Lauren Mason – Page 3

Three-dimensional topological magnetic monopoles and their interactions in a ferromagnetic meta-lattice

Topological magnetic monopoles (TMMs), also known as hedgehogs or Bloch points, are three-dimensional (3D) nonlocal spin textures that are robust to thermal and quantum fluctuations due to their topology. Understanding their properties is of fundamental interest and practical applications. However, it has been difficult to directly observe the 3D magnetization vector field of TMMs and probe their interactions at the nanoscale. Now, a STROBE team from UCLA, CU Boulder, UC Berkeley and LBNL collaborated with the Penn State MRSEC reports the creation of 138 stable TMMs at the specific sites of a ferromagnetic meta-lattice at room temperature. They developed 3D soft x-ray vector ptychography to determine the magnetization vector and emergent magnetic field of the TMMs with a 3D spatial resolution of 10 nm. This spatial resolution is comparable to the magnetic exchange length of transition metals, enabling them to probe monopole-monopole interactions. The team found that the TMM and anti-TMM pairs are separated by 18.3±1.6 nm, while the TMM and TMM, anti-TMM and anti-TMM pairs are stabilized at comparatively longer distances of 36.1±2.4 nm and 43.1±2.0 nm, respectively. They also observed virtual TMMs created by magnetic voids in the meta-lattice. This work demonstrates that ferromagnetic meta-lattices could be used as a new platform to create and investigate the interactions and dynamics of TMMs. Furthermore, it is expected that soft x-ray vector ptychography can be broadly applied to quantitatively image 3D vector fields in magnetic and anisotropic materials at the nanoscale.

Detecting, distinguishing, and spatiotemporally tracking photogenerated charge and heat at the nanoscale

Since dissipative processes are ubiquitous in semiconductors, characterizing how electronic and thermal energy transduce and transport at the nanoscale is vital for understanding and leveraging their fundamental properties. For example, in low-dimensional transition metal dichalcogenides (TMDCs), excess heat generation upon photoexcitation is difficult to avoid since even with modest injected exciton densities, exciton-exciton annihilation still occurs. Both heat and photoexcited electronic species imprint transient changes in the optical response of a semiconductor, yet the distinct signatures of each are difficult to disentangle in typical spectra due to overlapping resonances. In response, it is necessary to simultaneously map both heat and charge populations in materials on relevant nanometer and picosecond length- and time scales.

By further honing stroboSCAT, a time-resolved optical scattering microscopy capable of capturing spatiotemporal energy flow in a wide range of materials, a STROBE team from UC Berkeley collaborated with Caltech to map both heat and exciton populations in few-layer TMDC MoS₂ on the relevant length- and time scales and with 100-mK temperature sensitivity. We discern excitonic contributions to the signal from heat by combining observations close to and far from exciton resonances, characterizing photoinduced dynamics for each. Our approach is general and can be applied to any electronic material, including thermoelectrics, where heat and electronic observables spatially interplay, and lays the groundwork for direct and quantitative discernment of different types of coexisting energy without recourse to complex models or underlying assumptions. This work illustrates the ability to, finally, simultaneously observe and distinguish photogenerated heat from charge in a broad range of systems critical to the performance of next-generation energy conversion modules.

Relationships between Compositional Heterogeneity and Electronic Spectra of (Ga1−xZnx)(N1−xOx) Nanocrystals Revealed by Valence Electron Energy Loss Spectroscopy

Many ternary and quaternary semiconductors have been made in nanocrystalline forms for a variety of applications, but we have little understanding of how well their ensemble properties reflect the properties of individual nanocrystals. STROBE researchers at CU Boulder examined electronic structure heterogeneities in nanocrystals of (Ga_1−xZn_x)(N_1−xO_x), a semiconductor that splits water under visible illumination. They used valence electron energy loss spectroscopy (VEELS) in a scanning transmission electron microscope to map out electronic spectra of (Ga_1−xZn_x)(N_1−xO_x) nanocrystals with a spatial resolution of 8 nm. They examine three samples with varying degrees of intraparticle and interparticle compositional heterogeneity and ensemble optical spectra that range from a single band gap in the visible to two band gaps, one in the visible and one in the UV. The VEELS spectra resemble the ensemble absorption spectra for a sample with a homogeneous elemental distribution and a single band gap and, more interestingly, one with intraparticle compositional heterogeneity and two band gaps. They observe spatial variation in VEELS spectra only with significant interparticle compositional heterogeneity. Hence, they reveal the conditions under which the ensemble spectra reveal the optical properties of individual (Ga_1−xZn_x)(N_1−xO_x) particles. More broadly, they illustrate how VEELS can be used to probe electronic heterogeneities in compositionally complex nanoscale semiconductors.

