{"id":78103,"date":"2026-05-04T14:03:29","date_gmt":"2026-05-04T12:03:29","guid":{"rendered":"https:\/\/www.iemn.fr\/?p=78103"},"modified":"2026-05-11T09:55:35","modified_gmt":"2026-05-11T07:55:35","slug":"pierre-kolejak-receives-a-werner-von-siemens-award-for-his-french-czech-phd-on-spintronic-thz-ellipsometry","status":"publish","type":"post","link":"https:\/\/www.iemn.fr\/en\/newsletter\/pierre-kolejak-receives-a-werner-von-siemens-award-for-his-french-czech-phd-on-spintronic-thz-ellipsometry.html","title":{"rendered":"Pierre Kolej\u00e1k receives a Werner von Siemens Award for his French-Czech PhD on spintronic THz ellipsometry"},"content":{"rendered":"<section  class='av_textblock_section av-lnbgevvn-a8f666e95d37b0aa1926e2ad8b84c4b3'   itemscope=\"itemscope\" itemtype=\"https:\/\/schema.org\/BlogPosting\" itemprop=\"blogPost\" ><div class='avia_textblock'  itemprop=\"text\" ><h1 style=\"text-align: center;\"><span lang=\"EN-US\" style=\"color: #668ac9;\">Pierre Kolej\u00e1k receives a Werner von Siemens Award for his French-Czech PhD on spintronic THz ellipsometry<\/span><\/h1>\n<h1 style=\"text-align: center;\"><span class=\"field field--name-title field--type-string field--label-hidden\">\u00a0<\/span><\/h1>\n<\/div><\/section>\n<div  class='hr av-3dbvnru-c453a2543459e6836d4ed72ae1e012d6 hr-default  avia-builder-el-1  el_after_av_textblock  el_before_av_textblock'><span class='hr-inner'><span class=\"hr-inner-style\"><\/span><\/span><\/div>\n\n<style type=\"text\/css\" data-created_by=\"avia_inline_auto\" id=\"style-css-av-lq4xuguo-c174deeb5f4b4eb2604ce82486968744\">\n#top .av_textblock_section.av-lq4xuguo-c174deeb5f4b4eb2604ce82486968744 .avia_textblock{\nfont-size:24px;\n}\n<\/style>\n<section  class='av_textblock_section av-lq4xuguo-c174deeb5f4b4eb2604ce82486968744'   itemscope=\"itemscope\" itemtype=\"https:\/\/schema.org\/BlogPosting\" itemprop=\"blogPost\" ><div class='avia_textblock'  itemprop=\"text\" ><h4 style=\"text-align: center;\"><strong><span style=\"color: #bd8e44;\"><em>A distinction highlighting a successful French\u2013Czech research trajectory at the interface of terahertz photonics, spintronics and advanced materials metrology.<\/em><\/span><\/strong><\/h4>\n<\/div><\/section>\n<div  class='hr av-mafk8n-e03a5dc4b63ca49d0c5bd60f570c3a50 hr-default  avia-builder-el-3  el_after_av_textblock  el_before_av_four_fifth'><span class='hr-inner'><span class=\"hr-inner-style\"><\/span><\/span><\/div>\n\n<style type=\"text\/css\" data-created_by=\"avia_inline_auto\" id=\"style-css-av-nf0z20-80b96fa3a1ee2cfacdfeadd3b8792083\">\n@keyframes av_boxShadowEffect_av-nf0z20-80b96fa3a1ee2cfacdfeadd3b8792083-column {\n0%   { box-shadow:  0 0 0 0 #e2e2e2; opacity: 1; }\n100% { box-shadow:  0 0 10px 0 #e2e2e2; opacity: 1; }\n}\n.flex_column.av-nf0z20-80b96fa3a1ee2cfacdfeadd3b8792083{\nbox-shadow: 0 0 10px 0 #e2e2e2;\nborder-width:1px;\nborder-color:#ededed;\nborder-style:solid;\nborder-radius:15px 15px 15px 15px;\npadding:15px 15px 15px 15px;\n}\n<\/style>\n<div  class='flex_column av-nf0z20-80b96fa3a1ee2cfacdfeadd3b8792083 av_four_fifth  avia-builder-el-4  el_after_av_hr  el_before_av_hr  first flex_column_div shadow-not-animated'     ><section  class='av_textblock_section av-lq4ycxg7-6b651811e8bbd77289cf0acc7f49ff0a'   itemscope=\"itemscope\" itemtype=\"https:\/\/schema.org\/BlogPosting\" itemprop=\"blogPost\" ><div class='avia_textblock'  itemprop=\"text\" ><p>IEMN warmly congratulates <strong><span style=\"color: #668ac9;\">Pierre Kolej\u00e1k, Ph.D<\/span>.