We present a simple design for a Mach-Zehnder interferometric autocorrelator that is aimed at real-time laser pulse diagnostics. The device is based around a symmetric and balanced mechanical oscillator that confers a simple and compact design, while still allowing the measurement of a broad range of pulse durations with high speed and high resolution. The device requires a very low drive level and possesses a very weak mechanical coupling to the environment. The apparatus provides two outputs: one output is proportional to the instantaneous velocity of the interferometer arms, which can be integrated to determine the arm position. This gives the means to calibrate the arm position accurately and thereby account for any nonuniformity of the motion. The second output, from a two-photon photodetector, is used to determine the pulse duration. The present device can measure pulses from the femtosecond through to the picosecond domain. (C) 2005 American Institute of Physics.