This paper presents reliable high power and high brightness 9xx-nm single emitter laser diodes, which have been designed for various multi-emitter fiber-coupled modules. Diode lasers from legend generation have been life-tested with currents up to 14A at heat-sink and junction temperatures of 50°C and 80°C respectively, and have accumulated more than 15,000 hours of life-test duration. In order to further improve reliable operational power and optimize beam quality, new generation devices have been developed. The new devices demonstrated more than 20W CW rollover power without catastrophic optical mirror damage (COMD). Near-field/far-field patterns have also been improved significantly. In addition to step-stress life-tests, a 7-level multi-cell life-test was designed to investigate acceleration factors relative to the operation conditions. Junction temperatures ranging from 60°C to 110°C and current from 14A to 18A were used in this multi-cell life-test. The ongoing multi-cell life-test has accumulated 1.3 million raw device hours and shown very few device failures in up to 7000 hours duration. Such a low failure rate doesn't allow a meaningful estimation of acceleration factors. When nominal acceleration factors are used, multi-cell life-test data supports ~500 FIT, with 90% confidence, at 10W, 33°C/50°C heat-sink/junction temperatures.

Higher power laser diodes (LDs) with a wavelength of 637-639nm are strongly demanded as a light source of display applications because luminosity factor of laser light is relatively high. In order to realize reliable high power operation, we have optimized LD structure, focusing on improvement of power saturation and sudden degradation. As a result, 40μm-wide broad-area (BA) LDs with window-mirror structure have been designed. We fabricated two kinds of single emitter LDs of 1.0mm cavity and 1.5mm cavity. The single LD is installed in conventional φ5.6 mm TO-CAN package. The 1.0mm LD showed very high wall plug efficiency (WPE) of 33% at 25 ºC (23% at 45 ºC) in the power range of around 300mW (30 lm). High output power of 600mW (60 lm) is realized by the 1.5mm LD. Both LDs have operated for over 1,000 hours without any degradation. Estimated mean time to failure (MTTF) is 10,000 hours. In addition, we fabricated an array LD consisting of 20 emitters (BA-LD structure), which shows reliable CW operation of 8W (at junction temperature of 50 ºC) for 10,000 hours.

Northrop Grumman Cutting Edge Optronics has developed a family of arrays for high-power QCW operation. These arrays are built using CTE-matched heat sinks and hard solder in order to maximize the reliability of the devices. A summary of a recent life test is presented in order to quantify the reliability of QCW arrays and associated laser gain modules. A statistical analysis of the raw lifetime data is presented in order to quantify the data in such a way that is useful for laser system designers. The life tests demonstrate the high level of reliability of these arrays in a number of operating regimes. For single-bar arrays, a MTTF of 19.8 billion shots is predicted. For four-bar samples, a MTTF of 14.6 billion shots is predicted. In addition, data representing a large pump source is analyzed and shown to have an expected lifetime of 13.5 billion shots. This corresponds to an expected operational lifetime of greater than ten thousand hours at repetition rates less than 370 Hz.

Performance, lifetest data, as well as failure modes from two different device structures will be discussed in this paper, with emitting wavelengths from 780nm to 800nm. The first structure, designed for high temperature operation, has demonstrated good reliability on various packages with output power up to 10W from a 200μm emitting area. The device structure can be operated up to 60°C heatsink temperatures under CW conditions. Then a high efficiency structure is shown with further improvement on operation power and reliability, for room temperature operation. With ongoing lifetest at 12A and 50°C heatsink temperature, <1000 FIT has been achieved for 6.5W and 33°C operation, on both designs. MTT10%F at 10W and 25°C operation is estimated to be more than 20,000 hours. Devices retain more than 20W rollover power under CW conditions, when re-tested after several thousand hours of accelerated lifetest. Paths for reliability improvement will also be discussed based on observed lifetest failure modes from these two structures.

In this work we show that mini-bar-based 8xx products show the reliability characteristics of independent emitter failures and "non-degrading" drift plots similar to those of their 9xx counterparts. This fact is in part an outcome of the bonding process and heat-sink design. Multi-cell life testing gives projected reliable operation of compact, fiber-coupled modules (200-μm-diameter, 0.15 NA) at 30 W and 808 nm, with 35 W at 880 nm.

