CHEM01200604009 Sreejith Kaniyankandy - Homi Bhabha ...

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The electrical signal is then channeled to CFD and subsequently to TAC, which stops
charging. The TAC output is channeled to a MCP which gives a numerical value for the time
delay through an analog to digital converter. The value associated is added to different
channels corresponding to different delay times and a combined histogram is generated for
each of the channels and the waveform obtained is the decay profile at that wavelength.
Once the signal is detected it needs to be analyzed to delink lamp profile and different
components in decay. If excitation pulse is a delta (δ)-pulse or sharp pulse and detection is
very fast the decay profile is the actual decay of the system. However excitation pulse always
has a finite width and detection system also has a finite response time. Therefore the decay
profile measured is actually a convolution of decay profile of the samples and the light
source. Hence mathematical deconvolution procedure is used to obtain the fits. To perform a
deconvolution procedure we need to obtain the profile of the light source. This is done by
using a scattering solution with no emission and measure Rayleigh scattering for that
excitation wavelength. The profile hence obtained is called an instrument response function.
The width contains information on profile of both detector and lamp profile. Decay profiles
are generated with a fixed angle between excitation and emission polarization, this angle is
called magic angle (54.7˚). This is done to avoid anisotropy effects in decay profiles
generated. The maximum decay counts was taken as 5000 or 10000 for all the samples
measured. This is done to ensure good statistics for fitting. TAC range used in the present
thesis was set from 50-250ns depending on different systems studied in the present thesis.