Several acousto‐optical characteristics of cinnabar have been measured at 6328 and at 10 600 Å. All observed figures of merit are far higher than those of the most efficient photoelastic materials and the acoustic losses are quite low. For instance, at 6328 Å, the figures of merit M1, M2, and M3 are, respectively, 211, 632, and 513 times greater than the corresponding values in fused silica. The associated acoustic attenuation is only 7.1 dB∕cm at 500 MHz. To demonstrate the potential of cinnabar, an XY deflector has been calculated from measured acoustic and photoelastic constants. 100% of an incident laser beam (6328 Å) could be deflected in 62 500 different positions with an access time of 1 μsec, the acoustic power needed being only 210 mW for each stage!