A multichannel spectroscopic ellipsometer based on the rotating-compensator principle was developed and applied to measure the time evolution of spectra (1.5–4.0 eV) in the normalized Stokes vector of the light beam reflected from the surface of a growing film. With this instrument, a time resolution of 32 ms for full spectra is possible. Several advantages of the rotating-compensator multichannel ellipsometer design over the simpler rotating-polarizer design are demonstrated here. These include the ability to: (i) determine the sign of thep-swave phase-shift difference &Dgr;, (ii) obtain accurate &Dgr; values for low ellipticity polarization states, and (iii) deduce spectra in the degree of polarization of the light beam reflected from the sample. We have demonstrated the use of the latter spectra to characterize instrument errors such as stray light inside the spectrograph attached to the multichannel detector. The degree of polarization of the reflected beam has also been applied to characterize the time evolution of light scattering during the nucleation of thin film diamond by plasma-enhanced chemical vapor deposition, as well as the time evolution of thickness nonuniformities over the probed area of the growing diamond film. In this article, a detailed description of calibration and data reduction for the new instrument is provided. Future applications of this instrument are expected for real time characterization of film growth and etching on patterned surfaces for microelectronics and on thick transparent substrates for large area displays and photovoltaics. ©1998 American Institute of Physics.