High frequency electron nuclear double resonance at 239 GHz using a far-infrared laser source

Abstract
We report on the application of 14N electron nuclear double resonance (ENDOR) at 8.5 T and 239 GHz (λ=1.2 mm) in a γ‐irradiated betaine arsenate single crystal. A laser was used as a far‐infrared radiation source in a transmission‐type electron paramagnetic resonance (EPR) setup without a cavity. The four expected nitrogen ENDOR lines were observed, but due to insufficient saturation of the EPR transitions the signal/noise ratio was not larger than 10 and the signals vanished at temperatures above 20 K.