Wavelength Stabilized Fiber-coupled Laser Modules for DPSS and Fiber Laser Pumping

It is well documented that increases in pump module power enables higher power DPSS or CW fiber lasers, but it is important to recognize that increasing the efficiency by which the DPSS or CW fiber laser is pumped drives down both system complexity and cost. Additionally due to the narrow absorption band of the common laser mediums like Ytterbium and Neodymium, it is advantageous to maximize the spectral overlap between the emission of the pump module and the absorption band of the host medium; one way to accomplish this is by the use of Volume Bragg Gratings (VBGs) to both narrow and stabilize (meaning to minimize change with current and/or temperature) the emission of the diode pump module. To this end, we report on the continued progress by nLIGHT to develop and deliver the highest efficiency wavelength-stabilized, diode-laser pumps using single-emitter technology at similar to 885nm for neodymium DPSS pumping, and 969/976 nm for ytterbium laser pumping. The basis for these improvements is the ensuring the epitaxial structure of the laser diode is optimized not only for efficiency and power but is also properly optimized to minimize the amount of spectral shift with current. Due to the proprietary nature of our epitaxial structures, we are unable to provide exact details. However, throughout this paper, we will abstractly discuss the improvements made to our epitaxy, and how those changes directly affect, and improve upon the module level performance with VBGs, and provide COS and module level results for our element (R) packages with VBGs to support these claims, with key examples being: at 969/976 nm a 2x6 module with 140 W into 105 mu m - 0.16 beam NA, and a 969/976 nm 400 W 2x12 into 200 mu m - 0.16 beam NA, along with 888 nm diode module, in a 2x12 layout outputting a maximum of 370 W with 52 % electro-optical efficiency when coupled into 200 mu m - 0.18 beam NA