Precision absolute measurements of strong and highly inhomogeneous magnetic fields.

The low-temperature ([similar or less than]4 K) dependence of the photoconductance in n-type silicon on the conduction electron and bound donor electron spin state serves as the basis of a high-precision, wide-range magnetic field measuring probe, which by virtue of its very small dimensions is well suited for spatial mapping of highly inhomogeneous fields produced by superconducting magnets. The probe may also be adapted to power and frequency measurement of microwave sources operating at approximately mW power levels and frequencies up to approximately 500 GHz.