Optimization of broad-area InGaAs-AlGaAs strained-quantum-well lasers has led to successful demonstration of high power and high efficient operation for industrial applications. State-of-the-art broad-area single emitters show an optical output power of over 20W and a power conversion efficiency of over 70% under CW operation. However, understanding of long-term reliability and degradation processes of these devices is still poor. This paper investigates the root causes of catastrophic degradation in broad-area lasers by performing accelerated lifetests of these devices and failure mode analyses of degraded devices using various techniques. We investigated MOCVDgrown broad-area strained InGaAs-AlGaAs single QW lasers at ~975nm. Our study included both passivated and unpassivated broad-area lasers that yielded catastrophic failures at the facet and also in the bulk. Our accelerated lifetests generated failures at different stages of degradation by forcing them to reach a preset drop in optical output power. Deep-level-transient-spectroscopy (DLTS) was employed to study deep traps in degraded devices. Trap densities and capture cross-sections were estimated from a series of degraded devices to understand the role that point defects and extended defects play in degradation processes via recombination enhanced defect reaction. Electron-beam-induced-current (EBIC) was employed to find correlation between dark line defects in degraded lasers and test stress conditions. Time-resolved electroluminescence (EL) was employed to study formation and progression of dark spots and dark lines in real time to understand mechanisms leading to catastrophic facet and bulk degradation. Lastly, we present our physics-of-failure-based model of catastrophic degradation processes in these broad-area lasers.

We report on the continued development of high brightness laser diode modules at nLIGHT Photonics. These modules, based on nLIGHT's Pearl^TM product platform, demonstrate excellence in output power, brightness, wavelength stabilization, and long wavelength performance. This system, based on 14 single emitters, is designed to couple diode laser light into a 105 μm fiber at an excitation NA of under 0.14. We demonstrate over 100W of optical power at 9xx nm with a diode brightness exceeding 20 MW/cm2-str with an operating efficiency of approximately 50%. Additional results show over 70W of optical coupled at 8xx nm. Record brilliance at wavelengths 14xx nm and longer will also be demonstrated, with over 15 W of optical power with a beam quality of 7.5 mm-mrad. These results of high brightness, high efficiency, and wavelength stabilization demonstrate the pump technology required for next generation solid state and fiber lasers.

Lasers for marking, direct application laser systems as well as high power solid state lasers require highly reliable, high efficient and low cost laser diodes. Especially fiber lasers and direct diode systems have additionally the need for high brightness. For a very long time either single emitter solutions with low brightness and costs or beam shaped bar solutions with high brightness and high costs served those needs. Since roughly 2 years multiple single emitter solution are more and more penetrating the market showing a high potential for serving all needs of a broad customer base. Based on the 50W product introduced by the middle of 2009 we would like to show the design which is based on qualified and highly stable single emitters.

Further acceptance and fiber lasers and direct diode systems commercial success greatly depend on diodes' availability and cost ($/W). These two parameters should not compromise pumps' performance and reliability. We report on two high-brightness CW devices: high-power module launching over 100W and a pump capable of launching 50W of wavelength-stabilized emission. Devices are based on a single emitter platform and utilize a 105 μm core diameter fiber; radiation is confined within NA<0.13 in both designs. These hermetically sealed modules require passive cooling and are designed to operate with ≤ 30°C diodes' junction overheat. CW peak power efficiency is higher than 55% for both devices. The 25-30dB isolation option (feedback protection at 10XX-nm) is optional in either package. Modules have the industry's smallest footprint and are perfectly suited to serve pumping fiber lasers and direct materials processing markets.

Until now, diode laser concepts were used in applications in the multi-kilowatt range, in which actively cooled diode bars were used and combined via stacking. Per diode stack, laser outputs of just over a kilowatt can be achieved. If outputs of several kilowatts are to be achieved, the radiation of several stacks must be combined. A multi-kilowatt laser with industrially useful beam quality can only be realized through appropriate procedures such as wavelength or spatial combining. The beam quality of the coupled stacks corresponds to the quality of the individual stacks. If the beam quality of such systems is pushed to the limit of the feasible, this reduces the efficiency of the total system considerably. Today, such conventional fiber delivered diode lasers with a beam quality of about 100 mm*mrad achieve an outstanding efficiency of about 40%, but can only be used for laser soldering or other surface processing. With conventional diode lasers, if the beam quality is improved to about 40 mm*mrad, the efficiency falls to about 32%. In order to tap all the efficiency advantages of direct application of diode lasers and further improve the beam quality, TRUMPF has implemented a new concept in its direct diode lasers of the TruDiode series. The basis of this concept is the use of a fiber-coupled diode module with previously unachieved technical output characteristics. Another major advantage of the approach is that the diodes are passively cooled. This paper will highlight those characteristics, as well as provide technical details of the TruDiode series, extremely low running cost and associated application fields.

