High Power Diode Laser Research Articles

Elimination of catastrophic optical mirror damage in continuous-wave high-power laser diodes using multi-section waveguides.

One of the persistent obstacles for high-power laser diodes (LDs) has been the catastrophic optical mirror damage (COMD), which limits the operating power level and lifetime of commercial high-power LDs. The output facet of LD reaches a critical temperature resulting in COMD, which is an irreversible device failure. Here, we fabricate multi-section LDs by tailoring the waveguide structure along the cavity that separates the output facet from the heat-generating lasing region. In this method, the LD waveguide is divided into electrically isolated laser and window sections along the cavity. The laser section is pumped at a high current to achieve high output power, and the window is biased at a low current with negligible heat generation. This design restricts the thermal impact of the laser section on the facet, and the window section allows lossless transport of the laser to the output facet. The lasers were operated continuous-wave up to the maximum achievable power. While standard LDs show COMD failures, the multi-section waveguide LDs are COMD-free. Our technique and results provide a pathway for high-reliability LDs, which would find diverse applications in semiconductor lasers.

Investigation of the Implementation of Laser Surface Alloying of Cu with Cr-WC.

This paper presents research on the microstructure and mechanical properties of an alloyed composite copper (Cu) surface layer, reinforced with a mixture of chromium–tungsten carbide (Cr–WC) powders. Copper alloying was performed using a high-power diode laser (HPDL). In the tests, three mixtures of powders with different percentage contents (75%Cr 25%WC, 50%Cr 50%WC, 25%Cr 75%WC) were injected into the melting pool during the laser surface alloying process. Microstructural evolution and the properties of the surface layer of copper after laser alloying were investigated. Structural investigations were performed using light microscopy, scanning and transmission electron microscopy (SEM, TEM) and X-ray diffraction (XRD). Microhardness and wear resistance of the modified surface layer were examined as well. After laser treatment the applied powders appear as uniformly distributed particles in the alloyed zone as well as nanoscale precipitates in the Cu matrix. Several types of precipitate characteristics, in terms of morphology, structure and chemical composition, were observed. Laser alloying of the surface layer modified the microstructure, which resulted in an increase in the hardness of the surface layers compared to the base material.

Entropy Generation Analysis on Magnetohydrodynamic Eyring-Powell Nanofluid Over a Stretching Sheet by Heat Source/Sink

In this communication, the analysis of the entropy generation on magnetohydrodynamic (MHD) Eyring-Powell nanofluid over a stretching sheet with the effects of heat source/sink is reported. The presence of thermophoresis and Brownian motion are responsible for the enhancement in the properties of heat transfer. With the help of suitable similarity transformation entity, the involved governing partially differential equations (PDEs) are converted into nonlinear coupled ordinary differential equations (ODEs). Further, converted differential equations are solved by numerical methods such as Runge-Kutta fourth order correlated with shooting technique. Influence of various pertinent physical parameters is discussed via velocity, temperature, concentration and entropy profiles. The effect of these variables on the quantities of engineering advance such as Nusselt and Sherwood number are furnished in illustrative form and discussed. Further, the major findings of the outcomes are laid down as follows; the Brownian motion of the particles enhances the fluid temperature whereas thermophoresis retards significantly. The entropy generation overshoots due to the increase in the Reynolds number. Nanofluids with high critical heat fluxes and high-power density have the potential to provide the required cooling effect in military ships, submarines, wave energy converters and high-power laser diodes.

Scaling Challenges in High Power Photonic Crystal Surface-Emitting Lasers

Since the initial proposal in 1999 by Noda <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">et al.</i> , photonic crystal surface emitting lasers (PCSELs) have shown to achieve large area, coherent lasing with a narrow, single mode beam. Owing to their unique orthogonal electrical/optical cavity scheme, PCSELs have emerged as one of the most promising platforms for high power diode lasers. In this paper, we report the performance trade-offs and challenges in power scaling, modal competition, and charge injection control. To address these challenges, we investigate the electrical and optical performances of PCSELs under high-power operation. Heterostructure designs with electron block layers were incorporated for efficient and balanced electrical charge injection. Symmetry breaking strategy was introduced in the photonic crystal design to engineer the in-plane momentum dependent quality factor (Q(k)) for mode discrimination and single mode operation. The impact of electrode designs was also investigated to achieve large area uniform charge injection. Simulation results of these designs indicate promising solutions and improved performances for large-area high-power and single-mode PCSEL operations.

