A tunable general purpose Q-band resonator for CW and pulse EPR/ENDOR experiments with large sample access and optical excitation

► We built a tunable multipurpose TE011 microwave resonator for pulsed and CW EPR/ENDOR at 34 GHz. ► The resonator contains an optical window and enables ESEEM, ENDOR, and ELDOR experiments at variable temperatures (4-300 K). ► The construction of this resonator is extremely robust. ► The resonator can handle RF powers up to 500 W CW. ► The resonator accepts large sample tubes (3 mm OD) and has excellent concentration sensitivity.