26.5–40 GHz Ka-band pulsed EPR spectrometer

The design and performance of a new homebuilt Ka-band pulsed electron paramagnetic resonance (EPR) spectrometer is described. The spectrometer is unique in that it is broadband and allows experiments to be performed at any operational frequency within the range from 26.5 to 40 GHz. The high-power microwave amplifier employed in this spectrometer allowed us to use resonators with low quality factor and to achieve a minimum inversion microwave pulse duration of 11 ns. As a result, this spectrometer can be used for all types of pulsed EPR experiments, including electron spin echo envelope modulation (ESEEM), electron-nuclear double resonance (ENDOR), and electron-electron double resonance (ELDOR) with a difference between the pumping and observation frequencies of up to several hundred megahertz. The timing is controlled by an arbitrary waveform generator with 12 digital outputs and 1 ns time resolution. The spectrometer control/data acquisition software is home-written and allows an easy implementation of any one- or two-dimensional experiment using sweep definition tables.