Physicists at the Max Planck Institute of Quantum Optics, led by Nathalie Picqué, have developed a new technique for ultraviolet spectroscopy, a method used to study light and matter. The technique can detect and quantify many substances with high chemical selectivity, even at extremely low light levels. This advancement could lead to new applications in photon-level diagnostics, such as precision spectroscopy of single atoms or molecules for fundamental tests of physics and ultraviolet photochemistry in the Earth’s atmosphere or from space telescopes. The research was published in the scientific journal Nature.
Advancements in Ultraviolet Spectroscopy
Researchers at the Max Planck Institute of Quantum Optics (MPQ) have developed a new technique that enhances the understanding of light and matter properties. This technique can detect and quantify multiple substances with high chemical selectivity, even at very low light levels. This development opens up new possibilities for photon-level diagnostics, such as precision spectroscopy of single atoms or molecules, and ultraviolet photochemistry in the Earth’s atmosphere or from space telescopes. The research findings have been published in the scientific journal Nature.
Ultraviolet Spectroscopy and its Importance
Ultraviolet spectroscopy is crucial in studying electronic transitions in atoms and rovibronic transitions in molecules. These studies are vital for tests of fundamental physics, quantum-electrodynamics theory, determination of fundamental constants, precision measurements, optical clocks, high-resolution spectroscopy in support of atmospheric chemistry and astrophysics, and strong-field physics. The team led by Nathalie Picqué at the Max-Planck Institute of Quantum Optics has made a significant advancement in ultraviolet spectroscopy by successfully implementing high-resolution linear-absorption dual-comb spectroscopy in the ultraviolet spectral range. This achievement opens up new possibilities for conducting experiments under low-light conditions, which could have various scientific and technological applications.
Dual-Comb Spectroscopy: A Powerful Technique
Dual-comb spectroscopy is a powerful technique for precise spectroscopy over broad spectral bandwidths. It measures the time-dependent interference between two frequency combs with slightly different repetition frequencies. A frequency comb is a spectrum of evenly spaced, phase-coherent laser lines, which acts like a ruler to measure the frequency of light with extreme precision. The dual-comb technique does not suffer from the geometric limitations associated with traditional spectrometers, and offers great potential for high precision and accuracy.
Dual-Comb Spectroscopy at Low Light Intensities
Dual-comb spectroscopy typically requires intense laser beams, making it less suitable for scenarios where low light levels are critical. However, the MPQ team has demonstrated that dual-comb spectroscopy can be effectively employed in starved-light conditions, at power levels more than a million times weaker than those typically used. This breakthrough was achieved using two distinct experimental setups with different types of frequency-comb generators. The team developed a photon-level interferometer that accurately records the statistics of photon counting, showcasing a signal-to-noise ratio at the fundamental limit. This achievement highlights the optimal use of available light for experiments, and opens up the prospect of dual-comb spectroscopy in challenging scenarios where low light levels are essential.
Future Applications and Challenges
The MPQ researchers addressed the challenges associated with generating ultraviolet frequency combs and building dual-comb interferometers with long coherence times. They exquisitely controlled the mutual coherence of two comb lasers with one femtowatt per comb line, demonstrating an optimal build-up of the counting statistics of their interference signal over times exceeding one hour. This innovative approach to low-light interferometry overcomes the challenges posed by the low efficiency of nonlinear frequency conversion, and lays a solid foundation for extending dual-comb spectroscopy to even shorter wavelengths. Future applications include the development of dual-comb spectroscopy at short wavelengths, to enable precise vacuum- and extreme-ultraviolet molecular spectroscopy over broad spectral spans. Currently, broadband extreme-UV spectroscopy is limited in resolution and accuracy, and relies on unique instrumentation at specialized facilities. However, ultraviolet dual-comb spectroscopy has now become a realistic goal as a result of this research.
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