The University of Louisville Laser Lab (UL3) closed effective June 30, 2026. Please contact Dr. Jinjun Liu at jinjun.liu.01@gmail.com.
Thank you for your support and generosity over the past fourteen and a half years.
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Research in the University of Louisville Laser Lab (UL3, www.theul3.com), led by Prof. Jinjun Liu, focuses on high-resolution spectroscopic investigations of small (though far from simple) molecules using advanced laser spectroscopy techniques. Our studies center on the detection and characterization of reactive chemical intermediates such as free radicals and electronically excited molecules.
The experimental techniques employed include laser-induced fluorescence / dispersed fluorescence (LIF/DF), cavity ring-down (CRD), and Doppler-free saturation absorption spectroscopy. In addition, we are developing a novel cavity-enhanced two-photon double-resonance technique, enabled by our state-of-the-art laser systems, to probe otherwise inaccessible molecular “dark states.” These efforts provide quantitative insights into molecular structure, dynamics, and the nature of chemical bonding. Rigorous identification and analysis of experimental spectra are essential prerequisites for subsequent investigations of chemical reactions involving transient intermediates.
Recently, we have extended our research to metal-containing molecules of astrochemical interest, which also represent highly promising candidates for direct laser cooling and for probing new physics. We are particularly interested in molecular species that exhibit the Jahn-Teller (JT) and pseudo-Jahn–Teller (pJT) effects - vibronic (vibrational-electronic) interactions that drive spontaneous symmetry-breaking distortions in polyatomic molecules. Our group also develops advanced spectroscopic models to analyze the rotational and fine structure of open-shell molecules (free radicals) in degenerate and nearly degenerate states subject to JT, pJT, and spin–orbit (SO) interactions.
Complementing our experimental work, we employ quantum chemical methods, including density functional theory (DFT), complete active space self-consistent field (CASSCF), and coupled-cluster (CC) approaches, to elucidate molecular energy-level structures and to simulate and interpret observed spectra.
Research at UL3 has been funded by the National Science Foundation (NSF), the Department of Energy (DOE), NASA, the Kentucky Science and Engineering Foundation (KESF), the American Chemical Society (ACS), and the American Physical Society (APS).
[Read our recent publications]
The goal of the ultrafast spectroscopy study in our group, which is carried out in the Conn Center for Renewable Energy Research, is to contribute to renewable energy science and technology through fundamental spectroscopic studies using ultrafast laser systems. Femtosecond (fs) transient absorption (TA) spectroscopy and time-resolved photoluminescence spectroscopy are used in our lab. Our research efforts in the field of ultrafast spectroscopy are focused on the characterization of solar cell materials, especially nanostructures and polymers. We aim to understand the fundamental photoinduced processes in the materials and their interfaces, which are essential to their functions and applications.
Prof. Jinjun Liu is the Chair of the International Advisory Committee of the International Symposium On Molecular Spectroscopy (ISMS). He has served as Chair of the 37th International Symposium on Free Radicals (see the J. Phys. Chem. A Viewpoints) and co-Chair of the 26th International Conference on the Jahn-Teller Effect.
" Spin-vibronic interactions in asymmetric-top open-shell molecules and their effects on vibrational and rotational branching ratios", presented at the 2022 "Laser-Cooling of Molecules" Workshop of the Institute for Theoretical Atomic, Molecular and Optical Physics (ITAMP) at the Harvard & Smithsonian Center for Astrophysics (CfA).
Molecular Spectroscopy and the continuous-wave optical parametric oscillator (CW OPO) system from Toptica Photonics, Interview with Dr. Jinjun Liu
WHAS-TV reporting UofL Laser Labs:
Introducing the UofL Laser Labs:
Jahn-Teller distortion and pseudo-rotation. Molecular physics is fun!
Ch 06.04-pseudo-rotation.mp4Google Sites
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