Dispersion measurements on polytetrafluorethylene in the far infrared

The reflection spectrum of polytetrafluorethylene has been determined in the far infrared over the range 22-143 micro by a Fourier method using observations made on a dispersive two-beam interferogram. The utility of the method, particularly when applied to the anomalous dispersion associated with a resonance absorption, is demonstrated, and values of the real and imaginary parts of the complex refractive index are determined. The relation between these parts of the index for the resonance at 202 cm(-1) (49.5 micro) agrees with the classical expectation of a circular plot in the complex plane.