Combination of differently structured pump beams for selective mode excitation

Digital micromirror devices (DMD) enable the flexible and selective excitation of transverse resonator modes through spatial gain shaping. With the aim to increase the output power limited by the DMD damage threshold, a pump beam combining approach was investigated. One pump beam was shaped by a DMD, such that a gain distribution adapted to a target mode was realized, whereas a second pump beam provided additional but mode-unspecific gain for a wide range of transverse modes. Although the second pump beam allowed to reduce the power incident on the DMD by a factor of three to five, output power scaling could also be achieved by adapting the mode-like pattern displayed on the DMD instead. Still, modal analysis of the observed multi-mode lasing revealed characteristic properties of pump distributions adapted to Hermite-Gaussian HG_m,0 modes: a center-heavy pump distribution at first distinctly excites the target mode and eventually low-order modes, whereas an eccentric pump distribution reduces the lasing threshold at the expense of distinction to the neighboring modes.