Blue Laser Diodes Research Articles

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.

2.53 W of 261 nm continuous wave generation in a pr: YLF laser pumped by blue laser diode at 444.2 nm

2.53 W of 261 nm continuous wave generation in a pr: YLF laser pumped by blue laser diode at 444.2 nm

Efficient yellow Dy:ZBLAN fiber laser with high-brightness diode-pumping at 450 nm.

We report on a low-threshold efficient yellow Dy-fiber laser with good beam quality featuring high-brightness pumping. It employs a single-clad 0.2 mol% Dy:ZBLAN fiber pumped by two 450-nm blue GaN laser diodes. The continuous-wave Dy-fiber laser delivers a maximum output power of 109 mW at 575 nm with a laser threshold of 218 mW, a slope efficiency of 19.6%, and beam quality factors M2 x,y ∼ 1.5. The overall optical efficiency versus incident pump power is 13.9%, being record-high, to the best of our knowledge, for this type of laser. The laser performance is simulated based on the spectroscopic data, being in good agreement with the experiment.

47 Gbps 100 m ultra-high-speed free-space visible light tricolor laser communication system utilizing time domain hybrid Huffman coding.

The escalating demand for greater transmission capacities in the forthcoming 6 G communication landscapes necessitates the investigation of upper segments of the electromagnetic spectrum by both academic institutions and the industrial sector. This effort aims to circumvent the impending spectrum resource limitations. Against this backdrop, laser diodes (LDs) emerge as a critical technology for high-speed visible light communication (VLC), owing to their significant modulation bandwidth potential. This paper details what we believe to be a novel visible light laser communication (VLLC) system powered by red/green/blue (RGB) tricolor laser diodes. It highlights a successful 100-meter free-space transmission achieved through a time domain hybrid huffman coding (TDHHC) technique. The system's performance review unveiled impressive data transmission rates for the red, green, and blue laser diodes channels at 16.852 Gbps, 14.442 Gbps, and 15.755 Gbps, respectively, culminating in a cumulative transmission rate of 47.049 Gbps while maintaining a bit error rate (BER) beneath the stringent threshold of 3.8E-3, mandated by 7% hard decision forward error correction (HD-FEC) standards. As far as we known, this marks the highest data rate documented in a long-distance tricolor VLLC system.

1.01-W narrow-linewidth ultra-violet laser by Pr: YLF

We presented the first report of a high-power narrow-linewidth 261 nm laser. This laser relies on a diode-pumped Pr: YLF crystal and employs a ring cavity design that integrates TSAG (Terbium Scandium Aluminum Garnet) as the magneto-optical crystal. A double-ended pumping configuration is established through the utilization of two 10-W 444-nm blue diode laser arrays as pump sources. Through intracavity frequency doubling facilitated by a BBO (Beta-Barium Borate) crystal, we have achieved a final output of 1.01 W narrow-linewidth laser radiation at 261 nm.

Visible light generation and lasing from a fluoroindate glass fiber

We report on a Dy3+-doped fluoroindate glass fiber laser operating in the yellow (∼576 nm) wavelength region that is pumped by a blue GaN diode laser (∼450 nm). Using single-clad Dy3+-doped fluoroindate glass fiber with 0.5 mol% concentration and a ∼0.48 m length, a slope efficiency of ∼26.6% and maximum output power of ∼467 mW was produced. This result demonstrates that fluoroindate glass fiber has a sufficiently low background loss at visible wavelengths to support efficient visible light generation. We compared all our measurements with a Dy3+-doped fluorozirconate glass fiber and found that most of the laser performance and spectroscopic parameters are similar to ZBLAN. We therefore conclude that fluoroindate glass fiber can be further developed for visible light emission.

Blue GaN-based DFB laser diode with sub-MHz linewidth.

Distributed feedback laser diodes (DFBs) serve as simple, compact, narrow-band light sources supporting a wide range of photonic applications. Typical linewidths are on the order of sub-MHz for free-running III-V DFBs at infrared wavelengths, but linewidths of short-wavelength GaN-based DFBs are considerably worse or unreported. Here, we present a free-running InGaN DFB operating at 443 nm with an intrinsic linewidth of 685 kHz at a continuous wave output power of 40 mW. This performance is achieved using a first-order embedded hydrogen silsesquioxane (HSQ) surface grating. The frequency noise is measured using a cross-correlated self-heterodyne frequency discriminator, and two estimations of integrated linewidth are evaluated using 1/π integration and β-separation line integration methods.

