At Photonics West 2005 a new technology was described for building a new, non corrosive micro cooling heat sink for diode lasers made of stainless steel with the procedure of three dimensional laser melting. Due to the thermal conductivity, which is 20 times worse than the conductivity of copper, first test leads to the result, that it is not possible to compensate the worst thermal conductivity by an optimized inner structure, regarding wall thicknesses and flow rate. So the solution was searching a different material, with a better thermal conductivity to achieve a thermal over all resistance that is usable for the cooling of high power laser diodes. Searching that material leads to a special nickel alloy in the field of nuclear industry. The new generation of micro coolers are named TEX series. All TEX Series coolers were made out of a special nickel alloy, specially developed as a corrosion protection material. Therefore, the TEX coolers have excellent corrosion resistance. In addition, due to the manner and way of using three dimensional laser melting, the surface of the inner structure was hardened. The hardening HV1 is 380, so that there is no danger regarding erosion or a combination of erosion and corrosion. Metallization and soldering the semi conductor also had been tested. The commonly used structure with Nickel and Gold is possible as well as the metallization only with gold. With both variations the semi conductor can be soldered and the connection to the cooler surface is very strong.

High power water-cooled diode lasers are finding increasing demand in biomedical, cosmetic and industrial applications, where repetitive cw (continuous wave) and pulsed cw operation modes are required. When operating in such modes, the lasers experience numerous complete thermal cycles between "cold" heat sink temperature and the "hot" temperature typical of thermally equilibrated cw operation. It is clearly demonstrated that the main failure mechanism directly linked to repetitive cw operation is thermo-mechanical fatigue of the solder joints adjacent to the laser bars, especially when "soft" solders are used. Analyses of the bonding interfaces were carried out using scanning electron microscopy. It was observed that intermetallic compounds, formed already during the bonding process, lead to the solders fatigue both on the p- and n-side of the laser bar. Fatigue failure of solder joints in repetitive cw operation reduces useful lifetime of the stacks to hundreds hours, in comparison with more than 10,000 hours lifetime typically demonstrated in commonly adopted non-stop cw reliability testing programs. It is shown, that proper selection of package materials and solders, careful design of fatigue sensitive parts and burn-in screening in the hard pulse operation mode allow considerable increase of lifetime and reliability, without compromising the device efficiency, optical power density and compactness.

The lifetime of high-power diode lasers, which are cooled by standard copper heatsinks, is limited. The reasons are the aging of the indium solder normally employed as well as the mechanical stress caused by the mismatch between the copper heatsink (16 - 17ppm/K) and the GaAs diode laser bars (6 - 7.5 ppm/K). For micro - channel heatsinks corrosion and erosion of the micro channels limit the lifetime additionally. The different thermal behavior and the resulting stress cannot be compensated totally by the solder. Expansion matched heatsink materials like tungsten-copper or aluminum nitride reduce this stress. A further possible solution is a combination of copper and molybdenum layers, but all these materials have a high thermal resistance in common. For high-power electronic or low cost medical applications novel materials like copper/carbon compound, compound diamond or high-conductivity ceramics were developed during recent years. Based on these novel materials, passively cooled heatsinks are designed, and thermal and mechanical simulations are performed to check their properties. The expansion of the heatsink and the induced mechanical stress between laser bar and heatsink are the main tasks for the simulations. A comparison of the simulation with experimental results for different material combinations illustrates the advantages and disadvantages of the different approaches. Together with the boundary conditions the ideal applications for packaging with these materials are defined. The goal of the development of passively-cooled expansion-matched heatsinks has to be a long-term reliability of several 10.000h and a thermal resistance below 1 K/W.

This paper is mainly dedicated to a short-time scale reliability study of different packages applied to the same type of laser diode bars: indium and gold-tin packaged laser bars are operated in cw hard-pulse mode with increasing currents until their destruction. The destruction currents serve as guide values for long-time aging tests that should be performed at lower currents. Gold-tin packaged diode lasers turn out to have clearly higher destruction currents in hard-pulse mode. This result is underlined by long-time aging tests at appropriate currents.

