Terahertz Continuous Wave System For Measuring Sub-100-μm -Thick Samples Using Gouy Phase Shift Interferometry

Terahertz continuous wave (CW) system for measuring sub-100-μm-thick samples using Gouy phase shift interferometry is proposed and demonstrated. When the optical path difference (OPD) of the interferometer is zero, destructive interference pattern is produced. In this case, OPD change induced interference signal change is sensitively detected and can be predicted with calculation. By minimizing the difference between the measured and the calculated signal, thickness of a sample can be determined. Thicknesses of sub-100-μm-thick samples are determined with the 5 % accuracy at 625 GHz.