[en] A wide variety of thin film coatings, deposited by different techniques and with potential applications in various important areas, have been characterised by the Phase Modulated Spectroscopic Ellipsometer, installed recently in the Spectroscopy Division, B.A.R.C. The Phase Modulated technique provides a faster and more accurate data acquisition process than the conventional ellipsometry. The measured Ellipsometry spectra are fitted with theoretical spectra generated assuming an appropriate model regarding the sample. The fittings have been done objectively by minimising the squared difference (χ²) between the measured and calculated values of the ellipsometric parameters and thus accurate information have been derived regarding the thickness and optical constants (viz, the refractive index and extinction coefficient) of the different layers, the surface roughness and the inhomogeneities present in the layers. Measurements have been done on (i) ion-implanted Si-wafers to investigate the formation of SiC layers, (ii) phenyl- silane coating on glass to investigate the surface modifications achieved for better adsorption of rhodamine dye on glass, (iii) GaN films on quartz to investigate the formation of high quality GaN layers by sputtering of GaAs targets, (iv) Diamond-like-coating (DLC) samples prepared by Chemical Vapour Deposition (CVD) to investigate the optical properties which would ultimately lead to an accurate estimation of the ratio of sp³ and sp² bonded carbon atoms in the films and (v) SS 304 under different surface treatments to investigate the growth of different passive films. (author)