How thick should the sample be for a transmission THz-TDS measurement? Shouldthe sample be as thick as possible? The answer is `no'. Although more thicknessallows T-rays to interact more with bulk material, SNR rolls off with thicknessdue to signal attenuation. Then, should the sample be extremely thin? Again,the answer is `no'. A sample that is too thin renders itself nearly invisibleto T-rays, in such a way that the system can hardly sense the differencebetween the sample and a free space path. So, where is the optimal boundarybetween `too thick' and `too thin'? The trade-off is analysed and revealed inthis paper, where our approach is to find the optimal thickness that results inthe minimal variance of measured optical constants.
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