{
  "abstract": "Understanding the dynamics of highly polarized spins using electron spin resonance (ESR) is increasingly relevant to dynamic nuclear polarization (DNP), polarized targets, and spin-based quantum technologies.In this regime, however, conventional echo-detected ESR is no longer a linear reporter of spin polarization, because the electron spin coherence time T2 itself depends on polarization through suppression of electronelectron flip-flops.Here, we present a dual ESR/nuclear magnetic resonance instrument operating at 7 T and temperatures down to ~1.3 K, where the sample is immersed in a liquid helium bath and the electron spin polarization reaches ~99.8%.The system combines a resonator-free quasi-optical 190-196 GHz spectrometer with a low-heat-load smooth-wall waveguide, and a compact dual NMR coil/ESR waveguide.Resonator-free operation eliminates ring-down and enables free induction decay (FID) detection.Using 40 mM TEMPOL in DNP juice as a model system, we show that frequency-swept ESR spectra from echo and FID detection agree, whereas saturation-recovery measurements of the longitudinal relaxation time T1S diverge strongly.This discrepancy between the two approaches arises due to the nonlinearity of echo-detection at high polarization, which we show to be difficult to correct without the introduction of severe bias.FID detection is thus a more robust and quantitative probe of electron spin dynamics at near-unity polarization.This work paves the way towards the accurate characterization of the dynamics within networks of coupled, highly polarized electron spins relevant to DNP at 1 K and the monitoring of short-lived photo-excited spin systems.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": null,
  "author_total": 5,
  "authors": [
    {
      "name": "Quentin Stern",
      "orcid": "0000-0002-8490-030X"
    },
    {
      "name": "Hoang M. Le",
      "orcid": "0009-0006-4803-2150"
    },
    {
      "name": "Martyna Judd",
      "orcid": "0000-0003-2867-0922"
    },
    {
      "name": "Joshua S. Straub",
      "orcid": "0000-0003-4830-8541"
    },
    {
      "name": "Songi Han",
      "orcid": "0000-0001-6489-6246"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/22rr98xxzh5sw.bib",
  "cited_by": 0,
  "doi": "10.26434/chemrxiv.15010273/v1",
  "fulltext_url": null,
  "id": "22rr98xxzh5sw",
  "issns": [],
  "landing_url": "https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010273/v1",
  "language": null,
  "licence": "CC-BY",
  "licence_label": "CC BY",
  "licence_source": "journal",
  "licence_url": "https://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": null,
  "native_subjects": [
    [
      "openalex",
      "1304|Electron Spin Resonance Studies"
    ]
  ],
  "openalex": "W7221564440",
  "pdf_url": "https://chemrxiv.org/doi/pdf/10.26434/chemrxiv.15010273/v1",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-12",
  "publisher": "American Chemical Society (ACS)",
  "ris": "https://research.draconitic.com/paper/22rr98xxzh5sw.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:17:22Z",
      "native_id": "10.26434/chemrxiv.15010273",
      "source": "chemrxiv",
      "url": "https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010273/v1"
    }
  ],
  "subjects": [
    {
      "field": "biochemistry",
      "origin": "openalex:1304|Electron Spin Resonance Studies",
      "subfield": "biophysics"
    }
  ],
  "title": "Free induction decay-detected high-field electron spin resonance for accurate monitoring highly polarized spin dynamics",
  "title_text": "Free induction decay-detected high-field electron spin resonance for accurate monitoring highly polarized spin dynamics",
  "type": "preprint",
  "updated_at": "2026-10-30T12:17:22Z",
  "url": "https://research.draconitic.com/paper/22rr98xxzh5sw",
  "venue": "ChemRxiv",
  "versions": []
}