On the Use of a Rotating Polarizer to Measure Optical Constants in the Infrared

The optical constants of a surface from which plane polarized light is reflected may be determined by measuring the principal angle of incidence, ϕ¯, and the principal azimuth ψ¯. If the polarizer be rotated and the reflected light be examined by an analyzer, the intensity is modulated at twice the frequency of rotation. The resultant signal vanishes at ϕ¯,ψ¯, a tuning condition which is unique, is easily found and is not affected by polarizing influences subsequent to the analyzerThe effect of stray polarization is examined and it is shown that the quality of the polarizer affects only the sensitivity. The bearing of the signal to noise ratio on experimental errors is considered since this ratio is limited in the infrared. It is shown that the method is valuable if the extinction coefficient lies in the range 0.4≤κ≤5.5. Outside this range the accuracy rapidly deteriorates. This limitation is shared by all techniques based on measurement of the principal angles. Experimental details and results are presented.