Recently developed high-power high-efficiency laser bars emitting at 760 nm for aesthetic applications such as hair removal will be introduced. During the development procedure different laser structures utilizing ternary and quaternary active regions, resulting in TE and TM polarized light, embedded in AlxGa1-xAs wave-guiding material were grown by means of MOVPE/MOCVD. The limits of the developed structures processed into laser bars with 1.5 mm cavity length and 50% fill-factor were investigated experimentally. The developed laser bars operate at 90 W (CW operation) and 250 W (pulsed operation) with more than 60% electro-optical efficiency, hence comparable to efficiency and output power of our 808 nm laser bars. Moreover, a reliable CW operation at 80 W for more than 9800 h as well as 40 Mshots at 90 A (long pulse operation at 70°C junction temperature) are already verified. The power-current characteristics as well as results of the lifetime tests at different junction temperatures and current density levels will be presented. The failure mechanisms will be discussed shortly.
Laser diodes emitting at wavelengths around 1060 nm are of great interest as light sources for both medical and industrial applications. For these applications a reliable and efficient operation at high output power is required. In this paper we report on continuous progress in the development of high power laser bars and single emitters emitting at 1060 nm. The development was focused on the epitaxial laser structure design for reliable, long operation at high power levels and various operation modes. As a result we demonstrate 10.000 h life time of laser bars with output power of 200 W in CW hard-pulse mode, as well as 150 Mshots on short cavity laser bars operating at 350 W under pulsed condition. Moreover, initial lifetime tests on single emitters operating at output power of 10 W were performed showing promising reliability.
An overview is presented on the recent progress in the development of high power laser bars at wavelengths around 1060nm. The development is focused on highly efficient and reliable laser performance under pulsed operation for medical applications.
The epitaxial structure and lateral layout of the laser bars were tailored to meet the application requirements. Reliable operation peak powers of 350W and 500W are demonstrated from laser bars with fill-factor FF=75% and resonator lengths 1.5mm and 2.0mm, respectively. Moreover, 60W at current 65A with lifetime <10.000h are presented. The power scaling with fill-factor enables a cost reduction ($/W) up to 35%.
An overview is presented on the recent progress in the development of high power laser bars and single emitters emitting at wavelengths around 1060 nm. The development is focused on high reliability, thermal stability and high efficiency of the laser devices.
Single emitters emitting at a wavelength around 808 nm are highly-desired as pump sources of low power solid state lasers. The latest development of high-power single emitters having emitter apertures of 95 μm, 100 μm and 200 μm based on TM-polarized material are presented. The devices were characterized up to their maximum optical output powers of 15 W from 100 μm wide emitters and 22 W from 200 μm wide emitters. The operation point of these devices is set to 7 W and 10 W, respectively with wall-plug efficiencies of ~55%. Furthermore first results on 5- emitters bars operating at 40 W are presented.
High-energy class laser systems operating at high average power are destined to serve fundamental research and commercial applications. System cost is becoming decisive, and JENOPTIK supports future developments with the new range of 500 W quasi-continuous wave (QCW) laser diode bars. In response to different strategies in implementing high-energy class laser systems, pump wavelengths of 880 nm and 940 nm are available. The higher power output per chip increases array irradiance and reduces the size of the optical system, lowering system cost. Reliability testing of the 880 nm laser diode bar has shown 1 Gshots at 500 W and 300 μs pulse duration, with insignificant degradation. Parallel operation in eight-bar diode stacks permits 4 kW pulse power operation. A new high-density QCW package is under development at JENOPTIK. Cost and reliability being the design criteria, the diode stacks are made by simultaneous soldering of submounts and insulating ceramic. The new QCW stack assembly technology permits an array irradiance of 12.5 kW/cm². We present the current state of the development, including laboratory data from prototypes using the new 500 W laser diode in dense packaging.
Laser bars, laser arrays, and single emitters are highly-desired light sources e.g. for direct material processing, pump
sources for solid state and fiber lasers or medical applications. These sources require high output powers with optimal
efficiency together with good reliability resulting in a long lifetime of the device. Desired wavelengths range from
760 nm in esthetic skin treatment over 915 nm, 940 nm and 976 nm to 1030 nm for direct material processing and
pumping applications.
