Sol–gel formulations were applied to replace silicone as matrix material for phosphors in pc-LEDs. The content of organic groups was minimized in order to reduce yellowing during the operation of the elements. It was possible to evenly embed YAG:Ce particles in sol–gel binders. Further processing on LED chips resulted in operational light sources; and their performance was compared to standard silicone-based elements. Additional deposition of ALD laminates seals possible defects within the sol–gel matrix as additional protection of the phosphors and the underlying LEDs.

Blue high-power semiconductor lasers have increased greatly in performance over the recent decade enabling new application fields from high brightness projection up to materials processing beyond 1000W output power systems. Base for best system performance is optimal chip design and reliability of the semiconductor device. In this paper chip design optimization of blue high-power semiconductor laser bars will be shown: In contrast to IR laser bars with high lateral emitter fill factors beyond 50%, optimum design with maximum output power and efficiency for GaN laser bars is currently at very low fill factors in the range of 10%. Laser bar designs ranging from 5% fill factor up to 12.5% fill factor were fabricated and investigated. Additionally, two different emitter pitches with 200μm and 400μm were compared. The design with an emitter width of 30μm and a pitch of 400μm resulted in overall best performance. Additionally, lifetime investigations of single emitters in TO-packages will be discussed. The laser diodes were tested up to 5000h duration at different conditions in operating temperatures ranging from 64°C to 96°C and output power up to 3.5W. Dominating degradation mechanism is wear-out which is accelerated by optical output power and additional thermal activation. Extrapolation of the test results in combination with an acceleration model points towards a median lifetime of up to 65.000h for 25°C operation.

We present an analysis of optical and thermal properties of GaN-based blue-emitting high-power diode laser arrays (bars). Parameters such as emission power and temperature are monitored for each single emitter of arrays consisting of 23 emitters. The obtained data are compared with modeling of the electro-optic properties. In contrast to the well-known infrared bars, the thermal properties in the blue-emitting bars control the individual emitter properties to a very high degree and lead to considerable variations in emitter power, in extreme cases up to 50%. Such extreme cases occur, for example, when emitters fail and thus act as a heat source for their surroundings. Nevertheless these bars reach record output powers and are on the way to becoming major sources of photonic power in the blue spectral range.

With the advent of high power blue laser diodes in general and blue laser bars in particular new applications are emerging, utilizing this new technology. Possibly the biggest benefits compared to traditional high power diode laser wavelengths in the infrared spectral range are the improvements seen in copper welding applications, both in weld quality and overall process efficiency. A new generation of high power diode lasers with emission wavelengths near 450 nm is being developed at Coherent DILAS. These modules achieve high brightness levels combined with high power, suitable for materials processing applications. 500 W of optical output power from a 200 μm core fiber and 550 W from a 400 μm core fiber, each with an NA of 0.22, have been demonstrated. Modules are based on existing infrared product platforms already manufactured in high volume, allowing the usage of known-good processes and fully automated manufacturing equipment. At the same time, material costs are kept low, due to the large volume produced at other wavelengths. The main challenge in developing industrial grade laser modules in the blue spectral range is the required life time. While tremendous progress has been made in recent years, the chip material is still more sensitive to environmental factors compared to other high power diode laser bars. The issue is approached by Coherent DILAS in multiple ways with the goal of finding the best possible solution to minimize complexity in module design and operation, while meeting reliability requirements. Latest results, including life-test data under a variety of operating conditions, are presented.

More and more applications are using GaN laser diodes. Visible blue laser devices are well established light sources for converter based business projection of several thousand Lumens. Additional laser-based concepts like near-to-eye projection push device requirements above heretofore limits. In 2017, threshold currents of 10 and 20mA were reported for single mode blue and green laser, respectively. We will present a drastic reduction of laser threshold of green R&D laser samples by more than a factor of 2 down to 10mA. We also will discuss turn-on delay as a limiting factor for modulation speed and spatial resolution of flying spot projection. On the other side, new applications may occur in the near future. We will present research data on blue laser bars as a possible component for industrial applications like for materials processing. LIV characteristics are measured up to power levels of 107W. We observe power conversion efficiencies of 44% at 60W output power for our best samples.