We present a summary view of the DARPA SHEDS and ADHELS programs. The goal of these programs is development of technology of a future compact, field-deployable high energy laser (HEL) system.

Ongoing optimization of epitaxial design within Coherent device engineering has led to a family of high power-conversion-efficiency (PCE) products on conductively cooled packages (CCP) and fiber array packages (FAP). At a 25°C heat sink temperature, the PCE was measured at 71.5% with 75W CW output power on 30% fill-factor (FF) bars with passive cooling. At heat sink temperatures as high as 60°C the PCE of these bars is still maintained above 60%. Powered by such high efficiency 9xx nm diodes, Coherent FAP products have consistently exceeded 55% PCE up to 50W power levels, with 62% PCE demonstrated out of the fiber. High linear-power-density (LPD) operation of 100μm x 7-emitter bars at LPD = 80 mW/μm was also demonstrated. Bars with 7-emitter were measured up to 140W QCW power before catastrophic optical mirror damage (COMD) occurred, which corresponds to a COMD value of 200mW/μm or 2D facet power density of 29.4 MW/cm². Leveraging these improvements has enabled high power FAPs with >90W CW from an 800μm-diameter fiber bundle. Extensive reliability testing has already accumulated 400,000 total real-time device hours at a variety of accelerated and non-accelerated operating conditions. A random failure rate <0.5% per kilo-hours and gradual degradation rate <0.4% per kilo-hours have been observed. For a 30% FF 50W CW 9xx nm bar, this equates to >30,000 hours of median lifetime at a 90% confidence level. More optimized 30% FF 9xx nm bars are under development for power outputs up to 80W CW with extrapolated median lifetimes greater than 20,000 hours.

We report results of multi-cell life tests performed on nearly (500) laser diodes representing our new generation of very efficient high power broad area 9xx nm lasers. The acceleration model showed a steep power dependence of the failure rate with an exponent of nearly 6. Improvement in the facet passivation process resulted in significantly less power acceleration of failures. Analysis of the life test on upgraded lasers showed median lifetime of 1,500,000 hours at operating conditions of 8W and 350°C. Optical powers as high as 17.8W for thermally limited CW operation and 32W for 20 μs pulsed operation were recorded. The CW life test was complemented by a life test performed at power cycling conditions (1Hz repetition rate, 50% duty cycle).

Manufacturers of Nd:YAG lasers continue to demand 808 nm pump sources that deliver ever lower operating costs (measured in $/kW-hour). Responding to this demand, Coherent has developed a new generation of high power, 808 nm laser bars. These lasers are most ideal for high power QCW applications, but also perform very well in CW pumping applications. The key to the improved power for QCW bars is increase in catastrophic optical damage (COD) threshold. Through a combination of advances in epitaxial structure design and coating technology after aging COD limit for new generation of bars has been increased by 40%. This allowed us to achieve reliable QCW operation at 270W of peak power. Life test results shows that lifetime of these bars at these conditions exceed 2e9 shots. We also developed similar structure optimized for CW operations. When mounted on micro-channel water cooled packages CW bars operate reliably at an output power of 150 W. Highest power conversion efficiency (PCE) for CW bars was more then 55% with typical PCE value >50%.

Peak optical power from single 1-cm diode laser bars is advancing rapidly across all commercial wavelengths. Progress in material performance is reviewed and we show that current trends imply there is no fundamental barrier to achieving peak powers of 1-kW per 1-cm diode laser bar. For bars with such high peak powers, commercially available reliable devices would be expected to deliver ~ 300-W per bar. Progress to date has allowed us to demonstrate > 400-W peak output from single 1-cm diode laser bars at emission wavelengths from 800-nm to 980-nm. The available range of emission wavelengths has also been increased, with 90-W bars shown at 660-nm and 24W at 1900-nm, complementing the 100-W bar previously demonstrated at 1470-nm. Peak power is seen to correlate closely peak efficiency. Further advances in diode laser efficiency and low thermal resistance packaging technology continue to drive these powers higher. The most critical improvements have been the reduction in the diode laser operating voltage through optimization of hetero-barriers (leading to 73% efficient 100-W bars on copper micro-channel) and a reduction in packaging thermal resistance by optimizing micro-channel performance (leading to < 0.2-^oC/W thermal resistance).

