This PDF file contains the front matter associated with SPIE Proceedings Volume 11983, including the Title Page, Copyright information, Table of Contents, and Conference Committee listings.

The High-Power Diode Laser Technology conference was first presented at SPIE Photonics West in 2003. At that time high power laser diodes were just approaching 50-60% in efficiency, a couple of companies were developing systems based on these diodes, and fiber lasers were not yet an industrial product. Since then, laser diodes can exceed 70% electrical efficiency, power levels have grown from the 50-Watt bar level to today’s heights of several hundred Watts. New wavelengths have been introduced and laser diode systems have increased in power from the couple of kWatts in 2003 to over 40 kWatts today. This technology area continues to expand with new applications, and new heights every year. We will review the hot topics of the time, technology, applications, and state-of-the art performance levels. What problems have been solved, and which remain today, twenty years later?

GaAs-based high-power laser diodes in the 9xx nm wavelength-range are at the heart of modern materials processing systems. The continuing increase in reliable operating power and efficiency of these diodes has been one of the driving factors behind their wide adoption in fiber laser and direct diode systems and has been a major factor fueling the growth of the materials processing market. II-VI as a leading manufacturer of both VCSEL and edge-emitting GaAs-based laser diodes has pioneered the adoption of 6-inch GaAs laser diode technology in high-volume manufacturing. In this presentation we will review the developments of the high power pump laser diode market in recent years that required the adoption of larger diameter wafer substrates, discuss selected highlights and challenges of our 6-inch GaAs laser production, and present latest chip performance results.

GaAs-based 1-cm bars based on extreme-triple-asymmetric (ETAS) epitaxial designs are presented. The investigated structure shows low optical loss and weak power saturation at high current allowing high output power P_opt and power-conversion-efficiency ηΕ. The resulting ETAS bars containing 20 emitters with 395 μm wide stripes and 4 mm long cavity, operate with the highest-to-date quasi-continuous-wave power (200 μs, 10 Hz) P_opt = 1.9 kW, delivered from just one quantum well, with maximum ηΕ = 67% at T_HS = 298 K heat-sink temperature. High ηΕ = 62% is maintained at 1.0 kW and remains 55% at 1.5 kW. Even higher P_opt = 2.26 kW is achieved at a reduced T_HS = 203 K. At 203 K, maximum ηΕ climbs to 74% while maintaining a high ηΕ < 60% up to 2 kW, and reaches 55% at 2.26 kW. We also present progress in lateral bar layout, which is further optimized for narrow lateral beam divergence and evaluated for the first time up to 2 kA current. Experimental results show that lateral far field at 95% power can be lowered by 2-3° without sacrificing P_opt and ηΕ, reaching ~15° at 1.8 kW at 298 K. Polarization purity also remains < 95% across the full measured range.

Fiber lasers are becoming dominant in the industrial metal cutting market up to 6kW levels due to their increasing performance delivered at aggressive price levels. A key force behind this is the availability of low-cost diode pump modules, consisting of combined single emitter laser chips. To further develop low pump cost an increase the reliable power available from each chip is required, and in principle this can be achieved by reducing facet power density, current density and lowering operational temperature by widening the emitter and increasing cavity length. Here we present the latest development of high-power laser diode chips at 976 nm wavelength designed for operation in 300W+ per pump module applications. For high power/high brightness applications we show a 150 μm contact opening, 5 mm cavity length chip delivering 20W at 20A CW at BPP of <5.5 mm.mrad. This laser has been deployed in several pump module product configurations from 155 W to 320 W with multi-cell module life test demonstrating over 20,000 hours at 90% survivability. For further power scaling we demonstrate design and performance of single emitter lasers with emitting facets of 220 μm to 300 μm. With 300 μm contact opening and 500 μm single emitter chip width 30W operation power is achieved at 32A with far field divergence less than 12°. Life testing is running at 46A with optical power of 41W for 2000 hours.

