Fall 2023 Colloquia

August 22, 2023 – NO PHYSICS COLLOQUIUM

Thomas Fix
University of Strasbourg, ICube Laboratory

New concepts and emergent materials for optoelectronics and photovoltaics

Abstract: This seminar will give an overview of three different topics currently investigated in the Materials for electronic and photovoltaic devices team (MaCEPV) of ICube laboratory.

• Downshifting and downconversion for solar cells

Downshifting and downconversion are advanced concepts for solar cells enabling a better match between the solar cells and the solar spectrum. It consists in the conversion of one ultraviolet photon into one (downshifting) or two (downconversion) photons in the visible or near-infrared.

[a] Photon Converters for Photovoltaics, A. Nonat, T. Fix, in Advanced micro- and nanomaterials for photovoltaics, Elsevier 2019, ISBN: 978-0-12-814501-2

• Oxide solar cells and ferroelectric solar cells

Our team has been developing emergent oxide materials as absorbers for solar cells. In particular, we focused in ferroelectric oxide solar cells where no pn junction is necessary and the separation of electron hole pairs is enabled by the ferroelectric polarization of the absorber.

[b] R. Hoye, J. Hidalgo, R. Jagt, J.-P. Correa-Baena, T. Fix, J. MacManus-Driscoll, Advanced Energy Materials, 2100499, pages 1-59 (2021)

• Silicon clathrate films for optoelectronic applications

Silicon clathrates are exotic forms of silicon, forming cages, that present the advantage of a direct and adjustable bandgap. Our team is one of the three actors in the world producing such films.

[c] T. Fix, R. Vollondat, A. Ameur, S. Roques, J.-L. Rehspringer, C. Chevalier, D. Muller, and A. Slaoui, J. Phys. Chem. C 124, 14972–14977 (2020)

Thomas Fix is a CNRS researcher in the ICube laboratory, University of Strasbourg – CNRS. He obtained his PhD in physics in 2006 at IPCMS and worked for six years as a research associate at the University of Cambridge, UK. His field is advanced concepts and innovative materials for optoelectronics and solar cells.

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September 5, 2023 – PHYSICS COLLOQUIUM-HAZARDOUS WASTE GENERATOR TRAINING REFRESHER

September 12, 2023 – NO PHYSICS COLLOQUIUM-CAREER DAY

Extreme Universe on a Super Pressure Balloon 2: Mission, Science, and Adventure

Abstract: Ultra-high energy cosmic rays are the highest energy subatomic particles known to exist. Although much harder to detect, very high-energy neutrinos also carry information about the most extreme environments in the universe. And since they have zero charge, they point back to their creation point. The Extreme Universe Space Observatory on a Super Pressure Balloon II (EUSO-SPB2) was designed to search for PeV energy neutrinos from steady-state and transient astrophysical sources and to measure PeV and EeV cosmic rays using optical techniques from sub-orbital altitude. This exploratory mission of opportunity was a pathfinder for a space observatory such as the Probe of Extreme Multi Messenger Astrophysics (POEMMA). EUSO-SPB2 flew two astroparticle telescopes that featured wide fields of view, 1 meter diameter entrance pupils, and specialized camera systems to measure fast pulses of light from extensive air showers in the atmosphere. A fluorescence telescope was pointed down to measure scintillation light from EeV cosmic ray interactions. A Cherenkov telescope was pointed toward the earth’s limb. This instrument could be tilted a few degrees above the limb to observe Cherenkov emission from PeV energy cosmic rays or tilted below the limb to search for Cherenkov emission from air showers induced through neutrino interactions in the earth’s limb. The gondola could be rotated in azimuth to point the CT to observe sources of interest just before they rise or just after they set. After several years of preparations, lab tests, field tests, reviews, and integrations, the payload was delivered to NASA’s mid-latitude launch site in Wanaka NZ, and launched May 13, 2023. Unfortunately, the balloon developed a bad leak and the entire flight train was terminated into the Pacific Ocean after just two nights aloft. Despite all this, the instruments turned on successfully and worked, with almost 60 GB of data downloaded. Data analysis is in progress with some performance and preliminary results reported at conferences this summer. Planning for a follow-up mission is in progress.

