This PDF file contains the front matter associated with SPIE Proceedings Volume 8605, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

Constant advancement in laser sources leads to commercial and industrial lasers with ever higher output powers and brilliance. The increasing capabilities of diode laser sources in particular produces extreme challenges for fibre launching. The difficulties arise due to the nature of the diode lasers, which are often designed with a numerical aperture (NA) exceeding the optical fibre’s NA and a spot size overfilling the fibre core so as to maintain the best possible brilliance. In addition to these properties, the spot imaged onto the fibre facet is typically rectangular. The combination of these properties result in an imperfect launch efficiency, forcing the connector built around the optical-fibre to cope with the radiation which is “lost” from the core of the fibre. Improvements in the Optoskand SMAQ connector are discussed, along with the presentation of results showing the increased power- and loss- handling capabilities when used with a variety of diode laser sources at 976nm. The sources used in the tests are optimised for an optical-fibre of core diameter (Ø) 200μm and NA of 0.22. The sources range in maximum power from 150W to 1000W with a coupling efficiency of between 80 and 90%. Additional complimentary results are shown for a Ø=400μm fibre guiding light of NA=0.12 where launch efficiency is 90 to 95%.

New applications require diode lasers to be driven with short pulses in the sub-micro second range. The goal is to minimize both the cost and size of the diode laser module by minimizing the number of laser bars required while maintaining the lifetime that is desired for the application. Products demanded by the market using such short pulses range from QCW stacks to fiber coupled modules. While many short pulsed applications use high fill factor bars, these bars are not suited for high brightness applications or coupling into small fiber cores. The focus of this work is the analysis of CW diode designs commonly used for high brightness fiber coupled modules under short pulsed conditions.

Three key parameters need to be known in order to design a diode laser module that is suited for high peak powers. First is the damage threshold of the facet. The damage threshold determines the maximum power level at which the laser can be operated safely, considering a proper safety margin dependent on application. The damage threshold is a function of the input pulse width and amplitude. The second parameter which is influenced by the drive current is the slow axis divergence of the diode laser. Knowledge of this parameter is critical when designing the system optics. The third parameter is the effective emitter size which may increase with operating current. An increase in emitter size will lead to larger divergences after collimating optics for a given focal length lens and may result in a larger spot when coupling into an optical fiber. All these parameters have to be considered when designing a new product.

Presented here is a study on these three critical parameters as a function of operating conditions. Results for different diode designs will be presented. The data presented includes damage thresholds, as well as near field and far field data at various operating currents. A design study for fiber coupled modules with high pulse energies based on the test results will be shown for various wavelengths.

Reliable single emitters delivering <10W in the 9xx nm spectral range, are common energy sources for fiber laser pumps. The brightness (radiance) of a single emitter, which connotes the angular concentration of the emitted energy, is just as important a parameter as the output power alone for fiber coupling applications. We report on the development of high-brightness single emitters that demonstrate <12W output with 60% wall-plug efficiency and a lateral emission angle that is compatible with coupling into 0.15 NA delivery fiber. Using a purpose developed active laser model, simulation of far-field patterns in the lateral (slow) axis can be performed for different epitaxial wafer structures. By optimizing both the wafer and chip designs, we have both increased the device efficiency and improved the slow-axis divergence in high-current operation. Device reliability data are presented. The next-generation emitters will be integrated in SCD's NEON fiber pump modules to upgrade the pump output towards higher ex-fiber powers with high efficiency.

We report on the continued development of high performance fiber coupled laser diode modules at nLIGHT. We show that by optimizing the laser resonator design single emitter diode lasers can be tailored for high brightness or for reduced $/W applications. For instance, a fiber laser pump module based on 6 single emitter diode lasers couples efficiently into a 105 μm, 0.15 NA fiber with peak operating efficiency <59% and output power < 65W. These results are made possible by optimizing the diode laser slow axis brilliance and by increasing the optical to optical efficiency to 90%. We will also report on the development of tailored laser resonator that meets the power, brightness, and cost targets for industrial applications. For instance, a wider emitter has reliable performance of <18W of output power while maintaining the slow axis divergence required for coupling into a fiber with a 12 mm-mrad beam parameter product. The corresponding 50% increase in output power significantly improves the $/W performance. These results of high brightness and high efficiency demonstrate the pump technology required for next generation solid state, fiber lasers, and materials processing applications.