In this publication we present our latest developments for the different application-defined wavelengths in continuouswave
operation mode. At 760nm laser bars with 30 % filling factor and 1.5 mm resonator length show optical output
powers around 90-100 W using an optimized design. For longer wavelengths between 915 nm and 1030 nm laser bars
with 4 mm resonator length and 50 % filling factor show reliable output powers above 200 W. The efficiency reached
lies above 60% and the slow axis divergence (95% power content) is below 7°. Further developments of bars tailored for
940 nm emission wavelength reach output powers of 350 W. Reliable single emitters for effective fiber coupling having
emitter widths of 90 μm and 195 μm are presented. They emit optical powers of 12 W and 24 W, respectively, at
emission wavelengths of 915 nm, 940 nm and 976 nm. Moreover, reliability tests of 90 μm-single emitters at a power
level of 12W currently show a life time over 3500 h.
High-power quasi-CW laser bars are of great interest as pump sources of solid-state lasers generating high-energy ultrashort
pulses for high energy projects. These applications require a continuous improvement of the laser diodes for
reliable optical output powers and simultaneously high electrical-to-optical power efficiencies. An overview is presented
of recent progress at JENOPTIK in the development of commercial quasi-CW laser bars emitting around 880 nm and
940 nm optimized for peak performance.
At first, performances of 1.5 mm long laser bars with 75% fill-factor are presented. Both, 880 nm and 940 nm laser bars
deliver reliable power of 500 W with wall-plug-efficiencies (WPE) <55% within narrow beam divergence angles of 11°
and 45° in slow-axis and fast-axis directions, respectively. The reliability tests at 500 W powers under application quasi-
CW conditions are ongoing. Moreover, laser bars emitting at 880 nm tested under 100 μs current pulse duration deliver
1 kW output power at 0.9 kA with only a small degradation of the slope efficiency. The applications of 940 nm laser bars
require longer optical pulses and higher repetition rates (1-2 ms, ~10 Hz). In order to achieve output powers at the level
of 1 kW under such long pulse duration, heating of the laser active region has to be minimized. Power-voltage-current
characteristics of 4 mm long cavity bars with 50% fill-factor based on an optimized laser structure for strong carrier
confinement and low resistivity were measured. We report an output power of 0.8 kW at 0.8 A with <60% conversion
efficiency (52% WPE). By increasing the fill-factor of the bars a further improvement of the WPE at high currents is
expected.
A new generation of diode-pumped high-energy-class solid-state laser facilities is in development that generate multijoule pulse energies at around 10 Hz. Currently deployed quasi-continuous-wave (QCW) diode lasers deliver average inpulse pump powers of around 300 W per bar. Increased power-per-bar helps to reduce the system size, complexity and cost per Joule and the increased pump brilliance also enables more efficient operation of the solid state laser itself. It has been shown in recent studies, that optimized QCW diode laser bars centered at 940…980 nm can operate with an average in-pulse power of > 1000 W per bar, triple that of commercial sources. When operated at pulsed condition of 1 ms, 10 Hz, this corresponds to > 1 J/bar. We review here the status of these high-energy-class pump sources, showing how the highest powers are enabled by using long resonators (4…6 mm) for improved cooling and robustly passivated output facets for high reliability. Results are presented for prototype passively-cooled single bar assemblies and monolithic stacked QCW arrays. We confirm that 1 J/bar is sustained for fast-axis collimated stacks with a bar pitch of 1.7 mm, with narrow lateral far field angle (< 12° with 95% power) and spectral width (< 12 nm with 95% power). Such stacks are anticipated to enable Joule/bar pump densities to be used near-term in commercial high power diode laser systems. Finally, we briefly summarize the latest status of research into bars with higher efficiencies, including studies into operation at sub-zero temperatures (-70°C), which also enables higher powers and narrower far field and spectra.
A new high-power semiconductor laser diode module, emitting at 760 nm is introduced. This wavelength permits
optimum treatment results for fair skin individuals, as demonstrated by the use of Alexandrite lasers in dermatology.
Hair removal applications benefit from the industry-standard diode laser design utilizing highly efficient, portable and
light-weight construction. We show the performance of a tap-water-cooled encapsulated laser diode stack with a window
for use in dermatological hand-pieces. The stack design takes into account the pulse lengths required for selectivity in
heating the hair follicle vs. the skin. Super-long pulse durations place the hair removal laser between industry-standard
CW and QCW applications. The new 760 nm laser diode bars are 30% fill factor devices with 1.5 mm long resonator
cavities. At CW operation, these units provide 40 W of optical power at 43 A with wall-plug-efficiency greater than
50%. The maximum output power before COMD is 90 W. Lifetime measurements starting at 40 W show an optical
power loss of 20% after about 3000 h. The hair removal modules are available in 1x3, 1x8 and 2x8 bar configurations.
