High-field/high-frequency EPR spectrometer operating in pulsed and continuous-wave mode at 180 GHz

A novel electron paramagnetic resonance (EPR) spectrometer is reported, which has been developed to allow pulsed EPR experiments with high sensitivity and time resolution at a microwave (MW) frequency of 180 GHz (G-band) and wavelengths of approximately 1.6 mm. This corresponds to a magnetic field of about 6.4 T forg ≈ 2 signals. The “hybrid” system architecture combines components of quasioptical as well as conventional MW techniques, making it possible to achieve excellent spectrometer performance with respect to sensitivity and time resolution. Quasioptical MW components have been used to design an MW circulator allowing high sensitivity and low bias operation in the reflection mode. A miniaturized, closed-type cylindrical cavity provides a high sample filling factor and an adequate MW field strength (B₁) enhancement and thus permits reasonably short MW pulses (60 ns for a π/2 pulse) even with a moderate MW input power (15 mW at the cavity). Commercial quartz capillaries (up to 0.5 mm internal diameter) can be used as sample holders for a broad range of applications.