Light sources discrete

Laterally inhomogeneous films and patterned structures of microelectronic and optoelectronic applications require small measuring spots. Today s measurements in 50 pm X 50 pm areas are standard for p-spot spectroscopic ellipsometers used in fa-blines. Areas more than ten times smaller can be analyzed by use of discrete-wave-length ellipsometers equipped with laser-light sources. 

Historically, this has been the most constrained parameter, particularly for confocal laser scanning microscopes that require spatially coherent sources and so have been typically limited to a few discrete excitation wavelengths, traditionally obtained from gas lasers. Convenient tunable continuous wave (c.w.) excitation for wide-held microscopy was widely available from filtered lamp sources but, for time domain FLIM, the only ultrafast light sources covering the visible spectrum were c.w. mode-locked dye lasers before the advent of ultrafast Ti Sapphire lasers. 

Xenon arc lamp was chosen over the standard mercury option because Xenon lamps are a more stable light source than mercury. The stability was further maximized by connecting the lamp to a high stabilized power source. Xenon lamps emit excitation light over a broad spectral range (250-1 OOOnm) where as mercury lamps emit discrete principal lines (10). 

These work at predefined wavelengths, they have no moving parts. Because LEDs emit radiation of discrete wavelengths, these instruments do not need any wavelength selector (filter, monochromator etc.). Additional interference filters can be used in order to limit the spectral bandwidth. Advantages are the possibihty of miniaturisation and the high stability of these light sources. 

Step 3 The heart of calculation in ALM is a fuzzy interpolation and curve fitting method which is entitled IDS (Ink Drop Sptread). The IDS searches fuzzily for continuous possible paths on data planes. Assume that each data point on each x-y plane is a light source with a cone or pyramid shape illumination pattern. Therefore, with increase of distance of each data point, the intensity of light source decreases and goes toward zero. Also the illuminated patterns of different data points on each x-y plane are combined and new bright areas are formed. The IDS is exerted to each data point (pixel) on the normalized and discretized x-y planes. The radius of the base of cone or pyramid shape illumination pattern in each x-y plane is related to the positions of data in it. The radius increases until the all of the domain of variable in x-y plane be illuminated Figures 2c and 2d show the created illumination pattern (IL values) after the combination of the illumination patterns of different points in xi-y and X2-y planes, respectively. Here, pyramid shape illumination pattern has been used. 

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