Laser stacks emitting short light pulses are ideally suited for medical and cosmetic applications. Developing enhanced, stable and reliable assembly processes, Jenoptik is reaching for higher energy densities and lower manufacturing costs. In this paper an improved technology for actively cooled QCW stacks is presented. Based on simulations and experimental data, the impacts on the laser stack performance are described and shown as power-current and thermal impedance plots. We show that the bar-to-bar pitch can be reduced from 1.7 mm to 1.2 mm without detrimental thermal effects for pulse durations up to 100 ms.
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.
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).
The industry of laser marking, direct application and solid state laser pumping requires highly reliable and highly
efficient laser diodes. In general, all applications demand improved brightness and temperature stability, and this by
decreasing costs per watt. Instead of increasing the cavity length, we demonstrate in this paper an increase of power
with standard cavity length with a clear focus of cost reduction and high efficiency. Improvements in the semiconductor
material and packaging enable higher power and higher operation temperature. This technology raised the efficiency by
6 % of 808 nm bar with 50 % filling factor and a resonator length of 1.5 mm.
Now, passively cooled diode lasers have reached nearly the performance of actively cooled ones. With this new design
new fiber coupling modules with high brightness and high operation temperature for air cooled systems can be
achieved.
KEYWORDS: Semiconductor lasers, Reliability, Diodes, Resonators, High power lasers, Pulsed laser operation, Continuous wave operation, Electro optics, Near field optics
We report present advantages of high power 9xxnm diode laser bars for pumping of disc laser and especially for
pumping fibre lasers and amplifiers.
The strong demand for reduce system costs needs to have a good compromise in improved diode laser power, conversion
efficiency, reliability and beam quality leading to simplified system designs. Basis of the new generation for the 9xxnm
laser diode bars at JENOPTIK Diode Lab is a low loss wave guide AlGaAs - structure with low vertical far field angle of
27° (FWHM). Recently we demonstrate an output power in excess of 500W in CW operation from a diode laser bar with
50% filling factor and 3.0mm cavity length. This record was possible due to high power conversion efficiency of >68 %,
optimised facet coating technology and an excellent active cooling. New results on conductive cooled high brightness
laser bars of 20% filling factor with special emphasis to the needs of high efficiency fibre coupling will be presented.
Lifetime tests under long pulse conditions have demonstrated a very high reliability for 120 W laser bars with 50 %
filling factor and for 60 W laser bars with 20 % and 30 % filling factor.
The new packaging technology from JENOPTIK Laserdiode GmbH and the new chip technology from JENOPTIK
Diode Lab GmbH increases the output power, the quality and durability of new broad area lasers.
Tests with different pulse widths and duty cycles have been conducted. A maximum linear power density of
213mW/&mgr;m has been found for 808nm and 980nm laser, limited by thermal rollover. The tests were performed for duty
cycles from 0.1% to 5% and pulse widths of 50&mgr;s and 100&mgr;m. Over 32W output power was reached for 150&mgr;m emitter
at a 0.1 % duty cycle and 50&mgr;s pulse length. With the new diode laser technology 10mm bars with a 44% filling factor
were produced. These laser bars, mounted on micro channel coolers, reached a maximum output power of 1000W. To
our knowledge this is the highest power reported up to now for 980nm material with 100&mgr;s pulses and 0.1% duty cycle.
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.
High power diode laser bars and stacks are of great interest in industrial applications due to their high electro-optical efficiency, their small type of construction and maintenance free operation. With highly sophisticated beam shaping optics diode lasers can be used as pumping sources for solid state and fiber lasers and direct for material processing, e.g. welding, soldering and marking metals. We have developed different fiber coupled diode laser systems with output power up to greater than 2 kW cw into a spot 0 1.0 mm (power density greater than 250 kW/cm2) and systems with output power 170 W cw into a spot 0 0.38 mm (power density about 150 kW/cm2). The 2 kW system operates with a 0 1.5 mm fiber (N.A. 0.32) and consists of polarization and wavelength coupled stacks with an overall electro-optical efficiency of 23%. The smaller system operates either with a 0 0.6 mm (N.A. 0.22) or 0 0.4 mm (N.A. 0.33) fiber and consists of a single stack. Polarization and wavelength coupling will be realized in future. The overall electro-optical efficiency is about 27%.
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