High power diode lasers are widely used as the pump sources for fiber lasers and solid-state lasers, or the light sources for direct diode laser systems. To meet the emerging needs of fiber lasers, solid state lasers and direct diode laser systems, diode lasers are moving towards higher volume manufacturing, along with higher performance and lower cost. In this paper, we will present our progresses in these areas. We have set up a 6" GaAs wafer production line for high power diode laser chips, which includes MOCVD epitaxy and wafer fabrication. With the 6" wafer production line, we are producing multi-million chips per month for fiber laser pumping. The 6" wafers show great uniformity and reproducibility. Device performance is outstanding, with near 70% efficiency and high CW roll-over power.

Results of an extended series of experimental studies into the beam parameter product (BPP) of high-power diode lasers are summarized, covering efforts to clearly diagnose the limiting factors and develop novel device technology to address these limits. We review diagnostic studies, separating BPP empirically into bias-dependent (thermal) and bias-independent (non-thermal) terms for convenience of analysis. First, we use monolithically grating-stabilized lasers to confirm the presence of a well-defined series of guided modes, rather than filaments. Second, we present results from a series of custom devices and tests (guided by targeted simulations). Third, we show that effects driven by thermal lensing and current spreading dominate the variation in BPP with bias. The residual bias-independent BPP background remains around 30- 50% of the total, and is most likely partly limited by gain-guiding effects. Fourth, the presence of longitudinal temperature variation due to non-uniform optical intensity along the resonator further degrades the bias-independent background level. Lateral current blocking technology is shown to reduce current spreading, and improve the bias-dependent BPP. Thermal engineering also improves bias-dependent BPP, achieved by varying epitaxial layer structure and by targeted changes in bar layout, clarified using measurements in thermography cross-referenced to simulation. In summary, we contend that experimental studies have allowed the effects that limit lateral BPP to be largely clarified, so that research efforts can now focus on developing device technology suitable for reducing BPP without other penalties. The background level to BPP remains an open topic, and further study is needed to better understand and address this.

Solid State and Fiber Lasers performance benefits from utilizing highly efficient high brightness wavelength-stabilized pumps. Full wavelength locking in the wide range of operating current and heatsink temperature significantly simplifies overall construction of the Solid State and Fiber Lasers. Thus, stability of lasing wavelength against current and temperature variation has recently become an additional imperative requirement. We report on high power multimode pumps that operate at 878.6nm and 975nm. We discuss on chips’ and packaged pumps’ performance that features high power conversion efficiency (PCE) (up to 60% ex-fiber) and full wavelength locking (40-45 dB) in the wide range of driving current. Laser diode chip and packaged pump devices are produced by high-volume scalable technology which ensures full wavelength stabilization in the wide range of heatsink temperatures (10°C to 50°C range). We present performance of several 878.6nm pump models rated to operate reliably in 30W-120W power range as well as performance of 975nm pumps designed for high efficiency operation at elevated temperature.

The performance characteristics of two stack modules (emitting near 780 nm) each consisting of 24 wide-aperture (1200 μm) diode laser chips is presented and the results are discussed. The stack modules are constructed using diode lasers from two different epitaxial design iterations. Compared to the first iteration, the second iteration was optimized for higher conversion efficiency and optical in-pulse power (lower losses), without compromising the beam characteristics. The stack modules make use of an established (field-proven) FBH design that utilizes innovative edge-cooling of both sides of the diode stack with large-channel (micro-channel free), water-cooled, thermally-expansion-matched heatsinks. We investigate here their performance up to high duty cycles and results for pulse width up to 10 ms at high duty cycle (50 %) operation is presented. Test of the completed modules show that the iteration 2 (power-optimized) chips deliver about 15 % more optical power without compromising the beam propagation ratio. Specifically, the stack module with first iteration chips delivers approx. 1.4 kW whereas the stack module with the optimized chips delivers approx. 1.6 kW. For the stack module that uses the first chip iteration a fiber coupling to a 1 mm core fiber was demonstrated with approx. 90 % coupling efficiency and loss channels are discussed. Finally, very high duty cycle operation (50 %) is demonstrated for the first time, using an iteration 1 stack module.