<\/strong>, who received the <strong>\u00a0<span style=\"color: #668ac9;\">silver medal in the \u201cBest Doctoral Thesis\u201d category of the 2025 Werner von Siemens Awards<\/span><\/strong> for his dissertation entitled <em>Terahertz Time-Domain Ellipsometry Based on Spintronic Phenomena<\/em>. The Werner von Siemens Awards are among the most visible Czech distinctions for young scientists, students and educators in engineering and natural sciences. In the 2025 edition, 662 submissions were evaluated and 22 laureates were selected by expert juries [1].<\/p>\n<p>Pierre\u2019s thesis was carried out in a <strong><span style=\"color: #668ac9;\">French\u2013Czech cotutelle framework<\/span><\/strong> between <strong><span style=\"color: #668ac9;\">V\u0160B\u2013Technical University of Ostrava<\/span><\/strong><span style=\"color: #668ac9;\"><strong><span style=\"color: #668ac9;\"> and IEMN<\/span>,<\/strong><\/span> under the joint supervision of <strong><span style=\"color: #668ac9;\">Kamil Postava <\/span><\/strong>and <strong><span style=\"color: #668ac9;\">Mathias Vanwolleghem<\/span><\/strong>. The collaboration brought together complementary expertise: the original ellipsometry perspective and metrological motivation came from the Czech partner, while IEMN provided the environment in which the spintronic THz source platform, ultrafast THz instrumentation and photonic source-engineering concepts were developed.<a href=\"https:\/\/www.iemn.fr\/wp-content\/uploads\/2026\/05\/pierre.png\"><img loading=\"lazy\" decoding=\"async\" class=\"alignright wp-image-78148\" src=\"https:\/\/www.iemn.fr\/wp-content\/uploads\/2026\/05\/pierre.png\" alt=\"\" width=\"450\" height=\"338\" srcset=\"https:\/\/www.iemn.fr\/wp-content\/uploads\/2026\/05\/pierre.png 600w, https:\/\/www.iemn.fr\/wp-content\/uploads\/2026\/05\/pierre-300x225.png 300w, https:\/\/www.iemn.fr\/wp-content\/uploads\/2026\/05\/pierre-16x12.png 16w\" sizes=\"auto, (max-width: 450px) 100vw, 450px\" \/><\/a><\/p>\n<p>Under the guidance of <strong><span style=\"color: #668ac9;\">Mathias Vanwolleghem,<\/span><\/strong> spintronic THz emitters entered IEMN as a new research direction and rapidly developed into one of the active axes of the THz Photonics group. Pierre\u2019s PhD played a major role in this acceleration. While the long-term scientific horizon of the thesis was complete THz time-domain ellipsometry, many of its most mature and visible innovations concerned the physics, engineering and control of <strong><span style=\"color: #668ac9;\">spintronic THz emitters<\/span><\/strong> themselves.<\/p>\n<p>The scientific motivation was a central challenge in terahertz metrology: how to bring the analytical power of ellipsometry into the THz range while fully exploiting the phase-sensitive nature of time-domain spectroscopy. Conventional optical ellipsometry is a reference technique for measuring optical constants, thin-film thicknesses and anisotropies, but its extension to the THz domain remains technically demanding. Complete access to the polarization response of general anisotropic samples requires both amplitude and phase information, together with a high degree of control over the emitted THz polarization state.