Laser Light Can Help Electron Microscopy

Laser Light Can Help Electron Microscopy
Laser Light Can Help Electron Microscopy - A delayed laser pulse is shaped by the spatial light modulator (right), while a laser pulse collects electrons (SLM) from a sharp metal dot (left). The electron is crossed by this shaped light and leaves a pattern in the beam. A smiley face pattern is used in this example, but crosses, arcs, and other patterns can also be used to increase the resolution of the electron microscope. APS/Alan Stonebraker

The resolution of the electron microscope can be increased by a new technique that simultaneously generates and shapes electron beams using laser light.

With the electron microscope, the structure can be seen at length scales ranging from submicron to atomic. The advancement of technology has produced some stunning visuals such as images of nanorobots and tiny organisms as well as transition videos of atomic dislocations. However, there is much more to explore in the microscopic realm because, in the words of renowned physicist Richard Feynman, “there is plenty of room at the bottom.” A discovery by Thomas Juffmann of the University of Vienna and colleagues may provide new insight into the extremely small. By applying short laser pulses, scientists changed the shape of an electron beam and imprinted it with patterns of bars, crescents and even a smiley face.

This programmable electron beam shaping can be used to improve electron focus for ultrafast imaging or to reduce damage to biological samples that can damage electrons.

While the field of electron microscopy is in good standing, it can be improved with targeted efforts. The three biggest problems are that electron microscopes are too slow, too dangerous, and too blurry. Turbidity is a result of aberrations caused by defects in electron lenses. Although significant progress has been made in correcting aberrations, lens imperfections still pose a challenge. In addition, quantum inconsistency caused by electrons interacting with the structure of the microscope may also be limiting spatial resolution. The importance of the deadline is linked to the damage that electrons can do to a biological specimen.

It is true that biomolecules can be visualized using electron microscopy, and this ability was recognized with the 2018 Nobel Prize in Chemistry. However, it has not been possible to visualize living, functional organisms using electron microscopy because they cannot withstand the levels of damage caused by the electron present. Finally, the slowness is due to the inability of electron microscopes to observe atomic action on the attosecond scale. Although femtosecond electron microscopy has been in use for some time, it is still not possible to achieve spatial resolution at the atomic scale or time resolution at the atomic scale.

The field of electron microscopy needs creative solutions to overcome these barriers. The work of Juffmann and colleagues is a great example of a potentially revolutionary line of research.

In their approach, they blend two well-known electron beam technologies. The first was demonstrated in 2006 and involves removing electrons from metal nanotypes using femtosecond laser pulses. The second involves using laser light to manipulate the quantum state of free electrons, which was first demonstrated in 2001. The researchers also use a technique where they write a pattern on laser light.

In their experiment, the Juffmann group first sends a laser pulse to a metal tip, and the pulse's electric field causes a burst of electrons to be ejected directly from the point. The researchers then carefully time another laser pulse to change the electron beam by traversing the free electrons.

A single electron interacts with two photons in laser light in a technique known as stimulated Compton scattering to produce the manipulation. With this interaction, first predicted by Kapitza and Dirac in 1933, the electron's phase changes and this affects how the electron moves.

Since the Kapitza-Dirac effect is proportional to the number of photons, the power of light in a certain part of the pulse affects the electrons there more. This ratio is used by Juffmann and others to shape the electron beam. They direct the course of the second laser pulse through a spatial light modulator. The modulator produces density changes that control the behavior of electrons in a predetermined, programmable way.

Scientists demonstrate how they can manipulate hundreds of "pixels" in an electron beam to create complex patterns like a smiley face and a cross. Astigmatism is one of the aberrations in the electron microscope that must be constantly corrected, and the cross pattern is very important to do so.

Now that this new technology is available, what topics can be explored? It might be interesting to try electron pycography, which creates images by evaluating data from many exposures of an object. While this method does not require a lens, it does require a certain level of control over the incoming electron beam that the new shaping method can provide. Image resolution can be increased, which is the main benefit of electron ptychography.

As mentioned earlier, uncorrected lens aberrations and degradation from interactions with surrounding materials in the microscope currently limit resolution. Both of these problems can be avoided by controlling the electron velocity with laser light.
The recently demonstrated uses of electron ghost imaging of the new technology are equally interesting [5]. Ghost imaging involves illuminating the target element with a series of predetermined electron patterns that are used to create an image from electrons whose predetermined structure is then detected. The possible benefit is the ability to select entry patterns that expose the target object to fewer electrons.

Thanks to the laser manipulation of Juffmann and colleagues, initial patterns can be produced with a better spatial resolution compared to previous electron ghost imaging methods. If high resolution ghost imaging is paired with new techniques such as coating the biological object with graphene layers to protect the biological cells, we can observe living tissues under the electron microscope.

Source: https://physics.aps.org/articles/v15/145

 

 

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