Jiří Luňáček

Spectral interferometry and reflectometry used for characterization of a multilayer mirror

A white-light spectral interferometric technique is used to retrieve a relative spectral phase and group delay of a multilayer mirror from the spectral interferograms recorded in a dispersive Michelson interferometer. The phase retrieval is based on the use of a windowed Fourier transform in the wavelength domain, and characterization of the multilayer mirror is completed by a three-step measurement of the reflectance spectrum of the mirror in the same interferometer.

Simple method for determination of the thickness of a nonabsorbing thin film using spectral reflectance measurement

A method to determine the thickness of a nonabsorbing thin film on an absorbing substrate is presented. A linear relation between the thin-film thickness and the tangent wavelength of the reflectance spectrum for a specific interference order is revealed, which permits the calculation of the thickness provided that the wavelength-dependent optical parameters of the thin film and the substrate are known. The thickness can be calculated precisely from the reflectance spectrum by using one extreme only, as is demonstrated theoretically for SiO(2) thin film on a Si substrate. The application of this method is demonstrated experimentally for the same thin-film structure but with different Si substrates. The results are compared with those given by the algebraic fitting method, and very good agreement is confirmed.

Dispersion error of a beam splitter cube in white-light spectral interferometry

We revealed that the phase function of a thin-film structure measured by a white-light spectral interferometric technique depends on the path length difference adjusted in a Michelson interferometer. This phenomenon is due to a dispersion error of a beam splitter cube, the effective thickness of which varies with the adjusted path length difference. A technique for eliminating the effect in measurement of the phase function is described. In a first step, the Michelson interferometer with same metallic mirrors is used to measure the effective thickness of the beam splitter cube as a function of the path length difference. In a second step, one of the mirrors of the interferometer is replaced by a thin-film structure and its phase function is measured for the same path length differences as those adjusted in the first step. In both steps, the phase is retrieved from the recorded spectral interferograms by using a windowed Fourier transform applied in the wavelength domain.

Spectral interferometry-based surface plasmon resonance sensing of liquid analyte refractive index change

Theoretical study of a polarimetric setup intended to measure the refractive index change of a liquid analyte is presented. The detection scheme is based on the excitation of surface plasmon resonance in Kretschmann configuration combined with spectral interferometry. The principle of the method is to observe the spectral interference fringes as a result of mixing of two orthogonal linearly polarized waves with an analyzer. The waves are reflected from the base of a coupling prism covered by a thin metal layer used for generation of surface plasmon waves. The polarimetric setup consists of a linear polarizer, a birefringent crystal, a SF10 coupling prism covered by a gold layer and a linear analyzer. The attenuated total reflection at the prism base serves for the excitation of surface plasmon waves. The output optical field is then analyzed by a spectrometer. The phase change of resulting interference spectrum contains the information about the refractive index change of investigated analyte. The shift of phase curve is related to the analyte refractive index change. The model computation is performed in the frame of thin-film optics and the dispersion properties of all included materials are taken into account.

Spectral polarimetry-based measurement of the thickness of a thin film

A simple polarimetry configuration is used for measuring the thickness of a nonabsorbing thin film on an absorbing substrate from the ratio between the spectral reflectances of p- and s-polarized components reflected from the thin-film structure. The spectral reflectance ratio measured at a fixed angle of incidence is fitted to the theoretical one to obtain the thin-film thickness provided that the optical constants of the thin-film structure are known. This procedure is used for measuring different thicknesses of a SiO2 thin film on a Si substrate. Moreover, an approximate linear relation between the thin-film thickness and a wavelength of the maximum of the reflectance ratio for a specific angle of incidence is revealed when the substrate is weakly absorbing. The application of this method is once again demonstrated in determining the thicknesses of the SiO2 thin films. The results of the techniques are compared with those obtained by a technique of spectral reflectometry, and a very good agreement is confirmed.

Spectral ellipsometry based on a channeled spectrum detection to measure the thickness of a thin film

We describe a new concept of spectral ellipsometry based on a channeled spectrum detection in a polarimetric configuration with a birefringent crystal to measure the thickness of a thin film. We use a two-step technique to retrieve the ellipsometric phase of a thin-film structure from the recorded channeled spectra. In the first step, the phase difference between p- and s-polarized waves propagating in the birefringent crystal alone is retrieved. In the second step, the additional phase change that the polarized waves undergo on reflection from the thin-film structure is retrieved. Moreover, in the same polarimetric configuration, the ratio between the reflectances of both polarization states is determined. The new concept of ellipsometry is used in measuring the data for a SiO2 thin film on a Si substrate in a range from 550 to 900 nm and in determining the thin-film thickness provided that the optical parameters of the structure are known. The thicknesses of different samples obtained are compared with those resulting from previous interferometric and reflectometric measurements, and good agreement is confirmed.