Experimental verification of the uniaxial stress-optic law in the terahertz frequency regime

The stress-optic law is fundamental to photoelasticity, and has been a prevalent method for measuring stress. However, its effectiveness in the terahertz (THz) regime has not been completely characterized. In this paper, the effects of uniaxial tensile stress on THz transmission through a polytetrafluoroethylene (PTFE) sample are investigated. Specifically, THz time domain spectroscopy (THz-TDS) has been used to measure the phase delay of transmitted THz radiation for different PTFE stress states. Differences in the refractive index of the PTFE are calculated from the measured phase delay. The calculated refractive index grows linearly with the applied stress, which can be considered a verification of the uniaxial stress-optic law in the terahertz frequency regime.