High-speed GaN-based laser diode with modulation bandwidth exceeding 5 GHz for 20 Gbps visible light communication

Visible light communication (VLC) based on laser diodes demonstrates great potential for high data rate maritime, terrestrial, and aerial wireless data links. Here, we design and fabricate high-speed blue laser diodes (LDs) grown on c-plane gallium nitride (GaN) substrate. This was achieved through active region design and miniaturization toward a narrow ridge waveguide, short cavity length, and single longitudinal mode Fabry–Perot laser diode. The fabricated mini-LD has a low threshold current of 31 mA and slope efficiency of 1.02 W/A. A record modulation bandwidth of 5.9 GHz (−3 dB) was measured from the mini-LD. Using the developed mini-LD as a transmitter, the VLC link exhibits a high data transmission rate of 20.06 Gbps adopting the bit and power loading discrete multitone (DMT) modulation technique. The corresponding bit error rate is 0.003, satisfying the forward error correction standard. The demonstrated GaN-based mini-LD has significantly enhanced data transmission rates, paving the path for energy-efficient VLC systems and integrated photonics in the visible regime.

Tri-wavelength blending method for speckle reduction and color space enhancement in laser projection systems

A novel tri-wavelength blending speckle reduction method was proposed and studied both experimentally and theoretically. In the proposed method, a 543 nm diode pumped solid state (DPSS) laser was employed to cooperated with a shorter wavelength 523 nm laser diode (LD) and a common 532 nm DPSS laser. Comparing to the traditional speckle reduction method, the proposed method takes into account both speckle reduction and color space coverage of a project system. It was shown that speckle contrast ratio (SCR) as low as 3.3 % was achieved when the power ratio of 523 nm, 532 nm and 543 nm light were set to 4:1:1. The effect on the color gamut after the use of tri-wavelength blending method was also investigated. It was found that by using the proposed tri-wavelength blending green lasers together with the commercially available red (635 nm) and blue (467 nm) laser diodes, a color space coverage as large as 97.6 % of the Rec.2020 color gamut can be achieved.

Blue diode laser and its applications in manufacturing: A brief review

Blue diode laser and its applications in manufacturing: A brief review

Laser-induced fluorescence spectroscopy of certain essential oils by blue and violet diode laser excitation

Laser-induced fluorescence (LIF) spectroscopy of 8 essential oils (rosemary, basil, orange, lavender, peppermint, rose, pomegranate and tea tree oil) has been performed using compact blue and violet lasers operating at 447 nm and 405 nm respectively. The various features of the obtained spectra and their possible molecular origins have been discussed. Important constituents in these oils have been identified, such as two types of chlorophylls (A and B), in addition to a type of tocopherol (vitamin E). It may be possible to roughly estimate, qualitatively, the relative abundance of these constituents in these essential oils. To the best of our knowledge, the analysis of a significant number of essential oils by laser induced fluorescence (LIF) technique has not been performed before. As a future application, the technique can be used for the efficient and rapid detection adulterants in essential oils.

Crystal growth and spectroscopic performances of Dy3+:YPO4 and Dy3+/Tb3+:YPO4 crystal as potential yellow laser gain mediums

Exploring new Dy3+-doped laser gain medium is still a challenge for constructing efficient yellow solid-state laser at current stage. In this paper, high quality Dy3+:YPO4 and Dy3+/Tb3+:YPO4 crystals were grown by the high temperature solution method. The crystal structure, chemical composition, phonon energy, polarized absorption and emission spectra, fluorescence lifetime were investigated. The obtained large FWHMs (6 nm) and absorption cross-sections (3.87×10−21 cm2) of Dy3+:YPO4 and Dy3+/Tb3+:YPO4 crystals at 454 nm indicate that they can be efficiently pumped by the commercial blue laser diodes. J-O intensity (Ω2, Ω4, Ω6), fluorescence branching rate and radiative lifetime of Dy3+ ions were calculated by J-O theory. Benefiting from the appropriate phonon energy, the emission cross-section of Dy3+: YPO4 crystal at 575 nm can reach 5.04×10−21 cm2. Moreover, after co-doping Tb3+ as deactivating ion, the emission cross-section of Dy3+/Tb3+: YPO4 crystal at 575 nm was promoted to 5.98×10−21 cm2 by a resonance energy transfer process between the Dy3+-6H13/2 and Tb3+-7F4. Therefore, both Dy3+:YPO4 and Dy3+/Tb3+:YPO4 crystals are potential candidates for yellow laser gain mediums.

Weldability and Mechanical Properties of Pure Copper Foils Welded by Blue Diode Laser.