KEYWORDS: Heatsinks, Semiconductor lasers, Near field optics, Reliability, Resistance, High power lasers, Resonators, Laser development, Absorption, Materials processing
High-power laser bars and single emitters have proven as attractive light sources for many industrial applications such as direct material processing or as pump sources for solid state and fiber-lasers. There is also a great interest in quasi-CW laser bars for high-energy projects. These applications require a continuous improvement of laser diodes for reliable optical output powers, high electrical-to-optical efficiencies, brightness and costs. In this paper JENOPTIK presents an overview of recent research for highly efficient CW and quasi-CW laser devices emitting in a wide wavelength range between 880 nm and 1020 nm. The last research results concern the 9xx single emitters and laser arrays. The 9xx nm 12 W single emitters and 976 nm 55 W laser arrays have efficiencies above 65%. New life time tests for single emitter devices currently exceed 1300 hours of reliable operation at room temperature and over 1500 hours at 45°C. Because of the small far field distribution of the optical power, the high output power and the small near field the 55 W arrays show a brightness of 75 MW x cm-2sr-1 with 95% power content. The technology for new generation 940 nm high fill-factor bars has been currently extended to emission wavelengths of 976 nm and 1020 nm with excellent results: 200 W output power with 63% efficiency using passive cooling. The innovative design of the laser structure enables, moreover, the realization of 500 W 880 nm quasi-CW laser bars with wall-plug efficiencies of 55% and a narrow fast-axis divergence angle of 40° (95% power content).
High-power laser bars and laser arrays are attractive light sources for many industrial applications such as direct material processing or as pump sources for solid state and fiber lasers. There is also a great interest in quasi-CW laser bars for laser ignition and fusion applications. These applications require a continuous improvement of laser diodes for reliable operation at high output powers densities and simultaneously high electrical-to-optical efficiencies. JENOPTIK presents an overview of recent progress in the development of highly efficient CW and quasi-CW laser devices emitting in a wide wavelength range between 880 nm and 1020 nm. Laser arrays emitting in the wavelength range 915 nm to 976 nm exhibit very high efficiencies above 65%. Our technology of new generation 940 nm high fill-factor bars has been currently extended to emission wavelength of 1020 nm with excellent results: 200 W output power with 63% efficiency using passively cooled heatsinks. Additionally, performances of high brightness low fill-factor laser bars with resonator lengths of 4 mm are shown. The innovative design of the laser structure enables, moreover, the realization of 500 W - 880 nm quasi-CW laser bars with wall-plug efficiencies of 55% and a narrow fast-axis divergence angle of 40° (95% power content).
KEYWORDS: Semiconductor lasers, Heatsinks, Resistance, Continuous wave operation, High power lasers, High power diode lasers, Laser development, Laser applications, Waveguides, Active optics
High-power diode lasers are highly efficient sources of optical energy for industrial and defense applications, either directly or as pump sources for solid state or fiber lasers. We review here how advances in diode laser design and device technology have enabled the performance to be continuously improved. An overview is presented of recent progress at JENOPTIK in the development of commercial diode lasers optimized for peak performance, robust high-yield manufacture and long lifetimes. These diode lasers are tailored to simultaneously operate with reduced vertical carrier leakage, low thermal and electrical resistance and low optical losses. In this way, the highest electro-optical efficiencies are sustained to high currents. For example, 940-nm bars with high fill factor are shown to deliver continuous wave (CW) output powers of 280 W with conversion efficiency of < 60%. These bars have a vertical far field angle with 95% power content of just 40°. In addition, 955-nm single emitters with 90μm stripe width deliver 12 W CW output with power conversion efficiency at the operating point of 69%. In parallel, the Ferdinand-Braun-Institut (FBH) is working to enable the next generation of high power diode lasers, by determining the key limitations to performance and by pioneering new technologies to address these limits. An overview of recent studies at the FBH will therefore also be presented. Examples will include structures with further reduced far field angles, higher lateral beam quality and increased peak power and efficiency. Prospects for further performance improvement will be discussed.
High-power single emitters and laser bars are used as light sources in many industrial applications such as materials processing or as pump sources for solid state or fiber lasers. Those applications require laser devices with high optical power, high efficiency and high brightness. To fulfill the requirements the laser design in both directions, vertical and lateral, is continuously improved. We have realized a new generation epitaxial structure, emitting at 940 nm, for a reduced vertical carrier leakage, lower thermal and electrical resistance resulting in high electro-optical efficiency up to high currents. Furthermore the fast axis divergence angle containing 95% power was reduced to 40°. 280 W CW-power with the wall-plug efficiency greater than 60% was reached from the new generation laser design when processed as high fill-factor laser bars. The epitaxial design was adapted to wavelengths 915 nm, 955 nm and 976 nm allowing for fabrication of powerful and high brightness single emitters, laser arrays an laser bars emitting in this wavelength range.
