This PDF file contains the front matter associated with SPIE Proceedings Volume 8241, including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

TeraDiode has produced kW-class ultra-high brightness fiber-coupled direct diode lasers. A fiber-coupled direct diode laser with a power level of 2,040 W from a 50 μm core diameter, 0.15 numerical aperture (NA) output fiber at a single center wavelength was demonstrated. This was achieved with a novel beam combining and shaping technique using COTS diode lasers. The fiber-coupled output corresponds to a Beam Parameter Product (BPP) of 3.75 mm-mrad and is the lowest BPP kW-class direct diode laser yet reported. This laser is suitable for industrial materials processing applications, including sheet metal cutting and welding. This 2-kW fiber-coupled direct diode laser has comparable brightness to that of industrial fiber lasers and CO₂ lasers, and is over 10x brighter than state-of-the-art direct diode lasers.

New solid-state laser architectures require higher pump powers. In this paper we report the development of a new fibercoupled diode laser capable of generating 15 kW from a 2 mm diameter fiber with a 0.22 NA, representing a brightness of 220 mm.mrad at a single wavelength. In this design a special beam transformation technique has been developed to achieve these specifications at a single wavelength without the wavelength combination technique employed in high power diode lasers used in material processing applications. The specific laser presented here is at 938 nm with a spectral bandwidth of 3.1 nm FWHM, but the same architecture is possible for wavelengths between 910 and 1060 nm.

A new series of high power diode laser line sources is reported. The modules are designed for the industrial materials processing market and include both fiber coupled and direct beam configurations. Typical applications include welding, hardening and semiconductor processing. The biggest challenge in delivering line sources lies in the variety of application specific requirements. This problem is approached with modular concepts that allow for power scaling and custom beam shaping. All modules are available either as an OEM laser head or as a turn-key solution including power supply and chiller. Fiber coupled diode laser modules are available at power levels ranging from 600W to 4kW at various wavelengths. New developments include a 1kW module with a single wavelength and 400um / 0.22NA fiber and a 2kW module based on two wavelengths. Dilas offers up to 5kW from a 1mm / 0.22NA fiber with a single wavelength. At 200 μm fiber diameter, power levels of 850W are available with a single wavelength. While fiber coupled modules allow for easy power scaling, free space systems are capable of even higher overall electrooptical efficiencies and lower cost. Based on modular building blocks, Dilas provides customized solutions that are optimized for individual applications. Two modules will be described in detail. The first module is a 600W line source with line dimensions of 10.5mm x 350 μm at a working distance of 160mm. The second module operates at 3kW output power and creates a homogenized line with dimensions of 9mm x 1.3mm at a working distance of 200mm. Optical design trade-offs will be discussed and concepts for the modules described above are shown. Experimental results are presented.

Laser cladding has become a useful tool in materials processing for improving the surface properties of the substrate materials, and has been widely used in industry in recent years. In this paper, we study the 3000W CW laser cladding system based on the high power diode lasers. The beam control method is proposed to reduce the collimated beam pointing errors caused during the packaging of the laser stack. At the input current of 84A, the output power and the optical coupling efficiency of this laser cladding system are 3738W and 93.7%, respectively, and at work face the beam spot size is 2.5mm*7.9mm with symmetry intensity distribution. The laser cladding system is also used in cladding the nickel powder onto the iron substrate and the nickel powder can be clothed onto steel plate uniformly.

High power diode laser bars are subjected to single pulse step tests carried out up to and beyond their ultimate limits of operation. Laser nearfields and thermal behavior are monitored for pulse widths in the 10 μs-2 ms-range with streak- and thermo-cameras, respectively. The final phase of the tests allows the in situ observation of the catastrophic optical damage (COD) effect. We find perfect agreement between the location of COD signatures observed by transient emission and thermo-camera measurements on the one side, and optical inspection of the degraded bars on the other side. COD thresholds are determined and the observed dependence on the pulse length is qualitatively explained. This approach allows for testing hardness and homogeneity of facet coatings on a bar level with or without consideration of accidental early single-emitter failure effects and thermal crosstalk between the emitters. It helps embanking sudden degradation and provides insight into the mechanisms governing the device emission behavior at ultimate output powers.