High-brightness laser diode arrays operating at a duty cycle of 10% - 20% are in ever-increasing demand for the optical pumping of solid state lasers and directed energy applications. Under high duty-cycle operation at 10% - 20%, passive (conductive) cooling is of limited use, while micro-coolers using de-ionized cooling water can considerably degrade device reliability. When designing and developing actively-cooled collimated laser diode arrays for high duty cycle operation, three main problems should be carefully addressed: an effective local and total heat removal, a minimization of packaging-induced and operational stresses, and high-precision fast axis collimation. In this paper, we present a novel laser diode array incorporating a built-in tap water cooling system, all-hard-solder bonded assembly, facet-passivated high-power 940 nm laser bars and tight fast axis collimation. By employing an appropriate layout of water cooling channels, careful choice of packaging materials, proper design of critical parts, and active optics alignment, we have demonstrated actively-cooled collimated laser diode arrays with extended lifetime and reliability, without compromising their efficiency, optical power density, brightness or compactness. Among the key performance benchmarks achieved are: 150 W/bar optical peak power at 10% duty cycle, >50% wallplug efficiency and <1° collimated fast axis divergence. A lifetime of >0.5 Ghots with <2% degradation has been experimentally proven. The laser diode arrays have also been successfully tested under harsh environmental conditions, including thermal cycling between -20°C and 40°C and mechanical shocks at 500g acceleration. The results of both performance and reliability testing bear out the effectiveness and robustness of the manufacturing technology for high duty-cycle laser arrays.

Individually addressable high power single-mode diode laser arrays are an enabling technology for industrial applications. Precision micro-optics for beam-shaping and transfer of the laser emission to the application focus is giving access to free space diode laser functions not realized yet. Manufacturing and assembly of micro-optics therefore is analysed to be selected according to thorough optical analysis and concepts for minimized production cost.

Direct semiconductor diode laser-based systems have emerged as the preferred tool to address a wide range of material processing, solid-state and fiber laser pumping, and various military applications. We present an architectural framework and prototype results for kW-class laser tools based on single emitters that addresses a range of output powers (500W to multiple kW) and beam parameter products (20 to 100 mm-mrad) in a system with an operating efficiency near 50%. nLIGHT uses a variety of building blocks for these systems: a 100W, 105um, 0.14 NA pump module at 9xx nm; a 600W, 30 mm-mrad single wavelength, single polarization building block source; and a 140 W 20 mm-mrad low-cost module. The building block is selected to realize the brightness and cost targets necessary for the application. We also show how efficiency and reliability can be engineered to minimize operating and service costs while maximizing system up-time. Additionally we show the flexibility of this system by demonstrating systems at 8xx, 9xx, and 15xx nm. Finally, we investigate the diode reliability, FIT rate requirements, and package impact on system reliability.

In this work we report on high-power diode laser modules covering a wide spectral range from 410 nm to 2200 nm. Driven by improvements in the technology of diode laser bars with non-standard wavelengths, such systems are finding a growing number of applications. Fields of application that benefit from these developments are direct medical applications, printing industry, defense technology, polymer welding and pumping of solid-sate lasers. Diode laser bars with standard wavelengths from 800 - 1000 nm are based on InGaAlAs, InGaAlP, GaAsP or InGaAs semiconductor material with an optical power of more than 100 W per bar. For shorter wavelengths from 630 - 690 nm InGaAlP semiconductor material is used with an optical power of about 5 W per bar. Extending the wavelength range beyond 1100 nm is realized by using InGaAs on InP substrates or with InAs quantum dots embedded in GaAs for wavelengths up to 1320 nm and (AlGaIn)(AsSb) for wavelengths up to 2200 nm. In these wavelength ranges the output power per bar is about 6 - 20 W. In this paper we present a detailed characterization of these diode laser bars, including measurements of power, spectral data and life time data. In addition, we will show different fiber coupled modules, ranging from 638 nm with 13 W output power (400 μm fiber, NA 0.22) up to 1940 nm with more than 50 W output power (600 μm fiber NA 0.22).

We present a novel optical system for fiber coupling of a commercial high power diode laser stack and the application of this laser system to transmission welding of engineering thermoplastics. The diode laser stack is made up of two 20% fill factor bars, emitting at 808 nm and with a total maximum output power of 120W CW. The stack was collimated using FSAC micro-optics lenses in the fast and slow axis, with a full angle divergence of <4mrad and <25mrad respectively. The optical design and simulations were carried out using ZEMAX®. Based on the design we built an optical set up, which is divided in two subsystems. The first one collimates the laser beam in order to achieve the best focus and couple it into the 400μm core fiber with NA0.22 and 70% efficiency. The second subsystem is designed for beam conformation after the fiber output, using collimation and beam shaping to have a Gaussian beam profile on the work piece. The laser system was applied to study the welding of polycarbonate plastics, based on the effects of selected welding parameters on the seam geometry and surface integrity. The quality of the spot welding has been analyzed obtaining welded seams with a mean diameter about 500-600μm, preserving the good technological properties of the thermoplastic considered in this work. The results show that we have successfully developed a novel laser system which is highly efficient for thermoplastics processing.

