Order-of-magnitude SNR improvement for high-field EPR spectrometers via 3D printed quasi-optical sample holders

• Published in: Science advances 2023-09, Vol.9 (38), p.eadi7412-eadi7412
• Main Authors: Sojka, Antonín, Price, Brad D., Sherwin, Mark S.
• Format: Article
• Language: English
• Subjects: Applied Physics; Applied Sciences and Engineering; Physical and Materials Sciences; SciAdv r-articles
• ISSN: 2375-2548; 2375-2548
• DOI: 10.1126/sciadv.adi7412

Here, we present a rapidly prototyped, cost-efficient, and 3D printed quasi-optical sample holder for improving the signal-to-noise ratio (SNR) in modern, resonator-free, and high-field electron paramagnetic resonance (HFEPR) spectrometers. Such spectrometers typically operate in induction mode: The detected EPR (“cross-polar”) signal is polarized orthogonal to the incident (“co-polar”) radiation. The sample holder makes use of an adjustable sample positioner that allows for optimizing the sample position to maximize the 240-gigahertz magnetic field B 1 and a rooftop mirror that allows for small rotations of the microwave polarization to maximize the cross-polar signal and minimize the co-polar background. When optimally tuned, the sample holder was able to improve co-polar isolation by ≳20 decibels, which is proven beneficial for maximizing the SNR in rapid-scan, pulsed, and continuous-wave EPR experiments. In rapid-scan mode, the improved SNR enabled the recording of entire EPR spectra of a narrow-line radical in millisecond time scales, which, in turn, enabled real-time monitoring of a sample’s evolving line shape. Quasioptics at 8.6 T improve 240 GHz EPR SNR by 6, enabling video rate kinetics studies and dead-time free pulsed EPR.