The demand for high-power and high-brightness fiber coupled diode laser devices is mainly driven by applications for solid-state laser pumping and materials processing. The ongoing power scaling of fiber lasers requires scalable fibercoupled diode laser devices with increased power and brightness. For applications in materials processing multi-kW output power with beam quality of about 30 mm x mrad is needed. We have developed a modular diode laser concept combining high power, high brightness, wavelength stabilization and optionally low weight, which becomes more and more important for a multitude of applications. In particular the defense technology requires robust but lightweight high-power diode laser sources in combination with high brightness. Heart of the concept is a specially tailored diode laser bar, whose epitaxial and lateral structure is designed such that only standard fast- and slow-axis collimator lenses in combination with appropriate focusing optics are required to couple the beam into a fiber with a core diameter of 200 μm and a numerical aperture (NA) of 0.22. The spectral quality, which is an important issue especially for fiber laser pump sources, is ensured by means of Volume Holographic Gratings (VHG) for wavelength stabilization. In this paper we present a detailed characterization of different diode laser sources based on the scalable modular concept. The optical output power is scaled from 180 W coupled into a 100 μm NA 0.22 fiber up to 1.7 kW coupled into a 400 μm NA 0.22 fiber. In addition we present a lightweight laser unit with an output power of more than 300 W for a 200 μm NA 0.22 fiber with a weight vs. power ratio of only 0.9 kg/kW.

High power 780-820 nm diode lasers have been developed for pumping and material processing systems. This paper presents recent progress in the development of such devices for use in high performance industrial applications. A newly released laser design in this wavelength range demonstrates thermally limited >25W CW power without catastrophic optical mirror damage (COMD), with peak wallplug efficiency ~65%. Ongoing accelerated lifetesting projects a time to 5% failure of ~10 years at 5 and 8 W operating powers for 95 and 200 μm emitter widths, respectively. Preliminary results indicate the presence and competition of a random and wear-out failure mode. Fiber-coupled modules based on arrays of these devices support >100W reliable operation, with a high 56% peak efficiency (ex-fiber) and improved brightness/reliability.

Fiber lasers require diode laser pumps of ever increasing power and brightness delivered via low-NA multimode fiber. The preferred fiber pump construction is based on the combination of the outputs of several diode lasers (single emitters) in single-strand multimode delivery fiber with NA ≤ 0.15. We report on the recent advances in the reliability and output power of single emitters at several wavelengths from 800 nm to 980 nm, with an emitting aperture optimized for coupling into 105 μm core fiber. By the use of long laser cavities and low-loss epitaxal design, we have achieved single emitter powers close to 20 W. Lifetest data from these emitters under high optical load are presented and analyzed using a reliability model.

High power VCSEL arrays can be used as a versatile illumination and heating source. They are widely scalable in power and offer a robust and economic solution for many new applications with moderate brightness requirements. The use of VCSEL arrays for high power laser diode applications enables multiple benefits: Full wafer level production of VCSELs including the combination with micro-optics; assembly technologies allowing large synergy with LED assembly thus profiting from the rapid development in solid state lighting; an outstanding reliability and a modular approach on all levels. A high power VCSEL array module for a very uniform line illumination is described in detail which offers >150W/cm optical output and enables less than 1% non-uniformities per mm along the line. The applied optical principle of near field imaging and massively superposing many thousand VCSELs by arrays of micro-lenses gives perfect control over the intensity distribution and is inherently robust. A specific array of parallelogram shaped VCSELs has been developed in combination with an appropriate micro-lens design and an alignment strategy. The concept uses parallel and serial connection of VCSEL arrays on sub-mounts on water coolers in order to realize a good combination of moderate operating currents and reliability. Lines of any desired length can be built from modules of 1cm length because this optical concept allows large mounting tolerances between individual modules. Therefore the concept is scalable for a wide range of applications. A demonstrator system with an optical output of 3.5kW and a line length of 20cm has been realized.

With the increasing applications of high power semiconductor lasers in industry, advanced manufacturing, aerospace, medical systems, display, entertainment, etc., semiconductor lasers with high power and high performances are required. The performance of semiconductor lasers is greatly affected by packaging structure, packaging process and beam shaping. A novel macro channel cooler (MaCC) for stack array laser with good heat dissipation capacity and high reliability is presented in this work. Based on the MaCC package, a high power stack array diode laser is successfully fabricated. A series of techniques such as spectrum control and beam control are used to achieve narrow spectrum and high beam quality. The performances of the semiconductor laser stack array are characterized. A high power 20kW QCW hard solder packaged stack array laser is fabricated; a narrow spectrum of 3.94 nm and an excellent rectangular beam shape are obtained. The lifetime of the stack array laser is tested as well.