Two-color high-harmonic generation from relativistic plasma mirrors

Circularly polarized x-rays have a number of microscopy applications that leverage the rotational nature of some physical systems, one of the most common applications being magnetic dichroism of nanoscale magnetic devices. Generating circularly polarized x-rays, particularly coherent x-rays with ultrafast pulse durations is practically difficult and inefficient. One of the major successes of STROBE was the development of not just one, but two mechanisms for generating circularly polarized x-rays using light at moderate intensities in the strong field regime. In this work, we lay the foundation for scaling analogous mechanisms into the relativistic regime. In this regime, the energy cutoff can be much higher than in the strong field. Performing numerical simulations, we confirm that despite the physical mechanism being completely different at relativistic intensities, the same conservation laws observed in the earlier STROBE work are still valid in the relativistic regime. Experiments are being planned to demonstrate this mechanism in the lab, which can leverage new facilities such as the NSF ZEUS which would enable high single shot flux in dichroism experiments.

Dynamic Electrochemical Phenomena at the Mesoscale

Abstract: Classically the electrode-electrolyte interface is considered the heart of electrochemistry. More recently the use of electrochemistry to drive bulk ion insertion (e.g., Li) has powered the battery revolution. As such electrochemical ion insertion is also extensively studied as a bulk phenomena which also has applications in advanced computing (e.g., ionic memory devices) and dynamic tuning of functional materials (e.g., electrochromics). Bridging the length-scale gap between interfaces and bulk is the fascinating mesoscale (tens to hundreds of nanometers). It is an under-investigated length scale in electrochemistry yet it is the length of particles the building block of porous electrodes. In this talk I will provide an overview of emergent electrochemical phenomena at the mesoscale focusing on how lithium intercalation take place in a many-particle ensemble. Breakthroughs in operando microscopy techniques have led to unexpected observations such as mosaic inter-particle phase separation metastable solid-solution and fictious phase separation. These behaviors can be rationalized by carefully considering the competition between bulk and interfacial free energy as well as between reaction and diffusion kinetics. With these fundamental insights at hand we can finally explain mesoscale phenomena in terms of fundamental thermodynamics and kinetics rather than in terms of unexplained heterogeneities providing practical design rules on engineering more uniform electrochemical devices.

Speaker Bio: William (Will) Chueh is an Associate Professor in the Department of Materials Science and Engineering and Energy Science & Engineering, a Senior Fellow of the Precourt Institute for Energy at Stanford University, and a faculty scientist at SLAC National Accelerator Laboratory. He leads a group of more than thirty researchers pursuing the following missions: (1) understand reactions and transport involving ions and electrons, and (2) decarbonize various energy transformation pathways. Additionally, he directs the SLAC-Stanford Battery Center and Stanford’s StorageX Initiative that builds academic-industrial partnerships. He received his BS in applied physics, and his MS and PhD in materials science from Caltech. Prior to joining Stanford in 2012, he was a Distinguished Truman Fellow at Sandia National Laboratories. Chueh has received numerous honors, including the David A. Shirley Award (2023), Friedrich Wilhelm Bessel Research Award (2022), MRS Outstanding Young Investigator Award (2018), Volkswagen/BASF Science Award Electrochemistry (2016), Camille Dreyfus Teacher-Scholar Award (2016), Sloan Research Fellowship (2016), NSF CAREER Award (2015), Solid State Ionics Young Scientist Award (2013), and Caltech Demetriades-Tsafka-Kokkalis Prize in Energy (2012)). In 2012, he was named as one of the “Top 35 Innovators Under the Age of 35” by MIT’s Technology Review. He serves on the editorial boards of numerous journals including ACS Nano and Energy & Environmental Science.

Congrats to Ruiming Cao for Receiving the Hitachi High-Tech Best Presentation Award at the SPIE Photonics West Conference

Hitatchi sponsors two High-Tech Best Presentation Awards in High-Speed Biomedical Imaging and Spectroscopy at the SPIE Photonics West Conference. Congratulations to Ruiming Cao for receiving this award in 2023!

Two Postdoctoral Fellow Research Positions with Prof. Chen-Ting Liao at Indiana University Bloomington

Two postdoctoral fellow positions available in physics/engineering at Indiana University Bloomington

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(1) A postdoctoral fellow position in classical- and quantum-enhanced imaging

Job Description. A postdoctoral fellow position is now available at the Department of Physics (or jointly at Department of Intelligent Systems Engineering), Indiana University, Bloomington, Indiana, U.S.A. This project uses spatial, temporal, wavefront, and polarization-structured light beams to mimic quantum imaging properties for biological applications. The project aims to conduct proof-of-concept experiments of enhanced imaging performance using optical coherence tomography (OCT) as the bioimaging modality. The overarching goal is to show that the new approaches could overcome and outperform existing OCT disadvantages, either for those based on classical supercontinuum light sources or single-photon quantum light sources. This experimental research will involve designing, developing, constructing, and characterizing several types of structured light, generating beams with entangled degrees-of-freedoms (dubbed classical entanglement of light or mode-entanglement). Then, these visible and near-infrared beams will be used to test Mach–Zehnder interferometry-like OCT imaging setup. Some simulations will be accompanied to verify and guide the experiments. In this exciting role, you will work under the direction of Prof. Chen-Ting Liao (physics) and Prof. Hui Min Leung (engineering).

