We report the latest development of a high power conductively cooled laser module using a novel design approach. The laser bar is directly bonded to two heatsinks in a sandwich configuration without employing submounts as buffers for stress relief caused by CTE mismatch. Simulations were performed to aid the laser module design. The accuracy of the simulations was verified by experimental tests on the laser modules. Production data were collected and used to determine the key performance parameters, statistical distribution, lifetime, and failure mechanism. The laser module thermal rollover could reach 480W at 500A drive current under CW running mode. Furthermore, it could continuously operate under a harsh-hard pulse driving condition at 300A drive current with 300ms pulse width and 1Hz repetition rate.
High power diode laser systems with homogenized intensity distribution have been widely used in laser annealing, cladding and surface heating. New applications such as semiconductor wafer annealing prefer adjustable laser beam size for process optimization, especially during process development stage. Here we report a development of a diode laser system with an adjustable beam size and highly uniform line beam intensity. Beam size in two dimensions perpendicular to its propagation direction can be adjusted independently with higher than 97% intensity uniformity in length dimension. The beam width is adjustable from 60 to 90um (FWHM) and the beam length is adjustable from 11mm to 12mm (FWHM). The output power can reach 1500W at 808nm wavelength with a power density reaches ~170KW/cm2. Detailed misalignment sensitivities of the Micro-Lens Arrays (MLAs), with respect to the lateral position, the rotating angle, and the distance between the two MLAs are studied. Beam back reflection isolation is also considered in the design to accommodate for high reflectivity materials processing. This new laser system can adapt to the requirement of different beam size quickly and precisely by simply adjusting the lens group position, without interrupting production process and increasing manufacturing cost.
KEYWORDS: Semiconductor lasers, Copper, Reliability, Continuous wave operation, Corrosion, High power lasers, Laser development, High power diode lasers, Ceramics, Resistance
An insulation micro-channel cooling (IMCC) has been developed for packaging high power bar-based vertical stack and horizontal array diode lasers, which eliminates many issues caused in its congener packaged by commercial copper formed micro-channel cooler(MCC), such as coefficient of thermal expansion (CTE) mismatch between cooler and diode laser bar, high coolant quality requirement (DI water) and channel corrosion and electro-corrosion induced by DI water if the DI-water quality is not well maintained The IMCC cooler separates water flow route and electrical route, which allows tap-water as coolant without electro-corrosion and therefore prolongs cooler lifetime dramatically and escalated the reliability of these diode lasers. The thickness of ceramic and copper in an IMCC cooler is well designed to minimize the CTE mismatch between laser bar and cooler, consequently, a very low "SMILE" of the laser bar can be achieved for small fast axis divergence after collimation. In additional, gold-tin hard solder bonding technology was also developed to minimize the risk of solder electromigration at high current density and thermal fatigue under hard-pulse operation mode. Testing results of IMCC packaged diode lasers are presented in this report.
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