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

Antonín Sojka; Brad D Price; Mark S Sherwin

doi:10.1126/sciadv.adi7412

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

Sci Adv. 2023 Sep 22;9(38):eadi7412. doi: 10.1126/sciadv.adi7412. Epub 2023 Sep 20.

Authors

Antonín Sojka^{1

2}, Brad D Price^{1

2}, Mark S Sherwin^{1

2}

Affiliations

¹ Department of Physics, University of California, Santa Barbara, Santa Barbara, CA, USA.
² Institute for Terahertz Science and Technology, University of California, Santa Barbara, Santa Barbara, CA 93106, USA.

Abstract

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 B₁ 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.