Commercially-available QCW diode laser stacks with bar pitch below 0.5mm can now deliver source power densities exceeding 10kW/cm². An increasing number of applications for these sources also specify high brightness, with collimation requirements ranging from equalization of fast and slow axis divergence to achieving fast-axis divergence within a small multiple of the diffraction limit. While collimation can be achieved by mounting an array of rod lenses in a frame with a suitable v-groove array, the resulting optical assembly has a large number of elements and associated adhesive bonds, and the size of the mounting frame limits the density at which stacks can be packed together. We present results exploiting an alternative approach using monolithic fast-axis collimator arrays. This approach greatly reduces the component count and minimizes the number of adhesive bonds required, providing a compact and rugged assembly well-suited to demanding applications. The monolithic collimator array also simplifies package design, and maximizes the achievable device stack packing density. Lens array properties may be tailored to generate applicationspecific divergence profiles or to match the geometry of individual stacks in order to achieve low divergence. Directwrite fabrication of these components allows mass-customization, offering a scalable, low-cost route to high volume collimation for fusion applications.

This work presents some aspects of development of ultra-high power single-mode pump modules at λ= 980 nm for erbium-doped fiber amplifiers. We report here on the results of numerical simulations and experimental data of modifications to the laser waveguide structure with a focus on improving the fiber coupling efficiency. The so-called integrated fiber wedge lens was used as a coupling element in the present investigation. Our simulations showed that between the two most widely used laser waveguide types: large optical cavity (LOC) and separate confinement (SCH or GRICC) heterostructures the difference in coupling efficiency can be as high as ten absolute percent We achieved an experimental coupling efficiency of 93 percent for LOC-like lasers structure. The SCH-based lasers showed maximum coupling efficiency of 83 percent. However, in spite of superior coupling efficiency, use of LOC-based lasers in pump modules does not bring any benefits because of subpar electro-optical performance. To improve the situation we had to find a reasonable compromise between LOC and SCH structures. Lasers resulting from this approach gave a coupling efficiency around 90 percent. The laser diodes based on the optimized structure achieve more than 3 W of output power and more than 2 W of kink-free power in CW regime at room temperature. They also demonstrate differential quantum efficiency above 85% and laser power conversion efficiency above 60 percent at use conditions. Thanks to the combination of all these factors pump modules built on these lasers produce 1W of wavelength-stabilized power at an operating current below 1.3 A. Maximum kink-free, wavelength-stabilized output from the pump module reached 1.8 W at room temperature.

For many innovative applications a significant improvement in the homogeneity of the laser beam is a critical requirement when using semiconductor lasers. There are several different methods for the homogenization of laser radiation. Homogenization using micro-cylinder lens arrays is a considerably elegant and compact solution. In this case the incident laser beam is separated into partial beams by one or more micro-lens arrays. These partial beams are then overlaid in the homogenization plane by the downstream optics. Depending on the arrangement and geometry of the micro-lenses, this enables homogeneously illuminated lines, rectangles or squares to be generated. The major advantage of this solution lies in the increased freedom of adjustment to account for the initial beam profile, as well as the extremely compact design. In addition to a comparison of different homogenization principles the paper describes new approaches of homogenization via micro-lens arrays and compares the impact on the array performance by different manufacturing approaches.

The scalability of semiconductor diode lasers to multi-kilowatt power levels has increasing importance in direct diode material processing applications. These applications require hard-pulse on-off cycling capability and high brightness achieved using low fill-factor (FF) bars with a tight vertical pitch. Coherent uses 20%FF bars operated at <60W/bar packaged on water-cooled packages with a 1.65mm vertical pitch in the Highlight D-series, which achieves <8kW of power in a < 1mm x 8mm beam line at a working distance of ~ 280mm. We compare thermal measurement results to thermal fluid flow simulations to show the emitters are cooled to low junction temperatures with minimal thermal crosstalk, similar to single emitter packaging. Good thermal performance allows for scaling to operation at higher power and brightness. We present accelerated life-testing results in both CW and hard-pulse on-off cycling conditions.

