Optical imaging thermometry of fast localized heating events

Instantaneous heat deposition into a medium can occur in a number of applications. This can include the heating from a pulse of focused laser source into water or from a focused ultrasound beam into tissue. The time scale can be on the order of milliseconds, and standard thermometry methods such as fine thermocouples are slow or have poor performance. Optical imaging bypasses these limitations.

In the laser ray bundle thermometry method under consideration, a planar array of fine laser rays is geometrically focused upon the heated spot in the optically clear medium to increase spatial resolution. A high-speed imager acquires a sequence of the ray deflection pattern, which is then converted into temperature distribution with excellent spatial and temporal resolution. The conversion process is direct, and does not require any numerical simulations, nor iterative trial and error steps. The only requirement is knowledge of the refractive index and the thermo-optic coefficient. Examples of actual experimental measurements are provided.