Lasers and Optics

Dr. Herman Batelaan

DEPARTMENT OF PHYSICS & ASTRONOMY (ATOMIC, MOLECULAR, AND OPTICAL PHYSICS)

Ghost Imaging

A team of two students will work on ghost imaging (one funded by REU and the other by local funds). One student will work on a laser-driven multi-fiber nanotip source in collaboration with Prof. Passian from Oak Ridge National Lab using single nanotip fibers that we have recently developed. Computational ghost imaging relies on a programmable source, which is what the multi-fiber tip will provide. The other student will perform the accompanying computer simulation, and computer control of the source.

Dr. Martin Centurion

DEPARTMENT OF PHYSICS & ASTRONOMY (ATOMIC, MOLECULAR, AND OPTICAL PHYSICS)

Ultrafast Dynamics

The Ultrafast Dynamics group focusing on understanding and controlling the conversion of light into chemical energy and heat at the molecular level. Upon absorption of a photon, a molecule undergoes structural transformations on the femtosecond scale, which lead to the breaking and making of chemical bonds, changes in the molecular geometry and triggering of different vibrational modes. In order to understand these transformations, it is essential to be able observe them on their natural time scales.

We have developed the method of diffractive imaging with femtosecond electron pulses, which allows us to capture molecular dynamics with atomic resolution on femtosecond time scales. Our work involves ultrafast laser, generation and characterization of electron pulses and retrieving structures from electron diffraction patterns. Previous student projects have involved work on sample delivery, characterization of laser and electron pulses, automation of experimental components, simulation of electron pulse propagation and data analysis.

Dr. Matthias Fuchs

DEPARTMENT OF PHYSICS & ASTRONOMY (ATOMIC, MOLECULAR, AND OPTICAL PHYSICS)

Next Generation X-ray Lightsource

The research of the Fuchs group is focused on the development of what might be called the next generation X-ray lightsource. The generated X-ray pulses have an ultrashort duration of only a few femtoseconds (1 fs = 10⁻¹⁵ s). The combination of X-ray wavelength and femtosecond pulse duration enables the direct observation of dynamics on atomic time- and length-scales. This allows for example the investigation of atomic rearrangement in chemical reactions or the atomic motion in solids in real time.

In our novel source, the X-rays are generated via the emission of synchrotron radiation from relativistic electrons traversing a periodic magnetic structure (called undulator) or a plasma structure. The use of a novel electron acceleration scheme based on ultrahigh-power lasers allows for a reduction of the dimension of the source, which for conventional sources is on the km-scale (or the length of about 10–20 football fields), to a setup that readily fits into a university-scale laboratory.

The projects offered to summer students are of a highly cross-disciplinary nature in the framework of the unique Diocles petawatt laser facility. Tasks include hands-on activities, such as setting up parts of the experiment as well as help in the design and computer simulations of the physics involved. The actual experimental runs involve working inside the target area, laser work and subsequent data analysis.

Dr. Timothy J. Gay

DEPARTMENT OF PHYSICS & ASTRONOMY (ATOMIC, MOLECULAR, AND OPTICAL PHYSICS)

Spin-polarized electrons

Prof. Gay’s research uses polarized electrons to study spin-dependent effects in electron-molecule scattering, with targets ranging from chiral polyatomics to H₂. In addition, we are developing spin-polarized electron sources based on our recent discovery of fast, multiphoton-induced electron emission from GaAs nanostructures. Such sources have the potential to enable imaging of spin-dependent chemical reactions and magnetic dynamics occurring in the solid-state on femtosecond time scales.

Our experiments have three primary research objectives:

(1) Studies of Polarized Electron Collisions with Chiral Molecules – How does chiral symmetry breaking affect the scattering of polarized electrons by chiral molecules? The underlying collision dynamics are unknown. Our recent observation of chirality-dependent molecular dissociation has provided an important validation of the Vester-Ulbricht hypothesis, which seeks to explain the origin of biological homochirality. This is one of the most fundamental questions in sciences.

(2) Studies of Fast Polarized Electron Emission from GaAs and Metallic Nanostructures – We have shown that femtosecond light pulses can emit pulses of spin-polarized electrons from GaAs tips and that these electron pulses are almost as short as the photon pulses that produced them. Importantly, these electrons are produced without the need for extensive surface preparation, so the operation of the source is very simple. We are this process with a variety of GaAs and chiral metallic nanostructures to see how fast, intense, and polarized we can make these pulses.

(3) Threshold Studies of Electron Scattering from H₂ – We recently observed a negative (oblate) alignment of excited-states of H₂ close to their excitation threshold. This result is not predicted by theory. We propose to couple a GaAs source to a monochromator to make high-energy resolution measurements of excitation in H₂ near threshold to test the latest theory for this process.

Dr. Alena Moon

DEPARTMENT OF CHEMISTRY

Light-matter interactions and spectroscopy

Spectroscopy—the interaction of electromagnetic radiation with atoms and molecules—is a ubiquitous tool for probing and understanding molecules and reactions across all molecular sciences. So much so that the American Chemical Society (ACS) has made its use required for undergraduates in accredited chemistry programs (ACS CPT). Though spectroscopy is fundamental to the practice of chemistry and much of STEM, undergraduate education about spectroscopy remains fragmented and limited by the absence of any systematic investigations of how students learn foundational concepts of light-matter interactions and spectroscopy.

