Coherent light is divided into a reference and a probing beam at a beam splitter. The reference mirror is mounted onto a piezoelectric transducer driven by a sawtooth generator triggered by a clock. The probing beam is focused by a lens onto the reflecting surface of the sample to be investigated. The ramp duration is somewhat longer than the duration of the deformation event at the sample. During the ramp, the reference mirror moves uniformly over about 2λ/3 giving a sinusoidal intensity variation at the photodetector. Two oscilloscopes of different time bases display the signal. One records the calibration signal, the other records the amplified and expanded section of the sine wave perturbed by the deformation of the sample. The lateral resolution of the interferometer is given by the focal spot diameter of the focusing system. The depth resolution (in beam direction) is determined by the SNR. Depth and time resolution are not independent variables. An investigation of the deformation of pulsed diode lasers (GaAs) is described. Displacements of 1 nm were detected with a time resolution of 40 n sec