M-lines spectroscopy (MLS) is an accurate, to within 10-3-10-4, nondestructive technique for measuring optogeometric
parameters (refractive index and thickness) of thin planar step-index waveguide films. Two exciting polarizations can be
used and information about the film anisotropy derived. Usually, MLS uses only one wavelength, which may be
disadvantageous in some cases. We have developed an MLS setup that includes a set of lasers emitting in the range of
405 to 1550 nm to conduct multi-wavelength MLS (MWMLS). MWMLS offers an opportunity to obtain more detailed
optical information, e.g., index profiles and dispersion curves, especially important for sol-gel prepared waveguide thin
films that are relatively porous and whose structure depends on the annealing treatment. The paper presents a detailed
description of the MWMLS setup. By using sol-gel prepared waveguide thin films of Y2O3, HfO2:Eu3+, and TiO2, optical
measurements are exemplified. Proceeding from the measurements, the advantages and limitations of the method are
discussed.
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