Optimization of material thickness for THz-TDS

Abstract

How thick should a sample be for a transmission-mode THz-TDS measurement? Should a sample be as thick as possible? The answer is 'no'. Although greater thickness allows T-rays to interact more with bulk material, the SNR rolls off with thickness due to signal attenuation. So, should a sample be extremely thin? Again, the answer is 'no'. A sample that is too thin renders itself nearly invisible to T-rays, in such a way that the system can hardly sense the difference between the sample and a free space path. Hence, where is the optimal boundary between 'too thick' and 'too thin'? The analytical expression to find the optimum thickness is revealed in this paper. This optimality results in the minimal uncertainty of measured optical constants. The derived model for optimal thickness is supported by the results from experiments performed with polyvinyl chloride (PVC) and other materials. ©IEEE.