Biography: Grew up in Vermont. AB Dartmouth College, MA, MPhil, PhD Columbia University (I don’t know why they hand out 3 degrees). Did particle physics as a grad student working on an experiment at the historic Alternating Gradient Synchrotron at Brookhaven National Labs. Thesis “Observation of Coulomb Effects in pp and np collisions at 27.5 GeV/c”. By the time I finished my PhD, I needed a change from accelerator laboratories (the uncertainty in accelerator scheduling was interfering with my climbing trips, among other things). Left the NYC area for a postdoc with the High Resolution Fly’s Eye Comic Ray experiment in the Utah West Desert (the HiRes schedule was driven by the moon). Discovered the rewards of working with UV laser systems in the desert, and mountain trail running, and telemark skiing. We made the first observation of high energy cosmic air showers in stereo with the fluorescence technique And made the first observation of the cosmic ray flux suppression around 10^20 eV, explained at that time by energy loss in the cosmic microwave background radiation. While at Utah, I joined the Pierre Auger Observatory project as construction was starting near Malargue, Argentina. I worked with a small team that designed and built a laser system in the middle of nowhere to mimic the optical signatures of high energy cosmic rays, but traveling in the wrong direction. By the time I joined the faculty at Mines in 2007, we had a second of these systems installed in the Pampas. A few months after arriving in Golden it blew up in a massive propane “anomaly”. Despite that, Fred Sarazin and I secured the first NSF grant for astroparticle physics at Mines. Organized a team to replace that system and upgraded the first, (Eric Mayotte who was a grad student at the time can tell you more about that experience). About 2012, we decided to expand the reach of the group by joining the JEM-EUSO collaboration. Although the goal of putting a fluorescence telescope to measure cosmic ray airshows from the ISS didn’t pan out, I participated in three balloon experiments to test techniques and instruments needed to measure high energy cosmic rays from the vantage point of space. I served as international deputy PI and project manager for the last two. Anyway, Mines is now on the map in astroparticle physics. It’s been a team effort including many great graduate and undergraduate students, and tremendous support from administrative and shop staff.

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Single Barium Ion Identification Technologies for Background-Free Neutrinoless Double Beta Decay Searches

Abstract: The goal of future neutrinoless double beta decay experiments is to establish whether neutrino is its own antiparticle, by searching for an ultra-rare decay process with a half life that may be more than 10^28 years. Such a discovery would have major implications for cosmology and particle physics, but requires multi-ton-scale detectors with backgrounds below 0.1 counts per ton per year. This is a formidable technological challenge that seems likely to require unconventional solutions. In this talk I will discuss new technologies emerging at the interfaces between nuclear physics, microscopy, AMO physics, and biochemistry that aim to identify the single 136Ba daughter nucleus produced in double beta decays of the isotope 136Xe. If these atoms or ions can be collected and imaged with sufficiently high efficiency, the radiogenic backgrounds limiting the sensitivity of all existing technologies could be entirely mitigated. This would enable a new class of large scale, ultra-low background neutrinoless double beta decay experiments.

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Mechanical Sensors for Dark Matter and Neutrinos

Abstract: The development of optomechanical systems has revolutionized the detection of tiny forces over the past few decades. As such technologies reach (and surpass) quantum measurement limits, they can enable new searches for weakly coupled phenomena, including dark matter, gravitational waves, “fifth’’ forces, and sterile neutrinos. As a demonstration of these techniques, I will describe an initial search for dark matter using an optically levitated nanogram mass sensor, which can exceed the sensitivity of even large underground detectors for certain classes of dark matter candidates in a few days of exposure. If a signal were detected, such sensors would also be able to correlate its direction with earth’s motion through the galaxy, allowing definitive confirmation that such a signal arose from dark matter. Finally, I will briefly discuss future applications of such sensors to neutrino physics in a table-top scale experiment.