<\/p>\n<p>Pierre\u2019s dissertation pursued this objective through <strong><span style=\"color: #668ac9;\">complete time-domain spectroscopic THz ellipsometry<\/span><\/strong>, or <strong><span style=\"color: #668ac9;\">THz-cTDSE<\/span><\/strong>. The method aims to retrieve the full complex Jones matrix of anisotropic and lossy samples and to derive the corresponding Mueller matrix used in conventional ellipsometry. Pierre also introduced a <strong><span style=\"color: #668ac9;\">Pauli-matrix-based representation<\/span><\/strong> of the polarimetric response, translating matrix data into physically interpretable quantities such as retardance and diattenuation in different polarization bases. This provides a clearer route from measured THz waveforms to the underlying material physics, especially for birefringent, dichroic, magneto-optical or otherwise anisotropic systems. The approach is particularly relevant in the THz range, where radiation probes conductivity, carrier dynamics, low-energy excitations, phonons and anisotropic responses in technologically important materials.<\/p>\n<div id=\"attachment_78117\" style=\"width: 380px\" class=\"wp-caption alignright\"><a href=\"https:\/\/www.iemn.fr\/wp-content\/uploads\/2026\/05\/Pierre-K.png\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-78117\" class=\"wp-image-78117\" src=\"https:\/\/www.iemn.fr\/wp-content\/uploads\/2026\/05\/Pierre-K.png\" alt=\"\" width=\"370\" height=\"329\" srcset=\"https:\/\/www.iemn.fr\/wp-content\/uploads\/2026\/05\/Pierre-K.png 450w, https:\/\/www.iemn.fr\/wp-content\/uploads\/2026\/05\/Pierre-K-300x267.png 300w, https:\/\/www.iemn.fr\/wp-content\/uploads\/2026\/05\/Pierre-K-14x12.png 14w\" sizes=\"auto, (max-width: 370px) 100vw, 370px\" \/><\/a><p id=\"caption-attachment-78117\" class=\"wp-caption-text\">Pierre Kolej\u00e1k, Ph.D., developed new spintronic terahertz emitters and contributed to the emergence of complete time-domain THz ellipsometry during his French\u2013Czech cotutelle PhD between V\u0160B\u2013Technical University of Ostrava and CNRS\/IEMN.<\/p><\/div>\n<p>At the heart of the PhD was the realization that such an ellipsometric platform requires more than a conventional THz source followed by external polarizing optics. The enabling element is the<span style=\"color: #668ac9;\"><strong> spintronic THz emitter itself<\/strong>,<\/span> used not simply as a broadband emitter, but as an actively controllable source of polarized THz radiation. In nanometric ferromagnet\/heavy-metal multilayers, an ultrafast laser pulse generates a spin current that is converted into a transverse charge current through spin\u2013orbit coupling, producing broadband THz emission. Because the emitted THz polarization is directly linked to the magnetization direction, spintronic emitters provide a unique route to controlling the polarization state <strong><span style=\"color: #668ac9;\">at the source<\/span><\/strong>, avoiding lossy or mechanically rotated THz polarizing optics.<\/p>\n<p>Pierre\u2019s work contributed to transforming spintronic THz emitters into <strong><span style=\"color: #668ac9;\">polarization-programmable metrological<\/span> <span style=\"color: #668ac9;\">components<\/span><\/strong>. A first major result was the demonstration of <strong><span style=\"color: #668ac9;\">full 360\u00b0 source-level polarization control<\/span><\/strong> using engineered magnetic anisotropy in spintronic multilayers. By designing emitters with controlled uniaxial magnetic anisotropy, the emitted THz polarization could be rotated continuously through the magnetic state of the emitter itself. This is a central point of the work: the polarization is programmed inside the emitting structure, rather than imposed afterwards by mechanically scanned THz optical components. [2]<\/p>\n<p>A