Publications

Individually addressable GaAs-based 9XX-nm Slab-Coupled Optical Waveguide (SCOW) laser and amplifier arrays have been demonstrated in a modular 2-D stacked architecture. Approximately 20 W of coherently-combined power was obtained from two optically stacked amplifier modules.

Cryogenically cooled solid-state lasers promise a revolution in power scalability while maintaining a good beam quality because of significant improvements in efficiency and thermo-optic properties. This is particularly true forYb3+ lasers because of their relatively lowquantum defect and relatively broadband absorption even at cryogenic temperatures. Thermo-optic properties of host materials, including thermal conductivity, thermal expansion, and refractive index at low temperature, are reviewed and data presented for YAG (ceramic and single crystal), GGG, GdVO4, and Y2O3. Spectroscopic properties of Yb:YAG and Yb:LiYF4 (YLF) including absorption cross sections, emission cross sections, and fluorescence lifetimes at cryogenic temperatures are characterized. Recent experiments have pushed the power from an end-pumped cryogenically cooled Yb:YAG laser to 455-W continuous-wave output power from 640-W incident pump power at anM2 of 1.4.

Linear arrays of slab coupled optical waveguide lasers (SCOWL) are ideal sources for beam combining of array elements using techniques such as wavelength beam combining (WBC) and possibly coherent beam combining (CBC). SCOWL array elements have very high brightness, low divergence nearly diffraction limited output beams. Arrays of up to 1.2 cm in width containing as many as 240 elements have been demonstrated. In this presentation, the packaging techniques developed to ensure proper performance of SCOWL arrays will be described, with particular emphasis on the application to beam combining. A commercial high performance micro impingement cooler (MIC) was used to provide thermal management for these arrays. Based on performance data for this cooler, a numerical thermal model was constructed and used to investigate the thermal performance for several packaging schemes. In order to promote uniform optical performance of SCOWL array elements, assembly procedures, which included fluxless soldering using In and AuSn solder alloys, along with the use of thermal expansion matching materials were investigated. These techniques resulted in minimal contraction ([approx] 2 um) and smile ([approx]1 um) of the laser bar during the packaging procedure. Precise control of these parameters is required in order to minimize any detrimental impact on the resultant WBC beam quality. CBC of SCOWL arrays requires phase control of the array elements. Array packaging providing for individual electrical addressability of the array elements has been developed and demonstrated, allowing for phase control by current adjustment.

We report the demonstration of a 1.5 um InGaAsP mode-locked slab-coupled optical waveguide laser (SCOWL) producing 10 ps pulses with energies of 58 pJ and average output powers of 250 mW at a repetition rate of 4.29 GHz. To the best of our knowledge, this is the first passively mode-locked slab-coupled optical waveguide laser. The large mode and low confinement factor of the SCOWL architecture allows the realization of monolithic mode-locked lasers with high output power and pulse energy. The laser output is nearly diffraction limited with M2 values less than 1.2 in both directions.