Links to additional information which may be of interest:

https://www.indiana.edu/

https://physics.indiana.edu

https://engineering.indiana.edu

https://graduate.indiana.edu/support/postdoc.html

https://www.visitbloomington.com/

Required qualifications:

• Ph.D. in physics, chemistry, optics/photonics, electrical engineering, or related fields.

• Ph.D. candidates in the ABD (all but dissertation) status will also be considered.

• Proven track record in scientific research and development.

• Hands-on experience with lasers and optical setups.

• Experience with data analysis using Matlab, Python, etc.

• Excellence in research and strong communication skills.

• High degree of independence together with the ability to work in a collaborative environment.

• Good working knowledge of written and spoken English.

Preferred qualifications:

• Experience with structured light, quantum optics, and OCT.

• Some experience with optics/photonics simulations using ZEMAX, Lumerical FDTD.

• Some experience with nanofabrication such as e-beam lithography.

• Some experience of using software (Matlab, Python, LabVIEW) to automate experimental controls.

• Some experience of using software such as SolidWorks for experimental setup designs.

The initial appointment for this position will be for 12 months. Additional 12-24 month extensions will be available based on performance, mutual agreement and funding. A competitive salary along with a benefits package will be offered. The starting date is flexible. Minority, women, and international candidates are strongly encouraged to apply. Interested candidates should send their (i) CV (including completed degrees, list of publications, research experience and expertise), (ii) a Cover Letter (briefly summarizing qualifications, motivations, and interests in this position), and (iii) contact information of at least two references to Prof. Chen-Ting Liao (chenting.liao [at] gmail.com).

Indiana University is an equal employment and affirmative action employer and a provider of ADA services. All qualified applicants will receive consideration for employment based on individual qualifications. Indiana University prohibits discrimination based on age, ethnicity, color, race, religion, sex, sexual orientation, gender identity or expression, genetic information, marital status, national origin, disability status or protected veteran status. Indiana University is committed to excellence through diversity. Indiana University has a strong commitment to principles of diversity and in that spirit seeks a broad spectrum of candidates including women, minorities, and persons with disabilities, and encourages applications from candidates with diverse cultural backgrounds.

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(2) A postdoctoral fellow position in quantum VUV and EUV light generation

Job Description. A postdoctoral fellow position is now available at the Department of Physics, Indiana University, Bloomington, Indiana, U.S.A. The project aims to explore potential pathways to generate quantum entangled and/or squeezed short-wavelength light sources (wavelength 1-100 nm), including vacuum- and extreme-ultraviolet (VUV and EUV) light. The overarching goal is to test the feasibility of several potential methods, based on quantum optics, nonlinear optics, and ultrafast optics, to experimentally explore how to generate VUV and EUV light carrying nonclassical properties. The properties include single-photon or Fock states, entangled states (in photon numbers, polarizations, wavelengths, and delay times), amplitude/phase squeezed states, and/or bright squeezed vacuum states of light. This experimental research will involve developing, creating, and characterizing various classical and quantum light sources, including the technologies used for near-infrared, visible, and ultraviolet, to VUV/EUV light. In this exciting role, you will work under the direction of Prof. Chen-Ting Liao and in collaboration with other researchers.

Links to additional information which may be of interest:

https://www.indiana.edu/

https://physics.indiana.edu

https://engineering.indiana.edu

https://graduate.indiana.edu/support/postdoc.html

https://www.visitbloomington.com/

Required qualifications:

• Ph.D. in physics, chemistry, optics/photonics, electrical engineering, or related fields.

• Ph.D. candidates in the ABD (all but dissertation) status will also be considered.

• Proven track record in scientific research and development.

• Hands-on experience with pulsed lasers, optical setups, and vacuum technologies.

• Experience with data analysis using Matlab, Python, etc.

• Excellence in research and strong communication skills.

• High degree of independence together with the ability to work in a collaborative environment.

• Good working knowledge of written and spoken English.

Preferred qualifications:

• Good working knowledge and understanding of quantum optics and ultrafast optics.

• Some experience of using software (Matlab, Python, LabVIEW) to automate experimental controls.

• Some experience of using software such as SolidWorks for experimental setup designs.