complementary route explored <strong><span style=\"color: #668ac9;\">voltage-controlled spintronic emitters<\/span><\/strong> based on magnetostrictive layers deposited on piezoelectric PMN-PT substrates. In this case, voltage-induced strain reorients the magnetization and thereby rotates the emitted THz polarization. This second approach pursues the same source-level control principle, but replaces magnetic-field actuation by an electrical stimulus. The resulting work on fully reversible magnetoelectric voltage control of THz polarization was published in <em>Applied Physics Letters<\/em>, selected as a Featured article, and highlighted on the journal cover. [3]<\/p>\n<p>Pierre also tackled one of the main limitations of spintronic THz technology: the relatively low optical-to-THz conversion efficiency of bare multilayer emitters. His work developed a rigorous electromagnetic strategy to maximize useful pump absorption in the ultrathin spintronic stack while also improving the extraction of the generated THz radiation. By integrating spintronic emitters with optimized photonic-cavity concepts, the work demonstrated strongly enhanced THz output while preserving the broadband character that makes spintronic emitters attractive. The resulting <em>Advanced Photonics Research<\/em> paper, <strong><span style=\"color: #668ac9;\">\u201cMaximizing the Electromagnetic Efficiency of Spintronic<\/span> <span style=\"color: #668ac9;\">Terahertz Emitters,\u201d<\/span><\/strong> was highlighted on the journal cover and is now recognized as a highly cited contribution in this emerging field. [4]<\/p>\n<p>These results are not isolated source optimizations. Together, they establish the source-side building blocks required for complete THz polarimetry and ellipsometry: broadband emission, enhanced efficiency, controllable polarization and compatibility with compact architectures. In that sense, the ellipsometry was not simply a final application added to the PhD, but the guiding metrological objective that gave coherence to the spintronic source developments.<\/p>\n<p>The scientific environment of the thesis was strongly shaped by the European <strong><span style=\"color: #668ac9;\">s-NEBULA FET Open project<\/span> \u2014<\/strong> <em>Novel Spin-Based Building Blocks for Advanced TeraHertz Applications<\/em>. The project aimed to create room-temperature spin-based THz building blocks and explicitly included polarization-programmable emitters for ellipsometry among its target applications. Pierre\u2019s work contributed directly to this ambition by addressing the source-side challenges \u2014 efficiency, polarization programmability, calibration and metrological use \u2014 that must be solved before spintronic emitters can become practical components for advanced THz instrumentation. [5]<\/p>\n<p>The <strong><span style=\"color: #668ac9;\">Barrande Fellowship Programme<\/span><\/strong> also played an important role by supporting the French\u2013Czech doctoral mobility framework. Barrande is designed to enhance scientific cooperation between French and Czech research teams and funds cotutelle PhDs and short research stays between the two countries. In Pierre\u2019s case, this support helped make the collaboration a genuinely bilateral doctoral project, combining the Czech ellipsometry tradition with the spintronic THz developments led at IEMN.