Precision Spectroscopy of Atomic Hydrogen

Abstract: Because of atomic hydrogen’s simplicity, its energy levels can be precisely described by theory. This has made hydrogen an important atom in the development of quantum mechanics and quantum electrodynamics (QED). While one can use hydrogen spectroscopy to determine the Rydberg constant and the proton charge radius, a discrepancy of these constants determined through different transitions, or in different species, can indicate new physics. Such discrepancies currently persist between different measurements in hydrogen and muonic hydrogen. With this motivation in mind, I will discuss several precision spectroscopy measurements of hydrogen as Colorado State University including a relatively recent measurement of the hydrogen 2S-8D two-photon transition, a measurement of the hydrogen 2S hyperfine splitting, and our future plans to measure several relatively narrow 2S-nS transitions in hydrogen. If these latter measurements are successful, they could provide some of the most precise measurements of the Rydberg constant along with insight into the experimental discrepancies.

October 17, 2023 – NO PHYSICS COLLOQUIUM-FALL BREAK

Quantum State Measurement via Common-Path Interferometry with Entangled Modes

Abstract: Entangled photons are a valuable resource for quantum logic, imaging, and information theory. While measuring entangled state amplitudes is relatively straightforward with coincidence-based correlation filters, the entangled state phases have received relatively little attention – despite the important role that phases play in defining and altering quantum states. In contrast to classical light, for which phase can be easily measured using interference with an ancillary reference beam, the reliance of coincidence detection for biphoton measurements makes it unclear how to implement the requisite reference. Furthermore, phase measurement of entangled states is not as simple as combining separate phase measurements of signal and idler photons, or of interfering them together. In short, a phase-measurement counterpart to direct amplitude measurements has remained elusive. I will show a method to directly measure the phase of biphoton states that uses the broader entanglement spectrum as a resource for interferometry. The technique is demonstrated with entangled photonic spatial modes in the Laguerre-Gaussian basis, and it is applicable to any quantum system that has multiple orthogonal modes. Two different implementations are demonstrated with measurements on entangled photons: a simple version that works in the case of a particular sparse entanglement spectrum, and another that works for general entangled states (including polarization entanglement). As one particularly useful application, we use the new methodology to directly measure the geometric phase accumulation of entangled photons.

Biography: Dr. Mark Siemens is a Professor in the Department of Physics and Astronomy at the University of Denver (DU). His research group uses lasers to characterizes quantum dynamics in materials, and in the lasers themselves. He is the faculty advisor for DU’s Society of Physics Students, which is widely recognized for their physics outreach. 

Inverse Midas Effect: Using Nuclear Physics to Explain a Mysterious Failure & Assess the Severity of a New Radiation Threat

Abstract: Watching a part fail while radiation testing is not an uncommon experience. However, when the previous testing on your part suggests that protons are too feebly ionizing to kill your part and it dies anyway…that will make you sit up and take notice! And when your billion-dollar satellite is already flying these same parts in a proton-rich portion of space, it will make your management take notice! The path to an answer is lined with gold, but in this case, the gold nuclei fission—an inverse Midas Effect, with the daughter ions bombarding the electronics and causing unanticipated failures. And once the mechanism is known, the real work begins as every mission at NASA strives to answer the question—is my satellite vulnerable to the same failures? Follow a tale of gold fever, bringing together topics from astrophysics to nuclear physics to exotic microelectronic failure modes to answer the question: How deep are we into the soup, and what can we do about it?

Biography: Dr. Ray Ladbury has served as a radiation physicist in the Radiation Effects and Analysis Group (REAG) at NASA Goddard Space Flight Center since January, 2000. He has served as lead radiation engineer for many NASA programs and missions, including the James Webb Space Telescope, SWIFT, LANDSAT8, OSIRIS-REx and the GOES and TDRS programs. Within the REAG, Dr. Ladbury’s research has centered on the radiation testing and qualification of complex devices for spacecraft applications and development of statistical models in radiation hardness assurance. He has authored or co-authored over 80 technical papers in peer-reviewed journals and three short courses on various aspects of radiation hardness assurance. He also authored two dozen popularized articles on cutting-edge physics research while serving as Editor at Physics Today. On the manned side of NASA’s operations, Dr. Ladbury has worked on NASA’s Commercial Crew program and its Human Landing Systems and related infrastructure for the agency’s return to the Moon. Dr. Ladbury earned his Bachelor of Science degree in physics from Colorado State University and his PhD in experimental particle physics from the University of Colorado. In addition to his work in radiation physics and editor for Physics Today Magazine, Dr. Ladbury has worked as a physics professor at Pikeville College in Pikeville, KY and a science teacher trainer with the Peace Corps in the Savannah Region of Togo, West Africa. He lives in Mt. Airy, MD with his wife on 3 acres they share with the local wildlife.