Fiber-coupled diode modules have various applications in material processing and fiber laser pumping because of their high efficiency and high reliability. Commercial fiber-coupled diode modules using spatial beam combining and polarization beam combining cannot be employed in high-brightness applications, for example metal cutting, which demands a laser power exceeding 1 kW with a BPP of a few mm*mrad. Dense wavelength beam combining (DWBC) technology showed the possibility of further scaling-up the output power of fiber-coupled diode modules while maintaining the same beam quality that allows for fiber-coupled diode modules to be used in high-brightness applications. The efficiency, reliability, and brightness of fiber-coupled diode modules can be improved by using single emitters instead of laser diode bars as power sources in DWBC. Two types of high-brightness 100 µm/0.22 NA 2 kW fiber-coupled diode modules employing single-emitter-based DWBC technology, which have a wavelength range from 953 to 991 nm with 50% efficiency and a narrower wavelength range with 48% efficiency respectively, were developed for material processing and Raman fiber amplifier pumping. Furthermore, we combined 15 high-brightness 100 μm/0.22 NA 1.4 kW fiber-coupled diode modules into a 600 μm/0.22 NA fiber, achieving more than 22 kW at the output.

Q-switched Nd-based lasers are used for a variety of medical and manufacturing applications and benefit from a high efficiency and stable diode pump, but limited commercially available solutions exist for single spatial mode direct pumping of Nd-based lasers at 885 nm. To satisfy this need, Freedom Photonics has developed ultra-robust watt-class diffractionlimited 885 nm diode lasers. We have demonstrated single-mode 885 nm diode lasers with an output power of <1.8 W (1 W rated) and 49% electricalto-optical efficiency. We employ facet passivation methods to protect against catastrophic optical mirror damage (COMD), and the optical power density we have demonstrated points to an effective facet passivation strategy. These devices may be used as high efficiency pumps for Nd-doped solid-state lasers.

The output power of a typical single-mode semiconductor laser is limited by its narrow waveguide width required to cut off high-order spatial modes. Conventional techniques rely on engineering the waveguide without introducing higherorder modes. In contrast, this work utilizes the concept of coupled-cavity (CC) structures. A single-mode lasing is achieved by employing a multi-mode and a neighboring single-mode waveguide. The CC approach is based on the resonant coupling of the high-order mode in the wide waveguide to the fundamental mode of a narrower lossy waveguide. First, geometrical dispersion of the CC lasers, such as their width, spacing, and their sensitivity to the resonance, was investigated. After optimizing the design, edge-emitting-lasers were fabricated using high-efficiency GaAs-based structures. Optical mode control and single-mode operation of the design are demonstrated through fundamental optical characterization measurements. The output power curves for the single and CC designs show similar slope efficiencies suggesting the proposed method as a promising approach towards high-power single lateral mode operation of edge-emitting lasers.

The increase of the optical power levels of diode lasers is a continuous and not trivial challenge. Single frequency diode lasers at 808 nm have maximum powers of the order of a few hundred milliwatts and by using a tapered amplifier can reach a power level of about 2 W. An approach to increase this optical power limit and widen the application fields of direct single frequency diode laser sources is the coherent beam combining (CBC) method. This paper presents the results on a CBC setup by using a purpose-built distributed Bragg reflector ridge waveguide laser (DBR-RWL) at 808 nm as a seed laser and two tapered amplifiers (TPA). The phase control between the two beams has been accomplished through the ridge waveguide current of one of the tapered amplifiers. The phase lock process has been automated with the creation of a reverse hill climbing algorithm and the use of a microcontroller ATmega328P. Remarkable CBC efficiencies over 80 % and an optical power of 3.5 W have been achieved. Full characterization of the DBR-RWL and TPA is presented.