There is an ongoing and increasing interest in using expansion matched micro-channel heat sinks for high-power diode laser bars. In this new approach the heat sinks are produced by μ-metal injection molding (μ-MIM). Unlike conventional heat sinks which are made of copper, these particular heat sinks are made of copper-tungsten because it combines two of low coefficient of thermal expansion (CTE) and reasonable thermal conductivity. Manufacturing heat sinks with the μ-MIM process allows for an economic mass production of complex micro near net shape parts. Especially when manufacturing over 10,000 parts with the μ-MIM process, manufacturing cost per part reduce considerably. The main goal is to use the opportunities μ-MIM offers. That means producing complex parts, which have a matched CTE in this case to gallium arsenide (GaAs). Therefore a material which combines high thermal conductivity behavior with a low coefficient of thermal expansion is needed. An additional advantage of the μ-MIM process is that the needed green bodies of the heat sink can be joint together in a co-sintering process. In this paper the current status of production of heat sinks with microstructured surfaces by μ-MIM for thermal management applications are presented. The range of operation and the limitations are outlined with special concern regarding the materials and the minimal structure size. The implication and advantages of using ultrafine powders are emphasized. Therefore sintering behavior, microstructure of sintered parts and characteristic properties as density, CTE, thermal conductivity and electro-optical characterization are shown identified.

High-power single-emitter semiconductor lasers may dissipate up to several Watts heat load during operation. The heat may be generated from a narrow stripe, as low as a few microns in width by several millimeters in length. Thermoelectric Coolers (TEC) are widely deployed to control the laser junction temperature in single-emitter semiconductor-laser packages. TEC manufacturers supply performance curves under the assumption of uniform heat load applied to the cold plate. In reality, the heat will spread laterally across the cold plate creating a temperature gradient across the couples. Consequently, the actual performance of the TEC may be significantly degraded as compared to that predicted from the manufacturer's guidelines. A quantitative analysis that includes these deviations is necessary to properly size the TEC and optimize the package design. This paper provides a simple method for modeling the TEC performance parameters on concentrated heat loads using commercially-available FEA software. Experimental data of TEC cooled single-emitter laser packages will also be presented that corroborate the results of our model.

High-power single emitters have recently become a viable alternative to laser diode bars for fiber pumping applications. Single emitters offer a tenfold increase in brightness over bars, and can be optically combined to scale the power towards 100 W with high brightness. Wall-plug efficiencies >60% are needed to warrant the use of fiber-coupled single emitters in fiber laser systems, which requires careful minimization of the optical loss, electrical resistance and operating voltage of the emitters. Epitaxial wafer design necessarily involves multiple trade-offs, since doping concentrations have opposing effects on the electrical resistance and optical losses. In this paper, we report asymmetric epitaxial waveguide designs for high-efficiency laser operation at 9xx nm. We present a simulation study of the influence of design parameters such as the number of quantum wells, doping profiles, and overlap integral of each epilayer. We also show that by introducing an auxiliary waveguide into the lower cladding, we can control the overlap of the optical mode with the doping profiles - as well as the vertical far-field - without compromising the electrical resistance. The optimized structures were grown and devices fabricated, with optical losses reduced to 0.5 cm^-1, and resistivity to 6.5 Ohm×sq.cm. An optical power of 10 W with >60% efficiency was achieved from 100 μm stripe emitters.

We report on the development of a novel active heat sink for high-power laser diodes offering unparalleled capacity in high-heat flux handling and temperature control. The heat sink receives diode waste heat at high flux and transfers it at reduced flux to environment, coolant fluid, heat pipe, or structure. Thermal conductance of the heat sink is electronically adjustable, allowing for precise control of diode temperature and the output light wavelength. When pumping solid-state lasers, diode wavelength can be precisely tuned to the absorption features of the laser gain medium. This paper presents the AHS concept, scaling laws, model predictions, and data from initial testing.

This paper gives an overview of recent development of high-efficiency 50-W CW TE/TM polarized 808-nm diode laser bar at Lasertel. Focused development of device design and MBE growth processes has yielded significant improvement in power conversion efficiency (PCE) of 50-W CW TE/TM polarized 808-nm laser bars. We have achieved CW PCEs of 67 % to 64 % at heat-sink temperature of 5 °C and 25 °C, respectively. Ongoing life-testing indicates that the reliable powers of devices based on the new developments exceed those of established, highly reliable, production designs.

The demand for high power laser diode modules in the wavelength range between 793 nm and 1060 nm has been growing continuously over the last several years. Progress in eye-safe fiber lasers requires reliable pump power at 793 nm, modules at 808 nm are used for small size DPSSL applications and fiber-coupled laser sources at 830 nm are used in printing industry. However, power levels achieved in this wavelength range have remained lower than for the 9xx nm range. Here we report on approaches to increasing the reliable power in our latest generations of high power pump modules in the wavelength range between 793 nm and 1060 nm.

