University of Texas at Austin, Austin, Texas
July 23, 2021 @ 4:00pm in PMA Hall Room 5.104 and via Zoom
Nonlinear Absorption Spectroscopy of Bulk Semiconductors and Nanocrystalline Silicon Quantum Dots
Brandon J. Furey1
1University of Texas at Austin
Nonlinear absorption spectra of bulk semiconductors and nanocrystalline semiconductor quantum dots are investigated with the aim of understanding the limitations and potential applications of bulk semiconductors in photonic applications and of nanocrystalline semiconductor quantum dots for biological imaging. These studies include open-aperture Z-scan measurements of GaP to measure degenerate two-photon absorption and rotational anisotropy. However, as this technique requires high light intensities, self-focusing and free-carrier absorption can complicate analysis. Pump-probe modulation spectroscopy can detect a measurable signal at much lower lighter intensities and was used to study GaP, GaAs, and Si. This allowed complete characterization of the degenerate imaginary part of the third-order nonlinear optical susceptibility tensor and analysis of the dynamics which was crucial for identifying anomalous cases due to non-instantaneous responses such as phase gratings. Size-dependence of two-photon excited photoluminescence (2PE-PL) in nanocrystalline Si quantum dots (nc-SiQDs) was measured at a single excitation wavelength by calibrating to one-photon excited photoluminescence (1PE-PL). My collaborators also demonstrated biological imaging of mouse cells using 1PE-PL and 2PE-PL confocal microscopy with nc-SiQDs encapsulated in liposomes. 2PE-PL spectra of nc-SiQDs were measured for two different nanocrystal sizes. Calculations of the efficiency of 2PE-PL imaging in biological tissues were also performed to compare to other quantum dots and molecular fluorophores to aid in the selection and optimization of biological imaging agents. This work opens the door to further investigation, especially in semiconductor quantum dots and other low-dimensional structures and their wide-ranging applications.
Link to host department: https://ph.utexas.edu/
Brandon J. Furey 