Differential Transmittance Spectra

The transient absorption spectrum of gold nanospheres can be modeled relating the changes in the differential transmittance AT/T to the laser-induced changes in the real and imaginary parts of the dielectric function Asi and As2- T is defined as the ratio of the transmitted to the incident light [A = — log(r)]. 

Figure 3.19. A single-channel detection scheme is unable to differentiate positive and negative frequencies in the rotating frame. This results in a mirror image spectrum being superimposed on the true one if the transmitter is placed in the centre of the spectrum.

One thing that affects the look of derivative features is whether the spectrum being differentiated is plotted in absorbance or transmittance. Figure 3.17 shows an absorbance band and its first derivative. Figure 3.18 shows the same peak plotted in percent transmittance and its first derivative. 

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