CBC Colloquium Series: "Imaging Chemistry in Action" by Dr. Mohammed Hassan

Chemistry is, at its core, the motion of electrons. Bond formation and breaking, charge transfer, and the 
earliest steps of photochemistry are all governed by valence and core electrons that rearrange on the 
attosecond timescale while moving over ångström distances. Capturing these dynamics directly requires an 
instrument that resolves motion in space and time simultaneously — a combination that has long remained 
out of reach, since attosecond probes typically sacrifice spatial detail and atomic-resolution imaging rarely 
reaches attosecond speeds [3,5].
This talk traces the development of ultrafast electron microscopy toward that goal, from femtosecond 4D 
electron microscopy [1] to attosecond electron imaging [3,5]. I will present “Attomicroscopy” — an optical-gating 

approach that compresses electron pulses [2] to generate the world’s fastest electron microscope (a 
Guinness World Record) — and show how it captures electron motion in graphene in real space, reciprocal 
space, and real time [6,7], resolving the interplay of interband and intraband dynamics that builds on 
attosecond electron-motion control first demonstrated in dielectrics [4]. I will then introduce Quantum 
Attomicroscopy, an attosecond scanning tunneling microscope that pairs attosecond light-field control with 
sub-ångström spatial resolution to probe charge migration in individual DNA base pairs [8]. This targets 
the open questions of how a hole moves following ionization, whether transport proceeds by coherent 
tunneling or classical hopping, and how long electronic coherence survives in a native biological setting.
Complementary results extend these tools to biological and material chemistry: imaging ultrafast electron 
and chemical dynamics in cable-bacteria nanowires, and field-driven control of monolayer water on 
graphite — including electric-field manipulation of molecular arrangement, dipole polarity, and ice-phase 
nucleation. Together, these advances open a route to watching, and ultimately steering, chemistry in action 
at the fundamental scale of the electron.
References
1. B. Barwick, H. S. Park, O.-H. Kwon, J. S. Baskin, A. H. Zewail. 4D imaging of transient structures 
and morphologies in ultrafast electron microscopy. Science 322, 1227–1231 (2008).
2. M. T. Hassan et al. Optical gating of electron pulses. Proc. Natl. Acad. Sci. USA 112 (2015).
3. M. T. Hassan. Attomicroscopy: from femtosecond to attosecond electron microscopy. J. Phys. B: At. 
Mol. Opt. Phys. 51, 032005 (2018).
4. D. Hui et al. Attosecond electron motion control in dielectric. Nature Photonics 16, 33–37 (2022).
5. M. Th. Hassan. Electron microscopy for attosecond science. Physics Today 77(6), 38–43 (2024).
6. D. Hui, H. Alqattan, M. Sennary, N. V. Golubev, M. T. Hassan. Science Advances 10, eadp5805 
(2024).
7. M. Yuan et al. Graphene attomicroscopy: electron motion imaging and control in real time and space. 
arXiv:2407.03537 (2024).
8. N. V. Golubev, M. T. Hassan. Imaging quantum chemistry in action with quantum attomicroscopy. 
Commun. Chem. 9, 192 (2026)

Bio:

Dr. Mohammed Hassan is an Associate Professor of Physics and Optical Sciences at The University of Arizona 
(UA). He earned his Ph.D. from the Max Planck Institute for Quantum Optics in Munich, Germany, in 2013, 
working in the research group of Prof. Ferenc Krausz (Nobel Laureate, 2023). He then joined the California Institute 
of Technology (Caltech) as a postdoctoral scholar in the group of Prof. Ahmed H. Zewail (Nobel Laureate, 1999), 
where he conducted research until 2017.
Some of Dr. Hassan scientific achievements can be summarized as follows:
Dr. Hassan is widely recognized for pioneering the field of attosecond electron microscopy, introducing the 
"Attomicroscope"—the world's fastest electron microscope capable of imaging electron motion in real time. This 
revolutionary tool has opened a new frontier in ultrafast imaging, enabling direct visualization of electron behavior 
in solid-state materials and advancing quantum science.
Dr. Hassan group developed the first petahertz quantum phototransistor , capable of switching on and off in just 
630 attoseconds—a speed equivalent to 1.6 petahertz, or over a million billion times per second. This unprecedented 
speed was demonstrated using a novel graphene-silicon-graphene (Gr-Si-Gr) transistor structure, marking a 
significant leap toward the future of ultrafast light-driven electronics.
Most recently, Dr. Hassan has demonstrated all-optical switching and quantum current switching on the 
attosecond timescale, setting a new world record for switching speed. Leveraging his expertise in light field 
synthesis, he has also developed methods to digital encode data onto ultrafast laser pulses. Additionally, he has 
introduced novel methodologies for sampling ultrafast laser light fields and measuring electronic response delays 
in neutral matter.
His research group has also achieved a major milestone in ultrafast quantum optics by demonstrating amplitude 

squeezed quantum light, which he has applied to developing highly secure, high-speed quantum communication 
technologies.
Early in his career, Dr. Hassan developed the light field synthesizer, which enabled the generation of the first 
optical attosecond pulse—the shortest light pulse ever recorded, earning recognition in the Guinness World 
Records. Using this breakthrough technology, he measured the time it takes for an electron to respond and move, 
providing unprecedented insight into ultrafast electron dynamics. He also utilized synthesized waveforms to 
generate extreme ultraviolet radiation from solids, offering a new temporal perspective on high harmonic generation 
and electron behavior in condensed matter.
During his postdoctoral tenure at Caltech, Dr. Hassan optimized ultrafast optical gating techniques to generate 
electron pulses, achieving the shortest electron pulse in an electron microscope. He also contributed to the first 
imaging of nanoparticle motion in a liquid state using ultrafast electron microscopy. His early breakthroughs were 
published in leading scientific journals.
Dr. Hassan won the Microscopy Today Innovation Awards 2025 for the Attomicroscopy. This award is given by 
the Microscopy Society of America innovations that significantly impact the microscopy community. The awards 
are recognized globally as a prestigious honor in the field of microscopy and microanalysis.
Dr. Hassan’s contributions have earned him numerous prestigious honors, including the International Max Planck 
Fellowship (2009), the Air Force Young Investigator Award (YIP, 2019), and major research grants from the 
Gordon and Betty Moore Foundation (2018) and the W. M. Keck Foundation (2019). In 2022, he received both 
the Inaugural AFOSR Director’s Research Initiative (DRI) Award and the Historically Black Colleges and 
Universities and Minority-Serving Institutions (HBCUs/MSIs) Award for his institution