Presenting my research on polarization-dependent second-harmonic generation and two-photon photoluminescence in thin-film silver iodide at the APS March Meeting 2025.
Author: Leonardo Landivar Scott | Major: Physics | Semester: Spring 2025
My name is Leonardo Landivar Scott, and I am a junior majoring in Physics with minors in Mathematics and Nanomaterials at the Fulbright College of Arts & Sciences, University of Arkansas. Under the guidance of my mentor, Dr. Hiro Nakamura from the Department of Physics, I have conducted research since Fall semester of 2023 and will conclude in Spring 2026.
My current honors project probes the anisotropic (direction-dependent) response of twophoton photoluminescence (2PPL) in silver-iodide (AgI) nanorods and compares it with the response in triangular AgI thin films. In simple terms, I shine an ultrafast pulsing laser on needle-shaped crystals only a few atoms thick and watch how they glow. Mapping that glow as I rotate the polarization of the laser reveals hidden symmetries— and asymmetries—inside the crystal lattice.
Nonlinear optical effects like 2PPL occur when a material absorbs two photons at once and emits one of higher energy. Because the process is highly sensitive to crystal symmetry, nanostructures that break symmetry in controlled ways can act as “on–off” gates for light itself. My work demonstrates that AgI nanorods amplify or suppress 2PPL depending on laser angle, hinting at tailor-made pixels for next-gen displays or secure quantum communication devices. For fellow students, the takeaway is that even a single crystal’s shape can unlock entirely new photonic behavior – proof that materials science is fertile ground for creative discovery.
My experiments start in a vacuum chamber where I grow ultrathin AgI crystals via physical vapor deposition (PVD). Temperature gradients and growth time dictate whether a crystal becomes a triangle, rod, or irregular flake. After that, I characterize thickness with atomic-force microscopy. The optical work happens under a femtosecond laser: I rotate the incoming polarization through 360°, collect emitted photons with a spectrometer, and plot intensity on polar graphs. MATLAB scripts (and a lot of coffee) handle curve-fitting to extract the directional nanorod’s response.
The data show striking 6-lobed patterns for second-harmonic generation (SHG) and peanut-shaped lobes for 2PPL – evidence that different nonlinear processes “see” the lattice differently. A significant milestone in my research journey was the opportunity to present my work at the APS (American Physical Society) March Meeting 2025, held in Anaheim, California. Presenting at this prestigious conference, particularly in the session dedicated to graduate-level research on 2D Material Optics, provided valuable feedback and validation of my findings. Fielding questions in real time sharpened my interpretation of the results and convinced me the work is publication ready.
Encouraged by this experience, I am currently preparing my research findings for publication in an academic journal. Writing a scientific manuscript will help formalize and disseminate the outcomes of my work, contributing valuable new insights to the broader scientific community. Additionally, I plan to explore further experimental avenues, such as temperature-dependent studies, to deepen my understanding of anisotropic optical phenomena in silver iodide nanostructures. Beyond these immediate objectives, my longer-term plan includes graduate studies, where I hope to expand upon this research and continue exploring fundamental questions in nonlinear optics and quantum photonics.