KEYWORDS: Semiconductor lasers, High power lasers, Broad area laser diodes, Laser development, Optical design, Continuous wave operation, Absorption, Waveguides, High power diode lasers
Many pumping and direct diode applications of high power diode lasers require sources that operate within a narrow (<
1nm) temperature stable spectral line. The natural linewidth of high power broad area lasers is too wide (4-5nm) and
varies too quickly with temperature (0.3-0.4nm/K) for such applications. The spectrum can be narrowed by introducing
gratings within the diode laser itself or by the use of an external stabilization via a Volume Bragg Grating, VBG. For
optimal loss-free, low cost wavelength stabilization with a VBG, the narrowest possible far field angles are preferred,
provided power and efficiency are not compromised. Devices that contain internal gratings are potentially the lowest
manufacturing cost option, provided performance remains acceptable, as no external optics are required. Therefore, in
order to address the need for high power with narrow linewidth, three different diode laser device designs have been
developed and are discussed here. For VBG use, two options are compared: (1) devices with high conversion efficiency
(68% peak) and reasonable far field (45° with 95% power content) and (2) devices with extremely small vertical far field
angle (30° with 95% power content) and reasonable conversion efficiency (59% peak). Thirdly, the latest performance
results from broad area devices with internal distributed feedback gratings (DFB-BA Lasers) are also presented,
constructed here using buried overgrowth technology. DFB-BA lasers achieve peak conversion efficiency of 58% and
operate with < 1nm linewidth operation to over 10W continuous wave at 25°C. As a result, the system developer can
now select from a range of high performance diode laser designs depending on the requirements.
High power broad area diode lasers provide the optical energy for all high performance solid state and fiber laser
systems. The maximum achievable power density from such systems is limited at source by the performance of the diode
lasers. A crucial metric is the reliable continuous wave optical output power from a single broad area laser diode,
typically for stripe widths in the 90-100 μm range, which is especially important for users relying on fibered multi-mode
pumps. We present the results of a study investigating the reliable power limits of such 980nm sources. We find that
96μm stripe single emitters lasers at 20°C operate under continuous wave power of 20W per emitter for over 4000 hours
(to date) without failure, with 60μm stripe devices operating reliably at 10W per stripe. Maximum power testing under
10Hz, 200μs QCW drive conditions shows that 96μm stripes reach 30W and 60μm stripes 21W per emitter, significantly above the reliable operation point. Results are also presented on step-stress-studies, where the current is step-wise increased until failure is observed, in order to clarify the remaining reliability limits. Finally, we detail the barriers to increased peak power and discuss how these can be overcome.
KEYWORDS: Semiconductor lasers, Waveguides, Quantum wells, Pulsed laser operation, High power lasers, Reliability, Gallium arsenide, High power diode lasers, Inductance
High power diode lasers are the root source of optical energy in all high performance laser systems. As their performance
advances, diode lasers are increasingly taking the place of other sources. Short pulse, sub-microsecond-class, high power
lasers are important for many applications but historically, diode lasers have not been able to reach high enough peak
pulse powers with adequate reliability, limited by physical effects such as facet failure. By combining robust facet
passivation with thick super large optical cavity waveguides, greatly increased optical output power can be achieved. We
present here the results of a study using commercial high current short pulse sources (>200A, <500ns) to assess the
performance and endurance limits of high power broad area devices. We find that our lasers can be driven with a peak
power density of over 110MWcm-2 without failure for more than 3×107 pulses. For example, on testing to 240A, single
emitter 200μm stripe 1100nm broad area devices reach 124W (46μJ) without failure, and 60μm stripes reach 88W. In
practice, high injection effects such as carrier accumulation in waveguide typically limit peak power. We review these
remaining limitations, and discuss how they can be overcome.
A narrow vertical divergence of about 30° including 95% of power is highly desired in many applications. Principal
designs for narrow divergence diode lasers like simple broad waveguide and more sophisticated resonant waveguide
structures are discussed. Devices with narrow divergence could be realized in the wavelength range 800nm to 1060nm
using very broad waveguide structures. More than 1W in fundamental mode and about 5W nearly diffraction limited
output could be achieved from ridge waveguide laser and from diode lasers with tapered resonator structure,
respectively.
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