Abstract. EPR distance determination in the nanometre region has become an
important tool for studying the structure and interaction of macromolecules.
Arbitrary waveform generators (AWGs), which have recently become
commercially available for EPR spectrometers, have the potential to increase
the sensitivity of the most common technique, double electron–electron
resonance (DEER, also called PELDOR), as they allow the generation of
broadband pulses. There are several families of broadband pulses, which are
different in general pulse shape and the parameters that define them. Here,
we compare the most common broadband pulses. When broadband pulses lead to a
larger modulation depth, they also increase the background decay of the DEER
trace. Depending on the dipolar evolution time, this can significantly
increase the noise level towards the end of the form factor and limit the
potential increase in the modulation-to-noise ratio (MNR). We found
asymmetric hyperbolic secant (HS{1,6}) pulses
to perform best for short DEER traces, leading to a MNR improvement of up to
86 % compared to rectangular pulses. For longer traces we found symmetric
hyperbolic secant (HS{1,1}) pulses to perform
best; however, the increase compared to rectangular pulses goes down to 43 %.
Optimising broadband pulses for DEER depends on concentration and distance range of interest