Despite major progress in developing brilliant laser sources a huge potential for cost reductions can be found in simpler setups and automated assembly processes, especially for large volume applications. In this presentation, a concept for flexible automation in optics assembly is presented which is based on standard micro assembly systems with relatively large workspace and modular micromanipulators to enhance the system with additional degrees of freedom and a very high motion resolution. The core component is a compact flexure-based micromanipulator especially designed for the alignment of micro optical components which will be described in detail. The manipulator has been applied in different scenarios to develop and investigate automated alignment processes. This paper focuses on the automated alignment of fast axis collimation (FAC) lenses which is a crucial step during the production of diode lasers. The handling and positioning system, the measuring arrangement for process feedback during active alignment as well as the alignment strategy will be described. The fine alignment of the FAC lens is performed with the micromanipulator under concurrent analysis of the far and the near field intensity distribution. An optimization of the image processing chains for the alignment of a FAC in front of a diode bar led to cycle times of less than 30 seconds. An outlook on other applications and future work regarding the development of automated assembly processes as well as new ideas for flexible assembly systems with desktop robots will close the talk.

Northrop Grumman Cutting Edge Optronics (NGCEO) has developed a laser diode array package with minimal bar-tobar spacing. These High Density Stack (HDS) packages allow for a power density increase on the order of ~ 2.5x when compared to industry-standard arrays. Power densities as high as 15 kW/cm² can be achieved when operated at 200 W/bar. This work provides a detailed description of the duty factor, pulse width and power limitations of high density arrays. The absence of the interposing heatsinks requires that all of the heat generated by the interior bars must travel through the adjacent bars to the electrical contacts. This results in limitations to the allowable operating envelope of the HDS arrays. Thermal effects such as wavelength shifts across large HDS arrays are discussed. An overview of recent HDS design and manufacturing improvements is also presented. These improvements result in reliable operation at higher power densities and increased duty factors. A comparison of the effect of bar geometry on HDS performance is provided. Test data from arrays featuring these improvements based on both full 1 cm wide diode bars as well as 3 mm wide mini-bars is also presented.

A custom designed compact, high brightness diode laser array stack was designed and manufactured using proprietary methods that are robust and suitable for low cost manufacturing. The diode laser stack consisted of four 10 mm-wide diode laser bars having lasing wavelength of 970 - 980 nm mounted onto high performance submounts separated by approximately 1mm. Each diode laser bar had a 50% fill factor. The cooling methodology employed used a combined passive and active scheme and not the traditional more expensive and more complicated standard microchannel coolers used for high duty cycle applications. The total combined optical power attained from the diode array stack was close to 1 kW for current levels up to 220 A, limited only by the capability of the power supply. In this paper, we summarize the performance results for this diode laser array and analyze the maximum expected optical performance as a function of operating current and pulse width and junction temperature limit.

High brightness, laser-diode bars are required for efficient coupling into small-core optical-fibers. Record power and brightness results were achieved using 20% fill-factor, 980nm, 1cm-wide, 4mm cavity-length bars. Lifetimes of single bars, operated CW at 200W and 20°C, exceed 1000hr. Due to superb thermal management, the power conversion efficiency (PCE) exceeds 60% at 200W output power. Similar lifetime and PCE were obtained for a 3-bar stack emitting 600W output power.

High power semiconductor laser arrays have found increased applications in many fields. In this work, a hard soldering microchannel cooler (HSMCC) technology was developed for packaging high power diode laser array. Numerical simulations of the thermal behavior characteristics of hard solder and indium solder MCC-packaged diode lasers were conducted and analyzed. Based on the simulated results, a series of high power HSMCC packaged diode laser arrays were fabricated and characterized. The test and statistical results indicated that under the same output power the HSMCC packaged laser bar has lower smile and high reliability in comparison with the conventional copper MCC packaged laser bar using indium soldering technology.

High Power Laser Diode (LD) modules are widely used as high-brightness light sources for pumping solid-state lasers and for direct diode laser processing utilizing a compact feature. The LD bars installed in modules are required with higher output power, efficiency and beam quality. We have optimized the LD bar structure for high output power and efficient operation. The water-cooled heat sink has been designed for excellent thermal performance as well as long-term stable cooling performance. We have also developed the thermal expansion controlled assembly technique to suppress the "smile". As a result, we have achieved an output power of over 200 W and a conversion efficiency of 58% from 940 nm LD bars under continuous wave (CW) operation with very low smile of 0.8 μm.