In this work, we use a multiphysics model of an external-cavity laser diode to study the influence of misaligned external optical feedback on the COD level of the device. The model solves the drift-diffusion equations for the electrical transport in the vertical-longitudinal plane self-consistently with a wave-optical model (including semiconductor chip and external resonator) and a 3D thermal model of chip and submount. A vertical misalignment of the FAC lens in an external resonator configuration consisting only of the FAC lens and feedback mirror leads to strongly reduced COD levels within the simulation if the feedback radiation hits the metal layers on the p-side of the device. The absorbed feedback radiation is the initial driver for the COD, whereas vertical leakage currents lead to ever increasing temperatures during thermal runaway. Experimental data of pulsed COD tests confirm the simulation results qualitatively. The minimum absorbed optical feedback power leading to COD depends on the operating point of the device. It increases with increasing external reflectivity due to the onset of COD at lower currents and corresponding lower internal optical power densities. For a low external reflectivity the output power is limited by thermal rollover instead of COD. The surface recombination velocity as the parameter quantifying the facet passivation quality has only a minor influence on the COD level in the simulation as for a low surface recombination velocity (high facet quality) the carriers can still recombine nonradiatively in the bulk layers due to the vertical leakage currents.

High-power broad-area InGaAs-AlGaAs strained quantum well (QW) lasers are indispensable components for space satellite communications systems. However, their degradation mode (catastrophic and sudden degradation) due to catastrophic optical damage is a major concern for space applications. Furthermore, these lasers predominantly degrade by a new failure mode due to catastrophic optical bulk damage (COBD). Also, InAs-GaAs quantum dot (QD) lasers have recently received much attention as an alternative to QW lasers especially for space applications, but their degradation mechanism is not well understood. For the present study, we investigated high-power broad-area lasers with two different active regions: 9×× nm strained InGaAs-AlGaAs QW and ~ 1 µm InAs-GaAs QD active regions. Both lasers had a window formed in backside n-metals. We performed accelerated life-tests, failure mode analyses, and physics of failure investigations using destructive and non-destructive techniques. First, we employed electroluminescence (EL) and timeresolved electroluminescence (TR-EL) techniques to study precursor signatures of failures including the formation of a hot spot through self-focusing of filaments and thermal lensing as well as the formation and propagation of dark line defects (DLDs) in degraded lasers during aging. Second, we employed high-resolution TEM techniques to study extended defects. Finally, we report our understanding on degradation processes in high-power broad-area QW and QD lasers.

Individually addressable laser diode arrays (IABs) have been successfully demonstrated first time in the 90’s. The main commercial success area has been the printing industry and more recently digital press. These laser arrays are typically working at 8xx nm and 9xx nm wavelengths1,2 . Individually addressable laser diode arrays operating in visible region has also been reported3,4. There is an increasing interest in different variants of individual addressable arrays not only in the printing industry & digital press, but also in various display applications including head-up displays and AR/VR products. Recently, novel applications have emerged, for example, in quantum computing and life science. Many applications benefit from tailored lasers that for example in printing meet the surging need for personalized printing materials, labels and packaging driven by eCommerce and constantly increasing need to personalized pharmaceutical packaging. In this work, we report the state-of-the-art high-brightness individually addressable diode laser arrays, that are presenting new possibilities for traditional applications, such as printing, and addressing the new requirements of the novel applications. The single-mode IAB design is scalable from a few individually addressable emitters up to 100 emitters and beyond per array with a highly uniform operation and repeatability and can be applied over the visible red spectrum from 630nm to 690nm or over the mid-infrared spectrum from 790nm to 980nm. Novel and traditional applications have set new requirements for the device density and resolution. Our new flexible individually addressable array designs enable dense device pitching, varying from 20µm to 100µm. This capability enables totally new features and benefits for the applications. Power levels up to 60mW per laser emitter enable high brightness solutions. The IABs show excellent uniformity and stable long-term operation. They are perfectly suited and bringing new capabilities, such as higher resolution, for printing and display applications. Additionally, they are enabling totally new capabilities in quantum computing and life science.

