Quantum-enhanced laser-Doppler vibrometer with 2.6 fm/√Hz sensitivity in the broardband demodulated signal

Advanced industrial applications in nanotechnology, MEMS, and semiconductor manufacturing demand laser-Doppler vibrometers with femtometer displacement sensitivity. Conventional heterodyne interferometers provide high linearity and accuracy for industrial measurements but are fundamentally limited by quantum shot noise, whose disruptive influence effectively decreases with increasing measured light power. Although laser safety regulations permit a laser power of up to 10mW for a 1550nm measuring beam, temperature-sensitive structures often require lower light power. Note that a laser power of 10mW focused on 10 µm^2 corresponds to an irradiance of 1GWm^(−2). Highest resolution needs to be achieved at low laser powers of the measurement beam, which presents a challenge for shot-noise-limited measurements. In this work, we present a new resolution record for the demodulated displacement signal of our squeezedlight- enhanced heterodyne laser-Doppler vibrometer. Our system achieved a displacement sensitivity of 2.6 fm/√Hz with only 0.36 mW of measurement power. Our results demonstrate improved performance beyond the shot noise limit without increasing optical power, approaching sub-fm precision in vibration measurements.