Calibration of polarization-state generators (PSG's), polarimeters, and Mueller-matrix ellipsometers (MME's) is an important factor in the practical use of these instruments. A new general procedure, the eigenvalue calibration method (ECM), is presented. It can calibrate any complete MME consisting of a PSG and a polarimeter that generate and measure, respectively, all the states of polarization of light. In the ECM, the PSG and the polarimeter are described by two 4 x 4 matrices W and A, and their 32 coefficients are determined from three or four measurements performed on reference samples. Those references are smooth isotropic samples and perfect linear polarizers. Their optical characteristics are unambiguously determined during the calibration from the eigenvalues of the measured matrices. The ECM does not require accurate alignment of the various optical elements and does not involve any first-order approximation. The ECM also displays an efficient error control capability that can be used to improve the MME behavior. The ECM is illustrated by an experimental calibration, at two wavelengths (458 and 633 nm), of a MME consisting of a coupled phase modulator associated with a prism division-of-amplitude polarimeter.
A broadband division-of-amplitude polarimeter (DOAP) is presented. It can provide the real-time measurement of any state of polarization of light, described by its Stokes vector, in large spectral windows. The light is split first into two beams by a prism and then into four beams by means of any polarizer device that will separate the two linear orthogonal states of polarization. Finally, the Stokes vector is directly deduced from the four measured intensities. To avoid interference effects, the splitting of light into four beams is induced only by refractive-index contrast effects between semi-infinite media that are weakly dependent on the wavelength. An experimental setup working from 0.4 to 2 mum is described. It provides similar sensitivities for all the states of polarization, and its characteristics are constant, on a scale of a few percent, within the spectral window. Calibrations performed at 458 and 633 nm display good agreement between theoretical and experimental values. The accuracy of the prism DOAP, evaluated by measurement of the Stokes vector produced by a rotating Glan polarizer, is better than 1%. An infrared extension of this polarimeter is also presented.
A method for light polarization modulation is described. It allows us to independently modulate, at a high frequency, the four components of the Stokes vector of light using a single phase modulator. It works in a double-pass configuration: the polarization of light is modulated a first time by the phase modulator, and is then modified by a coupling object before being modulated a second time by the same modulator. The coupling object consists of multiple glass plates, oriented at the Brewster angle, acting as a partial polarizer and in a right angle prism acting as a phase shifter and back reflector. Its polarimetric properties are obtained from refractive index contrast effects, which provides optimized and constant properties over a wide spectral range. The phase modulator can be either an electro-optic modulator providing a very high-frequency capability (up to 100 MHz) or a photoelastic modulator providing a wide spectral range capability. It is robust because there is no moving part and simple to implement because of the presence of one modulation. It displays a high level of sensitivity because all the components are high-frequency modulated. Two applications using this modulator in a polarimeter or in a polarization states generator are described. The four modulations, having the same fundamental frequency, are easily demodulated by numerical data processing. Optimized demodulation processing, adapted to the different kind of phase modulator is described. Its adaptation taking into account the bandwidth limitation and the variation of the sampling phase, are finally presented in the case of a photoelastic modulator.
A new polarization modulator is presented. It uses two phase-locked identical electro-optic phase modulators at 50 kHz. Thanks to a coupling object introduced between the two phase modulators, the four Stokes parameters of the light beam are independently modulated on the basis of the first and second complex harmonics of the modulation signal. A Mueller matrix ellipsometer (MME) using this new modulation and a multichannel polarimeter are also described. The data processing and the feedback control of Pockels cells is based on a numerical Fourier transform system. It allows one to measure simultaneously, in one modulation period (20 μs), the 16 coefficients of any Mueller matrix. This MME takes advantage of an easy-to-operate calibration method. The high-frequency modulation of the four parameters of the polarization enables low-light-level measurements (without any chopper and lock-in) and presents spectroscopic capabilities. It provides a promising tool for the study of many subjects of growing interest like, for example, rough surfaces treatment or particle characterization.
In this paper we present a simple method to quantify aggregates of 200nm magnetic particles. This method relies on the optical and magnetic anisotropy of particle aggregates, whereas dispersed particles are optically isotropic. We orientate aggregates by applying short pulses of a magnetic field, and we measure optical density variation directly linked to this reorientation. By computing the scattering efficiency of doublets and singlets, we demonstrate the absolute quantification of a few % of doublets in a well dispersed suspension. More generally, these optical variations are related to the aggregation state of the sample. This method can be easily applied to an agglutination assay, where target proteins induce aggregation of colloidal particles. By observing only aligned clusters, we increase sensitivity and we reduce the background noise as compared to a classical agglutination assay: we obtain a detection limit on the C-reactive protein of less than 3pM for a total assay time of 10min.
The EnMAP hyperspectral Imager (HSI) 1 will allow to acquire Images of the Earth surface in a push broom configuration. 230 wavelength bands between 420nm and 2450nm are simultaneously recorded with a ground resolution of 30m x 30m. The entire satellite is designed and built by OHB-Systems. Characterizing and calibrating a state-of-the-art hyperspectral instrument as the EnMAP HSI requires to establish measurement setups that outperform the test object in all relevant performance aspects to achieve the required measurement accuracies.
Improvements of the Fourier transform phase-modulated ellipsometry (FTPME) technique are described. Measurements performed on the silicon oxide-silicon wafer system are used to illustrate FI'PME performances. In particular, the chemistry of Si(100) and Si(ll1) surfaces after hydrofluoric acid (HF) treatment is investigated. Precisions on the ellipsometric angles T and A of +0.003" and tO.OOS", respectively, are obtained in the SM, stretching mode region. SiH and SiH, vibrations are identified at the Si surface revealing that submonolayer sensitivity can be achieved with FTPME. As a consequence, FTPME appears as a promising technique to perform detailed studies of interface formation and thin-film growth. 0 2995 American Institute of Physics.
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