Many pumping and direct diode applications of high power diode lasers require sources that operate within a narrow (< 1nm) temperature stable spectral line. The natural linewidth of high power broad area lasers is too wide (4-5nm) and varies too quickly with temperature (0.3-0.4nm/K) for such applications. The spectrum can be narrowed by introducing gratings within the diode laser itself or by the use of an external stabilization via a Volume Bragg Grating, VBG. For optimal loss-free, low cost wavelength stabilization with a VBG, the narrowest possible far field angles are preferred, provided power and efficiency are not compromised. Devices that contain internal gratings are potentially the lowest manufacturing cost option, provided performance remains acceptable, as no external optics are required. Therefore, in order to address the need for high power with narrow linewidth, three different diode laser device designs have been developed and are discussed here. For VBG use, two options are compared: (1) devices with high conversion efficiency (68% peak) and reasonable far field (45° with 95% power content) and (2) devices with extremely small vertical far field angle (30° with 95% power content) and reasonable conversion efficiency (59% peak). Thirdly, the latest performance results from broad area devices with internal distributed feedback gratings (DFB-BA Lasers) are also presented, constructed here using buried overgrowth technology. DFB-BA lasers achieve peak conversion efficiency of 58% and operate with < 1nm linewidth operation to over 10W continuous wave at 25°C. As a result, the system developer can now select from a range of high performance diode laser designs depending on the requirements.

High-power diode lasers in the mid-infrared wavelength range between 1.8μ;m and 2.3μm have emerged new possibilities for applications like processing and accelerated drying of materials, medical surgery, infrared countermeasures or for pumping of solid-state and semiconductor disc lasers. We will present results on MBE grown (AlGaIn)(AsSb) quantum-well diode laser single emitters with emitter widths between 90μm and 200μm. In addition laser bars with 20% or 30% fill factor have been processed. More than 30% maximum wall-plug efficiency in cw operation for single emitters and laser bars has been reached. Even at 2200nm more than 15W have been demonstrated with a 30% fill factor bar. Due to an increasing interest in pulsed operation modes for these mid-infrared lasers, we have investigated single emitters and laser bars at 1940nm for different pulse times and duty cycles. More than 9W have been measured at 30A with 500ns pulse time and 1% duty cycle without COMD for a single emitter. Most applications mentioned before need fiber coupled output power, therefore fiber coupled modules based on single emitters or laser bars have been developed. Single-emitter based modules show 600mW out of a 200μm core fiber with NA=0.22 at different wavelengths between 1870nm and 1940nm. At 2200nm an output power of 450mW ex fiber impressively demonstrates the potential of GaSb based diode lasers well beyond wavelengths of 2μm. Combining several laser bars, 20W out of a 600μm core fiber have been established at 1870nm. Finally for a 7 bar stack at 1870nm we have demonstrated more than 85W at 50A in qcw mode.

808 nm QCW bars were fabricated and mounted with hard solder technology onto H-mounts and G-stacks. At room temperature, reliable operation has been demonstrated at 400W at 400A per single 1-cm bar and for a G-stack at 3kW at around 300A. High temperature reliable operation has been demonstrated for both devices up to 95°C. Both types of devices were tested at various pulse widths and duty cycles. Both optical power and wavelength dependencies on the various conditions have been studied.

The demand for high power lasers emitting in the 14xx-15xxnm range is growing for applications in fields such as medical or homeland security. We demonstrate high power laser diodes with emission at 1430, 1470 and 1560 nm. Single multimode emitters at 1470nm emit about 3.5W in CW operation. Power conversion efficiency can reach values as high as 38.5%. With this base material, single and multi-emitter fiber coupled modules are built. Additionally, bars on passive and microchannel coolers are fabricated that deliver 25W and 38W respectively in CW mode, while obtaining more than 80 W in pulsed mode. All reliability tests show an outstanding stability of the material with no signs of wearout after 3750 hrs under strong acceleration conditions.

We present a new design that reduces the far field angles and increases the threshold for catastrophic optical damage of distributed feedback lasers with lateral gratings. The layer structure consists of an asymmetric large optical cavity where the active region is located very close to the upper cladding layer. The position and large refractive index of the active region results in a mode profile that is suitable for good coupling to the lateral grating. A large mode diameter on the facets is achieved by tapering the ridge from its original width to sub-micron dimensions close to the facets. This taper pushes the optical mode down into the core of the large optical cavity, leading to an increase of the mode diameter. The concept is fully compatible with standard facet coating and passivation processes. We present 980 nm laser diodes based on this concept with 5.2° and 13° full-width half-maximum of the farfield and catastrophic optical damage thresholds of 1.6 W.