Fiber coupled diode laser devices are attractive light sources for applications in the area of solid-state laser pumping and materials processing. The ongoing improvement in the brightness of diode lasers, which means power per beam quality, makes more and more industrial applications accessible to diode lasers. For many applications in materials processing multi-kW output power with a beam quality of better than 30 mm x mrad is needed. Previously we have reported on a modular diode laser platform based on a tailored bar design (T-Bar) and have demonstrated an output power of up to 785 W out of a 200 μm NA 0.22 fiber at a single wavelength of 976 nm. We have now extended that tailored bar platform to different wavelengths in the range from 900 nm to 1100 nm. At each single wavelength efficient fiber coupling into a 200 μm NA 0.22 fiber will be demonstrated. One important concept for power scaling is coarse wavelength multiplexing with a spectral separation of typically about 40 nm. Combining of different wavelengths enables scalable multi-kW high-brightness diode laser units. Further power scaling can be achieved by dense wavelength multiplexing with a spectral separation of only about 5 nm. In this paper we report on a diode laser unit with 3.5 kW output power and a beam quality of 25 mm x mrad.

High-power single emitters and laser bars are used as light sources in many industrial applications such as materials processing or as pump sources for solid state or fiber lasers. Those applications require laser devices with high optical power, high efficiency and high brightness. To fulfill the requirements the laser design in both directions, vertical and lateral, is continuously improved. We have realized a new generation epitaxial structure, emitting at 940 nm, for a reduced vertical carrier leakage, lower thermal and electrical resistance resulting in high electro-optical efficiency up to high currents. Furthermore the fast axis divergence angle containing 95% power was reduced to 40°. 280 W CW-power with the wall-plug efficiency greater than 60% was reached from the new generation laser design when processed as high fill-factor laser bars. The epitaxial design was adapted to wavelengths 915 nm, 955 nm and 976 nm allowing for fabrication of powerful and high brightness single emitters, laser arrays an laser bars emitting in this wavelength range.

The slow axis (SA) divergence of 20% fill-factor, 980nm, laser diodes (LDs) have been investigated under short pulsed (SP) and continuous (CW) operation. By analyzing the data collected under these two modes of operation, one finds that the SA divergence can be separated into two components: an intrinsic divergence and a thermally induced divergence. At low injected current and power, the intrinsic SA divergence is dominant while at high power their magnitudes are approximately equal. The thermal gradient across the broad stripe is negligible under SP operation and, the SA divergence increased at a much slower rate as a function of injected current, thereby increasing the brightness of the LD by 2X. SRL has redesigned microchannel coolers that remove the thermal gradient under CW operation thereby eliminating the thermally induced SA divergence resulting in LDs that are 2X brighter at 300W/bar.

We report on the development of a novel, ultra-low thermal resistance active heat sink (AHS) for thermal management of high-power laser diodes (HPLD) and other electronic and photonic components. AHS uses a liquid metal coolant flowing at high speed in a miniature closed and sealed loop. The liquid metal coolant receives waste heat from an HPLD at high flux and transfers it at much reduced flux to environment, primary coolant fluid, heat pipe, or structure. Liquid metal flow is maintained electromagnetically without any moving parts. Velocity of liquid metal flow can be controlled electronically, thus allowing for temperature control of HPLD wavelength. This feature also enables operation at a stable wavelength over a broad range of ambient conditions. Results from testing an HPLD cooled by AHS are presented.

nLIGHT optimized both the high-temperature (HT) and the high-efficiency (HE) epitaxial designs for efficient highpower continuous-wave (CW) operation by implementing nLIGHT’s facet passivation technology (nXLT) into our 808 nm diode laser bars. The application of a refined phenomenological model of the diode lasers allowed tailoring of the device parameters to obtain optimized bar performance. In other words, we adjusted modeling inputs such as bar layout and front facet coating reflectivity to optimize operational indicator outputs such as wall-plug efficiency and operation currents at specific power ratings. Thus, both time and cost were saved without the need of extra experimental runs. We demonstrated that both HT and HE epitaxial designs can support centimeter bar geometries with power ratings above 100 W/bar. At the standard power rating of 100 W/bar, the HE designs show advantages in both operating current and wall-plug efficiency when compared to the HT design. With the newly released HE epitaxial designs, wall-plug efficiency ~58% is achieved for a power rating of 150 W/bar.

