Far-infrared electron-paramagnetic-resonance spectrometer utilizing a quasioptical reflection bridge

We describe a far-infrared electron-paramagnetic-resonance (EPR) spectrometer for broadband (100–300 GHz) use. The spectrometer is operated in the reflection mode and uses broadband quasioptical methods to separate the transmitted from the reflected radiation. We describe and illustrate its operation at 170 GHz (1.8 mm) and compare its performance to that of our transmission mode spectrometer operating at 250 GHz. We also discuss the advantages of the reflection bridge for performing EPR experiments over a broad range of frequencies, and we consider methods of improving the performance of the bridge. This includes a novel design for variable coupling of the reflection-mode Fabry–Pérot resonator.