The 880 nm diode laser is emerging as the source of choice for pumping Nd:YV0₄ laser crystals because it offers higher pumping efficiency than 808 nm diode lasers[1]. This paper reports on recent progress in the development of high power, high reliability, 880 nm laser bars. Specifically, high performance has been achieved based on Coherent's aluminum-free active (AAA) epitaxial structures while maintaining lifetimes greater than 10,000 hours. This includes 30% fill factor, 1 cm bars on conductively cooled packages (CCP) operating at 51 W with proven manufacturability. We observed power conversion efficiency (PCE) of up to 56%. These lasers have a far field fast axis divergence of 32° (FWHM), and slow axis divergence of <7° (FWHM). Typical value of the FWHM of output spectrum is 2.5 nm. These bars were used to build fiber array packages (FAPs) operating at 45 W. We have achieved FAP PCE of 50% and numerical aperture of <0.12. Reliability of both bars and FAP was shown to exceed 10000h MTBF.

The effect of compressive and tensile strain of Quantum Wells (QWs) on the gain and transparency current density of high power laser diodes was studied. Material composition of InGaAlAs/AlGaAs and InGaAsP/InGaP was utilized for the study of compressive and tensile strain QWs, respectively. Variation in the strain degree was achieved by changing the In and P mole fraction accordingly. We found that the transparency current densities of compressively strained QWs decrease from 117 to 100 A/cm² as a function of strain. The transparency current in tensile strained QWs decrease from 140 to 130 A/cm² as the strain is increased. The material gain of compressively strained QWs is almost insensitive to the variation of strain degree (~1000 cm^-1), while for tensile strained QWs the material gain increases from 1000 cm^-1 to 1250 cm^-1 when the tensile strain is increased. In spite of the higher transparency densities the gain achieved at maximum strain is larger for tensile strained QW laser. This result is explained by the strain influence on the electron-hole recombination strengths. Consequently the effect of strain on the performance of High Power QCW and CW laser bars was also investigated. The threshold current of bars with compressively strained QWs is decreased to 8.5 A and the external differential efficiency is increased to 1.0 W/A as a function of strain. On the other hand, as the tensile strain in the QW is increased the threshold current reduces to 10 A and the slope efficiency increases to 1.2 W/A. As a result, tensile strain QWs bars are more efficient at high power operation.

For the application of broad-area laser diodes (BA-LDs) to display or printing, uniform distribution and stability of their near-field pattern (NFP) are the most important demand. In order to control the NFP, we have fabricated BA-LDs with index-guided structure and got better top-hat and stabler NFP than that for gain-guided BA-LDs. However, this mechanism is not understood yet. Therefore, we study the features of BA-LDs' NFP systematically, and set up a new model to understand their behaviors. The NFPs of BA-LDs evolve via three phases with increasing operation current: the first phase is "mode-progressing phase" in which the number of the spatial modes increases orderly, and the second phase is "transition phase" in which the spatial modes become unstable and fluctuate. The third phase has different properties according to the waveguiding structure of BA-LDs: "disordered phase" appears for gain-guided structure in which several specific modes dominate in the whole distribution (filamentation behavior), on the other hand "ordered phase" appears in the case of index-guided structure in which a top-hat distribution is obtained. This top-hat NFP is almost unchanged with increasing output power. With these experimental results, we propose the new model, in which the emitting area of a BA-LD is divided into several parts and they are discussed separately.

Today tapered diode lasers are mainly used in external resonator configuration for non-linear spectroscopy or frequency doubling for blue-green outputs. Now increased output power and brightness make tapered lasers even attractive for pumping of fibre amplifiers or lasers and fibre coupled modules. We have realized high-power ridge-waveguide tapered diode lasers emitting at 976 nm. The high material quality of the MBE-grown laser structures yields a high internal efficiency of more than 97% and low internal losses of 0.5 cm^-1. Tapered single emitters consist of a ridge section with a length of 500 μm and a taper section with a length of 3000 μm. The taper angle was 6°. A threshold current of 1.07 A corresponding to a threshold current density of 222 A/cm² has been obtained. The maximum slope efficiency of 1.09 W/A together with the low series resistance of 35 m Ω results in a high wall-plug efficiency of 58% at 5.5 W output power. This high wall-plug efficiency remains nearly constant up to operation currents of 9 A corresponding to output powers of more than 8 W. At an operation current of 15 A an output power of 12.5 W has been achieved, which is to our knowledge the highest output power in continuous wave mode for tapered diode lasers reported so far. At 8 W a nearly diffraction limited behavior with values for M² of less than 1.5 have been observed resulting in a brightness of more than 660 MW/cm².