High power diode lasers are increasingly important in many industrial applications. However, an ongoing challenge is to simultaneously obtain high output power, diffraction-limited beam quality and narrow spectral width. One approach to fulfill these requirements is to use a “master oscillator - power amplifier (MOPA)” system. We present recent data on MOPAs using PA designs that have low confinement factor (1%), leading to low modal gain, and low optical loss (<0.5cm^-1). Quantum barriers with low refractive index are used to reduce the optical waveguiding due to the active region, which should decrease susceptibility to filament formation. A truncated tapered lateral design was used. Conventional tapered designs have a ridge waveguide (RW) at the entrance of the devices with etched cavity- spoiling grooves at the transition to the tapered gain region. Our amplifier used a truncated tapered design with no RW entrance section. We show that for this approach cavity-spoiling grooves are not necessary, and achieve improved performance when they are omitted, which we attribute to the filament insensitivity of our structure. High beam quality was achieved from a 970nm amplifier with M² (1/e²) = 1.9, with efficiency of <48% in QCW condition, and <17W diffraction-limited beam maintained in the central lobe. The impact of the in-plane geometrical design was assessed and we show that large surface area is advantageous for device performance. The spectral properties of the amplifier replicated that of the DBRtapered laser, which is used as the master oscillator, with a spectral width of <30pm (FWHM). Design options for further increases in power are presented.

Incorporating monolithic distributed feedback (DFB) gratings into broad-area (BA) diode lasers results in ten times narrower spectral width and four-to-five times lower thermal shift in emission wavelength. We report on our progress to obtaining a high-power, high-efficiency DFB diode pump in the 1.4-1.6 μm wavelength range for use in industrial and military, eye-safe applications. Results for Fabry-Perot diode lasers emitting at 1530 nm are also discussed. We report on an index-guided, single-emitter design (0.15 x 0.01 cm²) capable of producing 2.5 W of continuous-wave output power at room-temperature with a peak power conversion efficiency of 50%.

The performance of high power and high brightness systems has been developing and is developing fast. In the multi kW regime both very high spatial and spectral brightness systems are emerging. Also diode laser pumped and direct diode lasers are becoming the standard laser sources for many applications. The pump sources for thin Disk Laser systems at TRUMPF Photonics enabled by high power and efficiency laser bars are becoming a well established standard in the industry with over two thousand 8 kW Disk Laser pumps installed in TruDisk systems at the customer site. These systems have proven to be a robust and reliable industrial tool. A further increase in power and efficiency of the bar can be easily used to scale the TruDisk output power without major changes in the pump source design. This publication will highlight advanced laser systems in the multi kW range for both direct application and solid state laser pumping using specifically tailored diode laser bars for high spatial and/or high spectral brightness. Results using wavelength stabilization techniques suitable for high power CW laser system applications will be presented. These high power and high brightness diode laser systems, fiber coupled or in free space configuration, depending on application or customer need, typically operate in the range of 900 to 1070 nm wavelength.

Diode lasers in the blue and red spectral range are the most promising light sources for upcoming high-brightness digital projectors in cinemas and large venue displays. They combine improved efficiency, longer lifetime and a greatly improved color space compared to traditional xenon light sources. In this paper we report on high-power visible diode laser sources to serve the demands of this emerging market. A unique electro-optical platform enables scalable fiber coupled sources at 638 nm with an output power of up to 100 W from a 400 μm NA0.22 fiber. For the blue diode laser we demonstrate scalable sources from 5 W to 100 W from a 400 μm NA0.22 fiber.

The impact of external feedback on high-power diode laser degradation is studied. For this purpose early stages of gradual degradation are prepared by accelerated aging of 808-nm-emitting AlGaAs-based devices. While the quantum well that actually experiences the highest total optical load remains unaffected, severe impact is observed to the cladding layers and the waveguide. Consequently hardening of diode lasers for operation under external optical feedback must necessarily involve claddings and waveguide, into which the quantum well is embedded.

Recent remarkable success of fiber lasers and amplifiers results from continued improvements in performance characteristics of broad-area InGaAs-AlGaAs strained quantum well (QW) lasers. Unprecedented characteristics of single emitters include optical output powers of over 20 W and power conversion efficiencies of over 70% under CW operation. Leading high power laser diode manufacturers have recently demonstrated encouraging reliability in these lasers mainly targeted for industrial applications, but long-term reliability of these lasers has never been demonstrated for satellite communication systems in the space environment. Furthermore, as reported by two groups in 2009, the dominant failure mode of these lasers is catastrophic optical bulk damage (COBD), which is a new failure type that requires physics of failure investigation to understand its root causes.

