Development of Line-narrowed Diode Pump Sources for DPAL systems

Advanced laser diode technology developed using silicon MEMS packaging enables the construction of an efficient and compact line-narrowed diode stack combined with a Volume Brag Grading (VBG) to create a Diode Pumped Alkali Laser (DPAL). A single laser diode bar, with 20pm spectral line-width, has demonstrated more than 30W of CW output power at 780nm pumping a rubidium vapor laser. However, current methods used to assemble laser diode stacks prevent narrowing the spectral line-width below 0.05 nm due to pointing inaccuracy of the individual laser diode bars and thermal stability issues with a large VBG. A new 3D silicon based laser diode technology enables all laser diode bars to be packaged in near perfect alignment to the VBG for narrowing down spectral line-width. In addition, the lower thermal resistance of the silicon laser diode package improves electrical-to-optical efficiency and stabilizes both turn-on time of the DPAL system and wavelength drift. The Silicon Macro-Channel (SMC) cooling technology will also be applied to the VBG element to stabilize wavelength drift and minimize any thermal gradient in order to maintain narrow line-width. The SMC and silicon MEMS packaging implemented in the new laser diode technology and VBG cooling has demonstrated improved laser diode performance and spectral line-width narrowing due to the accurate micron-level assembly of the laser diode bar. This technology will overcome the limitations of current diode approaches and prove the feasibly of a high performance and cost-effective pumping source for DPAL systems. Approved for Public Release 14-MDA-7739 (18 March 14).