Advances in performance and beam quality of 9xx-nm laser diodes tailored for efficient fiber coupling
2012
The impact of new direct-diode and fiber laser systems on industrial manufacturing drives the demand for highbrightness
diode laser pump sources suitable for simple fiber coupling with high efficiency. Within the German funded
project HEMILAS laser mini-bars with different bar geometries and small fill factors were investigated. We present
results on 9xx nm bars with tailored beam parameter products for simplified coupling to fibers with core diameters of
200μm and 300μm with a numerical aperture of 0.22 and compare beam quality parameters, brightness, conversion
efficiency, and thermal performance of different bar designs. Optimized epitaxy structures yield conversion efficiency
maxima above 66%. The slow axis divergence angle of mini-bars with a fill factor of 10% featuring five 100μm wide
and 4mm long emitters based on this epitaxy structure stays below 7°, which corresponds to a beam parameter product of
15mm mrad, up to very high output power of over 45W. This result was achieved for mounting on actively cooled
submounts using hard solder. A similar bar with 5mm cavity length and using soft soldering reached an output power of
60W at the same beam parameter product. At 4mm cavity length, no COMD failures were observed up to currents
exceeding the thermal rollover and the maximum output cw power was 95W.
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