High sensitivity differential Magneto-Optical Imaging with a compact Faradaymodulator

Abstract

We present here the design of a sensitive Compact Faraday-modulator (CFM) based optical magnetometer for imaging the distribution of weak local magnetic fields inside hysteretic magnetic materials. The system developed has a root mean square (rms) noise level of 50 mG.Hz-1/2 at a full frame rate of 1 frame per second with each frame being of size 512 x 512 pixels. By measuring the local magnetic field distribution in different superconducting samples we show that our magnetometer provides an order of magnitude improvement in the signal to noise (S/N) ratio at low fields as compared to ordinary magneto-optical imaging technique. Moreover, it provides the required sensitivity for imaging the weak magnetization response near a superconducting transition where a number of other imaging techniques are practically unviable. An advantage of our CFM design is that it can be scaled in size to fit into situations with tight space constraints.

16 pages, 7 figures

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• Magneto-optical imaging of stepwise magnetic domain disintegration at characteristic temperatures in EuB_6
• Planar pinning induced, lowering of vortex dimensionality and low field melting in a single crystal of Ba0.6K0.4Fe2As2
• Metastable inhomogeneous vortex configuration with non-uniform filling fraction inside a blind hole array patterned in a BSCCO single crystal and concentrating magnetic flux inside it
• Commensurate - Incommensurate vortex phase in a nanopatterned superconductor