{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,23]],"date-time":"2026-10-23T16:26:44Z","timestamp":1792772804982,"version":"4.5.0"},"update-to":[{"DOI":"10.1103\/dv32-v967","type":"correction","label":"Correction","source":"publisher","updated":{"date-parts":[[2026,10,23]],"date-time":"2026-10-23T00:00:00Z","timestamp":1792713600000}}],"reference-count":35,"publisher":"American Physical Society (APS)","issue":"11","license":[{"start":{"date-parts":[[2026,9,11]],"date-time":"2026-09-11T00:00:00Z","timestamp":1789084800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":["journals.aps.org"],"crossmark-restriction":true},"short-container-title":["Phys. Rev. Lett."],"accepted":{"date-parts":[[2026,8,17]]},"abstract":"<jats:p>\n                    X-ray free-electron lasers (XFELs) enable the exploration of matter with atomic-scale spatiotemporal resolution. Generating radiation wavelengths below one angstrom is critical for applications such as crystallography and M\u00f6ssbauer studies. Until now, achieving the subangstrom regime has required electron beam energies\n                    <a:math xmlns:a=\"http:\/\/www.w3.org\/1998\/Math\/MathML\" display=\"inline\">\n                      <a:mrow>\n                        <a:mo>\u2265<\/a:mo>\n                        <a:mn>8<\/a:mn>\n                        <a:mtext>\u2009<\/a:mtext>\n                        <a:mtext>\u2009<\/a:mtext>\n                        <a:mi>GeV<\/a:mi>\n                      <\/a:mrow>\n                    <\/a:math>\n                    and undulator\n                    <c:math xmlns:c=\"http:\/\/www.w3.org\/1998\/Math\/MathML\" display=\"inline\">\n                      <c:mi>K<\/c:mi>\n                    <\/c:math>\n                    parameters\n                    <e:math xmlns:e=\"http:\/\/www.w3.org\/1998\/Math\/MathML\" display=\"inline\">\n                      <e:mo>\u2265<\/e:mo>\n                      <e:mn>1.5<\/e:mn>\n                    <\/e:math>\n                    . In this Letter, we demonstrate the generation of high-power subangstrom FEL radiation using a 6.2\u00a0GeV electron beam and a\n                    <g:math xmlns:g=\"http:\/\/www.w3.org\/1998\/Math\/MathML\" display=\"inline\">\n                      <g:mi>K<\/g:mi>\n                    <\/g:math>\n                    parameter around unity and below. We show that exceptional electron beam brilliance\u2014characterized by high peak current and low slice emittance\u2014compensates for the reduced undulator coupling, enabling robust lasing. The demonstration was carried out at SwissFEL, where the subangstrom regime has already been successfully employed in user experiments. Our Letter paves the way for more compact and cost-effective accelerator designs through the optimization of electron beam quality.\n                  <\/jats:p>","DOI":"10.1103\/dv32-v967","type":"journal-article","created":{"date-parts":[[2026,8,17]],"date-time":"2026-08-17T11:34:18Z","timestamp":1786966458000},"update-policy":"https:\/\/doi.org\/10.1103\/crossmark-policy","source":"Crossref","is-referenced-by-count":0,"title":["Subangstrom Free-Electron Laser Operation with Undulator Deflection Parameter Reaching the Subunity Regime"],"prefix":"10.1103","volume":"137","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-7065-7417","authenticated-orcid":true,"given":"Eduard","family":"Prat","sequence":"first","affiliation":[{"id":[{"id":"https:\/\/ror.org\/03eh3y714","id-type":"ROR","asserted-by":"publisher"}],"name":"Paul Scherrer Institute"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-2932-196X","authenticated-orcid":true,"given":"Christopher","family":"Arrell","sequence":"additional","affiliation":[{"id":[{"id":"https:\/\/ror.org\/03eh3y714","id-type":"ROR","asserted-by":"publisher"}],"name":"Paul