We have developed a scanning SQUID microscope which uses a commercially ava
ilable closed-cycle refrigerator to cool a YBa2Cu3O7 bi-crystal de SQUID to
about 77 K. The system allows magnetic imaging of samples which are at roo
m temperature and pressure with spatial resolutions of 50 mu m or better. I
t is more compact and requires less maintenance than a more conventional li
quid-nitrogen cooled system, while delivering equal sensitivity. In order t
o reduce the SQUID-sample separation while maintaining vacuum thermal isola
tion of the SQUID, the sensor is separated from the sample by a 25 mu m thi
ck, optically transparent window. The noise spectrum of our SQUID shows a 1
/f spectrum below 500 Hz with 72 pT/root Hz field sensitivity at 10 Hz, and
a white noise level of 20 pT/root Hz.