We specialize in developing state-of-the-art techniques to generate intense electromagnetic radiation across the terahertz (THz), long-wavelength infrared (LWIR), and mid-infrared (MIR) spectra, which are considered challenging to produce. We integrate multimodal probing schemes like full-spectrum ellipsometry, Raman spectroscopy, and second-harmonic generation to unravel intricate dynamics at femtosecond resolution. We also collaborate with national facilities to leverage ultrashort X-ray pulses to capture atomic transformation directly. 

Generation of high-field terahertz pulses

THz radiation has a variety of compelling applications, including material diagnostics, industrial quality control, non-intrusive standoff sensing, homeland security, and wireless communication. Recently, the major experimental advances in intense THz pulse generation have set the stage for dramatic advances in our ability not just to understand matter but to coherently drive it into novel nonequilibrium phases by manipulating the key low-frequency modes. In our lab, we design innovative approaches to address the most challenging limitations inherent in high-field THz technology. We focus on the optical rectification process in a lithium niobate crystal to downconvert near-infrared (NIR) pulses to THz pulses at 0.2-3 THz range, with the phase-matching condition satisfied by the tilted-pulse-front technique. Upon readiness for experimentation, our high-field THz pulses will facilitate advanced probing to resolve subtle spectroscopic features across specific spectral ranges, including femtosecond stimulated Raman scattering, phase-sensitive second harmonic generation, sum-frequency vibrational spectroscopy, and THz multidimensional spectroscopy.

Selected publications: 

• Jiaojian Shi†, Daehan Yoo†, Ferran Vidal-Codina, Chan-Wook Baik, Kyung-Sang Cho, Ngoc-Cuong Nguyen, Hendrik Utzat, Jinchi Han, Aaron M. Lindenberg, Vladimir Bulović, Moungi G. Bawendi, Jaime Peraire, Sang-Hyun Oh, Keith A. Nelson, "A Room-Temperature Polarization-Sensitive CMOS Terahertz Camera Based on Quantum-Dot-Enhanced Terahertz-to-Visible Photon Upconversion", Nature Nanotechnology 17, 1288-1293 (2022).

• Jiaojian Shi†, Ya-Qing Bie†, Alfred Zong†, Wei Chen, Shiang Fang, Jinchi Han, Zhaolong Cao, Yong Zhang, Takashi Takashi, Kenji Watanabe, Xuewen Fu, Vladimir Bulović, Efthimios Kaxiras, Edoardo Baldini, Pablo Jarillo-Herrero, Keith A. Nelson, "Intrinsic 1T' phase induced in atomically thin 2H-MoTe2 by a single terahertz pulse," Nature Communications 14, 5905 (2023).

• Jiaojian Shi†, Frank Y. Gao†, Zhuquan Zhang†, Hendrik Utzat, Ulugbek Barotov, Ardavan Farahvash, Jinchi Han, Jude Deschamps, Chan-Wook Baik, Kyung-Sang Cho, Vladimir Bulović, Adam P. Willard, Edoardo Baldini, Nuh Gedik, Moungi G. Bawendi, Keith A. Nelson, "Terahertz Field-Induced Reemergence of Quenched Photoluminescence in Quantum Dots", Nano Letters 22, 4, 1718–1725 (2022).

• Jiaojian Shi†, Edoardo Baldini†, Simone Latini, Shunsuke A. Sato, Yaqing Zhang, Brandt C. Pein, Pin-Chun Shen, Jing Kong, Angel Rubio, Nuh Gedik, Keith A. Nelson, "Room Temperature Terahertz Electroabsorption Modulation by Excitons in Monolayer Transition Metal Dichalcogenides", Nano Letters 20, 5214-5220 (2020).

• Yaqing Zhang, Jiaojian Shi, Xian Li, Stephen L. Coy, Robert W. Field, Keith A. Nelson, "Nonlinear Rotational Spectroscopy and Many-Body Interactions in Water Molecules", Proceedings of the National Academy of Sciences 118 (40) e2020941118 (2021).