The initial appointment for this position will be for 12 months. Additional 12-24 month extensions will be available based on performance, mutual agreement and funding. A competitive salary along with a benefits package will be offered. The starting date is flexible. Minority, women, and international candidates are strongly encouraged to apply. Interested candidates should send their (i) CV (including completed degrees, list of publications, research experience and expertise), (ii) a Cover Letter (briefly summarizing qualifications, motivations, and interests in this position), and (iii) contact information of at least two references to Prof. Chen-Ting Liao (chenting.liao [at] gmail.com).

Indiana University is an equal employment and affirmative action employer and a provider of ADA services. All qualified applicants will receive consideration for employment based on individual qualifications. Indiana University prohibits discrimination based on age, ethnicity, color, race, religion, sex, sexual orientation, gender identity or expression, genetic information, marital status, national origin, disability status or protected veteran status. Indiana University is committed to excellence through diversity. Indiana University has a strong commitment to principles of diversity and in that spirit seeks a broad spectrum of candidates including women, minorities, and persons with disabilities, and encourages applications from candidates with diverse cultural backgrounds.

Senior Machine Learning Design Engineer

My team is under the ASML Brion Product Engineering Group (PEG) organization, which is responsible for feasibility study, product definition/design, flow integration, performance testing, and early customer engagement. My team is currently focusing on applying machine learning (ML) and data science (DS) techniques into semiconductor applications. Here are two example products we are working on now: Context based wafer level grouping (CBWG) and machine learning based image quality enhancement (ML-IQE). In CBWG, we use traditional machine learning models (e.g., trees) to group wafers based on context information (e.g., fab routing) and then do fine control based on groups. For ML-IQE we apply the state-of-the-art deep learning models to enhance the images from our scanning electron microscope (SEM) equipment. All these ML/DS products are very critical to ASML’s business and bring tremendous values to our customers. We are actively looking for candidates w/ solid background in ML and DS to work with us on solving those real-world challenging problems using latest ML/DS techniques.

The hiring manager emphasized that: “The candidates don’t have to be a ML/DS expert, solid background on simulation/modeling/optimization will work as well.”

Congrats to Jessica Ramella-Roman for Being Elected as a 2024 Optica Fellow

Jessica Ramella-Roman has been elected as a Fellow of Optica for her pioneering contributions to the study of polarized light transport in biological media through experimental and computational approaches.

The Board of Directors of Optica (formerly OSA), Advancing Optics and Photonics Worldwide, recently elected 129 members from 26 countries to the Society’s 2024 Fellow Class. Optica Fellows are selected based on several factors, including outstanding contributions to research, business, education, engineering and service to Optica and our community.

Fellows are Optica members who have served with distinction in the advancement of optics and photonics. The Fellow Members Committee, led by Chair Ofer Levi, University of Toronto, Canada, reviewed 216 nominations submitted by current Fellows. The Committee extends its thanks to all of this year’s nominators and references. As Fellows can account for no more than 10 percent of the total membership, the election process is highly competitive. Candidates are recommended by the Fellow Members Committee and approved by the Awards Council and Board of Directors.

The new Fellows will be honored at Optica conferences and events throughout 2024.

High-fidelity imaging of highly periodic structures enabled by vortex high harmonic beams

STROBE scientists solved a major imaging challenge by demonstrating high fidelity short wavelength imaging of highly-periodic structures for the first time, using engineered illumination via high harmonic extreme UV (EUV) beams carrying orbital angular momentum (OAM). This enables high-fidelity imaging and inspection of highly periodic structures for next-generation nano, energy and photonic devices.

Lensless imaging based on coherent diffractive imaging (CDI) enables near-perfect diffraction-limited microscopy at short wavelengths, overcoming the limits of imperfect and lossy optics. However, high fidelity imaging of highly periodic structures has been challenging. In CDI, a beam is scanned across a sample, and the scattered light is collected by a detector. A computer algorithm is then used to reconstruct an image of the sample. However, to retrieve high-fidelity images, the scatter patterns must change as the beam is scanned – which is not the case for highly periodic samples.

Graduate students Bin Wang and Nathan Brooks, working with Henry Kapteyn and Margaret Murnane, solved this long-standing challenge by using high harmonic beams carrying OAM. The high divergence and peak-intensity near their edges introduces strong interference fringes between adjacent diffraction orders in the far-field. These encode phase information into the scattered light as the beam is scanned, significantly enhancing diversity in the diffraction patterns so that the phase can be reliably retrieved. Moreover, defects in otherwise periodic grids can be more sensitively detected with improved signal-to-noise ratio > 100x, and with lower dose and sample damage than for scanning electron microscopy.

Visible laser beams carrying OAM (i.e. donut-shaped) beams revolutionized visible super-resolution microscopy. Now there is a path forward for bringing these powerful capabilities to shorter wavelengths.

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About Lauren Mason