Improved light output power of blue-violet laser diodes (BVLDs) is necessary in order to use them as a light source for crystallization of amorphous silicon (a-Si) thin films to fabricate thin film transistors (TFTs). A multi-emitter BVLD array is a promising solution to obtain high light output power. For realization of the high power blue-violet laser source, we carried out a thermal design using the finite element method (FEM). Because conventional packaging is significantly affected by heat dissipation, we mounted the multi-emitter BVLD array on micro-channel coolers (MCCs). A steady thermal analysis using FEM revealed that the direct-mounted BVLD array with appropriate emitter pitch had a flatshaped transverse temperature distribution across the array. In contrast, a convex-shaped distribution was obtained when a highly thermal conductive sub-mounts, such as a diamond-composite, was inserted between the array and the MCCs. The local temperature rise in the center emitter of the direct-mounted laser array was suppressed due to their relatively shorter heat transfer paths. The flat-shaped temperature distribution should contribute to achieving high optical output power. Therefore, the BVLD arrays were directly mounted on coefficient of thermal expansion (CTE) controlled MCCs using AuSn hard solder. Under continuous wave (CW) operation, we achieved an output over 10 W with a ten-emitter BVLD array, which is the highest reported output power for a blue-violet laser source.

We report the development of a fiber-coupled diode laser module with high spatial and spectral brightness. Four arrays of diode laser bars are multiplexed using polarization and narrow-band wavelength combination. The module achieves 500 W of output power from a 200 μm, 0.2 NA fiber. The output spectrum, composed of contributions from more than 150 emitters, is narrowed using VBGs and has nearly 100% content within +/- 1.5 nm of 975 nm at full power.

Multiple Single Emitter (MSE) modules allow highest power and highest brightness diode lasers based on standard broad area diodes. 12 single emitters, each rated at 11 W, are stacked in fast axis and with polarization multiplexing 200W are achieved in a fully collimated beam with a beam quality of 7mm*mrad in both axes. Volume Bragg Gratings (VBG) stabilize the wavelength and narrow the linewidth to less than 2nm. Dichroic mirrors are used for dense wavelength multiplexing of 4 channels within 12 nm. 400W are measured from a 0.2 mm fiber, 0.1 NA. Control and drive electronics are integrated into the 200 W platform and represent a basic building block for a variety of applications, such as a flexible turn key system comprising 12 MSE modules. An integrated beam switch directs the light in six 100 μm, or in one 0.2 mm and one 0.1 mm fiber. 800W are measured from the six 0.1 mm fibers and 700W from the 0.2 mm fiber. The technologies can be transferred to other wavelengths to include 793 nm and 1530 nm. Narrow line gratings and optimized spectral combining enable further improvements in spectral brightness and power.

Northrop Grumman Cutting Edge Optronics has developed large kilowatt class lensed laser diode arrays with subnanometer spectral width using Volume Bragg Grating (VBG) reflectors. Using these CW arrays with 100W bars at 885nm, excellent absorption in Nd:YAG is achieved, with lower thermal aberration than can be attained with 808nm pumps. The additional cost of the VBG reflectors and their alignment is partially offset by the much broader wavelength tolerance that is allowed in the unlocked array enhancing bar yield. Furthermore, the center wavelength of the arrays exhibit lower temperature sensitivity allowing the arrays to be operated over a wider current or temperature range than arrays without wavelength control. While there is an efficiency penalty associated with the addition of VBGs of 5-8%, it is more than compensated for by enhanced absorption, especially when used with narrowband absorption lines, such as 885nm in Nd:YAG. An overview of the design and manufacturing issues for arrays that are wavelength-locked with VBGs is presented along with the effect of post-construction hard UV exposure.

