The sample is excited via the high energy pump pulse at time zero, and then probed
with a lower energy probe pulse. The arrival time of the probe pulse can be varied
from -40 ps out to a maximum delay of 1450 ps after time zero. Both pulses are ~100
fs long in time. And can be tuned from 270 nm out to 7 μm.
The quantity measured is the change in transmission of the probe pulse upon pumping.
This is defined as the transmission of the probe in the pumped case minus that of
the unpumped case:
The ΔT/T signal is positive for the case of photoinduced bleaching as pictured.