Based on the most recent generation of Bookham's laser diode bars in the 9xx nm wavelength range which are able to deliver in excess of 250 W of output power from 50% filling factor 2.4 mm cavity length design, we have developed low 20% fill-factor bar devices for high brightness applications. Close to 200 W of output power has been achieved in CW mode from actively cooled micro-channel cooler devices without signs of damage. Mounted on conductively cooled copper blocks, still more than 130 W (CW) has been obtained, indicating the high conversion efficiency of >60% reducing the thermal load on the mounting assembly. Based on extensive reliability testing in excess of 5000 h and at power densities ranging up to 36mW/um and beyond, highly reliable operation of 20% fill-factor bars is expected. To facilitate fiber coupling into wide-core multi-mode fibers a further reduction of the emitter aperture has been realized. From a single 3.6 mm cavity length by 800 um wide emitter design ("MaxiChip") about 50 W output power has been obtained in CW mode from devices mounted on standard conductively cooled 1x1 inch copper blocks. While CW operation has been thermally limited, extremely high peak power operation can be expected in qCW operation. Due to the narrow aperture of this MaxiChip efficient and easy coupling into wide aperture multimode fibers can be achieved.

We report on the development of a new generation of very high power 980 nm single lateral mode ridge-waveguide quantum-well lasers. An asymmetric-waveguides vertical structure has been optimized for very low internal losses while keeping the vertical mode-size large, thus allowing a low vertical far-field beam angle of less than 19°. Careful optimization of the doping profiles, and epitaxial interfaces optimization for reduced scattering, allowed to obtain internal losses as low as 0.6-0.7 cm^-1. Such low losses are necessary to keep the external efficiency high in very long cavities, together with a high internal quantum efficiency. We thus reached our goal of keeping the external efficiency above 70% even for cavity lengths of 4.5 mm. The flared ridge waveguide has been designed to strongly filter higher order lateral modes, and kink-free operation has been obtained up to over 1.5 W output power, with very stable vertical and horizontal beam patterns. High saturation powers above 2 W have also been demonstrated at 25°C, and over 1.5 W at 75°C. Wavelength stabilized chips, by means of a fiber Bragg grating, reached linear fiber powers above 1.0 W with strong suppression of gain-peak lasing at all currents and good power stability.

During the last few years high power diode laser arrays have become well established for direct material processing due to their high efficiency of more than 50%. But standard broad-area waveguide designs are susceptible to modal instabilities and filamentations resulting in low beam qualities. The beam quality increases by more than a factor of four by using tapered laser arrays, but so far they suffer from lower efficiencies. Therefore tapered lasers are mainly used today as single emitters in external resonator configurations. With increased output power and lifetime, they will be much more attractive for material processing and for pumping of fiber amplifiers. High efficiency tapered mini bars emitting at a wavelength of 980 nm are developed, and in order to qualify the bars, the characteristics of single emitters and mini bars from the same wafer have been compared. The mini bars have a width of 6 mm with 12 emitters. The ridge waveguide tapered lasers consist of a 500 μm long ridge and a 2000 μm long tapered section. The results show very similar behavior of the electro-optical characteristics and the beam quality for single emitters and bars. Due to different junction temperatures, different slope efficiencies were measured: 0.8 W/A for passively cooled mini bars and 1.0 W/A for actively cooled mini-bars and single emitters. The threshold current of 0.7 A per emitter is the same for single emitters and emitter arrays. Output powers of more than 50 W in continuous wave mode for a mini bar with standard packaging demonstrates the increased power of tapered laser bars.