Broad area (BA) diode lasers with narrow, temperature-stable spectral lines are required for pumping narrow spectral lines in solid state lasers and for dense spectral multiplexing in direct applications. Two device technologies in particular have reached a high performance level, based on development work at the Ferdinand-Braun-Institut (FBH). Firstly, etched surface gratings can be used to form the rear facet reflector, in distributed Bragg-reflector (DBR) format. Secondly, gratings can be buried within the semiconductor using etch and overgrowth technology, to form distributed feedback (DFB) lasers. In this case, the rear facet has a high reflectivity coating, and the DFB operates effectively as the low reflectivity out-coupler. For both technologies, BA diode lasers with 90-100μm stripes operating at 975nm deliver peak continuous wave (CW) powers of over 12W within a spectral width of < 1nm (with 95% power content). Recently, reliable operation has been confirmed for CW powers of 10W, and power conversion efficiency of up to 63% has been demonstrated. However, the two technologies have different strengths. For example, DBR-BA lasers have low sensitivity to external feedback and are insensitive to the onset of spectral side-modes. In contrast, DFB-BA lasers achieve the highest reported power conversion efficiencies. A comparison of the relative merits of the two technologies for different high power laser applications is presented.

The majority of fiber laser volume applications are price sensitive. Therefore, the availability, quality and cost of singleemitter- based pumps will have decisive impact on the breadth of further fiber lasers' acceptance. Availability and cost should not come in expense of further improvement in pumps' performance and reliability. Here we report on optimized high-power and high-brightness wavelength stabilized CW devices. Performance of CW pumps rated for 100W and 50W power is discussed. Pumps launch over 98% output power into a spectral window of 975±0.5nm at driving currents ranging from 2A to 12A and the heatsink temperature variation from 20°C to 50°C. Such performance qualifies these wavelength-stabilized pumps for use in many air-cooled and special applications.

Surface-emitting distributed feedback (SE-DFB) diode lasers possess many advantages compared to edge emitters, in terms of power, brightness and spectral characteristics. We have demonstrated 312 W and 68 W of peak power at 1-μs pulse duration and 100-Hz repetition rate from single 97x nm SE-DFB laser chips with electrically-pumped stripe of 3.75 mm² and 0.18 mm² respectively, achieving a power density of 378 W/mm². Under the same pulsing condition, we have also demonstrated current-limited 206 W of peak power out of a 100 μm / 0.22 NA fiber with only two 2x1 chiplevel SE-DFB laser arrays.

We present performance data of recent high-power laser diodes emitting at typical pump wavelengths for alkali vapor lasers: 852 nm for cesium, 780 nm for rubidium, 766 nm for potassium, and 670 nm for lithium atoms. Due to different approaches in alkali laser systems, we report on usual pumps at these non-standard wavelengths with typical line widths of a few nm used for collisional and pressure broadened gas absorption lines as well as on wavelength stabilized laser diodes using volume Bragg gratings (VBGs) for systems with narrow gas absorption lines. The detailed characterization of laser diodes available at DILAS includes power, efficiency, spectral data, and life time results. While bars at 6xx and 7xx nm are limited in optical output power due to the strong in-built strain, especially the bars at 852 nm with a small inbuilt strain have the biggest potential in terms of pump power. The power conversion efficiency in cw operation is as high as 60% at 100 W. Higher power and operation at increased heat sink temperatures up to 50°C are possible depending on lifetime requirements.

Diode lasers in the 1400 nm to 1600 nm regime are used in a variety of applications including pumping Er:YAG lasers, range finding, materials processing, aesthetic medical treatments and surgery. In addition to the compact size, efficiency, and low cost advantages of traditional diode lasers, high power semiconductor lasers in the eye-safe regime are becoming widely used in an effort to minimize the unintended impact of potentially hazardous scattered optical radiation from the laser source, the optical delivery system, or the target itself. In this article we describe the performance of high efficiency high brightness InP laser bars at 1470nm and 1550nm developed at QPC Lasers for applications ranging from surgery to rangefinding.

Slab-coupled optical waveguide lasers (SCOWLs) and amplifiers (SCOWAs) are inherently low-confinement structures with large nearly-circular modes that are easily coupled to optical fibers or collimated for free-space applications. Recently SCOWL powers have increased to 3 W by increasing the cavity length to 1 cm and improving the heat removal. SCOWAs are coherently combined using active phase control to achieve a very high-brightness source. Our coherent beam combining system consists of single-pass amplifiers with angled-facet SCOWAs that suppress feedback. Single-pass, 5-mm long, SCOWAs have now been demonstrated with 1.5 W CW output with only 50 mW seed power. Arrays of 47 SCOWAs have demonstrated a raw power of 57 W with 50 mW of seed power per element. A coherent beam combining demonstration is currently being assembled.

