Sample vibration technique for HTS SQUID microscope

We have developed a scanning HTS SQUID microscope which provides fine images of very weak magnetic field distributions. To achieve a high spatial resolution, the microscope should have high signal to noise (S/N) ratio. We have investigated a sample vibration technique which modulates the magnitude of detected magnetic field of the sample to achieve a higher S/N ratio. The sample stage was vibrated perpendicular to the plane of the SQUID with a frequency of 380 Hz by using a piezo device. The displacement of the stage was about 40 mum. The SQUID output was connected to a lock-in amplifier, and magnetic field signal was obtained using lock-in detection. In order to evaluate performance of the sample vibration technique, we measured magnetic field distributions of laser printed patterns. Observed image showed that improved S/N ratio of the SQUID microscope led to a higher spatial resolution. (C) 2004 Elsevier B.V. All rights reserved.