nickel based super alloy by multibeam directed-energy-deposition with blue diode lasers

A bead of nickel based super alloy was deposited on an SS304 substrate by a multibeam directed energy deposition method using a blue diode laser. Previously, the fabrication of nickel based super alloy using a blue diode laser had not been performed. Therefore, the laser output power and sweep speed were varied to investigate the effects of these variables on the bead. The results showed that laser output power and sweep speed affected the bead height, width, fabrication efficiency, and dilution rate in the fabrication of nickel based super alloy beads. In addition, we were able to produce a lower dilution than previously reported.

Direct formation of pure copper layer on aluminum nitride by multibeam laser deposition with blue diode lasers

A demand of power module devices has been increasing for highly energy efficient social system. The insulated heat sink printed circuit board is the key component of power module devices, which is composed of copper and aluminum nitride (AlN) due to high thermal conductivity. The conventional method of the joining between copper and AlN is active metal brazing method, but there is an issue that the high heat treatment of this method generates thermal residual stress on the board and decrease the reliability. For that reason, the development of a direct bonding process between copper and AlN has been demanded. Therefore, we focused on the laser metal deposition (LMD) method, which is a selective heating and microfabrication process. The LMD method is a method in which a powder material is supplied to the processing point and irradiated with a laser to melt the powder and form layer on the surface of the substrate. Then, a blue diode laser with a wavelength of 450 nm, which has a high absorptivity of 60% for copper, is used as a heat source. In addition, the multibeam type LMD system has been installed for the uniform heating of powder. In this study, the laser power density, laser scanning speed, and powder feeding rate were changed to explore the conditions for forming a copper layer on the AlN substrate.

Effects of TMIn Flow Rate During Quantum Barrier Growth on Multi-quantum Well Material Properties and Device Performance in GaN-Based Laser Diodes

Abstract Multidimensional influence of indium composition in barrier layers on GaN-based blue laser diodes (LDs) are discussed through both material quality and device physics perspectives. LDs with higher indium content in the barriers demonstrate a notably lower threshold current and shorter lasing wavelength compared to those with lower indium content. Our experiments reveal that higher indium content in the barrier layers can partially reduce indium composition in the quantum wells, a novel discovery. Employing higher indium content barrier layers leads to improved luminescence properties of MQW region. Detailed analysis reveals that this improvement can be attributed to better homogeneity in the indium composition of the well layers along the epitaxy direction. InGaN barrier layers suppressed lattice mismatch between barrier and well layers, thus mitigating the indium content pulling effect in well layers. In supplement to experimental analysis, theoretical computations are performed, showing that InGaN barrier structures can effectively enhance carrier recombination efficiency and optical confinement of LD structure, thus improving output efficiency of GaN-based blue LDs. Combining these theoretical insights with our experimental data, we propose that higher indium content barriers effectively enhance carrier recombination efficiency and indium content homogeneity in quantum well layers, thereby improving the output performance of GaN-based blue LDs.

Pure copper coating by multibeam directed energy deposition with blue lasers for antimicrobial effect

Pure copper has antimicrobial effect, and the development of pure copper coating technology for product surfaces is needed to prevent the spread of infections. To achieve high antimicrobial performance in coatings, it is essential to form a coating with high copper purity and minimal defects. In this study, we attempted to form a pure copper coating layer on a SS304 substrate using multibeam directed energy deposition with blue diode lasers. In the coating layer formation process, multiple bead layers are overlapped to form a smooth surface and two different types of joining is conducted simultaneously: the similar material joining area with the remelted previous layer, and the dissimilar-material joining area with the substrate. However, it was challenging to conduct this process for SS304 and pure copper due to their significantly different thermal properties. Therefore, we varied the hatching distance to control the heat input to both joining areas and investigated the effect on the quality of the coating layer. The results showed that there is an optimal ratio of similar and dissimilar joining areas, at which a high-quality coating layer with few voids and low dilution is formed. Furthermore, antimicrobial tests showed that the pure copper coating layer formed in this study exhibited the antimicrobial performance equivalent to those of a pure copper plate.

