Step II - Preprocessing and Multilayer Setup

The next window offers many preprocessing options like DC offset removal, time-domain windowin, phase correction and appending zeros. Furthermore, the frequency range for which parameters should be extracted can be determined here.
 
loading time domain data in the teralyzer
 

In our case, we select the full available data range from 0 to 66.65 ps and apply a chebychev window with a slope of 5 ps. The DC offset is removed by averaging over the first 2 ps of the time domain data and subtracting this average from the data set. We select the zero adding function to artificially increase our frequency resolution, which is legitimate as the time signals at the end of the measured pulse have decreased to the noise level. As phase errors may occur at very low frequencies due to non-planar phase fronts and strong diffraction, we select a trusted phase regime from 0.3 to 0.8 THz. From the spectral data, we see that the noise starts at roughly 4 THz, so we chose this value and enter it into the programm. By hitting the "Apply" button, the changes take place.

Now, we enter the multilayer setup by pressing the "Multilayer setup" button in the center panel. The following window opens:

loading time domain data in the teralyzer

Previous to the cuvette data extraction, we characterized the single side walls of the cuvette with the teralyzer. This single layer evaluation is similar to the one performed in our first example, the alpha lactose compound. We saved that data as .mat file. Now, we click the "Get transmission data file" button to select this file.

loading time domain data in the teralyzer

The thickness of the side wall is stored in the .mat file. However, if a different thickness is required due to a changed setup you can manually enter it into the "thickness" edit box. You can create the multilayer system that you measured by adding layers from transmission files (using the "Add layer" button) and by adding an unidentified layer that you would like to characterize (by pressing the "Add investigated layer" button). In our case we enter the cuvette scenario with the unidentified layer in the middle surrounded by the cuvette walls. When you are finished with the multilayer setup, press "Ok".

Back in the preprovessing widow, we chose the sample thickness to be within 1355 µm +-25 µm and the iteration step size to 5 µm. The material parameter extraction frequency range is set to 0.5 THz to 1.6 THz. By hitting the "Analyze Sample" button, an initial evaluation is performed and the position of the Fabry Perot echoes is displayed in the time domain data plot. We see that 3 Fabry Perot echoes lie within our sample range. To procede we hit the ">>" button.

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