Abstract: An ellipsometer comprising several photodetectors and an electronic processing unit (4) produces a beam of light modulated at a modulation frequency (Fm) which is reflected by a sample. The photodetectors measure fluxes from parts of the reflected luminous beam, producing measured analog signals in input channels (6), and the electronic processing unit (4) calculates physical parameters of the sample. This electronic processing unit (4) comprises a multiplexing and digitizing unit (7) successively switching to the input channels (6) at a switching frequency (Fe) and a sequencer (19). The sequencer (19) comprises means (24, 35) to allow setting the switching frequency (Fe) as a multiple of the modulation frequency (Fm). The ellipsometer takes optical measurements in real time, in particular for depositing films on substrates.

Abstract: This invention concerns a spectroscopic ellipsometer modulated at a frequency (.omega..sub.m) intended for taking measurements of a sample (3). The spectroscopic ellipsometer is phase modulated, the sample being excited by external means (16) producing periodic, alternating excitation at a frequency (.OMEGA..sub.e). The measurement contains the ellipsometric parameter values (.psi., .DELTA.) of the sample, respectively in the presence of (.psi..sub.1, .DELTA..sub.1) and in the absence of (.psi..sub.2, .DELTA..sub.2) excitation of the sample, as a function of excitation frequency (.OMEGA..sub.e).