{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,23]],"date-time":"2026-10-23T13:38:20Z","timestamp":1792762700672,"version":"4.5.0"},"reference-count":18,"publisher":"AIP Publishing","issue":"10","funder":[{"DOI":"10.13039\/100000015","name":"U.S. Department of Energy","doi-asserted-by":"publisher","award":["DE-AC52-07NA27344"],"award-info":[{"award-number":["DE-AC52-07NA27344"]}],"id":[{"id":"10.13039\/100000015","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/100000015","name":"U.S. Department of Energy","doi-asserted-by":"publisher","award":["LDRD 23-FS-038"],"award-info":[{"award-number":["LDRD 23-FS-038"]}],"id":[{"id":"10.13039\/100000015","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":["pubs.aip.org"],"crossmark-restriction":true},"short-container-title":[],"published-print":{"date-parts":[[2026,10,1]]},"abstract":"<jats:p>Understanding the onset of thermonuclear burn and ignition in inertial confinement fusion implosions motivates the pursuit of time-resolved measurements of ion temperature and fuel density. At the National Ignition Facility (NIF), there are currently no diagnostics that can constrain ion temperature as a function of time. A single neutron time-of-flight (nToF) detector at an intermediate distance, or multiple detectors along a single line of sight, can in theory constrain the time evolution of the neutron energy spectrum. However, ultrafast time response is required. Refractive-index modulation in optically transparent media induced by ionizing radiation offers a novel ultrafast (sub-ps) measurement technique that could be applied to nToF spectroscopy. A related approach is used in RadOptic detectors, which have previously demonstrated x-ray detection. Here, the RadOptic technique is adapted to evaluate the sensitivity of refractive-index modulation in different materials to 14\u00a0MeV neutrons, a response that remains broadly uncharacterized. This work summarizes ongoing efforts toward development of a refractive-index-modulation-based nToF spectrometer at the NIF. To date, measurements include a pump\u2013probe experiment conducted 27\u00a0m from the target chamber center in which silicon and fused silica etalons serve as RadOptic media, which are pumped by neutrons and probed with a continuous-wave laser. The measured response at 27\u00a0m shows low signal-to-noise levels, however. A change in the refractive index in silicon of \u223c5\u00d7 10\u22127 is measured and steps are outlined for improving sensitivity toward development of an in-chamber diagnostic that can constrain the temporal evolution of the neutron spectrum.<\/jats:p>","DOI":"10.1063\/5.0350520","type":"journal-article","created":{"date-parts":[[2026,10,23]],"date-time":"2026-10-23T12:49:26Z","timestamp":1792759766000},"update-policy":"https:\/\/doi.org\/10.1063\/aip-crossmark-policy-page","source":"Crossref","is-referenced-by-count":0,"title":["Initial testing of neutron-induced refractive index modulation in optical materials at the National Ignition Facility"],"prefix":"10.1063","volume":"97","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-9109-1563","authenticated-orcid":false,"given":"J.","family":"Jeet","sequence":"first","affiliation":[{"name":"Lawrence Livermore National Laboratory , Livermore, California 94550,","place":["USA"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"B. W.","family":"Buckley","sequence":"additional","affiliation":[{"name":"Lawrence Livermore National Laboratory , Livermore, California 94550,","place":["USA"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6145-5269","authenticated-orcid":false,"given":"M.","family":"Eckart","sequence":"additional","affiliation":[{"name":"Lawrence Livermore National Laboratory , Livermore, California 94550,","place":["USA"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4822-564X","authenticated-orcid":false,"given":"S. M.","family":"Kerr","sequence":"additional","affiliation":[{"name":"Lawrence Livermore National Laboratory , Livermore, California 94550,","place":["USA"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-5874-9984","authenticated-orcid":false,"given":"E.","family":"Mariscal","sequence":"additional","affiliation":[{"name":"Lawrence Livermore National Laboratory , Livermore, California 94550,","place":["USA"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-2125-8882","authenticated-orcid":false,"given":"A. S.","family":"Moore","sequence":"additional","affiliation":[{"name":"Lawrence Livermore National Laboratory , Livermore, California 94550,","place":["USA"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8713-9448","authenticated-orcid":false,"given":"D. 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