Especially for fiber pump applications there is a strong demand for high-brightness diode lasers in the 10W power regime. Broad-area and tapered laser concepts seem to be the most promising candidates for high brightness, which is proportional to output power divided by beam quality. Within this talk we give a comparison of both concepts identifying the possibilities and limitations of both concepts. Whereas fast axis far fields show mostly a current independent behaviour, for broad-area lasers near- and farfields in the slow axis suffer from a strong current and temperature dependence, limiting the brightness. For tapered diode lasers the brightness is limited by the temperature characteristics of M² and astigmatism. Therefore for both concepts it is essential to have lasers with excellent thermal management, which can be realized by 4- 5mm long resonators in combination with wall-plug efficiencies well beyond 60%. To fulfill these issues, we have realized MBE grown InGaAs/AlGaAs broad-area and tapered lasers with resonator lengths between 4mm and 5mm and 45° fast axis far field emitting at 976nm. For a 5mm long broadarea laser with 90μm stripe width a beam parameter product of less than 5.9 mm x mrad (M²<10) has been achieved at 10W with a slope efficiency of 1.1W/A and a maximum wall-plug efficiency of 65%. For a tapered laser with a taper angle of 4° and 5mm resonator length, 10W have been demonstrated with a slope efficiency of 1.05W/A and a maximum wall-plug efficiency of 56%. Beam quality is below 3 up to 8W.

New direct diode laser systems and fiber lasers require brilliant fiber coupled laser diodes for efficient operation. In the German funded project HEMILAS different laser bar designs are investigated with tailored beam parameter products adapted for efficient fiber coupling. In this paper we demonstrate results on 9xx and 1020nm bars suitable for coupling into 200μm fibers. With special facet technology and optimised epitaxial structure COD-free laser bars were fabricated with maximum efficiency above 66%. For short bars consisting of five 100μm wide emitters 75W CW maximum output power was reached. In QCW-mode up to 140W are demonstrated. The 10% fill factor bars with 4mm cavity are mounted with hard solder. Lifetime tests in long pulse mode with 35W output power exceed 5000 hours of testing without degradation or spontaneous failures. Slow axis divergence stays below 7° up to power levels of 40W and is suitable for simple fiber coupling into 200μm NA 0.22 fibers with SAC and FAC lenses. For fiber coupling based on beam rearrangement with step mirrors, bars with higher fill factor of 50% were fabricated and tested. The 4mm cavity short bars reach efficiencies above 60%. Lifetime tests at accelerated powers were performed. Finally fiber coupling results with output powers of up to 2.4 kW and beam quality of 30 mm mrad are demonstrated.

Laser diodes and laser bars for the high-volume wavelength ranges at 808 nm and 940 nm are available in optimized design and high quality. However, a lot of other wavelengths in the NIR are needed for specialized applications also requiring high stability, reliability and a good efficiency with a good beam quality. An efficient adaptation of the laser diode design to optimize the laser performance at the customized wavelength is highly desirable. At JENOPTIK Diode Lab (JDL) we therefore focus on a flexible and competitive laser diode design resulting in a high output power and a high efficiency at reasonable production costs. Starting from excellent laser bars at 808 nm and 940 nm laser bars with emission wavelengths around 790 nm, 830 nm, 880nm (cw) and 940 nm (pulsed operation) are developed. For 792 nm a maximum output power of 90 W and an efficiency of 55 % has been achieved with an expected lifetime of more than 15000 hours. At 825 nm a maximum efficiency of 60 % and 60 W output power for more than 20.000 h with a high degree of polarization can be presented. Changing the quantum well material for 885 nm the output power reaches 125W with 63% efficiency also for more than 25.000 hours. Laser bars for pulsed applications (quasi-cw) at 940 nm result in an output power of 500 W with an efficiency of 60 %.

In this work, we present tapered diode lasers (TPL) emitting near 635 nm with an optimized lateral structure. To improve the beam quality as well as the output power, we varied the width of the ridge waveguide (RW) and the length of the RW and taper sections. All diode lasers were mounted p-side down with a common contact for both sections on a CVDdiamond heat spreader and soldered on C-mounts. Optimized TPLs emit 500 mW cw optical output power at a wavelength of 640 nm with a beam quality of M²(σ) = 2.6 and M²(1/e²) = 1.8, respectively. A maximum optical output power of 790 mW could be achieved.

