Theory of High-Power Spectral Beam Combining Laser Systems

Spectral Beam Combining (SBC) is currently the most successful incoherent laser beam combining approach since it scales the laser brightness properly. The current methods of high-power SBC systems involve using a high-efficiency grating fabricated on top of a high-reflectance multi-layer dielectric (MLD) stack, that is deposited on a suitable substrate. Heat equation solutions and thermoelastic modeling of the grating combining element and the resulting optical performance of the system is a difficult mathematical problem to solve. In the work reported here, we develop an accurate analytical thermal and thermoelastic solutions that shed light on the physics of the SBC problem and highlight the parameters governing its performance. Importantly, we developed a figure of merit formula to help in the design of an efficient SBC system. We also developed a relative figure of merit to compare different grating material choices on system performance.