Polarization insensitive efficient ultra-narrow diode laser strictly locked by a Faraday filter.

A Faraday anomalous dispersion optical filter (FADOF) could lock high-power diode lasers to atomic resonance lines with ultra-narrow bandwidth. However, the polarization sensitivity of the Faraday filter limits its applications since the standard diode module often employs polarization combination to increase pumping brightness. We proposed a polarization-insensitive mutual injection configuration to solve this problem and locked a standard polarization combined diode module to Rb D2-line. The laser bandwidth was narrowed from 4 nm to 0.005 nm (2.6 GHz, FWHM) with 38.3 W output and an external cavity efficiency of 80%. This FADOF-based polarization-insensitive external-cavity scheme would find many applications, such as high energy atomic gas laser pumping (alkali lasers, metastable rare gas lasers) and quantum optics, etc.

Microstructure distribution and bending fracture mechanism of 65Mn steel in the laser surface treatment

Laser surface treatment of 65Mn steel was conducted using a high-power diode laser. Based on the numerical simulation of the temperature field, the distribution of the microstructure and the peak temperature at various depths were analyzed. An empirical model was proposed to predict the hardened depth. The bending property and fracture mechanism were studied. The results indicated that the martensitic microstructure was coarser near the outer surface of the hardened layer owing to the higher peak temperature. The peak temperature decreased exponentially with increasing depth and increased linearly with laser power and the reciprocal of the square root of the scanning rate. The maximum hardness of the laser-hardened layer was approximately 950 HV, and the self-tempering effect decreased the maximum hardness. Because of the higher brittleness of the hardened layer and the concentration of deformation near the hardened layer, the bending properties deteriorated after laser surface treatment. However, the hardened layer increased the resistance to early bending deformation. Tempering at 150 °C slightly increased the bending strength. The bending fracture consists of three stages: first, tensile load induces the initiation of microcrack, and the crack propagates in an intergranular manner near the crack source; second, the crack propagates in a transgranular manner, and the fracture morphology exhibits quasi-cleavage; and finally, the fracture morphology changes to a ductile fracture in the substrate region.

Surface hardness and corrosion behavior of laser surface-alloyed Ti6Al4V with copper

Laser surface alloying of Ti6Al4V with different Cu contents (6, 8, 13 and 17 wt%) was successfully achieved using a high-power diode laser. With a higher Cu content, the grain size of the laser surface-alloyed Ti6Al4V specimens became finer, with more intermetallic phases (IMPs) formed and the hardness increased up to 646 ± 18 HV0.2. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were conducted to study the corrosion behavior of the laser surface-alloyed specimens in a 0.9 wt% NaCl solution at 37 °C. It was found that the specimen alloyed with 6 wt% Cu showed the mild micro-galvanic effect between CuTi2 and α-Ti. The specimen with 17 wt% Cu had the highest content of IMPs and possessed the lowest corrosion resistance due to the most significant micro-galvanic effect between the IMPs (cathode) and the α-T / β-Ti matrix (anodes). With an appropriate Cu content, laser surface-alloyed Ti6Al4V can also act as hard and corrosion resistant components possessing a high anti-bacterial efficacy by virtue of Cu.

Determining the Service Life of a High-Power IR Laser Diode Using a Model of an Autonomous Channel of Generation

Determining the Service Life of a High-Power IR Laser Diode Using a Model of an Autonomous Channel of Generation

Comparison of the Effects of High-Power Diode Laser and Electrocautery for Lingual Frenectomy in Infants: A Blinded Randomized Controlled Clinical Trial.