High-power multi-mode broad area InGaAs strained quantum well (QW) single emitters (λ ≈ 920-980nm) have been mainly used for industrial applications. Recently, these broad area lasers with CW output powers >5W have also found applications in communications as pump lasers for Er-Yb co-doped fiber amplifiers. This application requires very demanding characteristics including higher reliability than industrial applications. In contrast to 980nm single mode InGaAs strained QW lasers that are widely employed in both terrestrial and submarine applications, the fact that multimode lasers have never been used in optical communications necessitates careful study of these lasers. We report investigations of performance characteristics, reliability, and failure modes of high-power multi-mode single emitters. The lasers studied were broad area strained InGaAs-GaAs single QW lasers grown either by MOCVD or MBE. Typical apertures were around 100μm wide and cavity lengths were ≤4.2mm. AR-HR coated laser diode chips were mounted on carriers with junction down configuration to reduce thermal impedance. Laser thresholds were ≤453mA at RT. At 6A injection current typical CW output powers were over 5W at 25°C with wall-plug efficiency of ~60%. Characteristics measured included thermal impedance and optical beam profiles that are critical in understanding performance and reliability. Automatic current control burn-in tests with different stress conditions were performed and log (I)-V characteristics were measured at RT to correlate degradation in optical output power and an increase in trap density estimated from the 2κ•T term in bulk recombination current. We also report initial analysis of lifetest results and failure modes from these lasers.

We review recent advances in high power semiconductor lasers including increased spectral brightness, increased spatial brightness, and reduced cost architectures at wavelengths from the near infrared to the eye-safe regime. Data are presented which demonstrate both edge emitter devices and high power surface emitting 2-dimensional arrays with internal gratings to narrow and stabilize the spectrum. Diodes with multimode high spatial brightness and high power single mode performance in the 808 and 976nm regime are described, and advances in high power bars at eye-safe wavelengths are presented. These devices have the potential to dramatically improve diode pumped systems and enable new direct diode applications.

In this communication we present the characteristics of Bookham's MU7-9xx-01 laser module with multimode fiber output. This latest generation of our multimode modules is designed for light output power of up to 7 W in uncooled operation in the wavelength range between 915 nm and 975 nm. The key element of the module is our new SES8-9xx-01 broad area single emitter. These high power lasers in the 9xx nm wavelength range show a high slope efficiency of up to 1.2 W/A in CW room temperature operation. High efficiency combined with low threshold current and low operation voltage result in a maximum wall plug efficiency of above 65%. Almost 4000 h lifetest data at accelerated conditions are available for the laser diodes. The data give estimated reliability values of below 5 kFIT at operating conditions (between 8 A and 8.5 A injection current at up to 35°C heat sink temperature). The robustness of the new lasers is also illustrated by the fact that no catastrophic mirror damage was observed up to 22.5 W of light output power. The low divergence of the laser beam allows coupling into multimode fiber with 0.15 or 0.22 numerical aperture (NA) with a coupling efficiency above 90% at operation condition. Maximum ex-fiber light output powers of 11.5 W are shown. On module level around 2000 h lifetest data are accumulated without any failure or sign of degradation.

High-power high-brightness multimode edge emitting pumps have been developed. Comprehensive development efforts have resulted in 3 mm-long cavity diodes with far-field divergence reduced down to 26°. Output in excess of 20W CW from 90 μm-wide aperture single emitter was demonstrated for the first time. Peak power was reached at 25A CW driving current and was limited by power supply. Peak CW power efficiency was as high as 67%. Two coolerless package types designed to operate up to 10W output and up to 20W output are reported. About 95% fiber coupling efficiency into NA<0.12 was demonstrated in the entire range of driving currents for both types of pumps. For packages of the later design efficiency over 50% is maintained up to 16W CW ex-fiber output. Diode junction overheat above heatsink temperature is less than 20°C up to ~ 18W ex-fiber output.

