Characterization of thin polymer films using terahertz time-domain interferometry

An interferometer for broadband single-cycle THz pulses is developed based on the Michelson configuration. Total internal reflection of THz pulses in high-resistivity silicon prisms provides a nearly 180 degrees phase shift o f one arm relative to the other to achieve destructive interference. We sho w that due to automatic compensation for laser fluctuations by the interfer ometer, it is possible to measure the index and absorption of thin-film sam ples with more accuracy than is achievable with standard THz time-domain sp ectroscopy. We demonstrate characterization of the complex index of refract ion of 2 mum thick Mylar (polyester) films. By measuring the signal amplitu de directly in the time domain, the interferometer can be used for rapid me asurements of film thickness with a resolution of better than 1 mum. (C) 20 01 American Institute of Physics.