Absorption coefficient of Dupont Teflon FEP in the 20-130 wave-number range Mark A. Ordal, Robert J. Bell, Ralph W. Alexander, Jr., and Raymond E. Paul

When this work was done all the authors were with Uni­versity of Missouri-Rolla, Physics Department, Rolla, Missouri 65401; R. E. Paul is now with Naval Underwater Systems Center, New London, Connecticut 06320. Received 1 June 1985. 0003-6935/85/172746-01$02.00/0. © 1985 Optical Society of America. In certain applications1,2 one needs to know the absorp­

tion coefficient of a dielectric film for radiation propagating through it parallel to the surface of the film. We have made such measurements on Dupont Teflon FEP (fluorinated ethylene propylene).3

The absorption coefficient of Teflon FEP was measured with a RIIC FS-720 Fourier spectrometer in the 20-130-cm-1

region. Samples consisted of 2.5-cm high X 5-cm wide stacks of 25.4-μm Teflon FEP film clamped between thick metal plates. Radiation passed through the stacks parallel to the layers of Teflon FEP film. Three samples were used with lengths of 0.724, 0.916, and 1.782 cm.

Samples were run in permuted order to obtain 18 runs for each of the three pairings of samples. This procedure resulted in 54 data points at each frequency ω. These data points defined the ratio of measured intensities as a function of L, the difference in sample length. The absorption coefficient

Table I. Measured Values of the Absorption Coefficient of Teflon FEP Film

Fig. 1. α(ω) for Teflon. The solid circles with error bars are the data of Table I for Teflon FEP. The solid line is the data of Chantry5 for

Teflon TFE.

2746 APPLIED OPTICS / Vol. 24, No. 17 / 1 September 1985

α(ω) was obtained by fitting the 54 data points at each fre­quency ω to the function

where I1 was the intensity measured through a sample of length L1 cm, I2 is the intensity for a sample of length L2 cm, etc.

Table I lists our values for the absorption coefficient a of Teflon FEP along with the standard deviation obtained from our fit program.4 Figure 1 shows a vs ω, with the error bars representing the standard deviation in our measurements.

The values for the absorption coefficient of Teflon TFE (polytetrafluorethylene) found in the literature5 differ somewhat from our values for the absorption coefficient of Teflon FEP. The solid line in Fig. 1 is the data on Teflon TFE of Chantry.5

This work was supported in part by U.S. Army CRDC grant DAAA-15-85-K-0004 (M. Milham).

References 1. G. Brandli and A. J. Sievers, "Absolute Measurement of the Far-

Infrared Surface Resistance of Pb," Phys Rev. B 5, 3550 (1972). 2. M. von Ortenberg, "Application of the Strip Transmission Line

in Submillimetre Spectroscopy," Infrared Phys. 18, 735 (1978). 3. "Teflon FEP Fluorocarbon Film: Optical Properties," Dupont

Technical Bulletin T-5A, E.I. Du Pont De Nemours & Co. (Inc.), Plastics Products and Resins Department, Fluorocarbons Division, Wilmington, Del. 19898.

4. M. S. Caceci and W. P. Cacheris, "Fitting Curves to Data: The Simplex Algorithm is the Answer," Byte 9, 340 (1984).

5. G. W. Chantry, in Infrared and Millimeter Waves, Vol. 8, K. J. Button, Ed. (Academic, New York, 1983), Chap. 1, p. 44.