High Power Diode Laser Research Articles

High-power fiber-coupled diode laser welding of 10-mm thick Inconel 617 superalloy

In the present study, a high beam quality fiber-coupled diode laser was effectively utilized to weld 10-mm thick Inconel 617 superalloy in single pass. Influence of critical parameters of focusing distance and welding speed on weld characteristics was systematically investigated and optimized. At optimum process conditions with the power density of ≈106 W/cm2, crack-free full-penetration weld with minimal distortion, porosity, and no underfill/undercut/root-hump defects were obtained with 97%–99% joint efficiency. The weld joint quality produced was on par with multipass employing conventional lasers and advanced laser-hybrid welding techniques and sufficient enough to apply in various applications of thermal power plants, ship building, and heavy industries.

Ce:LuAG transparent ceramics for high-brightness solid-state lighting: Fabrication and effect of Ce concentration

Compared to phosphor and phosphor in glass, phosphor ceramics have higher thermal properties, and are less prone to thermal quenching. (Ce,Lu)3Al5O12 (Ce:LuAG) has better thermal stability than most of the phosphors, such as (Ce,Y)3Al5O12 (Ce:YAG). However, the high melting point of Lu3Al5O12 (LuAG; up to 2010 °C) presents a great challenge in producing transparent ceramics (TCs), so a series of Ce:LuAG nanopowders with high sintering activity were prepared by the co-precipitation method and then used as initial materials to obtain x at.% Ce:LuAG (x = 0.05, 0.1, 0.2, 0.3, 0.35, 0.4, 0.5, 0.55, 0.6, 0.65, 0.7) TCs by vacuum sintering at 1775 °C for 10 h. Moreover, the luminous properties of typical Ce-doped LuAG phosphors were systematically investigated using excitation by light-emitting diodes or laser diodes (LEDs/LDs). The emission intensity of 0.4 at.% Ce doped sample is the highest among all TCs with Ce amount ranging from 0.05 to 0.7 at.% at room temperature. The photoluminescence intensity of 0.4 at.% Ce:LuAG only decreases by 12.5% from 25 to 225 °C. The 0.4 at.% Ce:LuAG based on 0.8 W LEDs and 1.1 W LDs has the optimum luminous flux of 71.5 and 113.7 lm and the luminous efficiency of 89.3 and 101.4 lm∙W−1, respectively. As Ce concentration increases, a decrease in the luminescence saturation threshold of TCs is observed with a blue laser power density of 2.5–36.9 W∙mm−2. A high-flux yellow-green light of 1166.9 lm is obtained from 0.1 at.% Ce:LuAG when excited with a high-power LD with an energy density of 36.9 W∙mm−2. This work explored the best Ce doping level in Ce:LuAG TCs, as well as the luminescence saturation threshold in remote laser lighting applications.

Unraveling the formation dynamics of metallic femtosecond laser induced periodic surface structures

Femtosecond laser surface processing (FLSP) is an emerging fabrication technique to efficiently control the surface morphology of many types of materials including metals. However, the theoretical understanding of the FLSP formation dynamics is not a trivial task, since it involves the interaction of various physical processes (electromagnetic, thermal, fluid dynamics) and remains relatively unexplored. In this work, we tackle this problem and present rigorous theoretical results relevant to low-fluence FLSP that accurately match the outcomes of an experimental campaign focused on the formation dynamics of laser induced periodic surface structures (LIPSS) on stainless steel. More specifically, the topography and maximum depth of LIPSS trenches are theoretically and experimentally investigated as a function of the number of laser pulses. Moreover, precise LIPSS morphology measurements are performed using atomic force microscopy (AFM). The proposed comprehensive simulation study is based on two-temperature model (TTM) non-equilibrium thermal simulations coupled with fluid dynamic computations to capture the melting metal phase occurring during FLSP. Our rigorous simulation results are found to be in excellent agreement with the AFM measurements. The presented theoretical framework to model FLSP under low-fluence femtosecond laser pulses will be beneficial to various emerging applications of LIPSS on metallic surfaces, such as cooling high-powered laser diodes and controlling the thermal emission or absorption of metals.

Improved Far-Field Angle in Narrow-Ridge High-Power Laser Diodes Using a Double Stripe Structure

Improved Far-Field Angle in Narrow-Ridge High-Power Laser Diodes Using a Double Stripe Structure

Design and analysis of a group-III nitride superlattice structure based semiconductor laser diode for blue region emission

The demand for high-power blue laser diodes (LDs) in the range above 2 W has been steadily increasing due to their applications in solid-state lighting, projection displays, high-density optical data storage and underwater communication. However, current designs face limitations in terms of achieving both high power output and efficiency. This work focuses on the design, development and numerical analysis of a blue LD utilizing group-III nitride superlattice structures. The present study aims to overcome design challenges by investigating the fundamental factors affecting the performance of blue LDs based on superlattice InGaN structures through careful device parameter optimization. The results show that our device successfully emits at around 430 nm wavelength and is capable of achieving a differential quantum efficiency of 46.91%, with a maximal optical power output of 2.18 W for 1.71 A of current for a strip width of 15 µm. However, when the strip width is increased to 20 µm, 4.6 W optical power is achieved with 3 A of injection current. Numerical studies are performed with several calibrated physics models and finite-difference time-domain techniques. Our results provide an insight into the potential of using superlattice group-III nitride structures to enhance the performance of blue LDs, opening up new possibilities for high-power and high-efficiency devices in the future.

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.

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.

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.

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.

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

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.

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.

Thermal Lensing Effect Reduction on High-Power Multi-Mode Diode Lasers

High-power broad-area diode lasers are needed for a variety of applications. However, such lasers suffer from deteriorated beam quality due to multimode behavior in the lateral direction at high power. We propose an approach to reduce the thermal lensing effect by introducing a thermal compensation layer. As a result of reducing the thermal lensing effect, we demonstrated that the lateral divergence angle was reduced by 16.2%, the lateral beam parameter product was reduced by 12.8%, and the lateral brightness was increased by 18.4% for 230 μm wide diode operating at 50 A current while maintaining a good output power.