Physicists Use Picoscopes To Look Inside Atomic Matter

Light microscopes enable us to see tiny objects like living cells. So far it has not been possible to observe the much smaller electrons between the atoms in solids. Scientists from the working groups of Professor Eleftherios Goulielmakis from the Institute of Physics at the University of Rostock and the Max Planck Institute for Quantum Optics in Garching, together with staff from the Institute of Physics at the Chinese Academy of Sciences in Beijing, have succeeded in developing a new light microscope, the Picoscope to develop with a resolution of a few ten picometers. In the renowned journal Nature, you recently reported on how it was possible to create images that show how the electron cloud in the crystal lattice of solids is distributed to the atoms.

Since Antonie van Leeuwenhoek's invention of the light microscope in the 17th century, humanity has entered a new world on a microscopic scale. But there is a fundamental limit that light microscopy cannot cross. Anything smaller than bacteria cannot be resolved with light. The reason for this has been known since the end of the 19th century. It was discovered by Ernst Karl Abbe. With visible light you can only recognize objects whose size corresponds to the wavelength of the light, which is about a few tens of thousands of a millimeter. "To be able to see electrons, the microscopes would have to be able to increase their magnification a few thousand times," says Professor Eleftherios Goulielmakis, who moved from Munich to the University of Rostock two years ago.

“Scientists have been using laser flashes for decades to understand the inner life of the atomic microcosm. Such laser flashes can track ultrafast microscopic processes inside solids. But laser flashes still cannot spatially dissolve the electrons, ”says Goulielmakis. That means you cannot see how electrons occupy the tiny space between the atoms in crystals and how chemical bonds are formed that hold the atoms together.

To overcome this limitation, Professor Goulielmakis and his team went a different way. They developed a new type of microscope, the picoscope, which works with strong laser pulses. “A strong laser pulse can force electrons in crystalline materials to become a 'photographer' of the surrounding space themselves. When the laser pulse penetrates the inside of the crystal, it can grab an electron and set it in a fast, wobbling motion. When the electron moves, it senses the space around it, just like a car feels the uneven surface of a bumpy road, "explains Harshit Lakhotia, a doctoral student in Professor Goulielmakis' research group in Garching, the basic idea. If the laser-driven electrons are one of another Cross electrons or atoms generated bump, they are slowed down. The associated loss of energy is emitted as radiation of a certain frequency, which is much higher than that of laser light. "By recording and analyzing the properties of this radiation, we can derive the shape of these tiny bumps and calculate images that show where the electron density in the crystal is high or low," says Dr. Hee-Yong Kim, a physicist from the Extreme research group Photonics at the Institute of Physics at the University of Rostock and continues: "The laser picoscope combines the capabilities of opaque materials like looking with X-rays with the ability to probe free electrons, which is only possible on surfaces with scanning tunneling microscopes". The associated loss of energy is emitted as radiation of a certain frequency, which is much higher than that of laser light. "By recording and analyzing the properties of this radiation, we can derive the shape of these tiny bumps and calculate images that show where the electron density in the crystal is high or low," says Dr. Hee-Yong Kim, a physicist from the Extreme research group Photonics at the Institute of Physics at the University of Rostock and continues: "The laser picoscope combines the capabilities of opaque materials like looking with X-rays with the ability to probe free electrons, which is only possible on surfaces with scanning tunneling microscopes". The associated loss of energy is emitted as radiation of a certain frequency, which is much higher than that of laser light. "By recording and analyzing the properties of this radiation, we can derive the shape of these tiny bumps and calculate images that show where the electron density in the crystal is high or low," says Dr. Hee-Yong Kim, a physicist from the Extreme research group Photonics at the Institute of Physics at the University of Rostock and continues: "The laser picoscope combines the capabilities of opaque materials like looking with X-rays with the ability to probe free electrons, which is only possible on surfaces with scanning tunneling microscopes".

The theoretical solid-state physicist Sheng Meng from the Physics Institute in Beijing adds: “With such a microscope that is able to probe the density of the valence electrons, we may soon be able to overcome the limits of our computer-aided tools in solid-state physics. We can optimize modern, state-of-the-art models to predict the properties of materials more and more accurately. ”

Now the researchers are working on further developing the technology. They plan to probe electrons in three dimensions and to test the method on a wide range of materials. Professor Goulielmakis is optimistic that he may soon be able to obtain not just pictures but entire videos of what is going on inside the matter: "Since laser picoscopy can be easily combined with time-resolved laser techniques, it could soon be possible to create real films of electrons in To record materials. This is a long-awaited goal in the ultra-fast sciences and in the microscopy of matter ".