An x-band continuous wave saturation recovery electron paramagnetic resonance spectrometer based on an arbitrary waveform generator

Abstract

An X-band (ca. 9-10 GHz) continuous wave saturation recovery spectrometer to measure electron spin-lattice relaxation (T 1) was designed around an arbitrary waveform generator (AWG). The AWG is the microwave source and is used for timing of microwave pulses, generation of control signals, and digitizer triggering. Use of the AWG substantially simplifies the hardware in the bridge relative to that in conventional spectrometers and decreases the footprint. The bridge includes selectable paths with different power amplifications to permit experiments requiring hundreds of milliwatts to fractions of nanowatts for the pump and observe periods. The signal is detected with either a single or quadrature-output double balanced mixer. The system can operate with reflection or crossed-loop resonators. The source noise from the AWG was decreased by addition of a Wenzel high-stability clock. The source is sufficiently stable that automatic frequency control is not needed. The spectrometer was tested with samples that contained 1 × 10 15 to 8 × 10 17 spins and have T 1 between a few hundred ns and hundreds of µs. Excellent signal-to-noise ratio was obtained with acquisition times of 2-90 s. Signal-to-noise performance is similar to that of a conventional saturation recovery spectrometer with a solid-state source. The stability and data reproducibility are better than with conventional sources. With replacement of frequency-sensitive components, this spectrometer can be used to perform saturation recovery measurements at any frequency within the range of the AWG.

Tabletop 700 MHz electron paramagnetic resonance imaging spectrometer

“…32 In other tests at X-band the source noise of an AWG was substantially improved by using a Wenzel 500–29237C ‘golden’ clock to drive the AWG clock. 33 At 700 MHz the addition of the Wenzel clock did not substantially change the source noise observed with the CLR. Two-dimensional spectral-spatial images were collected using the Wenzel clock to achieve the highest possible signal to noise.…”

Long-Term Characterization of Oxidation Processes in Graphitic Carbon Nitride Photocatalyst Materials via Electron Paramagnetic Resonance Spectroscopy

“…Samples were placed in quartz/suprasil 1.6 mm EPR tubes. Saturation recovery measurements were performed using a modified Bruker E500T spectrometer described previously [ 29 ].…”

EPR Everywhere

“…At $300 for the SDR card, the addition of a laptop and supplies to build a coil enables the construction of an EPR spectrometer for ~ $1000. Given the bandwidth of the LimeSDR card (~ 3.5 GHz), it is also potentially a multi-frequency microwave source and detector for an inexpensive price, though practically the source noise may limit operation to low frequencies (< ~ 1 GHz) without the addition of a low noise fixed frequency source [ 77 , 150 ]. This same card was programmed to perform NMR experiments, so that one unit could provide stand-alone DNP hardware using both transmit and receive channels on a single card.…”