An interferometric ellipsometer based on a Zeeman laser has been developed. The so-called Zeeman-LePoole ellipsometer (ZLE) is a single wavelength ellipso-reflectometer with a time resolution of 1 mu s. The light source used is a Zeeman (two-frequency) He-Ne laser, operating at the 632.8 nm wavelength with a frequency difference of 1 MHz between the two modes. The optical system of the ZLE is based on an interferometric configuration. Two photo-diodes transform the light carrying the optical information from the sample into electrical signals with a frequency of 1 MHz, which are processed with high speed data-acquisition equipment. This new type of ellipsometer was designed for studying fast processes. As a test of the dynamic capabilities of the ZLE, we measured the optical response of a LCD and a Pockels cell, that were externally stimulated with time-dependent voltages. We also report on in-situ electrochemical experiments monitored with the ZLE. The advantages and disadvantages of the ZLE are discussed. The application of two coupled lasers in an interferometric ellipsometry set-up is a novel approach that allows for a variable time resolution and avoids the problem of frequency mixing. This new set-up also has a high potential for application in optical recording.