The availability of high-power blue diode-lasers established a new class of laser sources for materials processing recently. With the significantly shorter wavelength compared to conventional laser sources for materials processing new applications are moving into the range of the feasible. There is a strong demand for welding applications with copper due to the change from internal combustion engines to electric drives, which even prompts laser manufacturers to find complex solutions to obtain a laser source in the wavelength range where copper shows higher absorption. With the appearance of high-power diode-laser bars in the blue wavelength range, proven optical concepts can be adapted for the setup of straightforward blue high-power diode-laser sources for materials processing. In context of the research project “BlauLas”, which is funded by the German Federal Ministry of Education and Research (BMBF) within the photonic initiative “EFFILAS” [1], Laserline, in cooperation with OSRAM, intends to realize a blue fiber-coupled cw diode-laser with a power exceeding 1 kW. Building on the results of the earlier presented 700 W fiber coupled laser source we present our new blue fiber coupled laser source with output powers surpassing 1 kW. A brief description of the optical concept and setup as well as an outlook on future strategies to increase output power and radiance of blue laser sources based on diode-laser bars are given. Additionally recently carried out application trials with this new powerful laser source are presented.

Except for their primary emission, diode lasers frequently show emissions at lower photon energies. We present a study in which we record and analyze emission images of (In,Ga,Al) N-based 450 nm emitting diode lasers. Imaging is realized in the spectral ranges of two broad secondary emission bands, which are peaking in the yellow region at 580 nm (VIS) and in the infrared at 875 nm (IR). Both bands have their principal origin in the active region of the device. The VIS emission spectrum looks like the well-known yellow GaN-emission, but comes exclusively from the active region. It is very likely an electroluminescence that involves trapping of non-equilibrium carriers into defects located in the active region, followed by radiative recombination under emission of VIS photons. The IR emission involves also emission from the active region, but significant contributions are also observed in the substrate. The latter contribution could be generated by absorption of spontaneous primary emissions there. Moreover, we modelled emission images by raytracing. This allows the determination of absorption coefficients and refractive indexes of the active region, the unpumped epitaxial layer, and the substrate. The VIS signal from the active region proved to be proportional to the non-equilibrium carrier concentration. This makes it potentially interesting for analytical purposes, e.g., the imaging of carrier concentration profiles.

The catastrophic optical damage (COD) of 450-nm emitting InGaN/GaN diode lasers is investigated with special attention to the kinetics of the process. For this purpose, the COD is triggered artificially by applying individual current pulses. This makes it possible to achieve a sub-µs time resolution for processes monitored by cameras. COD appears as a "hot" process that involves decomposition of quantum well and waveguide materials. We observe the ejection of hot material from the front facets of the laser. This can be seen in two different wavelength ranges, visible/near infrared and mid infrared. The main contributions identified are both thermal radiation and 450-nm laser light scattered by the emitted material. Defect growth during COD is energized by the optical mode. Therefore, the defect pattern resembles its shape. Ultimately, the loss of material leads to the formation of an empty channel along the laser axis. COD in GaAs and GaN-based devices follows similar general scenarios. After ignition of the process, the defect propagation during the process is fed by laser energy. We observe defect propagation velocities of up to ~30 m/s for GaAs-based devices and 110 m/s for GaN-based devices. The damage patterns of GaN and GaAs-based devices are completely different. For GaN-based devices, the front facets show holes. Behind them in the interior, we find an empty channel at the position of the optical mode surrounded by intact material. In contrast, earlier studies on GaAs-based devices that were degraded under almost identical conditions resulted in molten, phase separated and both recrystallized and amorphous materials with well-defined melting fronts.

In this paper we report on further development of fiber coupled high-power diode lasers in the visible spectral range. New visible laser modules presented in this paper include the use of multi single emitter arrays @ 450 nm leading to a 120 W fiber coupled unit with a beam quality of 44 mm x mrad, as well as very compact modules with multi-W output power from 405 nm to 640 nm. However, as these lasers are based on single emitters, power scaling quickly leads to bulky laser units with a lot of optical components to be aligned. We also report on a new approach based on 450 nm diode laser bars, which dramatically reduces size and alignment effort. These activities were performed within the German government-funded project “BlauLas”: a maximum output power of 80 W per bar has been demonstrated @ 450 nm. We show results of a 200 μm NA0.22 fiber coupled 35 W source @ 450 nm, which has been reduced in size by a factor of 25 compared to standard single emitter approach. In addition, we will present a 200 μm NA0.22 fiber coupled laser unit with an output power of 135 W.

