  In this paper, we present a rapidly-prototyped, costefficient, 3D-printed
quasioptical sample holder for improving the signal-to-noise ratio (SNR) in
modern, resonator-free, highfield electron paramagnetic resonance (EPR)
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 improves SNR in three modes: continuous
wave, pulsed, and rapid-scan. An adjustable sample positioner allows for
optimizing sample position to maximize the 240 GHz magnetic field B1, and a
rooftop mirror allows for small rotations of the cross-polar signal to maximize
the signal and minimize the co-polar background. When optimized, the co-polar
isolation (the ratio of incident to detected co-polar signal) was around 50 dB,
an improvement of over 20 dB. This large isolation is especially beneficial for
maximizing the SNR of rapidscan EPR, but also improves the SNR in pulsed and
cwEPR experiments. Through minimal modification, the sample holder may be
incorporated into a variety of homebuilt, induction-mode hfEPR spectrometers in
order to significantly improve the SNR (approx. 6x), and thereby reduce the
acquisition time (by more than a factor of 30).
