We report high-throughput, nondispersive optical multiplexing of laser beams using a scanning galvanometer. We have utilized this technique for multispecies trace-gas detection using multiple quantum cascade laser photoacoustic spectroscopy. We demonstrate switching from one laser to another in less than 1 s, a performance level needed for a comprehensive multispecies sensor, and a high signal-to-noise ratio detection of five gaseous components, ${\mathrm{NH}}_3$ , ${\mathrm{NO}}_2$ , dimethyl methyl phosphonate (DMMP, a simulant for nerve agents), acetone, and ethylene glycol, in a room air gas mixture containing $\sim 3\mathrm{ppb}$ of ${\mathrm{NH}}_3$ , $\sim 8\mathrm{ppb}$ of ${\mathrm{NO}}_2$ , $\sim 20\mathrm{ppb}$ of DMMP, $\sim 30\mathrm{ppb}$ of acetone, and $\sim 40\mathrm{ppb}$ of ethylene glycol.