The use of composite pulses for improving DEER signal at 94 GHz

Abstract

The sensitivity of pulsed electron paramagnetic resonance (EPR) measurements on broad-line paramagnetic centers is often limited by the available excitation bandwidth. One way to increase excitation bandwidth is through the use of chirp or composite pulses. However, performance can be limited by cavity or detection bandwidth, which in commercial systems is typically 100-200MHz. Here we demonstrate in a 94GHz spectrometer, with >800MHz system bandwidth, an increase in signal and modulation depth in a 4-pulse DEER experiment through use of composite rather than rectangular π pulses. We show that this leads to an increase in sensitivity by a factor of 3, in line with theoretical predictions, although gains are more limited in nitroxide-nitroxide DEER measurements.

A Gadolinium Spin Label with Both a Narrow Central Transition and Short Tether for Use in Double Electron Electron Resonance Distance Measurements

“…Pulsed EPR measurements were carried out either with the high-power (150 W) Q-band (34 GHz) Bruker Elexsys E580 with an ER 5106QT-2w cylindrical resonator or the home-built high power (1 kW) W-band (94 GHz) "HiPER" spectrometer. 34,35 Echo-detected field sweeps. The echo-detected field sweeps were taken using a Hahn echo π 2 − τ − π − τ − echo pulse sequence.…”

High-sensitivity Gd<sup>3+</sup>–Gd<sup>3+</sup> EPR distance measurements that eliminate artefacts seen at short distances

“…The DEER experiments were carried out using the standard dead-time free four-pulse sequence (Pannier et al, 2000).…”

Integration of a versatile bridge concept in a 34 GHz pulsed/CW EPR spectrometer

“…Shaped microwave pulses, in which the carrier’s phase, frequency or amplitude are arbitrarily modulated, and related instrumental requirements have recently found applications in several well-known EPR spectroscopy experiments. The double electron-electron resonance (DEER) experiment, for example, has benefitted from shaped pulses as demonstrated from increased modulation depths by pumping at larger, more selective bandwidths [11, 12]. The original four-pulse DEER sequence [13] itself has been newly modified for the inclusion of Carr-Purcell pulse trains [6, 14–16], for pre-polarization of high-spin systems [17] and also for the use of an entirely new dipolar pathway in the experiment [18].…”