Magneto-optical high resolution measurement of small displacements between light beams of different color

Abstract

Abetrod-The magneto-optical Kerr-effect of a 40nm thin iron film is used t o modulate light beams of different color (e.g. red and green) u p t o 100kHz. Yielding a resolution of 35nm a t a total light power of 5 p W , the displacement between t h e two focal points of these beams is measured by t h e time difference of t h e corresponding photo diode signals. T h e relation between t h e time and a locally defined magnetization reversal of the film is achieved by a ferrite C-yoke with gradient pole shoes and t h e rectangular hysteresis of t h e iron film. Besides various optical measurement applications, t h e method is foremost useful for studiing t h e atmospheric refraction, where the dispersion of t h e refractive index leads t o small angles (Blprad) between light beams of different wavelengths.