Measurement of small distances between light spots by domain wall displacements

Abstract

Two laser beams are focused onto a thin permalloy film. By changing the direction of the magnetization of the permalloy film, the Kerr effect is exploited to either rotate the plane of polarization or modulate the amplitude of the reflected light. First, the film is characterized for our application by measuring the velocity of the domain wall displacements by two focused beams with known distances. By measuring the delay between the modulation of the reflected beams, it is possible to accurately determine the beam separation under the condition of reproducible wall movements. Therefore, a moving domain wall acts like a high-speed modulator. The method could be used for many applications, e.g., refraction measurements or rapid quality control of magnetic materials.

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

“…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. motion in a crystalline 1.2pm permalloy film for position resolving light modulation by the transversal Kerr-effect [4]. Acting as a modulating aperture, the velocity of the modulating wall dispacement is reproducibly determined both by amplitude and frequency of the applied field [5].…”