An optomechanical ultrasound detector includes: a micromirror substrate; a mechanical resonator that receives ultrasound waves, oscillates at resonator frequency f.sub.r, changes cavity length L.sub.c, and produces intra-cavity light; and an optical microcavity between the micromirror substrate and the mechanical resonator with cavity length Lc and cavity resonance frequency f.sub.c formed by the mechanical resonator and the micromirror substrate, such that the micromirror substrate produces cavity output light from the intra-cavity light, wherein the cavity output light optically encodes information about the ultrasound waves received by the mechanical resonator.