Time-resolved flow-velocity and concentration measurements using a traveling thermal lens.

The traveling thermal lens technique is a new all-optical method for probing concentration and velocity patterns in flowing media. A thermal lens created by absorption of a short laser pulse moves with the flow and can be probed by a cw laser beam further downstream as a deflection signal. This technique permits optical measurements of the flow-velocity component perpendicular to the probe laser at high spatial resolution. Its application requires no seeding with particulates, as is needed in most other optical techniques.