Miniature RF Technology

In high-technology areas such as microelectronics, materials science, nanotechnology and biotechnology, there is a drive towards imaging and analyzing ever-smaller structures. The electron microscope is one of the key instruments for this purpose. One of the exciting recent developments in electron microscopy and electron diffraction is the push towards time-resolved measurements, using electron pulses with duration in the femtosecond range. In femtosecond electron microscopy the usual approach up to now is to illuminate the tip with a femtosecond laser, thus producing in a hybrid photo-field emission mode single-electron pulses. Due to the limited repetition rate of the femtosecond laser, however, the average current is rather low. Moreover, the conventional electron microscopy field emission tips have not been optimized for photo-excitation, so the ensuing beam quality is far from ideal. Our approach is to use the electron microscope in a regular continuous mode and to generate the femtosecond electron pulses by chopping the beam downstream. For this purpose we use a miniaturized, low-power 3 GHz resonant cavity in TM110 mode in combination with a micrometer-sized slit. The beam emittance is not affected by the RF fields of the cavity and beam chopping can be done at frequencies as high as 3 GHz, leading to quite reasonable average currents. The system is ideally suited for doing time-resolved electron-energy-loss-spectroscopy (EELS). We are now using the chopped beam, which is synchronized to a femtosecond laser, for fundamental studies of light-electron interaction. In addition, we plan to add a 3 GHz cavity in TM010 mode, which should lead to even shorter pulse lengths and possibly enable aberration correction with time-dependent fields.

Keywords: Electron microscopy, electron diffraction, EELS, microwave/RF technology, femtosecond lasers.

People involved: The following people are or have been involved in this project:

PhD studentAdam Lassise
Former PhD studentsThijs van Oudheusden
Undergraduate students
Former studentsJoris Kanters
TechniciansEddy Rietman, Louis van Moll, Ad Kemper, Harry van Doorn, and Iman Koole
Staff membersPeter Mutsaers and Jom Luiten