The aim of this research, then, is to generate an evidence-based theoretical foundation for curriculum development in the form of a learning progression on light-matter interactions and spectroscopy. To achieve this goal, a sequential mixed-methods approach will be employed.

This research will occur in two stages: (1) cross-sectional qualitative investigation of students’ conceptual understanding and competency at interpreting spectra and using spectroscopic methods, and (2) development and testing of an assessment instrument for assigning students to learning progression levels. An undergraduate researcher on this project would design tasks and conduct interviews with students using those tasks. The researcher would then transcribe, analyze, and interpret interview data. In this way, an undergrad researcher would develop qualitative analysis skills along with an enhanced understanding of spectroscopy and its use in chemistry research.

Dr. Eva Schubert

DEPARTMENT OF ELECTRICAL & COMPUTER ENGINEERING

Chiral Heterostructure Nanomaterials for Photonic Applications

The Schubert lab has expertise in metamaterial fabrication, characterization, and optical in-situ growth monitoring. The lab employs bottom-up methods for self-organized growth such as oblique angle deposition (OAD) and atomic layer deposition, and extensively uses in-situ spectroscopic ellipsometry for real time growth monitoring. Metamaterials are particularly of interest for photonic and optical applications in sensors, filters, polarization-sensitive devices and for light harvesting. Si nanospirals have intriguing chiro-optical properties such as the recently observed tunable circular dichroism and optical activity. Small chiro-optical responses and limits in spectral tunability impose obstacles for applicability in devices.

Here we propose to incorporate plasmonic metallic segments (Au or Ag) into dielectric nanospirals from Si in order to investigate the influence of number and length of metal segments on the chiro-optical properties of spiral metamaterials. In the 10-week REU period, the student will (a) learn to prepare chiral metamaterials via oblique angle deposition and characterize their geometry using scanning electron microscopy (week 1-5), and (b) measure and analyze the chiro-optical properties for Si-Me nanospirals by means of Muller-Matrix spectroscopic ellipsometry (week 6-10). Through these studies, the student will receive basic training in operating ultra-high vacuum systems, and material deposition by e-beam evaporation and ion-beam assisted deposition. The student will learn how to operate commercial spectroscopic ellipsometry equipment and will be introduced to optical data analysis using modern regression algorithms. The REU student will work closely with a graduate student or postdoctoral researcher in the Schubert lab. The student must keep and maintain a laboratory notebook, which will be examined regularly by the supervising graduate student or postdoctoral researcher.

Dr. Kees Uiterwaal

DEPARTMENT OF PHYSICS & ASTRONOMY (ATOMIC, MOLECULAR, AND OPTICAL PHYSICS)

Augmented Reality in the Laser Lab

REU students will be involved in the development of interactable Augmented Reality products for three-dimensional visualization of our various experiments and experimental research topics. In 2020, we set up a first station for the development of Augmented Reality experiences. This includes a fully equipped desktop computer with a powerful GUI, various software packages needed for development of the product, and a Google Hololens 2 (similar stations are used for game development). A wide range of attractive topics for these immersive Augmented Reality experiences is available. We study the interaction of femtosecond laser pulses with matter. This includes ionization of molecules. We also investigate optical vortices: ‘whirling bullets of light’.

One of our achievements was the experimental creation of ultrashort optical vortices. Another new pathway of research is the linear and nonlinear propagation of laser pulses in liquids. One of our detection methods here is the fluorescence of marker dyes in the visible after two-photon absorption (2PA) in the infrared. We use this to characterize our infrared laser pulses, but also to study the interaction of such pulses with the dye, and with the solvent. Specific topics for Augmented Reality experiences could be optical vortices, beam propagation in liquids, holographic shaping of laser pulses, and mapping the various laser paths in the lab and inside our equipment.

Dr. Craig Zuhlke

DEPARTMENT OF ELECTRICAL & COMPUTER ENGINEERING

 Electro-Optics and Functionalized Surfaces

The Center for Electro-Optics and Functionalized Surfaces (CEFS) at UNL has developed techniques to directly functionalize or tailor the surface properties of metals using a technique known as femtosecond laser surface processing (FLSP). With FLSP, the properties of metals are altered by creating self-organized micron and nanoscale surface structures combined with la-ser-induced chemistry changes and subsurface microstructure changes using finely controlled ultra-short laser-matter interactions.

FLSP can be used to change the wetting properties of surfaces, to make surface superhydrophobic or superhydrophilic, or alter the optical properties of a surface (e.g. create broadband absorbing or high emissivity surfaces). FLSP has several distinct advantages compared to traditional functionalization techniques, such as lithography or coatings, because surface features are generated directly on the metallic surface through a combination of preferential laser ablation, fluid flow, plasma driven processes, and redeposition of ablated material in the form of nanoparticles The FLSP surfaces are highly permanent, do not suffer from the delamination issues often associated with coatings, and can be finely tuned to specific applications. Recently, CEFS has shown that these fs laser functionalized surfaces are useful in producing superhydrophobic surfaces, enhancing two phase heat transfer, altering optical absorption, producing anti-icing and anti-microbial surfaces, reducing drag, and producing high emissivity surfaces. The wide range of applications of FLSP and the large multidisciplinary research program by CEFS provides a number of opportunities for REU students to be involved in research.