Noncontact thermoacoustic imaging (TAI) has several desirable characteristics for applications such as explosive detection in high-water-content media. In this letter, we report a detection technique using millimeter-wave interferometry based on sensitive phase detection at W -band. The displacement sensitivity of the proposed W -band vibrometer at 95 GHz is of the order of 1 nm. We also analyze the effect of phase noise on the sensitivity of the vibrometer. Unlike laser-based sensors, a W -band sensor has several advantages; it can easily penetrate surface obscurants such as fur or cloth and it does not require a highly reflective surface of the target to detect the thermoacoustic vibrations.