Efficient, high-brightness wavelength-beam-combined commercial off-the-shelf diode stacks achieved by use of a wavelength-chirped volume Bragg grating

We report a method of scaling the spatial brightness from commercial off-the-shelf diode laser stacks through wavelength beam combining, by use of a linearly wavelength-chirped volume Bragg grating (VBG). Using a three-bar commercial stack of broad-area lasers and a VBG, we demonstrate $89.5\mathrm{W}\mathrm{cw}$ of beam-combined output with a beam-combining efficiency of 75%. The output beam has a propagation factor $M^2\sim 26$ on the slow axis and $M^2\sim 21$ on the fast axis. This corresponds to a brightness of $\sim 20\mathrm{MW}∕{\mathrm{cm}}^2\mathrm{sr}$. To our knowledge, this is the highest brightness broad-area diode laser system. We achieve 81% coupling efficiency into a $100\mathrm{\mu }\mathrm{m}$, $0.22\mathrm{N.A.}$ fiber.