Dual-module combination with littman crosstalk external cavity for narrow-linewidth blue diode laser

The dense spectral beam combination is vital for achieving high power and brightness output in diode lasers. High-power narrow-linewidth laser modules have been widely studied as the fundamental units. This study presents a dual-module shared external cavity linewidth compression structure with a transmission diffraction grating. With a driving current of 2.4 A and a cooling temperature of 20 °C, the blue diode laser’s external cavity achieved an output power of 49.8 W, a spectral linewidth of 0.321 nm, and a tuning range of 0.817 nm, with an external cavity spectrum locked efficiency of approximately 80.6 %. Additionally, it is observed that crosstalk has a significant influence on the linewidth of the two modules. When one module current locked at 2.4 A and the other increased from 0 A to 2.4 A, the linewidth was reduced from 0.377 nm to 0.321 nm, and linewidth locking was implemented over an output power range from 27 W to 49.8 W. This work reports the highest output power for a blue diode narrow-linewidth external cavity laser.

First fluoride ceramics lasing at 605 nm at ambient temperature fabricated from chemically synthesized powders

Laser ceramics have emerged as promising candidates of solid-state laser gain media. However, most laser ceramics are currently focused on lasing in the infrared wavelength range. The very limited options of host materials and the increased optical scattering losses at shorter wavelengths within ceramics have greatly limited the development of visible laser ceramics. Here we report visible laser ceramics with a composition of 0.5%Pr3+,5%Y3+:SrF2, in which a visible (orange) laser oscillation at 605 nm has been successfully achieved at room temperature pumped by InGaN blue laser diodes with a maximum slope efficiency of 8.1%. The ceramics were fabricated by vacuum hot pressing (VHP) of wet-chemistry synthesized 0.5%Pr3+,5%Y3+:SrF2 powders, followed by hot isostatic pressing (HIP). It was found that the visible laser ceramics exhibited a lower optical scattering loss along the processing pressure direction of the VHP process, indicating a uniaxial anisotropy in optical transmission within the ceramics. To our best knowledge, the current work is the first report on visible laser ceramics lasing in the orange region at ambient temperature, fabricated from chemically synthesized powders, which could pave the way for future scientific research on and industrial applications of more sophisticated and cost-effective visible laser ceramics.

Thermocavitation in gold-coated microchannels for needle-free jet injection

Continuous-wave lasers generated bubbles in microfluidic channels are proposed for applications such as needle-free jet injection due to their small size and affordable price of these lasers. However, water is transparent in the visible and near-IR regime, where the affordable diode lasers operate. Therefore, a dye is required for absorption, which is often unwanted in thermocavitation applications, such as vaccines or cosmetics. In this work, we explore a different mechanism of the absorption of optical energy. The microfluidic channel wall is partially covered with a thin gold layer, which absorbs light from a blue laser diode. This surface absorption is compared with the conventional volumetric absorption by a red dye. The results show that this surface absorption can be used to generate bubbles without the requirement of a dye. However, the generated bubbles are smaller and grow slower when compared to the dye-generated bubbles. Furthermore, heat dissipation in the glass channel walls affects the overall efficiency. Finally, degradation of the gold layer over time reduces the reproducibility and limits its lifetime. Further experiments and simulations are proposed to potentially solve these problems and optimize the bubble formation. Our findings can inform the design and operation of microfluidic devices used in phase transition experiments and other cavitation phenomena, such as jet injectors or liquid dispensing for bio-engineering.

The elicitation effects of diode and He-Ne laser irradiations on the alleviation of nutrient-deficiency induced damage in anthocyanin-producing red-fleshed apple cell suspension