High power diode lasers emitting at wavelengths between 1900 nm and 2300 nm open a wide range of defence applications as compact and efficient light sources in the fields of infrared countermeasures (IRCM) or pumping of solidstate lasers emitting in the 2-4μm regime as well as civilian applications in the fields of laser surgery and medical diagnostics. For all these applications multi-watt output power, long lifetimes, a low-cost packaging technology and fiber coupling are requested. Diode lasers fabricated using the (AlGaIn)(AsSb) materials system are naturally predestined for this wavelength range and offer clear advantages in comparison to InP based diode lasers in terms of output power and wall-plug efficiency. Laser structures for different wavelengths between 1900nm and 2300nm designed for <40° fast axis far field (FWHM) were grown on (100)-oriented 3-inch n-type GaSb:Te substrates by solid-source molecular beam epitaxy. Gain-guided broad-area lasers with stripe widths of 100μm, 150μm and 200μm and different resonator lengths have been fabricated using standard optical lithography combined with ICP etching techniques for lateral patterning. The wafers were cleaved either into single emitters with different resonator lengths or as laser arrays. The lasers can be soldered by soft solder as well as hard solder. Depending on the resonator design and the wavelength, these single emitters offer up to 1.7W in cw operation and more than 5.8W in µs-pulsed operation with efficiencies well beyond 25% and with demonstrated long lifetime. For even higher power levels linear arrays of 20 broad area emitters offer up to 20W cw output power or 30W in pulsed mode.

In addition to common parameters like wavelength, output power and brightness, requirements in defense vary from industrial products. Contrary to industrial applications, where key requirements are total cost of ownership and lifetime measured in operating hours, defense applications use size, weight and power (SWaP) as the key performance metrics. In addition, overall system efficiency is a crucial factor in saving space and weight. Reliability is typically measured in years of service with comparatively low overall laser on time and not in laser operating hours. We present new products based on the Coherent FACTOR series of fiber coupled high power diode laser modules, optimized for defense applications. Modules at 793 nm for Thulium fiber laser pumping and modules at 976 nm for Ytterbium fiber laser pumping are presented. Compared to industrial FACTOR series modules, these devices are optimized for highest output power and low weight compared to their industrial counter parts. Modules are designed, qualified and tested to ensure reliable operation in the demanding environmental conditions of defense applications. Modules at 793 nm ranging from 100 W to 500 W of output power are shown. The FACTOR-16 module is rated at 100 W from a 100 µm 0.22 NA fiber. 500 W are achieved from a T-Bar based packaged equipped with a 200 µm 0.2 NA fiber. At 976 nm, the new lightweight FACTOR-16 package with 150 W from a 100 µm 0.22 NA fiber is shown. In addition, power scaling results from FACTOR-22 and FACTOR-44 modules with power levels of 400 W and 600 W respectively are presented.

Copper is widely used in many industries due to its high electrical conductivity, and copper welding is significant technology. High power near-infrared fiber lasers have been used in laser material processing in many fields since they provide high electric-optic conversion efficiency and excellent laser beam quality. However, copper welding with nearinfrared fiber lasers is challenging. Absorption of copper is low for near-infrared radiation, and copper diffuses heat rapidly at welding spots due to its high thermal conductivity. Previously we reported a hybrid laser system with a 150-W blue laser and a 1-kW near-infrared fiber laser for copper welding. Blue laser irradiation generates stable molten pool at welding spots due to high absorption of copper at the wavelength, and it assists near-infrared fiber laser to generate stable and spatter-less welding during the process. In this paper, we present a hybrid laser system with a 1-kW blue laser and a 3-kW near-infrared laser. The blue laser consists of blue laser diode modules with 250-W optical output power from optical fiber with 110-m core diameter. The laser diode modules contain blue laser diode chips in side lead packages, and the optical output power from the package is 13.2 W at 8.5-A rated current. We have also demonstrated laser processing to pure copper with the hybrid laser system. Uniform beads and approximately 2 mm penetration depth has been generated.

For the plethora of applications that require a high-melting die-attach solder, 80Au20Sn is a great choice to ensure good performance and reliability, especially when used in one of its most highly demanded applications: semiconductor laser die-attach. However, difficulty managing thermal heat transfer has prevented the widespread use of semiconductor lasers. When the operational heat of these devices increases, their longevity and potential become limited. One option to improve thermal transfer is the use a thinner 80Au20Sn preform in the bondline, which allows the heat to transfer to the heat sink more quickly and efficiently. The creation of voiding hot spots – due to the lack of solder volume – is a perceived concern when using a thinner preform in the solder joint, which then contradicts the original intention. Voiding percentages were defined for several 80Au20Sn preform thicknesses – ranging from 0.002” to 0.00035” thick – allowing for conclusions to be drawn on the effect of 80Au20Sn preform thickness on thermal transfer in semiconductor laser technologies.