The aim of the study was to evaluate the release of the lingual frenulum through frenectomy in newborns zero to 90 days of age who breastfed and had diagnosis of ankyloglossia with an indication for surgery, comparing two methods: electrocautery and a high-power diode laser. Fifty-seven patients were randomly allocated to two groups (23 submitted to electrocautery and 34 submitted to a high power diode laser). Tongue movements were evaluated based on a clinical assessment and using the Bristol Tongue Assessment Tool (BTAT) before and 15 days after the surgical procedures. The visual analog scale was administered to the mothers on the same occasions for the measurement of pain during breastfeeding. Both groups had an increased BTAT score (favorable outcome) at the post-surgical evaluation, but the anterior third of the tongue was not always free to enable the movements necessary for lingual functions. It is fundamental for surgeons to have skill and in-depth knowledge of the equipment used to avoid accidents and complications in the region of important structures. Both techniques employed in this study were safe and effective, causing little bleeding and few postoperative complications. The group submitted to a high-power diode laser exhibited less post-surgical bleeding compared to the group submitted to electrocautery and no inflammation at the edges of the surgical cut.

High-power laser diode at 9xx nm with 81.10% efficiency.

In this study, a low-resistance, low-loss, continuously gradual composition extreme double asymmetric (CGC-EDAS) epitaxial structure is designed to improve efficiency. The structure and facet reflectivity of the broad area (BA) lasers are optimized to maximize the power conversion efficiency (PCE). In the experiment, the peak PCE of 75.36% is measured at 25°C. At 0°C, a peak PCE of 81.10% is measured and the PCE can still reach 77.84% at an output power of 17.10 W, which, to the best of our knowledge, is the highest value to date for any BA lasers.

An Efficiency Improvement Driver for Master Oscillator Power Amplifier Pulsed Laser Systems

The master oscillator power amplifier (MOPA) pulsed laser, one of the popular topologies for high-power fiber laser systems, is widely applied in industrial machining laser systems. In MOPA, the low-power pulsed laser, stimulated from a seed laser diode, is amplified by the high- power optical energy from pump laser diodes via the gain fiber. Generally, the high-power pump laser diodes are driven by lossy linear current drivers. The switched mode current drivers boost the driver efficiency but suffer from pulse energy consistency due to the current switching ripple. In this paper, a laser driver system that varies the switching frequency of current source to synchronize with pulsed laser repetition rate is analyzed and implemented. Experimental results are demonstrated using a 20 W pulsed fiber laser system.

High-power narrow-linewidth 780 nm diode laser based on external cavity feedback technology of volume Bragg grating

A diode-pumped alkali metal vapor laser (DPAL) combines the advantages of a solid laser and a gas laser. DPAL is useful in the industrial, medical, aerospace and military fields and can yield high output power while maintaining excellent beam quality. However, applications in many fields are limited due to the narrow absorption spectrum of the alkali metal vapor laser. In this study, a novel linewidth narrowing structure of the high-power diode laser based on volume Bragg gratings (VBGs) is proposed to match the absorption spectrum of the alkali metal vapor laser. With the combination of fast-axis collimating lens, beam transformation systems, slow-axis collimating lens, VBGs and metal ceramic heaters, the divergence angles of both fast and slow axis are compressed within 10 mrad. A high-power narrow linewidth diode laser source with a central wavelength of 780.044 nm, a spectral width of 0.138 nm, and an output power of 1090 W is achieved at an operating current of 50 A. Experimental results show that the effect of external cavity feedback based on VBG is improved and the multi-channel spectral linewidth is narrowed effectively by such a structure. The diode laser source based on this structure can be applied for pumping the rubidium alkali metal vapor laser.

