A method of examining a sample comprises exposing the sample to a pump
pulse of electromagnetic radiation for a first period of time, exposing
the sample to a stimulant pulse of electromagnetic radiation for a second
period of time which overlaps in time with at least a portion of the
first exposing, to produce a signal pulse of electromagnetic radiation
for a third period of time, and interfering the signal pulse with a
reference pulse of electromagnetic radiation, to determine which portions
of the signal pulse were produced during the exposing of the sample to
the stimulant pulse. The first and third periods of time are each greater
than the second period of time.