The paper describes the latest advancements in power upscaling of blue diode laser modules that rely on the same platform and assembly lines of the more common 9xx nm fiber coupled modules to obtain compact, high brightness, and high reliability devices. The new member of the family exploits a combination of spatial, polarization, and spectral multiplexing of wavelength stabilized chips to deliver up to about 180W in a 50 µm core - 0.22 numerical aperture fiber, with a beam parameter product lower than 4.5 mm · mrad. The high positioning accuracy enabled by the well tested machines used for the automatic assembly of the commercial off-the-shelf infrared multi-emitters allows using for the first time a single volume Bragg gratings to simultaneously lock an entire row of spatially multiplexed blue chips, easing the device manufacturability.

Many industrially important reflective metals absorb blue light significantly better than they absorb longer wavelengths. That fundamental physical advantage has led to increasing adoption of high-quality, high-speed blue laser welding in emobility, energy storage, and consumer electronics applications, and it was anticipated that the blue laser would bring comparable advantages to additive manufacturing/3d printing. Here we report results from the first integration of the blue industrial laser into a scanner based powder bed fusion system, the EOS M100 additive manufacturing system. The tests were performed with two very different laser systems: the AO-650 (650Watts – 30 mm-mrad) and AI-200 (200Watts – 5 mm-mrad). Test articles were printed with SS316L powder and pure copper powders. The blue laser printed the SS316L parts twice as efficiently as the conventional IR laser. Following minimal process optimization, tensile bars were fabricated and tested resulting in a density of <99% and an ultimate tensile strength of 80,000 psi when printed with the blue laser, even in these preliminary tests. Blue industrial laser printing of copper test blocks achieved <97% full density on as-printed parts. The EOS M100 IR laser could not be tested on the copper because it did not have sufficient power to melt the powder. Here we summarize the integration of these lasers into 3d printing, and present initial test results.

This paper describes the family of blue laser modules developed in Convergent Photonics, relying on a proprietary architecture of spatial and polarization multiplexing and making use of the same platform and assembly lines of similar 9xx nm laser diode multi-emitters. This proprietary technology leads to high emitted power, together with unprecedented - for blue laser sources - low SWaP (Size Weight and Power consumption) and high brightness, suitable for a cost reduction over high volume productions. Present realization is an extremely compact (53 mm × 138 mm × 14.6 mm) laser source, based on a spatial and polarization multiplexing of 20 diodes, with a 114 um core / 125 um cladding multimode fiber output. Prototypes demonstrated power in excess of 100 W at 450 nm, with 95 % of emitted power filling only 0.15 numerical aperture (N.A.).

Since the first blue lasers made from GaN-based semiconductors reached power levels making them suitable for industrial applications a few years ago, users where asking for more power. Quickly, output powers for fiber-coupled diode lasers increased from several hundred watts in early 2018 [1] to 1000 W in 2019 [2] and even 2000 W in 2020 [3]. But lifetime has always been an object of concern since the blue diode-laser moved out of the TO-can to enter the high power world. As part of the research project “FoulLas”, which started in 2019 and is funded by the German Federal Ministry for Economic Affairs and Energy (BMWi), Laserline took on the task of developing a cw fiber-coupled diode-laser exceeding 2 kW blue laser power for fouling removal of vessels and submarine structures. Caused by stronger restrictions on the use of biocide containing coatings for ship hulls, new strategies against marine fouling moved into the focus of development activities. A new approach is to lethally damage the microorganisms on the subsea surfaces by laser irradiation to be washed away by the streaming water. Apart from that, they can no longer contribute to the spread of species. This paper covers concepts and possibilities of power increase beyond 2 kW for fiber-coupled lasers based on blue diodelaser bars. Results of a laser with more than 2 kW output power are presented. In addition, new findings on degradation processes and lifetime tests are reported. To tie in with the application, insights into the maritime application of fouling removal are given.