We demonstrate, for the first time, a monolithic integrated lens for wide aperture gain-guided tapered laser beam quality enhancement by compensating the quadratic phase curvature. The 3mm long tapered laser with an output aperture of 170μm adopted in this design consists of a gain-guided tapered section and an index-guided ridge section and operated at 980nm. The lens design is implemented by focus ion beam etching (FIBE) technique, whereby the laser diode is mounted p-side up in order to facilitate the etching process. The lens is located 600μm away from the junction of the tapered and ridge sections, and is 40μm wide and 300μm long with a focal length of 800μm. The laser diode is characterised by light-current characteristics together with near- and far- field measurements before and after etching. The device is biased by current pulses of 1μs width and 0.1% duty cycle. Light-current measurement shows a drop of 10.5% in threshold current from 380mA to 340mA after the inclusion of lens. This is an evidence that the lens effectively equalised the curved phase in order to reduce the laser cavity loss by improving the coupling efficiency of backward travelling wave at the output facet. Throughout the whole current range tested, the width of near-field at waist is broadened by an average of 36% after the inclusion of lens. By successfully compensating the quadratic phase curvature of the mode, the beam divergence in the far-field is significantly narrowed by an average of 28.5%. M² factor is improved by an average of 12%.

The materials processing industry has recently mandated the need for more efficient laser systems with higher beam quality and longer life. Current multiplexing techniques, state-of-the-art laser diodes and novel cooling designs are now emerging as possibilities to meet the ever demanding industry needs. This paper describes the design and initial results of a direct diode system that is aimed at delivering 1.5 kW of output power and a beam divergence of 40 mm mrad on a long life macro-channel cooler. The design entails multiplexing 2 wavelength combined beams and 2 polarization combined beams. Each of the four branches of the direct diode system utilizes a novel stacking and cooling design. The results from one of these branches, 1 wavelength and 1 polarization, are presented where the light is coupled into a fiber with a 400 μm core diameter and a NA of 0.22. Each branch consists of 60 diode laser mini-arrays, where each mini-array consists of four 100 μm wide emitters and a lateral fill factor of 50%. An output power of 500W at 10°C water temperature and 420 W at 25°C are demonstrated through the 400 μm fiber.

The improved wall-plug efficiency and minimal maintenance of diode laser systems over Nd:YAG and CO₂ lasers has been admired by many manufacturers. Until recently, most diode laser systems could not compete at high-power levels or with the same beam quality. Nuvonyx reports the design and initial development of a diode laser system that delivers 2000 W from a 600 μm core fiber with a 0.22 NA. This system is suitable as a stand-alone industrial direct diode laser system or as a multi-kilowatt fiber laser pump source. The development of a high brightness bar technology by Nuvonyx and its collaborators along with the use of polarization beam combining is the core of this laser system. Each emitter operates with a single lateral mode resulting in a high brightness bar that outputs up to 50 W. The wavelength of the laser is centered at 975 nm with a width of less than ± 3 nm. The demonstration of this laser system defines a clear path to scale this technology to 4000 W.

At present methods of polarization and wavelength multiplexing with dielectric coatings are used to increase the brightness of diode lasers. The number of suitable diode laser wavelengths is limited by the temperature- and current-dependent spectral characteristics of the diode laser and the slope of dielectric edge-filters. By use of external volume diffraction gratings it is possible to constrict the emission spectra of diode lasers and to reduce the wavelength shift related to temperature or current injection. Due to the stabilization of the center wavelengths and the reduced bandwidth of the diode emission multiplexing of diode laser beams at small distance of the centre wavelengths can be realized. The performance of wavelength stabilization by use of volume diffraction gratings adapted to AR-coated diode laser arrays in an external cavity as well as to standard high power diode laser arrays is discussed. Furthermore modules of two diode laser beams are combined by wavelength dependent diffraction of an adapted volume diffraction grating. The spectra of the diode lasers of the same wafer are stabilized with a centre wavelength spacing of about 3 nm and more than 95% of the optical output power of each beam within a spectral width less than 0.7 nm. An efficiency of more than 80% for multiplexing of two diode laser bars with good beam quality in fast axis of M² < 2 is achieved.

