DETERMINATION OF VERDET CONSTANT FROM COMBINED AC AND DC MEASUREMENTS

Two methods of determination of the Verdet constant ( V) for an optically transparent medium are described. These methods use the same apparatus in which the intensity of a monochromatic beam of light is modulated by passing it, successively, through a polarizer, the medium under test (contained within a solenoid which carries ac of frequency f in its windings), and an analyzer. The emergent beam is incident on a detector which produces a steady output voltage U(o) for the special conditions of the optical system set for maximum transmittance and, simultaneously, zero modulation. Methods I and II, which were tested by determining V for water for the wavelength 643.3 nm, are based, respectively, on the ratios u1/U(o) and u2/U(o), where u1 is the rms value of detector output voltage varying at frequency f and U2 is the corresponding output varying at frequency 2 f. The three mean values of V from method I, method II, and a literature survey agree to within 1%. The standard deviation in the values of V by method I (eight determinations) is 0.8% of the mean and by method II (16 determinations) is 1.4%, leading to respective standard errors of the mean (attributable to random errors) of 0.3% and 0.4%. By either method there is, additionally, 0.4% systematic uncertainty in V arising from calibration accuracy of the instrumentation. The total range of Faraday rotation angles studied spanned the range 2X10(-4)-0.24 deg rms.