[¦äp·tə·kəl di‚tek·shən əv mag‚ned·ik ′rez·ən·əns] (spectroscopy) A type of electron paramagnetic resonance (EPR) spectroscopy that takes advantage of the sensitivity of electric dipole transitions, in which paramagnetic states are optically excited and the EPR signal is detected through changes in the optical absorption as the magnetic field is swept through one or more resonances. Abbreviated ODMR.