W-band Fabry-Pérot microwave reasonators for optical detected electron paramagnetic resonance and electron nuclear double resonance of paramagnetic defects in solids

The designs of W-band (∼95 GHz) Fabry-Pérot microwave resonators for optically detected electron paramagnetic resonance (ODEPR) and electron nuclear double resonance (ODENDOR) as well as the ODEPR/ODENDOR spectrometer are described. The Fabry-Pérot resonator was mainly designed for W-band EPR and ENDOR detected via the magnetic circular dichroism of the optical absorption (MCDA), but can also be used with slight modifications for photoluminescence (PL) detection of EPR/ENDOR. The microwave resonators were tested and successfully used for the first high-field MCDA-EPR/ENDOR investigation applied to the investigation of the paramagnetic EL2 defect in semi-insulating GaAs in which higher order effects could be suppressed which prevented the unambiguous analysis of previous K-band experiments. W-band PL-EPR was used to investigate dopants in SiC. The excellent performance of the microwave resonators encourages their use in wider applications of ODEPR and ODENDOR spectroscopy.