scientific staff

Prof. Dr. Rudolf Schäfer

Christian Becker

technical staff

Stefan Pofahl

Camera-based stroboscopic Kerr microscopy

                                                   Fig. 1: Setup of the camera based stroboscope

For the camera based stroboscope, the Kerr microscope has been extended with a gated image intensifier in front of a CCD camera for stroboscopic imaging (Fig.1). Images are taken at an exposure time of one-hundredth of the magnetic field period. The image exposure time is controlled by a delay generator that is synchronized to a function generator.  A power amplifier generates the desired magnetic field strength. Soft magnetic tape wound cores can be magnetized by the magnetic field of a current-carrying wire. To magnetize ribbons, several coils are available. Simultaneously to the domain observations, the magnetization curve can be measured. The magnetic field strength H is determined by measuring the magnetizing current as a voltage drop across a resistor UR. The induction B is obtained by integrating the induced voltage Uind in a pick-up coil wound around the sample. A feedback system is used to realize a sinusoidal induction voltage.

The displayed setup (Fig. 1) allows a time-resolution of a few ns and is well suitable for the observation of dynamic magnetization processes in soft magnetic ribbons. For stroboscopic observations on thin films, an additional camera-based stroboscope with a time resolution of 250 ps is available, working after a similar principle as the one displayed in Fig. 1.