A High-Resolution Combined Scanning Laser- and Widefield Polarizing Microscope for Imaging at Temperatures from 4 K to 300 K

摘要

Polarized light microscopy, as a contrast-enhancing technique for opticallyanisotropic materials, is a method well suited for the investigation of a widevariety of effects in solid-state physics, as for example birefringence incrystals or the magneto-optical Kerr effect (MOKE). We present a microscopysetup that combines a widefield microscope and a confocal scanning lasermicroscope with polarization-sensitive detectors. By using a high numericalaperture objective, a spatial resolution of about 240 nm at a wavelength of 405nm is achieved. The sample is mounted on a $^4$He continuous flow cryostatproviding a temperature range between 4 K and 300 K, and electromagnets areused to apply magnetic fields of up to 800 mT with variable in-planeorientation and 20 mT with out-of-plane orientation. Typical applications ofthe polarizing microscope are the imaging of the in-plane and out-of-planemagnetization via the longitudinal and polar MOKE, imaging of magnetic fluxstructures in superconductors covered with a magneto-optical indicator film viaFaraday effect or imaging of structural features, such as twin-walls intetragonal SrTiO$_3$. The scanning laser microscope furthermore offers thepossibility to gain local information on electric transport properties of asample by detecting the beam-induced voltage change across a current-biasedsample. This combination of magnetic, structural and electric imagingcapabilities makes the microscope a viable tool for research in the fields ofoxide electronics, spintronics, magnetism and superconductivity.