The need to manufacture components out of copper is significantly increasing, particularly in the solar technology, semiconductor, and electric vehicle sectors. In the past few decades, infrared laser (IR) and green laser (GL) have been the primary technologies used to address this demand, especially for small or thin components. However, with the increased demand for energy saving, alternative joint techniques such as blue diode laser (BDL) are being actively explored. In this paper, bead-on-plate welding experiments on 0.2 mm thick pure copper samples employing a BDL are presented. Two sets of parameters were carefully selected in this investigation, namely Cu-1: Power (P) = 200 W; Speed (s) = 1 mm/s; and angle = 0°, and Cu-2: P = 200 W; s = 5 mm/s; and angle = 10°. The results from both sets of parameters produced defect-free full penetration welds. Hardness test results indicated relatively softer weld zones compared with the base metal. Tensile test samples fractured in the weld zones. Overall, the samples welded with Cu-1 parameters showed better mechanical properties, such as strength and elongation, than those welded with the Cu-2 parameters. The tensile strength and elongation obtained from Cu-1 were marginally lower than those of the unwelded pure copper. The outcomes from this research provide an alternative welding technique that is able to produce reliable, strong, and precise joints, particularly for small and thin components, which can be very challenging to produce.

Lignin-derived carbon quantum dot/PVA films for totally blocking UV and high-energy blue light

Excessive exposure to UV and high-energy blue light (HEBL) can cause fatal eye and skin injuries. As a result, it is crucial to protect our bodies from UV and HEBL radiation. To achieve complete blocking of UV and HEBL, we developed a lignin-derived carbon quantum dot (L-CQD)/polyvinyl alcohol (PVA) film. L-CQD was synthesized from lignin, a waste woody biomass, and then blended with a PVA matrix to create a flexible L-CQD/PVA film. Thanks to simultaneous UV and HEBL absorption characteristics and bright color of L-CQD, the PVA film with 0.375 wt% L-CQD demonstrated outstanding blocking efficiency: 100 % in UV-C, UV-B, and UV-A, and at least 99.9 % in HEBL. It also exhibited a 44 % increase in lightness and a 12 % enhancement in transparency compared to lignin/PVA film. The film's ability to block UV and HEBL was further demonstrated by reducing >40 % UV-induced ROS formation in both cancerous and normal cell lines (Hs 294T, HeLa, CCD-986sk, and L929), as well as by blocking blue laser diode (LD) and LED. Since the L-CQD/PVA film is simple to produce, environmentally friendly, flexible, and thermally stable, it is suitable for use as a protective coating against sunlight and harmful emissions from IT devices.

Enhancing the blue GaN laser diodes by modifying the first barrier structure and adjusting the growth conditions of quantum wells

The structure of the first barrier (FB) of quantum wells was modified from the single-layer GaN to the GaN-InGaN-GaN composite structure. Experiments have shown that the composite first barrier can improve the crystal quality of the quantum wells, which increase the luminous power and reduce the stress accumulation before the InGaN quantum well. Furthermore, the composite first barrier can reduce the polarized electric fields and suppress the impact of quantum confinement Stark effect (QCSE) on the luminescence properties of the quantum wells. The growth conditions of the InGaN/GaN quantum wells were studied. Both the growth rate and the ammonia flow are related to the incorporation of In in InGaN quantum wells and the formation of In clusters. These two parameters have optimal values when the other one is fixed. After optimizing the growth rate and the ammonia flow, the internal quantum efficiency of the quantum wells was finally improved from 24.14 % to a commercial level of 77.2 %.

Blue Laser for Polymerization of Bulk Fill Composites: Influence on dentin bond strength and temperature rise during curing and co-curing method.

Blue diode lasers are alternative curing devices for dental composites. The aim of this study was to investigate the influence of blue diode laser polymerization on shear bond strength of bulk fill composites to human dentin and temperature rise during two types of polymerization. Composite cylinders of SDR Plus(SDR) and Ever X Flow(EX) were bonded to dentin slabs using Adhese Universal and curing devices blue diode laser (449nm, 1.6 W) and Power Cure LED. For each material and curing device there were two polymerization approaches: 1)conventional: separate curing of adhesive; 2)co-curing: simultaneous adhesive and composite curing. Polymerization modes for each material in conventional and co-curing(c) approach were: blue laser 2000 mW/cm2 for 5s (L5 and L5c); blue laser 1000 mW/cm2 for 10s (L10 and L10c); Power Cure 2000 mW/cm2 for 5s (LED5 and LED5c); Power Cure 1000 mW/cm2 for 10s (LED10 and LED10c). Temeperature was measured using thermal vision camera. For SDR, the highest bond strength was 24.3MPa in L10c, and the lowest 9.2MPa in LED5c. EX exhibited the highest bond strength(21.3MPa) in LED5, and the lowest in L5(7.7MPa). The highest temperature rise for SDR was in L10 and L5 (7.3 and 7.2°C), and the lowest in LED5(0.8°C). For EX, the highest temperature rise was in L5 (13.0°C), and the lowest in LED5 (0.7°C). Temperature rise was higher during blue laser polymerization, especially at high intensity and with conventional curing. Preferable blue laser curing mode is co-curing at 1000mW/cm2 for 10s.