We have applied zinc diffused window structures to 640 nm broad area stripe laser diodes (BALDs) for the first time. A solid-phase zinc diffusion technique was used for a thick single quantum well (SQW) in GaInP employing the short wavelength and disordered active layer possessed a blue shift of 58 nm in photoluminescence spectrum. We fabricated 10 mm arrays including twenty-five BALDs and each BALD consists of a 60 μm ridge stripe and a 1000 μm cavity. An initial catastrophic optical damage (COD) level of the window laser was increased by four times of a conventional none-window laser. A long-term reliability under automatic current control was investigated for initial output powers of 13W and 15W which overcome a previous demonstration of 7.2 W. Measured degradations within a period of 1000-hours were 5 % or less, in contrast a half-life period of our conventional none-window laser with an initial output power of 10 W was only 120-hours. Therefore the window structure improved the BALD in terms of the COD level and the long-term reliability.

We present our work on a single optical component that combines fast-axis smile and lens error correction with slowaxis collimation, produced with a laser-cut phase-plate technique. Customized focal length of slow-axis lenses allows optimization of fill-factor of diode laser bars. In this paper we report on excellent beam properties obtained for a 49- single mode emitter array, 975 nm bar providing 30W cw output, with RMS pointing error of 3% and 6% of far-field divergence in fast- and slow-axis, respectively. We observed a pitch mismatch of 0.03% between the slow-axis lens array, with emitter pointing clearly affected by chip thermal expansion.

We present experimental results on coherent beam combining from large arrays of high power broad-area semiconductor lasers. Our laser array consists of 47 high-power anti-reflection coated broad-area semiconductor lasers and each laser emitter is capable of emitting 1.8 W when uncoated with a maximum array output power of 80W. The total available power from the AR coated array is approximately 40W. By using an external V-shape cavity design, we experimentally demonstrated a coherently combined beam at the output power of ~13 W with the 0.07 nm FWHM spectrum linewidth that is limited by the sensitivity of the optical spectrum analyzer. We also discuss coherent beam combining of highpower broad area laser diode array in current driver pulse mode operation.

The state-of-the-art beam quality from high-brightness, fiber-coupled diode laser modules has been significantly improved in the last few years, with commercially available modules now rivaling the brightness of lamp-pumped Nd:YAG lasers. We report progress in the development of these systems for a variety of applications, such as material processing and pumping of solid state and fiber lasers. Experimental data and simulation results for wavelength stabilized outputs from 200 µm diameter fibers at 975 nm for power levels greater than 200 W will be presented. The enabling technology in these products is supported by key developments in tailored diode laser bars with low slow axis divergence, micro-optics, diode laser packaging, and modular architecture.

Coherent beam combining has been actively explored as a technique to increase the brightness of laser sources. Passive phase-locking of a diode array in a common resonator, in particular, is an attractive approach owing to its inherent simplicity and good beam quality. In this work, we present the coherent combining of an array of diode emitters in a conventional diode bar configuration using the coherent polarization locking technique. An external laser cavity is designed so that the diode emissions from several 976 nm diode emitters are spatially overlapped via a series of birefringent walk-off crystals and passively phase-locked by a polarizing beam splitter. The key optical element in this beam combining scheme is the novel YVO₄ birefringent spatial beam combiner that not only provides spatial overlap, but also identical optical path lengths for the diode beams. This facilitates design of the cavity for achieving a close match between the mode size of the Gaussian beam and the asymmetric emitting area at the front facet of the diode emitters. The phase-locking technique, coupled with the required standard bulk optical crystals and standard diode bar configuration, yields a robust laser architecture which retains the advantages of diode lasers in terms of cost, size and wavelength tunability. With the coherent combining of four diode emitters, we achieved a nearly diffraction limited beam at 1030 mW, which represents a 50 times increase in brightness over the standard incoherent diode bar. The coherent locking approach is highly scalable. Further experiments to coherently combine eight to sixteen diode emitters are in progress.

Phase-coupled stripe-array diode lasers show a strong double-lobed far-field because adjacent stripes tend to operate in the anti-phase supermode. One way to achieve a stable phase relationship and global coupling of the emitters of such a stripe-array is off-axis feedback. In this work several off-axis external cavity designs are discussed. A 400 μm wide emitter stripe array consisting of 40 stripes with a pitch of 10 μm was investigated. By operating this device in a Littrow type off-axis external cavity, more than 2 W of output power of near diffraction-limited, single longitudinal mode emission with a brightness as high as 88 MW/cm²-str could be achieved. The technique of off-axis feedback was also adapted to realize spectral beam combining of 25 emitters of a laser bar. The experimental data are compared with numerical simulations using a new theoretical model including feedback.