<\/p>\n<p>The work has also opened a durable research line at IEMN. Within the <strong><span style=\"color: #668ac9;\">PEPR SPIN \/ TOAST<\/span><\/strong> moonshot project, the group is now extending Pierre\u2019s source-level polarization-control concepts toward <strong><span style=\"color: #668ac9;\">fast THz polarization<\/span> <span style=\"color: #668ac9;\">modulation<\/span><\/strong>, with the aim of enabling modulation-based detection schemes, improved signal-to-noise ratios and new forms of polarization-resolved THz spectroscopy. In parallel, the <strong><span style=\"color: #668ac9;\">ANR PRCI SPINCHIP <\/span><\/strong>project, carried out with the <strong><span style=\"color: #668ac9;\">Hybrid Photonics Laboratory at EPFL <\/span><\/strong><span style=\"color: #668ac9;\">(\u00c9cole polytechnique f\u00e9d\u00e9rale de Lausanne)<\/span>, is pushing spintronic THz emitters toward photonic integrated platforms. SPINCHIP aims to develop hybrid photonic\u2013spintronic chips on silicon nitride for compact pulsed and continuous-wave THz generation, with IEMN and EPFL as partners. [6,7]<\/p>\n<p>In this sense, Pierre\u2019s Werner von Siemens Award recognizes more than an outstanding doctoral thesis. It highlights a successful French\u2013Czech research pathway, supported by Barrande mobility and amplified by the European s-NEBULA project. It also marks the emergence of a strong and continuing research axis at IEMN, linking fundamental spintronic THz source physics, complete polarimetric metrology and future integrated THz systems for non-destructive characterization of advanced materials.<\/p>\n<h3 style=\"text-align: center;\"><\/h3>\n<\/div><\/section><\/div>\n<div  class='hr av-3dbvnru-4-a6329428ba1855e32446004087e3c170 hr-default  avia-builder-el-6  el_after_av_four_fifth  el_before_av_one_full'><span class='hr-inner'><span class=\"hr-inner-style\"><\/span><\/span><\/div>\n\n<style type=\"text\/css\" data-created_by=\"avia_inline_auto\" id=\"style-css-av-2wjveka-05a13fade294e74be944ea8d5bcca9b4\">\n.flex_column.av-2wjveka-05a13fade294e74be944ea8d5bcca9b4{\nborder-width:1px;\nborder-color:#cecece;\nborder-style:solid;\nborder-radius:15px 15px 15px 15px;\npadding:15px 15px 15px 15px;\nbackground-color:#e8e8e8;\n}\n.flex_column.av-2wjveka-05a13fade294e74be944ea8d5bcca9b4 .avia-divider-svg-top{\nleft:-1px;\nright:-1px;\nwidth:auto;\ntop:-1px;\nborder-radius:15px 15px 0 0;\n}\n.flex_column.av-2wjveka-05a13fade294e74be944ea8d5bcca9b4 .avia-divider-svg-top svg{\nheight:20px;\nwidth:calc(65% + 1.3px);\nfill:#668ac9;\n}\n<\/style>\n<div  class='flex_column av-2wjveka-05a13fade294e74be944ea8d5bcca9b4 av_one_full  avia-builder-el-7  el_after_av_hr  avia-builder-el-last  first flex_column_div'     ><div class='avia-divider-svg avia-divider-svg-triangle avia-divider-svg-top avia-svg-original'><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" viewbox=\"0 0 1000 100\" preserveaspectratio=\"none\">\n\t<path d=\"M500,98.9L0,6.1V0h1000v6.1L500,98.9z\"\/>\n<\/svg><\/div><section  class='av_textblock_section av-lqc84mmi-2de73543dfd0764d37f06d76ddbb015d'   itemscope=\"itemscope\" itemtype=\"https:\/\/schema.org\/BlogPosting\" itemprop=\"blogPost\" ><div class='avia_textblock'  itemprop=\"text\" ><hr \/>\n<h3>Acknowledgement box<\/h3>\n<p><strong>Acknowledgements<\/strong> \u2014 Pierre Kolej\u00e1k\u2019s PhD was carried out in cotutelle between V\u0160B\u2013Technical University of Ostrava and IEMN (graduate school ENGSYS, University of Lille), with support from the <strong>Barrande Fellowship Programme<\/strong> for French\u2013Czech doctoral mobility. The work also benefited from the European H2020 FET Open project <strong>s-NEBULA<\/strong>, which provided the broader collaborative framework for the development of spin-based THz technologies. The research line is now continuing at IEMN through follow-up projects including <strong>PEPR SPIN \/ TOAST<\/strong>, on fast THz polarization modulation, and <strong>ANR PRCI SPINCHIP<\/strong>, with EPFL, on integrated spintronic THz photonics.