Dynamical Behavior of a Stacked Blue Laser Diode Consisting of Two Active Regions with Wide InGaN Quantum Wells and Two Tunnel Junctions

In nitride‐based laser diodes, the poor conductivity of the p‐type region, higher light absorption, and the difficult processing of an ohmic p‐contact with low resistance are major challenges. Recently interband tunnel junctions (TJs) have been used to replace much of the hole transport layers by electron transport layers, and also to allow for two n‐type contacts. In this work, GaN‐based laser diode stacks with TJs are analyzed. The devices are grown with plasma‐assisted molecular beam epitaxy and include two waveguides with active regions consisting of 25 nm wide InGaN quantum well (QW), each, which are connected through a TJ. A second TJ is placed on top to eliminate the p‐type contact. In this study, the time‐dependent spectral behavior of such structures is analyzed by streak camera measurements. The two QWs have different lasing thresholds and emission wavelength. Using the temporal resolution of the streak camera, a lasing onset of the second QW a few nanoseconds after the first one is observed. Single shot measurements show unusual intensity oscillations from both QWs, however, one is stable and the other laser diode (LD) has irregular oscillations.

A cyan-green-emitting garnet-structured Lu3-xScxAl2-yScyAl3-zSczO12: Ce3+ phosphor ceramics towards high-color-quality laser-driven lighting

For the laser-driven lighting, traditional phosphor ceramics (PCs), such as Y3Al5O12: Ce3+ (YAG: Ce) PC and Lu3Al5O12: Ce3+ (LuAG: Ce) PC, usually show a wide “cyan cavity” due to the ultra-narrow emission bandwidth (∼2 nm) of the blue laser diode (LD). In this regard, the attainable color rendering (Ra) is always <90 even via the combination of “YAG: Ce/LuAG: Ce + CaAlSiN3:Eu2+”. Evidently, the “cyan gap” is the bottleneck issue to attain high-color-quality laser-driven lighting. As such, we develop a novel cyan-green-emitting garnet-structured solid-solution Lu3-xScxAl2-yScyAl3-zSczO12: Ce3+ (abbreviated as LuScAG: Ce) PCs, derived from the LuAG: Ce PC. A comparative study is conducted to unearth its microstructure, luminescence properties and promising availability. It can be found that the LuScAG: Ce PCs shows large full width at half maximum (FWHM) and abundant cyan emission. Upon material optimization, bright cyan-green emission can be generated with internal quantum efficiency (IQE) of 87.4 % and FWHM of 87.17 nm. Remarkably, this new material yields high-power emitting light with luminous flux (LF) of 3230 lm and luminous efficacy (LE) of 89.7 lm/W upon 36.0 W blue LD driven in rotatory excitation mode, which can serve as an efficient laser color converter. As expected, due to the achieved affluent cyan emissive components of developed LuScAG: Ce PCs, the lighting source based on “LuScAG: Ce PC + CASN: Eu phosphor-in-glass film (PiGF)” shows high color quality with Ra of 90.6 and R12 (related with the cyan cavity) of 85.0.

Spatter reduction in deep penetration welding of pure copper using blue-IR hybrid laser

Bead-on-plate welding of pure copper with a blue-IR hybrid laser was conducted to achieve a spatter suppression in deep penetration welding of pure copper for the performance improvement of battery and power device of e-mobility. This hybrid laser combines an infrared (IR) laser and a blue diode laser as the welding source and preheating source, respectively. Preheating increases the light absorptivity of pure copper in the IR region. A 1.5-kW blue diode laser was employed to increase the light absorptivity by changing the phase of the preheated area from solid phase to liquid and gas phase. By experimentally investigating the influence of the blue diode laser intensity, the phase effects of the preheated area on pure copper welding with a blue-IR hybrid laser are elucidated. As a result, it was found that a liquid preheated area minimizes spatter during deep penetration welding.