For the present study, we investigated reliability, proton radiation effects, and the root causes of COBD processes in MOCVD-grown broad-area InGaAs-AlGaAs strained QW lasers using various failure mode analysis (FMA) techniques. Two different approaches, accelerated life-testing and proton irradiation, were taken to generate lasers at different stages of degradation. Our objectives were to (i) study the effects of point defects introduced during crystal growth and those induced by proton irradiation with different energies and fluences in the lasers on degradation processes and to (ii) compare trap characteristics and carrier dynamics in pre- and post-stressed lasers with those in pre- and post-proton irradiated lasers. During entire accelerated life-tests, time resolved electroluminescence (TREL) techniques were employed to observe formation of a hot spot and subsequent formation and progression of dark spots and dark lines through windowed n-contacts.

This paper presents recent progress in the development of high power single emitter laser diodes from 790 nm to 980 nm for reliable use in industrial and pumping applications. High performance has been demonstrated on diode lasers from 790 nm to 980 nm, with corresponding peak efficiency ~65%. Reliability has been fully demonstrated on high power diode lasers of 3.8 mm laser cavity at 3 major wavelengths. We report on the correlation between photon-energy (wavelength) and device failure modes (reliability). A newly released laser design demonstrates diode lasers with 5.0 mm laser cavity at 915-980 nm and 790 nm, with efficiency that matches the values achieved with 3.8 mm cavity length. 915-980 nm single emitters with 5.0 mm laser cavity were especially designed for high power and high brightness applications and can be reliably operated at 12 W to 18 W. These pumps have been incorporated into nLIGHT’s newly developed fiber coupled pump module, element^TM. Ongoing highly accelerated diode life-tests have accumulated over 200,000 raw device hours, with extremely low failure rate observed to date. High reliability has also been demonstrated from multiple accelerated module-level lifetests.

Fiber-coupled 405 nm diode laser systems are rarely used with fiber output powers higher than 50 mW. A quick degradation of fiber-coupled high power modules with wavelengths in the lower range of the visible spectrum is known for several years. Meanwhile, the typical power of single-mode diode lasers around 400 nm is in the order of 100 to 300 mW, leading to single-mode fiber core power densities in the 1 MW/cm² range. This is three magnitudes of order below the known threshold for optical damage. Our profound investigations on the influence of 405 nm laser light irradiation of single-mode fibers found the growth of periodic surface structures in the form of ripples responsible for the power loss. The ripples are found on the proximal and distal fiber end surfaces, negatively impacting power transmission and beam quality, respectively. Important parameters in the generation of the surface structures are power density, surface roughness and polarization direction. A fiber-coupled high-power 405 nm diode laser system with a high longterm stability will be introduced and described.

We present a novel, high-power stack of 20% fill-factor, 976nm, laser-diode bars, each directly attached to an enhanced lateral-flow (ELF), copper-based, water-cooled heat-sink. The heat-sinks contain mounting screws that form a kinematic mount to minimize detrimental mechanical-stress on the diode bars while also providing beneficial, double-side cooling of the bars. A stack of 18-bars, emitting 2.54kW, was constructed to validate the technology. Using standard optics and a polarization multiplexer, a 320μm diameter, 0.3NA focus is achieved with a 6-bar stack that robustly couples 450W, with a ~67% coupling efficiency, from a passive, 400μm, 046NA doubleclad fiber.

High power, high brightness diode lasers are beginning to compete with solid state lasers, i.e. disk and fiber lasers. The core technologies for brightness scaling of diode lasers are optical stacking and dense spectral combining (DSC), as well as improvements of the diode material. Diode lasers have the lowest cost of ownership, highest efficiency and most compact design among all lasers. Multiple Single Emitter (MSE) modules allow highest power and highest brightness diode lasers based on standard broad area diodes. Multiple single emitters, each rated at 12 W, are stacked in the fast axis with a monolithic slow axis collimator (SAC) array. Volume Bragg Gratings (VBG) stabilizes the wavelength and narrow the linewidth to less than 1 nm. Dichroic mirrors are used for dense wavelength multiplexing of 4 channels within 12 nm. Subsequently polarization multiplexing generates 450 W with a beam quality of 4.5 mm*mrad. Fast control electronics and miniaturized switched power supplies enable pulse rise times of less than 10 μs, with pulse widths continuously adjustable from 20 μs to cw. Further power scaling up to multi-kilowatts can be achieved by multiplexing up to 16 channels. The power and brightness of these systems enables the use of direct diode lasers for cutting and welding. The technologies can be transferred to other wavelengths to include 793 nm and 1530 nm. Optimized spectral combining enables further improvements in spectral brightness and power.