In diode laser applications for fibre laser pumping and materials processing high brightness becomes more and more important. At the moment fibre coupled modules benefit from continuous improvement of Broad-Area (BA) lasers on the chip level regarding output power, efficiency and far-field characteristics. To achieve high brightness not only the output power must be increased, but also the far field angles have to be maintained or even decreased because brightness is proportional to output power divided by beam quality. Typically fast axis far fields show mostly a current independent behaviour, for broad-area lasers far-fields in the slow axis suffer from a strong current and temperature dependence, limiting the brightness. These limitations can be overcomed by carefully optimizing epitaxy-design and processing and also thermal management of the mounted device. The easiest way to achieve a good thermal management of BA-Lasers is to increase the resonator length while simultaneously decreasing internal losses of the epitaxy structure. To fulfill these issues, we have realized MBE grown InGaAs/AlGaAs broad-area with resonator lengths between 4mm and 6mm emitting at 976nm. To evaluate the brightness of these broad-area lasers single emitters have been mounted p-side down. Near- and far-fields have been carefully investigated. For a 4mm long broad-area laser with around 100μm emission width a beam parameter product of less than 3.5 mm x mrad has been achieved at 10W with a slope efficiency of more than 1.1W/A and a maximum wall-plug efficiency of more than 67%. For a device with 6mm resonator length we have reached a BPP of less than 3.5mm x mrad at 14W in slow axis direction which results in a brightness around 130MW/cm² sr, which is to our knowledge the highest brightness reported so far for BA-lasers.

High power broad area diode lasers provide the optical energy for all high performance laser systems, either directly or as pump sources for solid-state lasers. Continuous improvement is required in the peak achievable output power of these diode laser devices in order to enable performance improvements in full laser systems. In recent years, device technology has advanced to the point where the main limit to optical power is no longer device failure, but is instead power saturation due to various physical effects within the semiconductor device itself. For example, the combination of large optical cavity designs with advanced facet passivation means that facet failure is no longer the dominant limiting factor. Increases in the optical power therefore require firstly a clear identification of the limiting mechanisms, followed by design changes and material improvements to address these. Recent theoretical and experimental diagnostic studies at the Ferdinand-Braun-Institut have helped trace the saturation effects to three main effects: gain saturation, longitudinal-holeburning and current driven carrier leakage. Design changes based on these studies have enabled increases in the achievable emitted power density from broad area lasers. Recent experimental examples include ~100W from 100μm stripes under short-pulsed conditions, > 30W from 100μm stripes under quasi-continuous wave conditions and > 10W from 30μm stripes under continuous wave conditions. An overview of the results of the diagnostic studies performed at the FBH will be presented, and the design changes necessary to address the observed power saturation will be discussed.

Diode lasers are ideally suited for the generation of optical pulses in the nanoseconds and picoseconds ranges by gainswitching, Q-switching or mode-locking. We have developed diode-laser based light sources where the pulses are spectrally stabilized and nearly-diffraction limited as required by many applications. Diffraction limited emission is achieved by a several microns wide ridge waveguide (RW), so that only the fundamental lateral mode should lase. Spectral stabilization is realized with a Bragg grating integrated into the semiconductor chip, resulting in distributed feedback (DFB) or distributed Bragg reflector (DBR) lasers. We obtained a peak power of 3.8W for 4ns long pulses using a gain-switched DFB laser and a peak power of more than 4W for 65ps long pulses using a three-section DBR laser. Higher peak powers of several tens of Watts can be reached by an amplification of the pulses with semiconductor optical amplifiers, which can be either monolithically or hybrid integrated with the master oscillators. We developed compact modules with a footprint of 4×5cm² combining master oscillator, tapered power amplifier, beam-shaping optical elements and high-frequency electronics. In order to diminish the generation of amplified spontaneous emission between the pulses, the amplifier is modulated with short-pulses of high amplitude, too. Beyond the amplifier, we obtained a peak power of more than 10W for 4ns long pulses, a peak power of about 35W for 80ps long pulses and a peak power of 70W for 10ps long pulses at emission wavelengths around 1064nm.

We present our recent efforts to improve power rating, efficiency, reliability, and cost of diode laser bars in the 88x nm wavelength band. QCW kW-class diode laser bars are grown by metal-organic chemical vapor deposition (MOCVD), and are cleaved, passivated, coated, and die bonded onto either standard copper CS-style heat sinks using indium solder, or onto expansion matched CuW CS heat sinks using AuSn solder. In an effort to realize high power operation, the high efficiency 880-nm epitaxial design has been optimized. Bars of varying fill factors, cavity lengths, and facet coating reflectivities are explored to improve the rated electrical to optical (E-O) efficiency up to approximately 70% under low duty cycle QCW operations. The enhanced E-O efficiency makes possible not only the passive cooling of the devices, but also reliable operation in the kW power range. We demonstrate that the semiconductor laser bars can survive over 100 million laser shots working in QCW mode. It is expected that the development of these passively cooled, highly efficient and highly reliable QCW kW-class diode laser bars will enable commercial applications.

