Abstract :: Cristian Bahrim, Lamar University :: 6 September 2023

Cristian Bahrim, Ph.D.
Department of Physics – Lamar University
Joint appointment with Phillip Drayer Department of Electrical Engineering
Director of the Office of Undergraduate Research

Interaction of Polarized Light with Matter. Photonic Applications
Spin alignment of atoms can be created through laser excitation using polarized light and studied using LIFS technique. This alignment can be easily altered due to atomic motion, and it is often decided by the frequency of collisions, which depends on temperature.  We report studies of atomic depolarization due to anisotropic and isotropic collisions in an energy range from 0.1 meV to 3eV (or equivalently from 10 to 1,000 Kelvin) using light rare gas atoms due to their lack of chemical reactivity. Our accurate potentials to describe rare gas transient molecules allow us to identify molecular (vibrational-electronic) states which account for the anharmonic motion of the atoms. One can excite these molecular states with IR picosecond radiation, and eventually trap an otherwise transient rare gas molecular system on long-lived vibrational electronic states identified inside potential wells and located at small internuclear distances ( Because collisional dephasing in spin aligned atoms is a big challenge for many applications, including quantum memory, we suggest a quantum entanglement mechanism using two circularly polarized laser beams interacting with atoms on Zeeman states assisted by a stronger linearly polarized laser. In our W-configuration, a linearly polarized laser entangles two circularly polarized lasers through quantum interference. This is an Electromagnetic Induced Transparency (or EIT) setting. Atomic spin alignment entangled with laser radiation is a more stable system with the temperature. For practical applications we propose an optoelectronic switch where two lasers (a weak probe and a stronger coupler) interfere on the vibratory dipoles of a dielectric silica-based surface assisted by an isotropic energy background from a capacitor configuration which basically uses the silica glass as dielectric. We show experimental evidence for locking the energy of a probe laser in the vibratory atomic dipoles located on the dielectric surface through destructive interference triggered by a stronger coupling laser which simultaneously irradiates (at normal incidence) the same dipoles. We measure the reflectance of a probe laser beam by a crown glass surface in a range 12 wide around Brewster angle, assisted by a coupling laser and a capacitor voltage, and observe a regular interference pattern with minima of negligible reflectivity. This indicates energy retention of the probe laser beam on the dielectric surface.

Biographical sketch:
Cristian Bahrim is Full Professor of Physics at Lamar University (2015-present) and from 2005 holds a joint appointment with the Phillip M. Drayer Department of Electrical Engineering. Dr. Bahrim received his Ph.D. degree from the University of Paris at Orsay, in 1997 as a French Government scholar. Between 1998 and 2001, he was postdoc at the Kansas State University and worked in the Theoretical Atomic Physics Group. In 2001, he joined Lamar University. In 2013-2014 he was the Interim Chair of the Physics Department. Along the years, Dr. Bahrim was involved in various research topics in theoretical physics with applications in engineering. Among his most significant scientific results we list: an improved Brewster angle method for finding accurate indices of refraction; optoelectronic switches; the interpretation of atomic depolarizations using a molecular model; the idea of using polarized photons for binary recording in a novel EIT-type W scheme; the formation of excimers with light noble gases. Dr. Bahrim is referee to several journals in the United States, Europe, India, and China. He published more than 130 papers in journals, books, and conference proceedings. As teacher at Lamar, Dr. Bahrim led several graduate and undergraduate students to outstanding academic success, including McNair Scholars, Beck fellows, or Goldwater recipients, with graduates in leading positions at Google Inc., NASA, US Navy, and many academic institutions. For these results, he received the 2015 Faculty Mentor Award at Lamar, and the 2019 Faculty Mentor Award of the Year in Physics and Astronomy in the United States, offered by the Council of Undergraduate Research in D.C. In 2019 he was the national finalist for the Advisor of the Year of the Society of Physics Students (SPS). Dr. Bahrim was Conference Chair for the 2016 and 2020 Joint Spring Meetings of the Texas Sections of APS, AAPT and SPS Zone 13. In 2017 and 2018, he was visiting professor at the Shanghai International Studies University. He is now the Director of the Office of Undergraduate Research at Lamar University, after five years as Assistant Director (2017-2019) and Interim Director (2019-2022).