Laser PIcoscope, A New Technique For Taking Pictures Of Electrons In Crystals - Santanu Mandal
From gazing at the vast cosmos to peeking at angstrom (10-10 meter) scale atoms, discovery of imaging technique has been the central thrust towards understanding the mysteries of nature. Since the invention of the light microscope by Antonie van Leeuwenhoek in the 17th century, mankind has opened a new world on the microscopic scale. But there is a fundamental limit that light microscopy cannot exceed. With visible light one can only recognize objects commensurable in size to its wavelength which is approximately few hundreds of nanometers. In order to be able to see electrons around atoms, the microscope would have to be able to increase its magnification power by a few thousand times. Mapping atomic arrangement has been century old science. The path breaking discoveries done in this field of crystallography has earned 29 Nobel prizes. The development of photon (X-ray crystallography), electron (scanning transmission electron microscope, STEM) and neutron-based microscopes have provided the atomic and electronic arrangements inside both crystalline and amorphous medium. Knowledge of atomic and electronic motion is essential to understand the optical and chemical properties of material. The above mentioned techniques provide the knowledge of core electron distribution, however the all
important valence charge (outer shell electrons of atom) density distribution, which also takes part in chemical bonding process, is still elusive. Since these are the charges which are responsible for most of the optical and chemistry, knowledge of their charge densities is of great importance to Physicists, Chemists, Material Scientists and others. Still the current techniques cannot spatially resolve electrons, that is, to see how electrons occupy the minute space among atoms in crystals, and how they form the chemical bonds that hold atoms together.
To overcome this limitation, the scientists at the University of Rostock (Germany) and Max Planck Institute of Quantum Optics (Germany) took a different experimental approach. They developed a new type of microscope that works with very powerful laser pulses. They call their device as the Light Picoscope or Picoscope. A strong laser pulse forces electron inside crystalline materials to become the photographers of the surrounding space. When the strong laser pulse penetrates inside the crystal material, it can grab an electron and set it in a fast wobbling motion. The laser driven electrons feel the uneven space (atomic electron density) around it just like a car feels the uneven surface of a bumpy road. When these moving electrons cross a bump created by other electrons or atoms, they are slowed down. The associated loss of energies is emitted as radiation of multiple frequencies of driving laser and these radiated energies can be very high. These radiations are recorded and analyzed. By analyzing the properties of this radiation, the
scientists derive the shape of these tiny bumps and composed images that illustrate how the electron density is distributed among the atoms in the crystalline structure of solids with a resolution of about 26 picometers – a unit of length that corresponds to billionths of millimeters. This laser Picoscope has the capability to look inside the bulk of material, like X-rays, with the ability to probe valence electrons, which is possible with scanning tunneling electron microscopes but only on surface. According to the Physicists, with a microscope capable of probing the valence electron density, it may be possible to benchmark the performance of computational solid-state physics tools. Modern, state-of-the-art models can be optimized to predict the properties of materials with ever finer detail. This is a very important aspect that laser Picoscopy brings in. This work paves the way towards developing a new class of laser-based microscopes that could allow physicists, chemists, and material scientists to peer into the details of the microcosm with unprecedented resolution and to deeply understand and eventually control the chemical and the electronic properties of materials.
Now, the researchers in Extreme Photonics group at Institute of Physics, University of Rostock, are working on further developing the technology with more precision, so that the Laser Picoscope starts to probe electrons in three dimensions and further the method can be tested with a broad range of materials. It may soon become possible to record real movies of electrons in materials by combining Laser Picoscopy with time-resolved laser techniques; which is a long
awaited goal in ultrafast sciences and matter microscopy. Understanding and controlling the microcosm at the level of electrons may turn essential in future photonic and electronic technologies whose building blocks size is gradually reducing from the mesoscopic to the atomic and molecular scales.
There is a great opportunity for the new researcher to join this exciting field of research. One can contact the Extreme Photonics Group leader to know more about the currently available research position.
- Lakhotia, H., Kim, H. Y., Zhan, M., Hu, S., Meng, S., & Goulielmakis, E. (2020). Laser picoscopy of valence electrons in solids. Nature, 583(7814), 55-59.
- Extreme Photonics Group (https://www.xplab.physik.uni-rostock.de/)
Santanu Mandal, DAAD PhD research fellow.
Extreme Photonics group
Institute of Physics, University of Rostock, Germany
Albert-Einstein-Straße 23, 18059 Rostock, Germany
After completing bachelor’s degree in physics from Vidyasagar University (Silver Medalist), West Bengal, he pursued his master’s degree in Physics from S. N. Bose National Center for Basic Sciences (SNBNCBS), Kolkata as Bose Fellow. Then he worked as a Junior Research fellow in the same institute. He have been pursuing his PhD at University of Rostock, Germany, since 2018 as DAAD research fellow. And his research areas are Attosecond Physics and Advancing laser-based
microscopy techniques with picometer resolution.