Extreme Double/Triple Asymmetric Epitaxial Structure Based Diode Lasers for High Powers and High Efficiencies

In edge-emitting high power laser diodes, the longitudinal spatial hole burning (LSHB) effect induced by the inhomogeneous photon and carrier distributions and the non-linear process, two-photon absorption (TPA), are demonstrated to the key causes of power saturation at the high injection level even in the absence of thermal roll-over. Laser diodes based on extreme, double/triple asymmetric (EDAS/ETAS) epitaxial structures show great potentials in high-power and high-efficiency applications owing to the reduced series resistance, low optical loss, and suppressed power saturation. In this paper, a novel semi-analytical calculation method is proposed to systematically analyze the impact of LSHB and TPA effects on the output characteristics of EDAS/ETAS-based broad area lasers (BALs). By leveraging the feature that it is flexible to adjust the confinement factor of ETAS epitaxial structure without compromising the internal loss and resistance level, the laser parameters are first optimized to minimize power saturation of ETAS-based BALs under pulsed and Continuous Wave (CW) operation.

Titanium boride and titanium silicide phase formation by high power diode laser alloying of B4C and SiC particles with Ti: Microstructure, hardness and wear studies

In this work a novel multiphase titanium metal matrix composite (TMMC) coating was developed by high power diode laser assisted alloying of Cp-Ti with the preplaced Boropak powder consisting of B4C and SiC ceramic particles. The XRD, optical microscopy, scanning electron microscopy, EDAX, microhardness and wear testing techniques were employed to investigate structural phase, hardness and wear properties of the alloyed coating. Under the influence of multipass laser alloying, the B4C and SiC ceramic particles decompose to yield boron, silicon and carbon species that react with molten titanium to form TiB2, TiB, TiC and Ti5Si3 phases in the laser alloyed coating. In addition, the un-melted B4C and SiC ceramic particles are dispersed in the titanium matrix. Microstructure of the alloyed coating consists of dendrites and coralline-like structure. The tips of the coralline-like structure are in the range of 150–500 nm. The ceramic multiphase TiB2, TiB, TiC and Ti5Si3 formation resulted in average microhardness around 800–2200 HV0.2 at different regions of the TMMC coating cross section. To correlate the phase formation and microstructural features, surface temperature evolved at the interaction area during laser surface alloying was estimated by a simple equation. Activation energy for the laser melted track was calculated using the Arhennius equation. The linear reciprocating wear test performed on laser alloyed coating against WC ball showed wear rate value of 1.623 х 10−4 mm3/N.m which is 6 times lower compared to the untreated titanium.

Spectral linewidth narrowing of broad-area blue diode bar in V-shape external Talbot cavity.

A 1-D linear array of 23 high-power broad-area laser diode (BALD) beams in the blue spectral region (447 nm) is combined employing a V-shape external Talbot cavity in Littrow configuration. A surface grating provides optical feedback via self-imaged diffractive coupling to the diode bar and induces all the emitters to lase at a common central wavelength. The external cavity reduces the spectral linewidth of the free-running laser diode bar from several nm to 20-50 pm (FWHM) with the power level of 11.8 W. The narrow spectrum of the external cavity stabilized laser can be tuned in the range of 3-4 nm by adjusting the tilt angle of the grating while the laser diode bar is operated in constant current mode at a temperature of 20°C.

Process optimization of laser hot-wire cladding with high-power direct diode laser via the response surface methodology

Process optimization of laser hot-wire cladding with high-power direct diode laser via the response surface methodology

High-power tunable dual-wavelength diode laser with a composite external cavity

A high-power tunable dual-wavelength composite external cavity architecture obtained by means of a holographic grating and a volume Bragg grating is proposed and demonstrated. The tunable frequency difference of the dual-wavelength output is from 0.41 THz to 3.89 THz. We obtain an output power of 2.1 W when the frequency difference is 1.86 THz. The side-mode suppression ratio of more than 29 dB is suppressed over the entire tunable dual-wavelength output range. The two corresponding wavelengths of the dual-wavelength output basically maintain the same intensity with the smallest power difference of only 0.10%.

