We have made a CCD detector based spectrometer but are facing a problem while taking the absorption spectra.
We are using tungsten lamp as source and stored its spectrum as Yref. Next we placed a transparent acrylic sheet in front of the source and stored the spectrum as Ysamp. We tried to plot both y1=Yref-Ysamp and y2=Ysamp/Yref.
We should obtain a flat horizontal line for absorption spectra of transparent material (since the absorption is almost equal for all wavelengths). But instead, in both y1 and y2 plots we see the trend of the source's spectrum i.e. a curve similar to the source's spectrum curve.