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SURFACEMETROLOGY


measuring photovoltaic material that is created for light absorption applications.


When measuring surface roughness, it is critical to measure with high lateral resolution (very small step sizes between data points). This will produce the most accurate representation of the surface roughness of the solar material.


Measurement principle


The axial chromatism technique uses a white light source, where light passes through an objective lens with a high degree of chromatic aberration. The refractive index of the objective lens will vary in relation to the wavelength of the light. In effect, each separate wavelength of the incident white light will re-focus at a different distance from the lens (different height). When the measured sample is within the range of possible heights, a single


monochromatic point will be focalized to form the image. Due to the confocal configuration of the system, only the focused wavelength will pass through the spatial filter with high efficiency, thus causing all other wavelengths to be out of focus. The spectral analysis is done using a diffraction grating. This technique deviates each wavelength at a different position, intercepting a line of CCD, which in turn indicates the position of the maximum intensity and allows direct correspondence to the Z height position.


Test discussion


From the surface roughness parameters, it can be observed that, as expected, the glass surface was much smoother than the photovoltaic material surface. As stated previously, glass solar material is as smooth as possible to avoid scattering and


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www.solar-pv-management.com Issue V 2010


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