Optical characterization of thin films by guided waves

Optical properties and microstructure of Ta2O5 biaxial film

This study investigates the optical properties and microstructure of Ta(2)O(5) film deposited with the glancing angle deposition technique. The tilted nanocolumn microstructure, examined with scanning electron microscopy, induces the optical anisotropy of thin film. The optical properties of thin film are characterized with an inverse synthesis method. Based on the Cauchy model, the dispersion equations of optical constants of film are determined from the transmittance spectra measured at normal and oblique incidence over 400-800 nm. The starting values derived with an envelope method quicken the optimization process greatly. The dispersion of the principal indices N(1), N(2), and N(3) and the thickness d of thin film are presented statistically. A good agreement between the measured optical properties and theoretical calculation is obtained, which validates the model established for thin film produced by glancing angle deposition.

Model-independent method for the determination of guiding thin-film optical parameters

A method for the determination of the optical constants of thin films based on the combination of a waveguide measurement procedure with the spectroscopic measurements made from the UV to the IR is presented. As a test material AlN thin film on sapphire substrates is investigated.

Serial bideposition of anisotropic thin films with enhanced linear birefringence

We describe a serial bideposition technique in which a tilted substrate is rotated stepwise by half a turn about a normal axis during the evaporation of a metal oxide from a single electron-beam source. Coatings formed by the new method develop a columnar nanostructure that is perpendicular to the substrate and has greatest width or bunching perpendicular to the common deposition plane. With appropriate choice of deposition parameters, the method produces biaxial films with large birefringence, principal axes aligned parallel and perpendicular to the substrate, and improved uniformity. Measured phase retardances for light incident normally on the films are double the corresponding values for tilted-columnar films.

Optical waveguiding in epitaxial PbTiO(3) thin films

Epitaxial lead titanate (PbTiO(3)) thin films on SrTiO(3) (100) substrate were grown in situ by radio-frequency sputtering for optical waveguiding applications. The crystalline quality of the PbTiO(3) films deposited at 550 degrees C has been investigated through x-ray diffraction analysis. It indicates that thin films are completely c-axis oriented (rocking curve FWHM of 0.2 degrees for the 001 reflection). The transmission spectrum method has been used to measure the dispersion of the refractive index. At 632.8 nm, the PbTiO(3) film with an (001) orientation exhibits a refractive index of 2.61, which represents 98% of the bulk material. The prism-coupling technique has been also employed to determine the optical attenuation in the planar waveguide. In this study, we report a low propagation loss of 2.2 ? 0.2 dB/cm obtained in a PbTiO(3) optical waveguide.

Empirical equations for the principal refractive indices and column angle of obliquely deposited films of tantalum oxide, titanium oxide, and zirconium oxide

Values of the transmittance T(s) and the phaseretardation D were recorded in situ at two angles duringthe growth of thin films of tantalum oxide, titanium oxide, andzirconium oxide for deposition angles theta(nu) in the range40 degrees -70 degrees . Column angles for the same films were determinedex situ from scanning electron microscopy photographs ofdeposition-plane fractures. We show that the experimental columnangles are smaller than the corresponding values predicted by thetangent-rule equation psi = tan(-1)(0.5 tan theta(nu)) and that the experimental values fit a modifiedform of the equation psi = tan(-1)(E(1) tan theta(nu)) where E(1) is less than 0.5. We also show that theprincipal refractive indices are represented well by quadraticfunctions of the deposition angle, for example, n(1)(theta(nu)) = A(0) + A(2) theta(nu)(2).

Anisotropy in thin films: modeling and measurement of guided and nonguided optical properties: application to TiO(2) films

The main purpose of this research is to study the anisotropic behavior of dielectric material in thin-film form. First we present a theory based on a 4 × 4 transfer matrix linking tangential components of the electromagnetic field on one interface to the tangential components of the electromagnetic field on the other interface of an anisotropic thin film. A biaxial model is associated with the columnar structure of the layer. The comparison between measurements of the transmission in normal incidence in cross-polarized light and of guided-mode propagation constants with the calculations allows us to study the biaxial behavior of TiO(2) films. The excellent consistency between measurements and computations demonstrates the validity of the model based on the columnar structure.

Direct observation of waveguided scattered light in multilayer dielectric thin films

When a focused laser beam falls on a multilayer thin-film coating, light is scattered from the volume over which the beam intersects the coating. Some of the light may be scattered into directions that correspond to guided modes of the thin-film structure. We report the observation of scattered light at locations removed from the region of incidence of the light on the coating, resulting from the secondary scatter of the guided scattered light. The shape of the pattern observed by secondary scatter clearly resembles the pattern expected for Rayleigh scatter from a point source. This observation has important implications for the design of scatter-measuring instruments as well as for the theoretical treatment of scatter from multilayer coatings.