Quantum Optics Meets Strong Field Physics: Novel Regimes of Coherent X-ray Generation with Strong Electron Correlation Dynamics and Attosecond Rabi Oscillations

Abstract: Ultrafast imaging and spectroscopies using coherent EUV – X-ray light based on the nonlinear process of high harmonic generation are already addressing grand challenges in complex molecular systems, plasmas, and advanced nanomaterials. The exquisite quantum control of the attosecond dynamics of the rescattering electrons in this extreme frequency upconversion makes it possible to sculpt the classical and quantum properties of the light with unprecedented tunability of the spectral, spatial, temporal shape,and spin and orbital angular momentum state. The superb coherence of this unique light allows for multidimensional imaging at the space-time extreme with 4D resolution of nanometers and femtoseconds, including access to an effective 5th dimension – the periodic table of elements – due to the X-ray absorption fingerprinting with elemental and chemical specificity. In this talk, I will present two novel quantum regimes of coherent X-ray generation where the design of the light properties is dominated by the dynamics of the entangled electrons in a simple He atomic system. Interestingly, the physics of these regimes extends beyond the well-established three-step high harmonic model. In the first regime, using strong UV laser fields, the entangled electron dynamics yield a characteristic plateau in the X-ray spectral region, extending well beyond the conventional cutoff. This is due to simultaneous double electron recombination where a single high-energy X-ray photon is emitted only in atomic systems with strongly correlated electrons. This low probability phenomenon paves a way to a sensitive attosecond spectroscopy as a probe of highly correlated interactions. Similar physics of high harmonics from solids might be able to characterize electron correlations in phase transition materials and nanosystems of relevance to quantum computing and superconductivity. In the second extreme regime, using intense EUV driving fields tuned to a resonance frequency of He can result in very bright harmonic emission in the X-ray regime. Favorable quantum dynamics of the electron wavepackets, and phase and group velocity matching of the light fields enhance the X-ray yield. Furthermore, record-fast attosecond Rabi oscillations are predicted to suppress the depletion of the ground state, which otherwise terminates the emission of X-ray photons. These new advances in quantum control over the coherent X-ray emission enable new insights into complex entangled electron dynamics and applications in nanoscience and quantum technology.

BIO: Prof. Tenio Popmintchev is an Assistant Professor in the Physics Department and the Center for Advanced Nanoscience at the University of California San Diego. He received his PhD in Atomic, Molecular, and Optical Physics from the JILA Institute and University of Colorado Boulder in 2010, where he conducted pioneering research on ultrashort pulse lasers and bright coherent X-ray generation with designer classical and quantum properties. Prof. Popmintchev is an internationally recognized leader in the field of Attosecond and X-ray Science. He has over 90 publications, including papers in Science, Nature Photonics, Nature Physics, and Physical Review Letters. Some of his honors include the Sloan Research Fellowship, European Research Council Starting Grant, Science News USA 10 Outstanding Young Scientist Award, Presidential Medal for Pioneering Contribution to Science and Technology. Prof. Popmintchev led groundbreaking work on scaling EUV attosecond pulses towards generating attosecond-to-zeptosecond X-ray pulses in the keV regime – the shortest events ever created in a laboratory. His research on developing bright coherent EUV and X-ray light with tunable spectral, spatial, and temporal shape, and tunable angular momentum, has been enabling new capabilities for ultrafast multidimensional imaging and spectroscopies at the space-time resolution extreme. Some of his current research directions expand towards novel quantum regimes of X-ray generation, merging quantum optics and strong field physics.