Facet passivation process of high-power laser diodes by plasma cleaning and ZnO film

Passivation of dangling bonds at the cleaved mirror facet and its durability are fundamental features of semiconductor lasers to obtain reliable operation with a long device lifetime. The high non-radiative recombination activity of the surface states needs to be controlled to prevent the Fermi level pinning before the deposition of mirror coating materials. Here, we report the incorporation of plasma cleaning of the facet and ZnO film as a passivation layer for the fabrication of high-power semiconductor lasers. The Argon plasma cleaning process was investigated to eliminate surface contamination without damaging the cavity surface. The ZnO passivation films were systematically studied by varying the chamber pressure and sputtering power of the radio frequency (RF) sputter coating process. We obtained homogeneous and dense ZnO films with high surface quality and optical absorption coefficient of zero. By incorporating the optimum plasma cleaning and passivation layer parameters, GaAs-based laser devices with significantly improved catastrophic optical mirror damage (COMD) power were achieved. COMD threshold was increased from 11.9 W to 20.7 W. The life test results demonstrate no failure for facet cleaned and passivated devices for more than 500 h, confirming the long-term effectiveness of the process for actual device integration.

Clinical experience of transbronchoscopic laser ablation for central airway stenosis using a high-power diode laser-ten years' experience at a single institute.

High-power diode (GaAlAs) laser systems have been used for transbronchoscopic laser ablation for central airway stenosis. Such diode laser systems show a similar clinical effect to a conventional Nd-YAG laser, but the instrument is more compact with easier handling. We use a high-power diode laser system with a non-contact probe for endobronchial ablative therapy. The present study reviewed our experience with transbronchoscopic laser ablation to explore a better clinical approach for managing central airway lesions. We retrospectively reviewed the patients who were treated for central airway lesions by transbronchial laser ablation using the non-contact-type probe from January 2005 to December 2015 at Chiba University Hospital. We investigated the cause of stenosis, number of treatments, laser setting, total amount of energy, complications, and simultaneously performed modality. Thirty-three patients underwent treatment a total of 72 times. There were 23 males, with an average age of 60.3 years old (range, 18-80 years old). The primary causes of the central airway stenosis were neoplastic disease in 22 (16 malignant tumors, 6 benign tumors) and non-neoplastic disease in 11. Among malignant tumors, there were eight tracheal cancer and five lung cancer patients as well as three patients with esophageal cancer. Among benign tumors, there were three hamartomas and one patient each with papilloma, smooth muscle tumor, and glomus tumor. The non-neoplastic causes of airway stenosis were intubation or tracheotomy in four patients, tuberculosis and granulation in two each, and trauma, burn, and surgery in one each. The numbers of treatments were 30 times (1.36 times/patient) for neoplastic diseases and 42 times (3.82 times/patient) for non-neoplastic disease. The total amount of energy was 1,936 J on average (1,674 J for neoplastic diseases and 2,098 J for non-neoplastic disease). There were no major complications related to transbronchial laser ablation therapy. Transbronchoscopic laser ablation using a diode laser system with a non-contact probe can be safely performed and is useful for endobronchial treatment of both neoplastic and non-neoplastic central airway lesions.

Thermoelastic stresses in high-power CW diode laser arrays assembled on CuW and AlN submounts

Comparative results are presented of 3D-calculation for thermoelastic stress (TES) profiles in diode laser arrays (LDAs) assembled on CuW and AlN submounts (temperature compensators) and operating at a continuous-wave (CW) thermal power load of up to 220 W. For the first time, the simulation has revealed substantial differences in the maximal TES values for the arrays assembled on CuW and AlN submounts, as well as pronounced features of TES distribution in LDA assemblies, in particular, near the rear (highly reflecting) mirror of the laser diode cavity in similar geometries of temperature compensators. Results of the numerical simulation qualitatively agree with thorough measurements of spectral distributions over the LDA emitting aperture. The obtained results are interesting for mastering the production technologies of high-power devices aimed at improving their output parameters and service life.