Scherrer Institute"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Marco","family":"Calvi","sequence":"additional","affiliation":[{"id":[{"id":"https:\/\/ror.org\/03eh3y714","id-type":"ROR","asserted-by":"publisher"}],"name":"Paul Scherrer Institute"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0003-0184-6577","authenticated-orcid":true,"given":"Nicole","family":"Hiller","sequence":"additional","affiliation":[{"id":[{"id":"https:\/\/ror.org\/03eh3y714","id-type":"ROR","asserted-by":"publisher"}],"name":"Paul Scherrer Institute"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Pavle","family":"Jurani\u0107","sequence":"additional","affiliation":[{"id":[{"id":"https:\/\/ror.org\/03eh3y714","id-type":"ROR","asserted-by":"publisher"}],"name":"Paul Scherrer Institute"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5527-1009","authenticated-orcid":true,"given":"Christoph","family":"Kittel","sequence":"additional","affiliation":[{"id":[{"id":"https:\/\/ror.org\/03eh3y714","id-type":"ROR","asserted-by":"publisher"}],"name":"Paul Scherrer Institute"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7797-6736","authenticated-orcid":true,"given":"Sven","family":"Reiche","sequence":"additional","affiliation":[{"id":[{"id":"https:\/\/ror.org\/03eh3y714","id-type":"ROR","asserted-by":"publisher"}],"name":"Paul Scherrer Institute"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-2701-538X","authenticated-orcid":true,"given":"Thomas","family":"Schietinger","sequence":"additional","affiliation":[{"id":[{"id":"https:\/\/ror.org\/03eh3y714","id-type":"ROR","asserted-by":"publisher"}],"name":"Paul Scherrer Institute"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Didier","family":"Voulot","sequence":"additional","affiliation":[{"id":[{"id":"https:\/\/ror.org\/03eh3y714","id-type":"ROR","asserted-by":"publisher"}],"name":"Paul Scherrer Institute"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Tobias","family":"Weilbach","sequence":"additional","affiliation":[{"id":[{"id":"https:\/\/ror.org\/03eh3y714","id-type":"ROR","asserted-by":"publisher"}],"name":"Paul Scherrer Institute"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"16","published-online":{"date-parts":[[2026,9,11]]},"reference":[{"key":"dv32-v967Cc1R1","doi-asserted-by":"publisher","DOI":"10.1103\/RevModPhys.88.015006","type":"journal-article"},{"key":"dv32-v967Cc2R1","doi-asserted-by":"publisher","DOI":"10.1088\/1361-6633\/aa7cca","type":"journal-article"},{"key":"dv32-v967Cc3R1","doi-asserted-by":"publisher","DOI":"10.1016\/0030-4018(84)90105-6","type":"journal-article"},{"key":"dv32-v967Cc4R1","doi-asserted-by":"publisher","DOI":"10.1016\/j.optcom.2007.10.044","type":"journal-article"},{"key":"dv32-v967Cc5R1","doi-asserted-by":"publisher","DOI":"10.1016\/S0168-9002(00)00114-5","type":"journal-article"},{"key":"dv32-v967Cc6R1","doi-asserted-by":"publisher","DOI":"10.1038\/nphoton.2010.176","type":"journal-article"},{"key":"dv32-v967Cc7R1","volume-title":"Proceedings of the 16th International Particle Accelerator Conference, Taipei, Taiwan","author":"Y. 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All rights are reserved, including those for text and data mining, AI training, and similar technologies.","name":"copyright_statement","label":"Copyright statement","group":{"name":"copyright","label":"copyright"}},{"value":"2026","name":"copyright_year","label":"Copyright year","group":{"name":"copyright","label":"copyright"}},{"value":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/","name":"creative_commons_license","label":"Creative Commons license","group":{"name":"licenses","label":"Licenses"}},{"value":"\u00a92026 The authors","name":"copyright_holder","label":"Copyright holder","group":{"name":"copyright","label":"copyright"}}],"article-number":"115001"}}