Special applications require low noise wavelength stabilized diode lasers for pumping of solid state lasers. We report on intensity noise in the frequency range of kHz to MHz due to bi-stable mode switching between external cavity modes in laser diodes with volume Bragg grating as external reflector. Two regimes of bi-stability are identified which are attributed to switching between longitudinal or lateral resonator modes. The origin of noise is explained by thermal bi-stability which can be suppressed by proper design of the external resonator. Low noise operation of single mode ridge waveguide lasers is demonstrated having the potential of scaling up the pump power by using ridge waveguide arrays.

Broad area lasers with narrow spectra are required for many pumping applications and for wavelength beam combination. Although monolithically stabilized lasers show high performance, some applications can only be addressed with external frequency stabilization, for example when very narrow spectra are required. When conventional diode lasers with vertical far field angle, Θ_V ^95% ~ 45° (95% power) are stabilized using volume holographic gratings (VHGs), optical losses are introduced, limiting both efficiency and reliable output power, with the presence of any bar smile compounding the challenge. Diode lasers with designs optimized for extremely low vertical divergence (ELOD lasers) directly address these challenges. The vertical far field angle in conventional laser designs is limited by the waveguiding of the active region itself. In ELOD designs, quantum barriers are used that have low refractive index, enabling the influence of the active region to be suppressed, leading to narrow far field operation from thin vertical structures, for minimal electrical resistance and maximum power conversion efficiency. We review the design process, and show that 975 nm diode lasers with 90 μm stripes that use ELOD designs operate with Θ_V ^95% = 26° and reach 58% power conversion efficiency at a CW output power of 10 W. We demonstrate directly that VHG stabilized ELOD lasers have significantly lower loss and larger operation windows than conventional lasers in the collimated feedback regimes, even in the presence of significant (≥ 1 μm) bar smile. We also discuss the potential influence of ELOD designs on reliable output power and options for further performance improvement.

The advances in laser-diode technology have enabled high efficiency direct diode base modules to emerge as a building block for industrial high power laser systems. Consequently, these systems have been implemented with advance robust, higher-brightness and reliable laser sources for material processing application. Here at the company, we use low-fill factor bars to build fiber-coupled and passively cooled modules, which form the foundation for “TruDiode,” the series of TRUMPF direct diode laser systems that can perform in the multi-kilowatt arena with high beam quality. However, higher reliable output power, additional efficiency and greater slow axis beam quality of the high power laser bars are necessary to further increase the brightness and reduce the cost of the systems. In order to improve the slow axis beam quality, we have optimized the bar epitaxial structures as well as the lateral design. The detailed near field and far field studies of the slow axis for each individual emitters on the bar provide us with information about the dependency of beam quality as a function of the drive current. Based on these study results for direct diode application, we have optimized the high brightness bar designs at 900-1070nm wavelengths. In addition, high power and high efficiency laser bars with high fill factors have been used to build the pump sources for thin disc laser systems at TRUMPF Photonics. For better system performances with lower costs, we have further optimized bar designs for this application. In this paper, we will give an overview of our recent advances in high power and brightness laser bars with enhanced reliability. We will exhibit beam quality study, polarization and reliability test results of our laser bars in the 900-1070nm wavelengths region for coarse wavelength multiplexing. Finally, we will also present the performance and reliability results of the 200W bar, which will be used for our next generation thin disk laser pump source.

We present performance and reliability data of high-brightness QCW arrays with a custom, compact and robust design for an operation with high duty cycles. The presented designs are based on single diodes consisting of a 1cm laser bar that is AuSn soldered between two CuW submounts. Arrays of up to 15 diodes as well as one single diode are connected to ceramic base plates on different heat sinks. The available optical output power is shown to be strongly depending on the wavelength and fill factor of the laser bars as well as on the duty cycle, the base plate temperature and the thermal conductivity of the applied ceramic materials. Operation at increased heat sink temperatures up to 45°C is possible without active water cooling or conduction cooling with the help of Peltier elements. Using an array of 15 bars at 980 nm with 20% fill factor and 2 mm cavity on standard ceramics, we can reach an optical output power of 1150 W at 45°C base plate temperature operating the array with 15 Hz and 15% duty cycle. Novel materials allow for more efficient operation and higher optical output powers.

