Non-Contact, Non-Destructive Sensor for Wet Layer Thickness of Marine Paints

PSI proposes to develop a real-time standoff paint thickness sensor for marine paints utilizing time-domain terahertz technology. The THz transceiver will operate in a mode analogous to a pulsed radar ranging system. Ultrashort pulses, ~300 femtosecond full width half maximum, of low-power, eye-safe THz radiation, comprising wavelengths between about 30 and 1000 microns, are focused onto a freshly painted surface. The reflected radiation is then collected and temporally resolved with ultrashort time resolution. Paint thickness will be determined by measurement of the temporal difference between reflections from the front and rear surface of the layers of paint with known indices of refraction. A prototype will be constructed that utilizes a femtosecond fiber laser pumped THz source for generation and detection of sub-picosecond THz pulses. This sensor will incorporate design elements aimed at mitigating the effects of sensor-to-target distance variations, and the ability of the sensor to operate under conditions similar to the shipyard environment encountered by the Automated Paint Application, Containment and Treatment System (APACTS) will be explored.