Abstract: A spatio-temporal profilometer performs time-resolved spatial profilometry and includes a substrate, a tapered optical collimator waveguide, a fluid channel, and a light-fluid interaction volume. The tapered optical collimator waveguide receives diverging light, internally reflects it, and collimates it. The fluid channel receives a fluid comprising microparticles and communicates the microparticles into the fluid channel. The light-fluid interaction volume is disposed in the fluid channel and provided by an overlap within the fluid channel of the collimated light from the tapered optical collimator waveguide and the fluid. The spatio-temporal profilometer produces product light from the collimated light in response to the microparticles interacting with the collimated light in the light-fluid interaction volume from which is determined a spatial and temporal profile of microparticles in the fluid channel.