  In interfacial science, there is an increasing need to measure flow velocity
fields at interfaces with ultrahigh spatial and temporal resolution to study
transport phenomena. Although laser-induced fluorescence photobleaching
anemometry (LIFPA) has achieved nanoscopic resolution for flow measurement, it
requires pre-calibration, which is unavailable for unknown flows. We present a
novel, calibration-free travel time after photobleaching velocimeter (TTAPV)
which can both measure fluid flow velocity and satisfy the long-anticipated
need of calibration for LIFPA.