We report on the development of high power, 9xx-10xx nm laser diode bars for use in direct diode systems and for solidstate and fibre laser pumping with applications in industrial markets. For 1 cm wide bars on micro channel cooler (MCC) we have achieved a reliable output power of 250 W across the 900 nm – 1060 nm range. At this output power level we have achieved power conversion efficiencies of 65-66 % and 90 % power content slow axis beam divergence of ~6.5°. Results of a 6400 h life test show an average power degradation of 0.6 % per 1000 h at this operating power level. We will also show results of high power bars assembled on the new OCLARO conductive cooler, the BLM. This new cooler has a small footprint of 12.6 mm × 24.8 mm and is designed for lateral or vertical stacking of diodes in multi kilowatt systems but with the benefits associated with a conductive cooler. The thermal properties are shown to be the same as for a standard CS mount. 1 cm wide high fill factor bars and 0.5 cm wide low fill factor half bars assembled on the BLM operate at 63-64 % power conversion efficiency (PCE) with output powers of up to 250 W and 150 W, respectively.

Based on the demand for a responsible use of natural resources and energy the need for lightweight materials is increasing. The most common materials for lightweight production are high and highest strength steel. These materials are difficult to machine using conventional sheet metal working processes because the high strength leads to a limited formability and high tool wear. The Fraunhofer IPT developed the laser-assisted sheet metal working. Selective laser based heating of the part directly before machining softens the material locally. Thus the quality of the following cut can be increased, for example for shearing 1.4310 the clear cut surface ratio can be increased from 20% up to 100% using a shearing gap of 10% of the sheet thickness. Because of the softening of the material and thus the increased formability, parts with a higher complexity can be produced. For example 1.4310 can be bent laser-assisted with a radius of 0.25 mm instead of 2-3 mm using the conventional process. For the first time spring steel can be embossed with conventional tools up to 50% of the sheet thickness. For the implementation in series production a modular system upgrade “hy-PRESS” has been developed to include laser and scanner technology into existing presses. For decoupling the sensitive optical elements of the machine vibrations an active-passive damping system has been developed. The combination of this new hybrid process and the system technology allows to produce parts of high strength steel with a high complexity and quality.

In this paper, we present a high power TM Polarized GaAsP laser diode of 808nm wavelength. For high power and narrow beam divergence, an asymmetry broad waveguide structure and a tensile strained GaAsP quantum well were used and the epilayers were grown by low-pressure metalorganic chemical vapor deposition. We have obtained an optical power of 20.86W at 20A without COMD and the vertical farfield of 27°. It is expected that Al-free GaAsP quantum well laser diodes will have good reliability without any facet treatment.

Within the past couple of years one can see a general trend in high power diode lasers among others towards the highest possible brightness. The product portfolio of TRUMPF high brightness diode lasers with output power < 1kW will be presented. The architecture of these diode lasers, their main specifications as well as the main features of the control unit are shown. Some examples of the applications of these lasers in such advanced material processing techniques as welding of plastics and welding of thin metal sheets is also presented.

Laser illumination makes it possible to perform high resolution imaging when ambient light level is insufficient to overcome camera noise. The relatively long coherence length of most lasers, however, causes coherent speckle in the camera image plane, which can result in a significant decrease of the image quality and the maximum achievable target identification range. We characterized several types of NIR and SWIR laser diode illumination sources, with emphasis placed on measuring the properties of coherent speckle observed in the camera image plane. Image plane speckle contrast was measured by illuminating the imaged Lambertian surface with single-mode laser, multi-mode laser, wide-stripe laser with two active junctions and broad-band emission, and NIR and SWIR vertical cavity surface emitting laser (VCSEL) arrays. The impact of various imaging system parameters, including pixel size, imaging lens focal length, F-number, and IFOV on the contrast and characteristic size of the speckle intensity distribution were determined. Speckle contrast dependence on the polarization properties of various reflecting surfaces was measured. The reduction of speckle contrast with increasing source spectral width, and increasing size of spatially incoherent VCSEL emitter arrays will be described. We show that a speckle contrast of 5-10% is achievable for a typical long range SWIR imaging system.