Preliminary Spatial Resolution Characterization of Radar REMPI for Local Measurement of Dielectric Material

In this work, we present the use of Radar REMPI for a twofold purpose: the thickness measurement of uniform Polytetrafluoroethylene (PTFE) Teflon® sheets and the demonstration that Radar REMPI localizes the thickness measurement to an area of the PTFE in the local vicinity of a focused laser spot. PTFE sheets of 1/8" and 1/4" thickness were placed in the path of a 34 GHz homodyne microwave transceiver. A femtosecond laser was focused onto Zinc Selenide placed on the opposite side of the sheet to create short lived conductivity to reflect the microwaves and allow them to make a double pass through the material. The phase of the return signal was monitored by homodyne detection. The intent is to develop time accurate measurements of dielectric properties. The maximum phase measurement error was within 7.5% of the expected value. Secondly, a paper card was translated normal to the microwave path to gradually obstruct the laser spot from the microwaves. The magnitude and phase of the scattering for 100 and 34 GHz microwaves were monitored to determine the point at which objects or material features come into view of the radiation. This point was chosen to be the distance from the laser spot at which appreciable and sharp changes in phase and magnitude occur. This distance was taken as the spatial resolution, and measurements indicate this to be on the scale of the wavelength of microwave radiation used, in this case 3.0 mm and 8.8 mm.