PRECISION TERAHERTZ RELATIVE REFLECTOMETRY USING A BLACKBODY SOURCE AND HETERODYNE RECEIVER

Instrumentation for making localized, precise relative reflection meas urements of metals and superconductors in the terahertz frequency rang e is demonstrated. The results can be used to determine the surface re sistivity of these materials which is of particular importance to deve lopment of high-temperature superconductors. Emission from a commerica lly available 1000 degrees C blackbody source was reflected from the m aterials under test and a reference reflector. The reflected signals w ere detected by a Schottky diode heterodyne receiver using a CO2-laser -pumped 214.5 mu m CH2F2 laser as the local oscillator. Double-sideban d bandwidth and receiver noise temperature were 2 GHz and 30 000 K, re spectively. The use of a broadband incoherent diagnostic source minimi zes instrumentation sensitivity to coherent interference effects. The heterodyne receiver provides for sensitive detection with good spatial and frequency resolution. Unoptimized spatial resolution of four time s the diffraction limit was achieved. The potential for relative refle ctivity measurement accuracy of better than 0.1% was demonstrated with 30 min measurement times though systematic errors limited actual meas urement accuracy to about 0.3%.