Purpose We explored the elicitation role of the laser irradiations on the alleviation of nutrient-deficiency induced damage in anthocyanin-producing red-fleshed apple cell suspension in continuous production of anthocyanin. Methods Anthocyanin-producing red-fleshed apple cells were irradiated by 4 intensity levels of red He-Ne (RHNL) and blue diode (BDL) lasers for 20 min. Results Nutrient deficiency indicated negative effect on total soluble proteins (TSP), superoxidase dismutase (SOD) activity, and total phenolics content (TPC) while it displayed a positive effect on malondialdehyde (MDA), total flavonoids content (TFC), O2 -, H2O2 - , and lipoxygenase (LOX) and polyphenol oxidase (PPO) activities in light controls, illustrating oxidative stress. The laser irradiations on suspension cells indicated variable effects on measured parameters and were time of growth-, levels of intensity-, and laser type-dependent. Likewise, the elicitation effects of lasers relied on a critical threshold among ROS generation and antioxidative system which determines the fate of cells against oxidative stress. The same trend was displayed by RHNL at 6.46 mWcm−2 intensity and BDL at 13.73 mWcm−2. These intensities resulted in a significant increase in SOD, APX, POD, and CAT activities and TSP, TPC, TFC, proline, and glycine betaine accumulation, while induced decrease in LOX, and PPO activities and MDA, and ROS generation, alleviating cellular injury from prolonged nutrient deficiency by diminishing lipid peroxidation and oxidative damages of cell membrane. Conclusion Results suggested that lasers application on mitigating nutrient deficiency stress relied on establishing a suitable balance between ROS generation and antioxidative system, which enables the nutrient-starved anthocyanin-producing cells to continuously produce anthocyanin.

Enhanced luminescence efficiency in GaN-based blue laser diodes by H plasma technology

To the best of our knowledge, this paper is the first to report the application of H plasma treatment technology to the treatment of laser diode ridge. Through the H plasma passivation on the ridge of the laser diode, a neutral complexes layer (i.e., Mg-H) is formed on the ridge, which effectively reduces ridge leakage current, thus reducing the threshold current of the laser diode and significantly improving the slope efficiency. The ridge were treated with H plasma using the Oxford Plasmalab System 100 ICP 180. The lasers' leakage current, optical power, emission wavelength, and other parameters were measured using a Cascade150 + B1505A probe station system, along with matched optical power meters and fiber optic spectrometers. Specifically, this study successfully fabricates a GaN-based blue laser diode characterized by a threshold current as low as 0.42 A and a slope efficiency as high as 1.96 W/A. Compared with the traditional silicon oxide-mediated ridge treated laser, the threshold current of the laser passivated by H plasma is reduced by 0.13 A, and the slope efficiency is increased by 0.56 W/A. This research not only enhances the performance of laser diodes but also has the potential to expand their application in multiple fields.

High-power diode laser spectrally narrowed with prism-etalon feedback.

A simple method for reducing the linewidth of a diode laser while maintaining high output power is described. It is based on a dispersive prism and a thin etalon for retroreflective feedback. The etalon creates two weak external cavities that provide spectral selectivity that is periodic with a period equal to the etalon's free spectral range. The method was applied to a multimode blue laser diode, which in the absence of feedback features a linewidth of several nanometers. The spectral properties of the laser were investigated for different etalon thicknesses and operating currents and tested in the presence of temperature fluctuations. With a SF11 equilateral uncoated prism near Brewster's angle and a 0.3 mm-thick uncoated fused silica etalon, the linewidth was reduced 20-fold to 70pm (3.6 cm-1) with an output power of 3W at a current of 2.15A. The largest diode current probed was 2.75A, which resulted in a linewidth of 100pm (5.1 cm-1) and an output power of 4W. In contrast to the use of, for example, a volume Bragg grating, a high degree of flexibility is afforded as the same prism-etalon pair can be used across the visible and near infrared.

Optimum Design of InGaN Blue Laser Diodes with Indium-Tin-Oxide and Dielectric Cladding Layers.

The efficiency of current GaN-based blue laser diodes (LDs) is limited by the high resistance of a thick p-AlGaN cladding layer. To reduce the operation voltage of InGaN blue LDs, we investigated optimum LD structures with an indium tin oxide (ITO) partial cladding layer using numerical simulations of LD device characteristics such as laser power, forward voltage, and wall-plug efficiency (WPE). The wall-plug efficiency of the optimized structure with the ITO layer was found to increase by more than 20% relative to the WPE of conventional LD structures. In the optimum design, the thickness of the p-AlGaN layer decreased from 700 to 150 nm, resulting in a significantly reduced operation voltage and, hence, increased WPE. In addition, we have proposed a new type of GaN-based blue LD structure with a dielectric partial cladding layer to further reduce the optical absorption of a lasing mode. The p-cladding layer of the proposed structure consisted of SiO2, ITO, and p-AlGaN layers. In the optimized structure, the total thickness of the ITO and p-AlGaN layers was less than 100 nm, leading to significantly improved slope efficiency and operation voltage. The WPE of the optimized structure was increased relatively by 25% compared to the WPE of conventional GaN-based LD structures with a p-AlGaN cladding layer. The investigated LD structures employing the ITO and SiO2 cladding layers are expected to significantly enhance the WPE of high-power GaN-based blue LDs.