The diode pumped alkali vapor lasers operating at subatmospheric pressure require developing of a new generation of high-power laser diode sources with about 10 GHz wide emission spectrum. The latest achievements in the technology of volume Bragg gratings (VBGs) recorded in photo-thermo-refractive glass opened new opportunities for the design and fabrication of compact external cavity laser diodes, diode bars and stacks with reflecting VBGs as output couplers. We present a diode laser system providing up to 250 W output power and emission spectral width of 20 pm (FWHM) at the wavelength of 780 nm. The stability and position of an emission wavelength is determined by the resonant wavelength of a VBG which is controlled by temperature. Stability of an emitting wavelength is within 5 pm. Thermal tuning of the wavelength provides maximum overlapping of emitting line with absorption spectrum of a Rb (rubidium)- cell. The designed system consists of 7 modules tuned to the same wavelength corresponding to D2 spectral line of Rb⁸⁷ or Rb⁸⁵ and coupled to a single output fiber. Analogous systems could be used for other Rb isotopes spectral lines as well as for lasers based on other alkali metal vapors (Cs and K) or any agents with narrow absorption lines.

Degradation analysis of 808nm QCW laser diode array for space application has been investigated by using individual emitter characterization technique. We found that homogeneity of electro-optical characteristics at emitter level along the bar is a relevant parameter to ensure the reliability of the bars. This work is focused on the importance of individual emitter characterization and aging test results analysis up to 4.47 Gshots.

In this work, we investigate experimentally optimized monolithic distributed-feedback (DFB) tapered master-oscillator power amplifiers (MOPA). The devices consist of three autonomously driven sections: a 1 mm long DFB ridgewaveguide (RW) laser, a 1 mm long RW pre-amplifier and 2 mm or 4 mm long tapered amplifiers. The ridge width and the full taper angle are 5 μm and 6°, respectively. Both laser facets are anti-reflection coated. The second order Bragg gratings in the DFB laser were realized by holographic photolithography, wet-chemical etching and a two-step epitaxy. The DFB tapered MOPAs emit nearly diffraction limited spectral single mode CW radiation at 1064 nm. The 6 mm long devices provide an optical power of about 12 W at DFB laser, pre-amplifier and tapered amplifier currents of 150 mA, 400 mA and 18 A, respectively. The 4 mm long devices generate more than 4 W at a tapered amplifier current of 7 A. The spectral drift versus output power is below 50 pm/W.

We report on laser diode bars with wavelengths ranging from 793 to 1080 nm and optimized for high power and high temperature operation. For 808 nm bars output power values of 300 W at 300 A drive current and 200 μs pulse length have been recorded at a cooler temperature of 75°C. Extending our wavelength range to 1080nm we report on bars with >65% power conversion efficiency in CW operation and more than 500 W output power for a wide range of qCW modes. Finally, the properties of a 6-bar stack with 3 kW output power at 460 A drive current and 200 μs pulse width will be discussed.

A 1043nm semiconductor disk laser with a diamond heatspreader is presented. 880mW continuous-wave output power is produced using a 3% output coupler with the incident pump power of 5900mW. The slope-efficiency is 16.7% and the optical- to-optical conversion efficiency is 14.9%. The effect of the diamond heatspreader on the laser is also analyzed.

A new class of high power high brightness 808 nm QCW laser diode mini bars has been developed. With nLight's nXLT facet passivation technology and improvements in epitaxial structure, mini bars of 3 mm bar width with high efficiency design have tested to over 280 W peak power with peak efficiency over 64% on conduction cooled CS packages, equivalent to output power density near 130 mW/μm. These mini laser bars open up new applications as compact, portable, and low current pump sources. Liftests have been carried out on conduction cooled CS packages and on QCW stacks. Over 370 million (M) shots lifetest with high efficiency design has been demonstrated on CS so far without failure, and over 80 M shots on QCW stacks with accelerated stress lifetest have also proven high reliability on mini bars with high temperature design. Failure analysis determined that the failure mechanism was related to bulk defects, showing that mini laser bars are not prone to facet failure, which is consistent with the large current pulse test and failure analysis on high power single emitters.

Due to the growing ranges of applications for stamped parts in the electrical and electronics industry (e.g. switch cabinet cladding and transformer plates) as well as in the automotive industry (e.g. stamp, bent and drawn components), flexible sheet metal forming has become a more important process. The inner and outer contours as well as the forming operations needed to reinforce metal sheets can be carried out by punching machines without re-clamping the metal sheet. In contrast, the potential of conventional punching machines is now exhausted in terms of the material spectrum that can be processed, the tool life and the quality of the machined product. Particularly in view of the machining quality of the sheared edges, the achievable clear-cut surface rates are limited due to the limited plasticity of the sheet materials. When cracks form between the grain boundaries of the sheet material during the conventional shearing process, the cutting edge is divided into a clear-cut surface zone (approx. 30% of the plate thickness when shearing stainless steel plates: 1.4301) and a shearing zone with crack formation. This shearing zone can not be used as a functional surface. The shearing process is divided into the four phases (DIN 8588) "warping", "clear-cutting", "fracture" and "ejection of the piece punched out".