A high-power blue laser source was long-awaited for processing materials with low absorption in the near infrared (NIR) spectral range like copper or gold. Due to the huge progress of GaN-based semiconductors, the performance of blue diode-lasers has made a major step forward recently. With the availability of unprecedented power levels at cw-operating blue diode-lasers emitting at 450 nm, it was possible to set up a high-power diode-laser in the blue spectral range to address these conventional laser applications and probably beyond that to establish completely new utilizations for lasers. Within the scope of the research project “BlauLas”, funded within the German photonic initiative “EFFILAS” [8] by the German Federal Ministry of Education and Research (BMBF), Laserline in cooperation with OSRAM aims to realize a cw fiber-coupled diode-laser exceeding 1 kW blue laser power. In this paper the conceptual design and experimental results of a 700 W blue fiber-coupled diode-laser are presented. Initially a close look had to be taken on the mounting techniques of the semiconductors to serve the requirements of the GaN laser diodes. Early samples were used for extensive long term tests to investigate degradation processes. With first functional laser-modules we set up fiber-coupled laser-systems for further testing. Besides adaption of well-known optical concepts a main task within the development of the laser system was the selection and examination of suitable materials and assembling in order to minimize degradation and reach adequate lifetimes. We realized R&D blue lasersystems with lifetimes above 5,000 h, which enable first application experiments on processing of various materials as well as experiments on conversion to white-light.

Industrial material processing like cutting or welding of metals is rather energy efficient using direct diode or diode pumped solid state lasers. However, many applications cannot be addressed by established infrared laser technology due to fundamental material properties of the workpiece: For example materials like copper or gold have too low absorption in the near infrared wavelength range to be processed efficiently by use of existing high power laser systems. The huge interest to enable high power kW systems with more suitable wavelengths in the blue spectral range triggered the German funded research project 'BLAULAS': Therein the feasibility and capability of CW operating high power laser bars based on the GaN material system was investigated by Osram and Laserline. High performance bars were enabled by defeating fundamental challenges like material quality as well as the chip processes, both of which differ significantly from well-known IR laser bars. The research samples were assembled on actively cooled heat sinks with hard solder technology. For the first time an output power of 98W per bar at 60A drive current was achieved. Conversion efficiency as high as 46% at 50W output power was demonstrated.

We present the improvements in power conversion efficiency of high power multi-mode blue laser diodes. The improved device architecture shows a peak wall plug efficiency of ~44.2 % at room temperature. Furthermore, the device delivers an optical output power reaching 3.7 W at the peak efficiency. The signs of thermal roll-over at room temperature start appearing near 5 A of injection current for this particular device design. The device generates an optical output power of more than 7.5 W with overstressed current injection at room temperature. We have also evaluated the high temperature electro-optical performance. The roll-over point is shifted by approximately 1 A when the device is operating at 85°C. The optical output power reaches 4.8 W at thermal roll-over.

Die Erfindung betrifft ein optoelektronisches Bauelement mit einer Schichtstruktur (2) mit einer aktiven Zone (1) zum Erzeugen einer elektromagnetischen Strahlung, wobei die aktive Zone in einer ersten Ebene angeordnet ist, wobei in die Oberflache der Schichtstruktur eine Ausnehmung (6, 25) eingebracht ist, wobei die Ausnehmung an eine Endflache (13) des Bauelementes angrenzt, wobei die Endflache in einer zweiten Ebene angeordnet ist, wobei die zweite Ebene im Wesentlichen senkrecht zur ersten Ebene angeordnet ist, wobei die Ausnehmung eine Bodenflache (9) und eine Seitenflache (7, 8) aufweist, wobei die Seitenflache im Wesentlichen senkrecht zur Endflache angeordnet ist, wobei die Seitenflache in einem Winkel geneigt ungleich 90° zu der ersten Ebene der aktiven Zone angeordnet ist, wobei die Bodenflache im Bereich der ersten Ebene der aktiven Zone angeordnet ist.