Protecting celtuce (Lactuca sativa L. var. augustana) slices against storage-induced oxidative stress and discoloration by using diode laser exposure

Diode laser irradiation is a novel approach applied to preserve the quality of fresh commodities and minimise oxidative processes, including browning in fresh-cut products. The objective of this study was to investigate the efficacy of diode laser treatment in enhancing the quality of celtuce slices during refrigerated storage at 4 °C. The celtuce slices were subjected to a 660 or 450 nm diode laser for 5 min and then stored for 10 d. Both laser treatments hindered the progression of weight loss and firmness increase in the celtuce slices. The use of a 450 nm diode laser effectively prevented the development of browning and preserved the surface colour by inhibiting the increase in a* and overall colour difference values, as compared to other treatments, during storage for 10 d. The diode laser treatment suppressed the increase in oxidative stress by lowering the levels of MDA, H2O2, and O-2 while retaining a high level of DPPH scavenging activity, AsA, and antioxdant enzyme activities, including SOD, CAT, APX, and GR, in comparison to the untreated slices. The treatment enhanced chlorophylls content due to the up-regulation of LsHEMA1 gene and down-regulation of LsNYC1 gene. The treatment also inhibited factors involving enzymatic browning reaction by suppressing PAL activity, total phenols content, PPO activity and LsPPO gene expression. These suggest that the blue diode laser exposure at 450 nm for 5 min is an effective approach hindering oxidative stress and discoloration of celtuce slices during storage.

Investigation of the mechanism of carrier recombination in GaN-based blue laser diodes before lasing

Abstract The carrier recombination behavior of GaN-based blue laser diodes (LDs) is studied and analyzed by experiments and simulation calculations before lasing, with a particular focus on the role of Auger recombination. It is found that Auger recombination plays a crucial role in the decrease in differential efficiency and threshold current of GaN-based blue LDs. The theoretical calculation results show that a large Auger recombination rate may lead to a dominant recombination channel before lasing, which could exceed the radiation recombination and result in an obvious decrease in the differential efficiency. Such a high Auger recombination will dissipate a large number of carriers in the quantum well, resulting in deterioration of device performance, a higher threshold current and a lower efficiency. This work presents a method to evaluate Auger recombination through differential efficiency and also provides evidence that suppressing the Auger recombination rate is beneficial to improve the performance of blue LDs.

Ca3Sc2Si3O12:Ce3+, Mn2+ phosphor ceramic: A promising color converter for full‐color laser lighting

AbstractPhosphor ceramics are considered to be promising color converters for high‐brightness laser lighting. However, current laser lighting usually suffers from a poor color rendering index (Ra ∼70) when using a single‐structured phosphor ceramic, due to the deficiencies in the cyan‐green and red components of the luminescence spectra. In this study, a series of Ca3Sc2Si3O12:Ce3+, Mn2+ (CSS:Ce3+, Mn2+) phosphor ceramics were prepared for the first time using a solid‐state reaction method. Based on the efficient energy transfer from Ce3+ to Mn2+ (with an energy transfer efficiency of ∼33.3%), these ceramics exhibit three distinct emission peaks appearing at 505, 580, and 680 nm, covering the cyan‐green, yellow, and deep red‐light regions, respectively. Additionally, the ceramics display excellent thermal stability, with a thermal quenching temperature (T0.5) exceeding 160°C. Finally, a laser lighting source was constructed by combining the CSS:Ce3+, Mn2+ ceramic with a blue laser diode. By optimizing the Mn2+ concentration, a tunable color from cyan‐green to white was achieved, and the resulting Ra and luminous efficacy of the white light were 86 and 65 lm/W, respectively. These results demonstrate that the CSS:Ce3+, Mn2+ phosphor ceramic is an excellent color converter for full‐color laser lighting.