Photon-induced near-field electron microscopy (PINEM) is an advanced technique using ultra-short laser pulses to observe the quantum coherent coupling interactions between photons and electrons, measurements which aid in the understanding of technologies such as quantum computing. PINEM has traditionally relied entirely on the use of transmission electron microscopes (TEMs), which come with a considerable price tag and typically feature an extremely small sample chamber only a few cubic millimeters in size, limiting the scope of experiments that can be performed. Researchers at the Friedrich Alexander University of Erlangen-Nuremberg have now designed a framework that can allow PINEM experiments to be performed using less costly scanning electron microscopes (SEMs), enabling a wider range of experiments to be performed studying these light-electron interactions.
The researchers were able to successfully modify a traditional SEM instrument to conduct PINEM experiments by designing 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. This method allows the 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 photon.
In addition to the financial benefits of allowing tests to be performed with a less expensive instrument, the modified system also takes advantage of the much larger sample chamber of the SEM, which can have a volume of up to 20 cubic centimeters. The larger chamber can be more easily configured with additional optical and electronic components such as lenses, prisms and mirrors, expanding the range of experiments that can be performed, and can potentially allow for thousands of photo-electron interaction sites compared with just one or two for TEM setups, according to the authors. This research was published in Physical Review Letters.
The authors predict that the benefits of using SEM for microscopic quantum experiments could ultimately lead the field to shift from TEM to SEM over the next few years. Their framework could potentially be used to facilitate experiments in electron wave packet shaping, quantum computing and spectral imaging with low-energy electrons, the authors wrote.