Ultrafast Spectro-Microscopy of Photo-Excited Systems: Harnessing the Power of X-Ray Tabletop and Facility-Scale Sources

Abstract: Ultrafast scattering, spectroscopy and imaging are essential tools for understanding and quantifying the functionality of nanoscale systems in space and time domains. The past decades witnessed a revolution in ultrafast pulsed sources, from optical lasers to pulsed X-rays sources. In the X-ray regime, X-ray Free-Electron Lasers (XFELs) provided intense and coherent X-ray pulses, enabling to combine novel experimental strategies, based on ultrafast element-selective core-level spectroscopies and scattering techniques. In parallel, soft X-ray/EUV light from compact High-Harmonic Generation (HHG) sources have proved extremely powerful for investigating electronic, structural and magnetic properties in complex nanostructured systems out-of-equilibrium, with nanometer spatial resolution and pulse durations in the femtosecond (fs)-to-attosecond (as) range. Specifically, the combination of HHG EUV light with ptychographic Coherent Diffractive Imaging (CDI), enabled revolutionary new nano-imaging capabilities, from ultrafast hyperspectral imaging to Bragg coherent small-angle scattering. In this talk I will present recent advances in this field with recent pioneering demonstrations.

Biography: Prof. Giulia Fulvia Mancini received her B.Sc. and M.Sc. degrees from the University of Pavia, and she obtained her Ph.D. in Physical Chemistry from the Federal Polytechnical School of Lausanne (EPFL), LUMES group (Prof. Fabrizio Carbone). In 2015, she moved to the United States and joined the Kapteyn-Murnane group as a PostDoctoral Fellow at JILA, University of Colorado-Boulder and NIST (USA). After holding a Team Leader position as Senior Research Associate at the Swiss Free Electron Laser (SwissFEL – PSI) with EPFL (Prof. Majed Chergui), she decided to re-invest the experience gained abroad in Italy. Giulia Fulvia Mancini is a tenured Associate Professor at the Department of Physics at the University of Pavia, (UniPv) since 2021, and Head of Research of the LUXEM team composed of 7 people (1 Marie Curie PostDoctoral Research Fellow, 2 Postdocs, 2 graduate students, 1 Executive Coordinator, 1 Lab Technician), and co-supervisor of 1 undergraduate student. In her group, the Laboratory for Ultrafast X-ray and Electron Microscopy (LUXEM), the research focus is in the understanding of structure-property relationships in functional nanomaterials and interfaces, in the ultrafast (10-15s) time domain, through novel experimental scattering and imaging techniques which integrate tabletop (HHG) and facility (Synchrotrons, Free-Electron Lasers) pulsed X-rays and electrons sources. LUXEM is an internationally recognized laboratory for ultrafast science that collaborates with key industry partners for XUV metrology and computational imaging, such as AXIS, KMLabs, and SESO Thales. Prof. Mancini relies on a consolidated network of international collaborations with world leading scientists in her research field. Her international track record and scientific standing was consolidated by the following awards: (i) a 4M€ LUXEM funding ID from International and National Grants; (ii) the 2020 Mildred Dresselhaus Junior Guest Professorship from the CUI Centre for Ultrafast Advanced Imaging of Matter and the Hamburg University, for “outstanding early scientific achievements”: (iii) the 2021 Young Scientist Prize in Optics for “contributions to imaging and scattering of nanostructured materials using high-harmonic soft X-ray sources and research on extreme ultraviolet imaging”; (iv) membership in the Executive Committee of the European XFEL User Organization to bridge users’ needs with the machine top management. She has co-authored 68 scientific publications in peer-reviewed journals and international proceeding of conferences top of her field, and 3 patents, contributing to breakthrough scientific discoveries in ultrafast and material sciences, with a h-index 20 in rapid growth. She was invited guest and public speaker to 40 international conferences and 5 public speaking events connecting researchers, investors, policy makers, and the public. Prof. Mancini is strongly invested in the professional development of the students and researchers under her supervision. In the past 8 years, she supervised 8 graduate students and 3 undergraduate students, now in permanent positions in responsibility roles in industry or academia (USA, Europe) and US or CH national laboratories. She is a mentor for women in science and STEM disciplines at UniPv and the University of Hamburg (DE), invited guest of the International Day of Women and Girls in Science Round Tables, and she is committee members of associations and workgroups aimed to promoting equality, diversity, and professional development for young researchers.

December 5, 2023 – PHYSICSFEST – HAPPY HOLIDAYS!