High power 14xx laser pumps are more and more required for eye safe industrial, medical, safety and defense applications as well as for increased telecom network capability (e.g. for 100 Gb Ethernet). However, this need of high power requires to control the overall power consumption in a range in line with systems requirements. In this respect, 3S PHOTONICS has developed a 14xx nm single mode laser diode with record internal losses of 1.5 cm^-1 compared to the 2.7 cm^-1 reported up to now. These lasers are based on p/nBH technology and use the asymmetric waveguide concept to reduce internal losses. The record loss value, coupled to an internal efficiency higher than 0.8, allows realization lasers of 3 mm length with external efficiency higher than 0.5 W.A^-1 at 25°C in AR/HR coating configuration. Modules using direct coupling technology were realized. High coupling efficiency is obtained thanks to the 8° x 14° far field pattern of the diode. Output power of 550 mW at 1.8 A is thus obtained, with or without FBG stabilization, with maximum output power above 700mW. Thanks to the lasers' length, voltage at this current level is below 1.9 V, which gives a reduced thermal load. Thus, the overall modules electrical consumption remains lower than 10 W at case temperatures ranging from 0°C to 75°C. The 3 mm length also guaranties high reliability of these laser diodes.

Wall plug efficiency (WPE) of 830 nm single mode LD is dramatically improved with AlGaInP material. Conventional near infrared LDs based on AlGaAs have poor temperature characteristics due to small energy gap in conduction band between a p-cladding layer and an active layer. An AlGaInP based LD is a most effective candidate for the excellent characteristics because of the large gap. A high power 830 nm LD is newly designed based on AlGaInP. The LD shows excellent temperature characteristics as To of 154 K, and its WPE is around 40% at 400mW, CW output, 60°C case temperature. They also show very stable operation at the condition up to 1,100 hours.

High power semiconductor lasers, single emitters and bars are developing fast. During the last decade key parameters of diode lasers, such as beam quality, power, spatial and spectral brightness, efficiency as well as reliability have been greatly improved. However, often only individual parameters have been optimized, accepting an adverse effect in the other key parameters. For demanding industrial applications in most cases it is not sufficient to achieve a record value in one of the parameters, on the contrary it is necessary to optimize all the mentioned parameters simultaneously. To be able to achieve this objective it is highly advantageous to have insight in the whole process chain, from epitaxial device structure design and growth, wafer processing, mounting, heat sink design, product development and finally the customer needs your final product has to fulfill. In this publication an overview of recent advances in industrial diode lasers at TRUMPF will be highlighted enabling advanced applications for both high end pump sources as well as highest brightness direct diode.

High-power single emitters and laser bars have proven as widely-used light sources in many industrial and medical applications or as pump source for solid state or fiber lasers. A steady increase in optical and cost efficiency is needed to find the way into new markets. Therefore laser structures and devices have to be designed according to new requirements. The epitaxial structures including the design of the laser bars and the single emitters as well as epitaxial growth process are optimized to enhance the laser performance. Important parameters include the efficiency, the maximum output power, the wavelength stability and finally the reproducibility of the whole manufacturing process. Single emitters have been developed in the wavelength range around 940 nm. For laser bars the wavelength ranges around 880 nm and 1060 nm are under consideration. A wavelength stabilization for 976 nm laser devices is developed.

The impact of new direct-diode and fiber laser systems on industrial manufacturing drives the demand for highbrightness diode laser pump sources suitable for simple fiber coupling with high efficiency. Within the German funded project HEMILAS laser mini-bars with different bar geometries and small fill factors were investigated. We present results on 9xx nm bars with tailored beam parameter products for simplified coupling to fibers with core diameters of 200μm and 300μm with a numerical aperture of 0.22 and compare beam quality parameters, brightness, conversion efficiency, and thermal performance of different bar designs. Optimized epitaxy structures yield conversion efficiency maxima above 66%. The slow axis divergence angle of mini-bars with a fill factor of 10% featuring five 100μm wide and 4mm long emitters based on this epitaxy structure stays below 7°, which corresponds to a beam parameter product of 15mm mrad, up to very high output power of over 45W. This result was achieved for mounting on actively cooled submounts using hard solder. A similar bar with 5mm cavity length and using soft soldering reached an output power of 60W at the same beam parameter product. At 4mm cavity length, no COMD failures were observed up to currents exceeding the thermal rollover and the maximum output cw power was 95W.

