We present an optical technique for measuring irregularities on a small local surface ( approximately lambda/100). This new technique uses a narrow laser beam as a local probe. The probe beam interferes with a reference beam. We use a 90 degrees phase delay on the reference beam to increase the sensitivity. We show that if the test surface vibrates laterally, the collected power of the interferogram encodes as amplitude modulations, on a sinusoidal temporal carrier, the local surface irregularities.