The emission characteristics of different LEDs are measured using an optical Fourier transform instrument originally designed for flat panel display characterization. In this approach all the light coming from the device is collected by a dedicated optics and imaged on a CCD sensor. The angular aperture of the instrument extends up to ±88° and all the azimuths for 0 to 360° are collected at the same time. The angular resolution is better than 0.5°. The luminous intensity and the color are measured rapidly and accurately. A large measurement spot size (~2mm) ensures to get all the emission of the device at the same time. It avoids any error and alignment requirements are reduced. In addition to get the luminous intensity distribution very accurately, we have noticed in some cases a dependence of the spectral emission with the angles. This dependence depends on the working conditions of the devices and in particular of the current injected in the LED. Polarization analysis of light emitted by different laser diodes is also presented.
We present a new way to obtain a precise and rapid characterization of the BRDF of a surface using Fourier optics. A special optical setup with Fourier optics allows us to measure the entire scattering pattern of the sample very rapidly with a large angular aperture both in incidence (0 to 80°) and azimuth (0 to 360°) using a CCD camera. The sample is illuminated true the same optics at fixed wavelength or with white light. The illumination angles can be controlled easily using the Fourier optics. The measurement spot size can be adapted from 100µm to 2mm. Anti blooming detector and multi exposures allow measurements with good signal/noise ratios very rapidly. The instrument is described and results on unprinted and printed paper are presented in relation with other more standard characterizations.
We present an innovating method to measure simultaneously the specular and non specular diffraction pattern of sub-micronic periodic structures. The sample is illuminated at fixed wavelength in the visible range (green laser) versus a large angular aperture both in incidence (0 to 80°) and azimuth (0 to 180°). A special optical setup including Fourier optics and a CCD camera allows to measure the entire diffraction pattern. The measurement spot size can be reduced to less than 50μm and its position can be visualized directly with the same optical setup. Polarimetric measurements can be made in less than two seconds. This new system is presented in details and the accuracy of the measurement is tested on homogeneous reference SiO2/Si samples. Then the system is applied to submicron gratings. We show that fixed incidence angle measurements are useful to visualize the specular and non specular order. So, the periodicity of the can be extracted directly. In addition the specular and non specular intensity can be used to extract more accurately the topology of the samples. We show that specular reflection versus azimuth angle can provide similar results than conventional techniques. First experimental results on bi-periodic structures are also shown.
In the present paper, we use a new photo goniometric method capable to measure the entire diffracted pattern of a sub micron grating at fixed wavelength very rapidly. The complete reflectance pattern is obtained versus incidence angle (0-80°) and azimuth angle (0-360°). Regression software based on RCWA simulations has been developed. It is used to adjust automatically the grating profile with an unprecedented rapidity. Regressions have been applied to our polarimetric measurements versus incidence angle θ and versus azimuth angle φ. Results are compared to those provided by spectroscopic ellipsometry (SE) and scanning electron microscopy (SEM). We show that fixed incidence angle specular reflection coefficients versus azimuth angle R(φ) curves are very sensitive to the profiles especially when the CD is reduced mainly because of the occurrence of diffracted orders matching the CD at given azimuths even if the wavelength is much larger than the CD. Mid space illumination measurements in a large angular aperture (0<θ<80° and 0<φ<180°) can be also used to deduce profile information. We show that specular reflection coefficients can be fitted in the entire angular aperture to provide precise structural shapes. Out of specular contribution which is measured simultaneously can also be used in the analysis. We show that it is more sensitive to the grating imperfections than the specular contribution.