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Professor Ahmed Zewail, Nobel laureate Chemistry (1999) for having developed what he named “Femtochemistry”, successfully ported the femtosecond pump-probe concept into the realm of Transmission Electron Microscopy and in doing so, created the fi eld of Ultra-fast Electron Microscopy or UEM. A laser pulse “pumps” the sample at t = 0, followed by an electron pulse “probing” the sample at a set time delay Δt. Traditionally the required sub-picosecond electron pulses are generated by aiming a femtosecond laser at the TEM cathode to produce a photo-generated electron pulse with a duration down to a few hundred femtoseconds. This approach has two main drawbacks, complexity of the electron-gun, and a very limited beam coherence in pulsed mode. Both these drawbacks can be eliminated by chopping a continuous electron beam, as opposed to generating electrons packets using short light pulses.

This webinar discusses a Resonant Radio Frequency cavity (RF-cavity) for generating electron pulses down to a few hundred femtoseconds, while maintaining the native coherence of the electron beam. With the RF-cavity synchronized to a sample pumping laser, PINEM (Photon-Induced Near-fi eld Electron Microscopy) experiments can be conducted, unequivocally demonstrating successful synchronization between pump and probe.

Key Points

• What is Ultra-fast Electron Microscopy (UEM).
• Understanding Ultra-fast stroboscopic imaging.
• Generating sub-picosecond electron pulses with an RF-cavity.
• Variable repetition rates.
• Synchronization between pump and probe.

About the Speaker

Eric Van Cappellen obtained his PhD in Solid State Physics in 1986 at the University of Antwerp, Belgium. Both his master’s degree and PhD are in the fi eld of Transmission Electron Microscopy. After several academic positions in Belgium, Congo, Germany and France, he joined Philips Electron Optics in 1993 which became FEI Company in 1997 and Thermo Fisher Scientifi c in 2016. In his current position, Eric uses his experience in advanced TEM imaging and analysis to evaluate emerging technologies, UEM being one of them.