Generation of high-field long-wavelength infrared and mid-infrared pulses

Our goal for surgical control of physicochemical processes necessitates the generation of intense light pulses in the LWIR and MIR ranges. We generate frequency-tunable LWIR and MIR pulses (10-100 THz) by difference frequency mixing of femtosecond NIR pulses (signal and idler) in a nonlinear crystal (e.g., GaSe), produced by optical parametric amplifiers. Stabilization of the carrier-envelope phase is achieved by mixing the signal and idler beams seeded by a common white light continuum. Employing the chirped-and-delay method allows the preparation of narrowband pulses with durations in the tens of picoseconds.

Selected publications:

• Jiaojian Shi†, Weiwei Sun†, Hendrik Utzat†, Ardavan Farahvash, Frank Y. Gao, Zhuquan Zhang, Ulugbek Barotov, Adam P. Willard, Moungi G. Bawendi, Keith A. Nelson, "All-Optical Fluorescence Blinking Control in Quantum Dots with Ultrafast Mid-Infrared Pulses", Nature Nanotechnology 16, 1355-1361 (2021).

• Jiaojian Shi†, Haowei Xu†, Christian Heide, Changan HuangFu, Chenyi Xia, Felipe de Quesada, Hongzhi Shen, Tianyi Zhang, Leo Yu, Amalya Johnson, Fang Liu, Enzheng Shi, Liying Jiao, Tony Heinz, Shambhu Ghimire, Ju Li, Jing Kong, Yunfan Guo, Aaron M. Lindenberg, "Giant Room-Temperature Nonlinearities in a Monolayer Janus Topological Semiconductor", Nature Communications 14, 4953 (2023).

• Jiaojian Shi†, Yijing Huang†, Christian Heide†, Burak Guzelturk, Carl-Friedrich Schön, Haowei Xu, Yuejun Shen, Yuki Kobayashi, Andrew F. May, Pooja Donthi Reddy, Duan Luo, Eammonn Hughes, Kunal Mukherjee, Mariano Trigo, Ju Li, Jian Zhou, Shambhu Ghimire, Matthias Wuttig, David A. Reis, Aaron M. Lindenberg, "Nonresonant Optomechanical Phase Control"

Ultrafast spectroscopy and control at single-molecule levels

Understanding the energy pathways of light deposition is a central focus in chemistry and materials research, with complexity stemming from ultrafast interactions between lattice ions, spins, and electrons. Meanwhile, dimensionality reduction leads to peculiar thermodynamics, quantum physics, and extreme environmental sensitivity. These effects engender substantial particle heterogeneity and inter-particle coupling, rendering measurements on densely packed or hierarchical materials to be of minimal value towards addressing the goal of elucidating fundamental dynamics. We focus on visualizing the energy flow of single molecules or nanoparticles by developing ultrafast single-molecule spectroscopy based on fluorescence detection. The integration of THz and MIR excitation broadens spectral features, offering refined control and profound insights at the single molecule level. They could open new avenues for extreme-scale characterization and synthetic improvements in quantum information and clean energy development.

Selected publications:

• Jiaojian Shi†, Yuejun Shen†, Fan Pan†, Weiwei Sun, Anudeep Mangu, Cindy Shi, Amy McKeown-Green, Parivash Moradifar, Moungi G. Bawendi, William E. Moerner, Jennifer A. Dionne, Fang Liu, Aaron M. Lindenberg, "Solution-Phase Single-Particle Spectroscopy for Probing Multi-Polaronic Dynamics in Quantum Emitters at Femtosecond Resolution", in press at Nature Materials (2024).

• Jiaojian Shi†, Weiwei Sun†, Hendrik Utzat†, Ardavan Farahvash, Frank Y. Gao, Zhuquan Zhang, Ulugbek Barotov, Adam P. Willard, Moungi G. Bawendi, Keith A. Nelson, "All-Optical Fluorescence Blinking Control in Quantum Dots with Ultrafast Mid-Infrared Pulses", Nature Nanotechnology 16, 1355-1361 (2021).

Intense THz-LWIR-MIR excitation at national X-ray facilities