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NanoPlus Operator’s Manual Particle Sizing by Dynamic Light Scattering
Mar 2014 E-5
The Time Domain Method
In the Time Domain (TD) method, the number of photon pulses between sampling times is
collected. The calculation of TD is a straightforward application of equation (2).
The TD method is advantageous when the photon counts per sampling time is large; that is, for
large particles with strong scattering levels and slowly decaying correlation functions that require
larger sampling times.
The Time Interval Method
For very small particles which diffuse quickly, sampling times short enough to capture the rapid
fluctuations are needed. But such particles usually scatter weakly and the situation is such that the
photon counts per sampling time become very low. In this case, the Time Domain method is an
inefficient means of data collection. With the Time Interval (TI) method, the number of sampling
times (clock pulses) between two photon pulses is collected and provides more efficient
determinations of the autocorrelation function for low signal levels. In this method, the frequency
distribution of time intervals between photon pulses (the total number of photon pulse pairs that
are

apart, 2

apart, and so on) is determined to obtain the autocorrelation function.
Having both the TI and TD methods allows you to see a wide range of particle sizes and
applicability. The large number of channels is important for analyzing a mixture of small particles
or to fully capture the movement of large particles.