A team at the University of Nebraska-Lincoln has figured out a possible way to observe and record the behavior of matter at the molecular level. That ability could open the door to a wide range of applications in ultrafast electron microscopy used in a large array of scientific, medical and technological fields.
The “lenses” in question are not made of glass like those found in standard tabletop microscopes. They’re created by laser beams that would keep pulses of electrons from dispersing and instead focus the electron packets on a target. The timescales required, however, are hardly imaginable on a human scale — measured in femtoseconds (quadrillionths of a second) and attoseconds (quintillionths of a second).
The physicists modeled two types of lenses. One was a temporal “thin” lens created using one laser beam that could compress electron pulses to less than 10 femtoseconds. The second was a “thick” lens created using two counterpropagating laser beams that showed the potential of compressing electron pulses to reach focuses of attosecond duration.
Here, we describe the “temporal lens” concept that can be used for the focus and magnification of ultrashort electron packets in the time domain. The temporal lenses are created by appropriately synthesizing optical pulses that interact with electrons through the ponderomotive force. With such an arrangement, a temporal lens equation with a form identical to that of conventional light optics is derived. The analog of ray diagrams, but for electrons, are constructed to help the visualization of the process of compressing electron packets. It is shown that such temporal lenses not only compensate for electron pulse broadening due to velocity dispersion but also allow compression of the packets to durations much shorter than their initial widths. With these capabilities, ultrafast electron diffraction and microscopy can be extended to new domains,and, just as importantly, electron pulses can be delivered directly on an ultrafast techniques target specimen.