Measurement of fluid flow velocity with high spatial and temporal resolution

A time of flight velocimetry system comprising:

• at least one laser, which generates an excitation laser beam configured as a MP-STED-LIFPA excitation beam;
• at least one dichroic mirror configured to receive the excitation laser beam and reflect the excitation laser beam;
• at least one objective, configured to receive the excitation laser beam received from the at least one dichroic mirror, wherein the at least objective focuses the excitation laser beam to increase spatial resolution;
• at least one detection system comprising at least one lens configured to collect the excitation laser beam from the at least one objective;
• at least one fluid pathway configured to contain a dye solution;
• and
• the dye solution contained in and flows along the fluid pathway after exposure to the excitation laser beam, wherein extent of photobleaching in the dye solution is directly proportional to an amount of time of exposure to the excitation laser beam.