Coherent Doppler Lidars (CDLs), operating at an eye-safe 1.5-micron wavelength, have found promising applications in the optimization of wind-power production. To meet the wind-energy sector's impending demand for more cost-efficient industrial sensors, we have focused on the development of continuous-wave CDL systems using compact, inexpensive semiconductor laser (SL) sources. In this work, we compare the performance of two candidate emitters for an allsemiconductor CDL system: (1) a monolithic master-oscillator-power-amplifier (MOPA) SL and (2) an external-cavity tapered diode laser (ECTDL).

We report on our progress to obtaining a 1540 nm SE-DFB laser with curved, second order grating capable of producing extremely high peak power for eye-safe range finding applications. Higher peak power can be extracted from SE-DFB lasers since the emission area is three orders of magnitude larger than for edge emitters. Ten-times narrower spectral width and four-times lower thermal shift of emission wavelength allows for the use of narrower filters on the range finder detector, providing a higher signal-to-noise ratio. Furthermore, a curved second-order diffraction grating in our SE-DFB laser allows for a higher brightness source, which makes transmitter optics geometry more compact and simpler.

A tunable 800 nm high-power dual-wavelength diode laser system with double-Littrow external-cavity feedback is demonstrated. The two wavelengths can be tuned individually, and the frequency difference of the two wavelengths is tunable from 0.5 to 5.0 THz. A maximum output power of 1.54 W is achieved with a frequency difference of 0.86 THz, the output power is higher than 1.3 W in the 5.0 THz range of frequency difference, and the amplified spontaneous emission intensity is more than 20 dB suppressed in the range of frequency difference. The beam quality factor M² is 1.22±0.15 at an output power of 1.35 W. The simultaneous oscillation of the two wavelengths is under test by the sumfrequency generation experiment in a bismuth triborate (BIBO) nonlinear crystal.

High power diode laser module operating at 808 nm is required for different applications, such as developing an efficient high power Nd³⁺-doped solid state laser and Tm3+ -doped silica fiber laser, industrial, medical and military applications. Optical and thermal images characterization for a fiber-coupled high power diode laser module is presented experimentally for 6.6 Watt output optical power .An external temperature controller system was designed, which stabilizes the central wavelength at 808 nm at 25°C over a wide range of diode laser driving current from 1A to 6 A. without this cooling system, the wavelength changes by 0.35nm/°C for temperature changes from 20°C to 40°C at the same range of the driving current. In this paper we have present a methodology for temperature reduction of a 808 nm high power diode laser module, based on dynamically thermal control, which is known as dynamic thermal management. Stabilization of the output wavelength has been done by using proportional speed control (PSC) of a CPU cooling fan with certain scheme of straight fins heat sink. Two electronic circuits based on pulse width modulation (PWM) in microcontroller and comparators IC have been used. This technique can be considered as an effective mechanism for reducing temperature and power dissipation to make stabilization of the diode laser output wavelength by preventing heat accumulation from the thermo electric cooling (TEC) inside the diode laser module confirmed by thermal images.

Continued improvements in broad-area InGaAs-AlGaAs strained quantum well (QW) lasers have led to unprecedented performance characteristics in these lasers including optical output powers of over 20 W and power conversion efficiencies of over 70% under CW operation. Catastrophic optical mirror damage (COMD) is responsible for failures in (Al)GaAs QW lasers, but InGaAs-AlGaAs strained QW lasers with optimized facet passivation predominantly fail by catastrophic optical bulk damage (COBD). Since COBD is relatively a new failure type, it requires physics of failure investigation to understand its root causes and then develop COBD-free lasers for high reliability applications including potential satellite systems. We recently proposed a model for degradation mechanism responsible the COBD process and this paper further investigates the root causes of COBD in the lasers using various failure mode analysis techniques. We investigated reliability and degradation mechanism in MOCVD-grown broad-area InGaAs-AlGaAs strained QW single emitters. During entire accelerated life-tests of the lasers we studied, time resolved electroluminescence (TR-EL) 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.