Researchers at the Johannes Gutenberg University Mainz (JGU) and the Helmholtz Institute Mainz (HIM) have developed a novel method for investigating the internal structure of atoms, discovering previously unknown atomic transitions in samarium, a rare earth element. Their findings were published in the renowned scientific journal Physical Review Applied.
The ability to describe the internal structure of atoms is not only important for understanding the composition of matter, but also for designing new experiments to explore fundamental physics. Certain experiments require samples of atoms or molecules with special properties that strongly depend on the phenomenon being investigated. However, knowledge of the energy level structure of many atoms is still incomplete, especially in the case of rare earth and actinide atoms.
Spectroscopy is one of the most commonly used techniques to study the structure of atoms. It is based on the principle that electrons absorb or emit energy when they move between the energy levels of an atom. Each element has a unique set of light wavelengths that are emitted or absorbed due to these transitions. These are called the atomic spectrum.
“High-resolution broadband Spectroscopy is essential for precision measurements in atomic physics and the search for new fundamental interactions,” explains Razmik Aramyan, a doctoral candidate in Prof. Dr. Dmitry Budker’s group and lead author of the publication. “However, progress is often hampered by the difficulty of measuring complex atomic spectra, mainly due to two technical limitations: the difficulty of correctly distinguishing the signals emitted by the sample, and the limited wavelength range that the instruments can capture.” To overcome these limitations, Aramyan and his colleagues applied and further developed a method called Dual-Comb Spectroscopy (DCS), which allows atomic spectra to be measured in a wide band of electromagnetic frequencies with high resolution and high sensitivity. DCS is based on the optical frequency comb technique, for which the Nobel Prize in Physics was awarded in 2005. Optical frequency combs are special lasers that measure the exact frequencies of light. In DCS, two of these combs are used in coherent mode, allowing the spectrum of the sample to be measured more accurately than with conventional methods.
One of the challenges in applying DCS is to detect weak signals with high precision. To overcome this, the researchers around Aramyan also implemented several photodetectors that improve the signal-to-noise ratio. With this combination, it was then possible to clearly read the experimental data and determine the different wavelengths of the spectrum. “We have developed an enhanced multichannel DCS approach that combines a photodetector array with a novel scheme for resolving frequency ambiguities, thus enabling ambiguity-free broadband measurements with a high signal-to-noise ratio,” Aramyan summarizes.
The development of this novel approach represents one of the first steps in the international project “Spectroscopy 2.0”, which aims to develop a “massively parallel spectroscopic tool”: a tool that allows a large number of spectroscopic measurements to be performed simultaneously. This should make it possible to perform Spectroscopy of denser atomic and molecular spectra under strong magnetic fields.
DCS is particularly well suited to filling gaps in atomic data, as the current publication confirms. Thanks to their innovative approach, Aramyan and the team were able to capture the spectrum of samarium vapor at different temperatures and analyze the spectral behavior at different samarium concentrations. When comparing their results with existing datasets, they found spectroscopic lines that were previously unknown.
“We have discovered several previously undescribed samarium absorption lines. This illustrates the potential of our method to reveal previously unknown atomic properties. It opens up promising possibilities for massively parallel Spectroscopy, for example for the Spectroscopy of atoms in pulsed, ultra-high magnetic fields,” says Aramyan.
R. Aramyan et al., Enhanced multichannel dual-comb spectroscopy of complex systems, Phys. Rev. Applied 24, L021002
DOI: https://doi.org/10.1103/7ktx-4h8m”
