Add to Calendar 2026-05-26T14:00:00 2026-05-26T15:00:00 Nonlinear optics on 2D materials and ultrathin films Event Information: Abstract: Two-dimensional (2D) materials and ultrathin films are becoming important materials and structures for basic research and new technologies due to their unique physical properties and further applications in science and industry. Nonlinear optics (NLO) is a crucial research tool in materials science. Nonlinear optics is like "X-rays or microscopy," helping us to understand deeper symmetries, electronic behavior, and ultrafast dynamics within matter, especially at the nanometer scale. This presentation will introduce some mechanisms and applications of nonlinear optics in two-dimensional materials and ultrathin films. It is a challenge to study and distinguish the influence of water molecules on 2D materials for the usage of gas sensors.  We propose nonlinear optics method to analyze the evolution of hyperpolarizability on WS2 while gas or water vapor adsorbed on WS2 surface. Second harmonic generation (SHG) is a nondestructive measurement on the hyperpolarizability evolution caused by gas adsorption on layered van der Waals materials. Simplified bond hyperpolarizability model (SBHM) acts as a leveraging function to facilitate the detection of material modifications in response to environmental influences, including the inevitable water molecules. Taiwan's advanced semiconductor manufacturing is a vital industry that influences the world. Interface trap density (Dit) is a crucial parameter in advanced semiconductor manufacturing processes We developed a comprehensive model to analyze time-dependent SHG (TD-SHG) signals, incorporating quantum tunneling effects and charge density evolution. By observing the multiphoton absorption of SiO2/Si under femtosecond laser irradiation, the evolution of the TD-SHG signal reveals the built-in electric field, indirectly analyzing Dits.      Event Location: Brimacombe 311