Frequency modulation effects in EPR and dynamic nuclear polarisation

We elaborate on new effects in electron paramagnetic resonance and dynamic nuclear polarisation, recently discovered in the large polarized target of SMC at CERN, and validate our theoretical concepts by experiment. The phenomena, called by us 'frequency modulation effects', appear in a target cavity in the presence of strong frequency modulated microwave field which excites the electron magnetic dipole transitions. The system exhibits properties similar to an optical interferometer, whose arms can be adjusted by a steady magnetic field. The EPR spectrum of the cavity intensity shows satellites at monochromatic irradiation; these satellites disappear when the microwave frequency is modulated. It is shown that on the edges of the EPR line the absorption of the frequency modulated field is strongly enchanced due to a new mechanism of magnetic losses. This contributes also to the average dynamic deuteron polarization which is increased by a dramatic factor of 1.7 giving the highest ever deuteron polarization exceeding 60% despite the large size of the target. Since the electrodynamics used in the standard formulation of EPR cannot describe these phenomena, we have obtained a precise formula for the field intensity and refined the formula for the absorption of energy, which explains now the experimental EPR data. This opens up new methods for advanced magnetic resonance investigations covering higher frequencies, and for practical applications of optical methods in the millimetre and micrometre wavelength regions.