<\/p>\n<h3>References<\/h3>\n<p>[1] https:\/\/www.siemenspress.cz\/ceny-wernera-von-siemense-2025\/<\/p>\n<p>[2] P. Kolejak, G. L\u00e9zier, K. Postava, Jean-Fran\u00e7ois, N. Tiercelin, and M. Vanwolleghem, \u201c360\u00b0 polarization control of terahertz spintronic emitters using uniaxial FeCo\/TbCo2\/FeCo trilayers\u201d, ACS photonics, American Chemical Society,, 2022, 9 (4), pp.1274\u22121285. ; doi:10.1021\/acsphotonics.1c01782<\/p>\n<p>[3] Geoffrey Lezier, Pierre Kolej\u00e1k, Jean-Fran\u00e7ois Lampin, Kamil Postava, Mathias Vanwolleghem, Nicolas Tiercelin, \u00ab\u00a0Fully reversible magnetoelectric voltage controlled THz polarization rotation in magnetostrictive spintronic emitters on PMN-PT\u00a0\u00bb, Special Topic on Ultrafast and Terahertz Spintronics, Applied Physics Letters, 2022, 120, pp.152404. doi: 10.1063\/5.0080372<\/p>\n<p>[4] Kolej\u00e1k, P., Lezier, G., Vala, D., Mathmann, B., Halaga\u010dka, L., Geln\u00e1rov\u00e1, Z., Dusch, Y., Lampin, J.-F., Tiercelin, N., Postava, K. and Vanwolleghem, M. (2024), Maximizing the Electromagnetic Efficiency of Spintronic Terahertz Emitters. Adv. Photonics Res., 5: 2400064. https:\/\/doi.org\/10.1002\/adpr.202400064<\/p>\n<p>[5] https:\/\/cordis.europa.eu\/project\/id\/863155<\/p>\n<p>[6] https:\/\/anr.fr\/ProjetIA-22-EXSP-0003<\/p>\n<p>[7] https:\/\/anr.fr\/Project-ANR-24-CE93-0018<\/p>\n<h3><strong>Contact Us<\/strong><\/h3>\n<p>Mathias.vanwolleghem<img loading=\"lazy\" decoding=\"async\" class=\"align=absbottom wp-image-73335 size-full\" src=\"https:\/\/www.iemn.fr\/wp-content\/uploads\/2025\/05\/arobase6.png\" alt=\"\" width=\"16\" height=\"14\" srcset=\"https:\/\/www.iemn.fr\/wp-content\/uploads\/2025\/05\/arobase6.png 16w, https:\/\/www.iemn.fr\/wp-content\/uploads\/2025\/05\/arobase6-14x12.png 14w\" sizes=\"auto, (max-width: 16px) 100vw, 16px\" \/>iemn.fr<\/p>\n<\/div><\/section><\/div>","protected":false},"excerpt":{"rendered":"","protected":false},"author":20,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[297],"tags":[],"class_list":["post-78103","post","type-post","status-publish","format-standard","hentry","category-newsletter"],"_links":{"self":[{"href":"https:\/\/www.iemn.fr\/en\/wp-json\/wp\/v2\/posts\/78103","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.iemn.fr\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.iemn.fr\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.iemn.fr\/en\/wp-json\/wp\/v2\/users\/20"}],"replies":[{"embeddable":true,"href":"https:\/\/www.iemn.fr\/en\/wp-json\/wp\/v2\/comments?post=78103"}],"version-history":[{"count":27,"href":"https:\/\/www.iemn.fr\/en\/wp-json\/wp\/v2\/posts\/78103\/revisions"}],"predecessor-version":[{"id":78225,"href":"https:\/\/www.iemn.fr\/en\/wp-json\/wp\/v2\/posts\/78103\/revisions\/78225"}],"wp:attachment":[{"href":"https:\/\/www.iemn.fr\/en\/wp-json\/wp\/v2\/media?parent=78103"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.iemn.fr\/en\/wp-json\/wp\/v2\/categories?post=78103"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.iemn.fr\/en\/wp-json\/wp\/v2\/tags?post=78103"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}