Ultraviolet spectroscopy: a leap in accuracy and precision under extremely low light levels

Ultraviolet spectroscopy plays a crucial role in the study of electronic transitions in atoms and rovibronic transitions in molecules. These studies are crucial for the testing of fundamental physics, quantum electrodynamics theory, determination of fundamental constants, precision measurements, optical clocks, high-resolution spectroscopy supporting atmospheric chemistry and astrophysics, and strong field physics.

The scientists of the Nathalie Picqu é group at the Max Planck Institute for Quantum Optics have made a significant leap in the field of ultraviolet spectroscopy, successfully achieving high-resolution linear absorption double comb spectroscopy in the ultraviolet spectral range. This breakthrough achievement has opened up new possibilities for conducting experiments under low light conditions and paved the way for new applications in various scientific and technological fields.

Double comb spectroscopy is a powerful technique for precise spectral analysis over a wide spectral bandwidth, mainly used for infrared absorption of small molecules in the gas phase. It relies on measuring transient interference between two frequency combs with slightly different repetition frequencies.

A frequency comb is a spectrum of laser lines that are uniformly distributed and phase coherent, and its function is similar to a ruler, which can measure the frequency of light extremely accurately. The dual comb technology is not limited by the geometry of traditional spectrometers, providing enormous potential for high precision and accuracy.

However, dual comb spectroscopy typically requires a strong laser beam, making it less suitable for scenarios with low light levels that are crucial. The MPQ team has now demonstrated through experiments that dual comb spectroscopy can be effectively used under low light conditions that are more than one million times weaker than commonly used power levels.

This breakthrough was achieved using two different experimental devices and different types of frequency comb generators. The team has developed a photon level interferometer that can accurately record statistical data of photon counting and display the signal-to-noise ratio at the basic limit. This achievement highlights the optimal utilization of available light in experiments and opens up prospects for dual comb spectroscopy in challenging scenarios where low light levels are crucial.

MPQ researchers have solved the challenges associated with generating ultraviolet frequency combs and constructing dual comb interferometers with long coherence times, paving the way for achieving this coveted goal. They cleverly controlled the mutual coherence of two comb lasers, with each comb line having a flying tile, proving the optimal accumulation of interference signal counting statistics over an hour.

"Our innovative low light interferometry method overcomes the challenges of low nonlinear frequency conversion efficiency and lays a solid foundation for extending the dual comb spectrum to shorter wavelengths," commented Xu Bingxin, a postdoctoral scientist who led the experiment.

In fact, an exciting future application is to develop short wavelength dual comb spectra to achieve precise vacuum and extreme ultraviolet molecular spectra over a wide spectral range. At present, broadband extreme ultraviolet spectroscopy is limited in resolution and accuracy, and relies on unique instruments in professional facilities.

"Although UV dual comb spectroscopy is a challenging goal, it has now become a realistic goal due to our research. Importantly, our research results extend the full functionality of dual comb spectroscopy to low light conditions, opening up new applications in precision spectroscopy, biomedical sensing, and environmental atmospheric detection," concluded Nathalie Picqu é.
The research results are published in the journal Nature.

Source: Laser Net