We explain some technical details regarding time-multiplexing of laser diodes, a method to improve the beam quality of diode lasers, which is still insufficient for many applications. Several pulsed laser diode beams are guided onto a common optical path to superpose the power of the laser diodes while maintaining the beam parameter product of a single laser diode. Pulsed operation of continuous wave laser diodes with average power equal to the specified cw-power of 4 W was tested for 150 hours without failure. We use a fast digital optical multiplexer built up by a cascade of binary optical switches. For the latter we use a Pockel's cell followed by a polarization filter, which allows addressing of two optical paths. Instead of direct on/off-switching we drive the crystals with a harmonic voltage course to avoid ringing caused by piezo-electricity. Up to now an optical power of 10.5 W was generated, 13 W are expected with some improvements. Furthermore we discuss the use of new 8 W laser diodes and the involved implications on driver technology.

High power diode lasers have become an established source for numerous direct applications like metal hardening and polymer welding due to their high efficiency, small size, low cost and high reliability. These laser sources are also used for efficient pumping of solid state lasers as Nd:YAG lasers. To increase the output power of diode lasers up to several kilowatts, the emitters are scaled laterally by forming a diode laser bar and vertically by forming a diode laser stack. For most applications like hardening and illumination, though, the undefined far field distribution of most commercially available high power diode laser stacks states a major drawback of these devices. As single emitters and bars can fail during their lifetime, the near field distribution does not remain constant. To overcome these problems, the intensity distribution can be homogenized by a waveguide or by microoptic devices. The waveguide segments the far field distribution by several total internal reflections, and these segments are overlaid at the waveguide's exit surface. By the microoptic device, the near field is divided into beamlets which are overlaid by a field lens. Both approaches are presented, and realized systems are described.

This paper reports on a novel pair of microlens arrays (MLA's) for efficient coupling of the high aspect ratio optical beam emitted by high-power laser diode linear arrays (also referred to as laser diode bars) into the core of multimode optical fibers. These novel MLA's overcome the limitations observed when using high fill factors laser diode bars. The MLA designs are described. Results from modelling work show good coupling performances for laser diode bars with fill factors up to 75%. The technique for fabricating the complex surface profiles of the MLA's is discussed. Masters are first fabricated and MLA's are then replicated, so that volume production at low cost can be envisioned. The fabricated MLA's have been used for reshaping and fiber coupling the output of a 10-mm laser diode bar. An efficiency of 74% has been obtained when coupling into an optical fiber having a core diameter of 400 μm and a numerical aperture of 0.22.

Multichannel resonators which should provide coherent emission of all its components are intensively studied for more than 25 years. However, no stable coherent emission with high efficiency was reported for such devices. The main problem preventing stable efficient coupling is a tendency of a multichannel system to switch between different modes of a complex resonator. This paper reports the use of thick Bragg grating recorded in a photothermo-refractive glass with an extremely narrow spectral width and angle selectivity that provided coherent coupling of two semiconductor laser diodes. In a described construction no oscillations of output power was observed and an interference patter with visibility close to unity was observed for a long time.

This paper describes the application of the Carrier Illumination technique to non-destructively measure dopant behavior before and after annealing for 65nm technology. Patterned wafers were implanted with different SDE energy and dosages. The detected signals from laser diode show good correlation with electrical performance (drive current, overlap capacitance). Another crucial application is to in-line monitor the thermal process. By splitting spike anneal temperature, we found detected signals were proportional to the junction depth of SIMS. The non-destructive, non-contact, and small spot size nature of the CI measurement method is capable of tracing low energy implant and spike anneal.

The high power diode laser systems with their laser diode bars and arrays not only require special fibers to couple directly to the diode emitters, but also require special fibers to couple from the laser to the application sites. These power delivery fibers are much larger than the internal fibers, but must be flexible, and have not only good strength but also good fatigue behavior. This is particularly important for industrial systems using robotic arms or robots to apply the high power laser energy to the treatment site. The optical properties of hard plastic clad silica (HPCS) fibers are well suited for the needs of delivery of high power from diode laser bars and arrays to an application site. New formulations for HPCS fibers have been developed which have demonstrated fibers with good mechanical strength in preliminary tests. A systematic study has been undertaken to determine the strength and fatigue behavior of three 'new' HPCS fibers and to compare them with results for earlier HPCS fibers. Benefits of stronger median dynamic strengths and tighter flaw distributions have been found. Short to medium length time to failure results, indicate that the static fatigue parameters of the new high numerical aperture (NA) optical fibers are at least as good as those for standard NA HPCS fibers, which is an advance from previous results on the older formulation clad fibers.

