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.
High power QCW diode laser stacks have been widely used in pumping applications for years. Different package structures of diode laser stacks are applied for pumping the cylindrical rod crystal, such as modular G-Stack, horizontal, vertical and annular arrays. Annular array is preferred in pumping of QCW mode with low duty cycle and short pulse width, due to the advantage of compact structural size, uniform light beam distribution and convenient electric connection. However, the development of annular diode laser array using hard solder is difficult because of the complex bonding process of diode laser on annular heatsink with conventional bonding fixture. Furthermore the stress and thermal behavior is yet to be well studied on the annular diode laser array. In this work, a sophisticated annular diode laser array was developed using hard solder. Optimized structure and thermal design were conducted to achieve uniform light beam distribution and good heat dissipation. Stress release structure of diode laser stack is applied to reduce the risk of chip crack and deviation of spatial spectrum. The annular diode laser array consists of 44 bars in a ring, with the peak output power of each bar over 500W. The maximum output power of each bar reaches 673 W.
High power density as the critical performance of laser diode pumps significantly affects both efficiency and power of a solid state laser. In this report, we designed a new packaging structure that two laser bars bonded on the top and bottom of a MCC, respectively, to achieve higher power density at the same bias current or the same power density at a reduced bias current with respective to one laser bar on a MCC. We achieve 1KW output power at a lower bias current 450A with 2.3W/A slope efficiency from a dual-bar MCC at a duty cycle of 8% (200 μs/400 Hz). Other performances like spectral width broadening, wavelength shift and reliability about 1KW quasi-CW high power laser diodes and 5KW for one vertical stack with five dual-bar micro-channel coolers (MCCs) also are discussed. The reliability of dual-bar MCC packaging structure is also studied by life-time testing, and the output peak power of all devices degraded less than 5% after working for 1353 hours.
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