DMD-based excitation of transverse laser modes by spatial pump beam shaping

The excitation of transverse laser modes, can be achieved by a cavity-internal amplitude or phase modulation of the laser light. For this purpose typically additional cavity-internal components are applied, which can result in increased losses and a limited resonator internal power [1]. Therefore, gain shaping based methods [2], where the selective mode excitation is achieved via a cavity-external modulation of the pump beam are of great interest, as they require no modification of the laser cavity itself. However, the so far presented gain shaping methods are strongly limited with respect to the number of modes that can be excited, as they apply pump beams of a fixed spatial shape. Here, we present a spatial gain shaping method that applies a digital micromirror device (DMD) as a shaping tool for the pump beam, enabling a high degree of freedom for the gain distributions that can be generated. We demonstrate the advantage of our approach by exciting nearly 1000 different single Hermite-Gaussian (HG) modes in an end-pumped Nd:YVO₄ laser, increasing the number of excitable HG modes by at least a factor of five in comparison to other excitation methods [2, 3].