We experimentally and theoretically studied degradation phenomena and their mechanism in broad-area semiconductor lasers (BA-LDs) with optical feedback (OFB). We made two types of BA-LDs (one is consisted of AlGaAs emitting at 808nm in TE mode, and another one is consisted of AlGaInP emitting at 642nm in TM mode), and investigated conditions of the degradations caused by an optical feedback. The both types of BA-LDs showed degradations depending on feedback rate and output power. For example, both BA-LDs were damaged with about 20% of intensity feedback rate at half of an output power of a catastrophic optical mirror damage (COMD) levels. To describe a theoretical model for the degradation, the optical power at a front facet of the BA-LDs was calculated and compared with the COMD level of the solitary BA-LDs. In the theoretical model, we included a threshold reduction caused by the OFB. We found that the degradation was explained by a constructive interference between internal and the feedback optical fields. The BA-LDs are damaged when a coherent sum of those fields exceeds the solitary COMD level. We found that the threshold reduction decreases a critical value of the feedback rate corresponding to the damage at low output power regime, and also found that there is an optimum reflectivity of the front facet. The theoretical results show a good agreement with experimental results. According to this model, we can avoid the damages induced by the OFB in the various applications.

A variety of applications such as spectroscopy or tunable frequency doubling of diode lasers for blue-green outputs necessitate diffraction-limited tunable narrow linewidths and high output powers in the multiwatt regime. For these applications, tapered devices based on a tapered amplifier gain-guided design are used in an external cavity set up. So far commercially available output powers are in the range of 1 W, limited by the mounting technology so far. The tuneability and the influence of different packagings on output performance was investigated. Used in littrow-configuration tapered diode lasers on optimized heatsinks show output powers of more than 3 W and an excellent spectral and spatial quality. The beam-quality parameter remains well below M² < 1.5 for output powers up to 3 W. A tuning range of more than 40 nm could be achieved.

High resolution spectroscopy of environmental and medical gases requires reliable, fast tunable laser light sources in the mid-infrared (MIR) wavelength regime between 3 and 5 μm. Since this wavelength cannot be reached via direct emitting room temperature semiconductor lasers, additional techniques like difference frequency generation (DFG) are essential. Tunable difference frequency generation relies on high power, small linewidth, fast tunable, robust laser diode sources. We report a new, very compact, alignment insensitive, robust, external cavity diode laser system in Littman/Metcalf configuration with an output power of 1000 mW and an almost Gaussian shaped beam quality (M²<1.2). The coupling efficiency for optical waveguides as well as single mode fibers exceeds 70%. The center wavelength is widely tunable within the tuning range of 20 nm via remote control. This laser system operates longitudinally single mode with a mode-hop free tuning range of up to 150 GHz without current compensation and a side-mode-suppression better than 50 dB. This concept can be realized within the wavelength regime between 750 and 1060 nm. We investigated this light source for high resolution spectroscopy in the field of Cavity Ring-Down Spectroscopy (CRDS). Our high powered Littman/Metcalf laser system was part of a MIR-light source which utilizes difference-frequency generation in Periodically Poled Lithium Niobate (PPLN) crystals. At the wavelength of 3.3 μm we were able to achieve a high-resolution absorption spectrum of water with four resolved isotopic H₂O components. This application clearly demonstrates the suitability of this laser for high-precision measurements.

A new-type tunable high power wavelength tunable ASE light source is fabricated. The device length is 1960μm. The waveguide is 100μm wide and tilted at 6° from the facet normal. Without external feedback, this device can provide 1.4Watt ASE light per facet at 12Amp injection current. The emitted spectrum has 20nm FWHM. The far field has narrow divergence angle and the near field is smooth without filamentation. When external feedback is applied, the slope efficiency is increased from 0.15W/Amp to 0.2W/Amp. Only 6Amp injection current is required to reach 1.06Watt output. Feedback from a grating can be used to control the emission wavelength and improve the beam quality.