Physicists at FAU have developed a new paradigm for quantum microscopy

Graphic of an electron microscope.
For every ultraviolet laser pulse (purple) impinging on the metal needle tip inside the electron microscope’s electron gun, about one electron is shot out of it. The electron (green) flies through the tube and is accelerated to a high velocity, about a quarter of the speed of light. At exactly the same time as it passes very close to another metal needle tip (see inset), within a few tens of a billionth (10^-9) of a meter and a thousandth of a billionth (10^-15) of a second, another laser pulse (red) impinges on the tip and electron, which changes the velocity of the electron in a quantum-mechanical manner. (Graphic: R. Shiloh, T. Chlouba, and P. Hommelhoff)

Investigating electrons with a traditional scanning microscope

Physicists at FAU have designed a framework that allows scientists to observe interactions between light and electrons using a traditional scanning electron microscope. The procedure is considerably cheaper than the technology that has been used to date, and also enables a wider range of experiments. The researchers have published their findings in the prestigious journal Physical Review Letters.

The quantum computer is just one example of how important an understanding of the fundamental processes underlying interactions between photons and electrons is. Combined with ultra-short laser pulses, it is possible to measure how photons change the energy and speed of electrons. This photon-induced electron microscopy (PINEM) has until now relied entirely on transmission electron microscopes (TEM). Although these have the resolution to pinpoint individual atoms, they are considerably more expensive than scanning electron microscopes (SEM), however, and their sample chamber is extremely small, only a few cubic millimeters in size.

Measuring differences down to a only a few hundred thousandths of a whole

Researchers at Prof. Dr. Peter Hommelhoff’s Chair of Laser Physics have now succeeded in modifying a traditional SEM to conduct PINEM experiments. They designed a special spectrometer based on magnetic forces which is integrated directly into the microscope. The underlying principle is that the magnetic field diverts electrons to a greater or lesser extent depending on their speed. Using a detector that transforms electron collisions into light, an accurate reading of this deviation is given. The method allows researchers to measure even the smallest changes in energy, up to differences of merely several hundred thousandths of the original value – enough to differentiate the contribution of a single light  energy quanta – a photon.

A wider spectrum of experiments possible in the future

The Erlangen physicists’ discovery is pioneering in more ways than one. From a financial point of view, being able to research photon-electron interactions without using TEM, that cost several million euros, could make research more accessible. Furthermore, as the chamber of an SEM generally has a volume of up to 20 cubic centimeters, a much wider range of experiments is now possible, as additional optical and electronic components such as lenses, prisms and mirrors can be placed directly next to the samples. The researchers expect that in few years’ time, the entire field of microscopic quantum experiments will shift from TEM to SEM.

Further information

Dr. Roy Shiloh
Chair of Laser Physics