We present a triple junction high power laser diode at 1550nm based on AlInGaAs/InP material system. The device was developed, fabricated, and tested. The laser stacks three AlInGaAs lasers epitaxially connected by two tunnel junctions and grown on InP substrate. The monolithic laser structure with tunnel junction layers is designed in a way to reduce the stress and improve the heat dissipation. Each tunnel junctions is formed with an n-type InGaAs layer and a p-type InGaAs layer. The active area of each junction comprises AlInGaAs barrier and quantum well layers. The design leads to three times the output power of a single junction laser and reaches 1W/A slope efficiency. We demonstrate over 100W peak optical output power at 100A with a 350m aperture and 10 nsec pulse width. A low operating voltage can be achieved with such triple junction design, thus the wall-plug efficiency is two times better. The monolithic triple junction with overall small source size allows efficient optic or fiber coupling, and is an ideal source for applications such as long range LiDAR. Using this new triple junction 1550nm laser diode we benchmark against 905nm in a single-emitter LiDAR for performance comparison. By considering eye safety standards, distance, target reflectivity, and atmospheric loss, the photon budget of 1550nm triple junction can be 80 times more than 905nm. With such advantage, a LiDAR with the new 1550nm triple junction can outperform 905nm by more than 60 times in SNR and more than 24 times in detection probability at a distance longer than 200m.

High peak power and brightness eye-safe lasers are desired in automotive LIDAR, for example. We address this need by developing tapered ridge waveguide lasers with highly asymmetric InGaAsP/InP epilayer emitting at around 1.5 μm wavelength. The structure allows state-of-the-art peak power of 7.3 W at 50 A current. Preliminary beam quality results indicate that the epi-design enables higher beam brightness than more traditional structures when driven with high amplitude current pulses. Results indicate that further improvements in power and brightness characteristics are possible with more optimized cavity layout and laser driver design.

In this study, a high-power diode laser bar assembly is developed with good heat dissipation in long pulse operation mode. The thermal behavior and stress distribution are investigated in order to characterize the cooling capability and reliability. The optimal thermal resistance reaches 0.81K/W for each bar, based on the custom designed cooling plate, which is 0.6K/W lower than conventional coolers. The maximum thermal stress of laser bar is 39.4MPa under the working condition, which is less than half of the stress for previous conventional diode laser. Reliability of the device is improved as the diode laser works in a low stress status with long pulse width mode. The light power of the diode laser achieves 120W/bar with pulse duration of 30ms in 10Hz, and 200W/bar with 10ms, 10Hz, respectively. The diode laser of lifetime test passed 4.5×10⁷ shots under the condition of 30ms, 10Hz@120A.

Quality control in large volume roll-to-roll manufacturing for printed electronics, photovoltaic cells, battery and display production demand high-resolution inline imaging. Frequently, defects, such as surface inhomogeneities, are hard to identify due to low image contrast using conventional 2D imaging. Photometric stereo, surface reconstruction based on reflectance behavior, can complement 2D observations by acquiring multiple illumination directions at line rates ≥100k lines/s provided by contemporary line-scan cameras. We extended the concept of time delay integration (TDI) in multi-line-scan cameras with time-multiplexed multi-directional illuminations - short multi-TDI. This improves signal-to-noise ratio (SNR) and dynamic range, which has the potential to visualize various production defects, otherwise difficult to identify in 2D. We implemented multi-TDI using diode line-lasers, which represent a power-efficient, bright illumination with a small mechanical form factor suitable for fast intensity modulation. Their beam can be fused to several lines acquired by multi-line-scan cameras. However, coherent illumination comes along with laser speckles, especially at high spatial resolutions. Our approach aggregates light over time during object-motion, thus inherently reducing speckle while simultaneously acquiring multiple illumination directions. This work examines parameters (laser intensity, number of light sources and number of aggregated lines) useful to outperform LED-based illumination in terms of acquisition speed, cost and integration size. Further, we demonstrate the achievable reduction in speckle contrast to quantify achievable speckle reduction. In summary, our proposed multi-TDI speckle reduction approach for laser illumination enables increased image quality in high-resolution inline photometric stereo, facilitating defect identification in roll-to-roll manufacturing processes for optimized production quality and reduced production resources.