Scientists at the Max-Planck Institute of Quantum Optics have achieved a remarkable breakthrough in ultraviolet spectroscopy. Led by Nathalie Picqué, their pioneering work has propelled dual-comb spectroscopy into the realm of low-light conditions, expanding its potential applications across diverse scientific and technological domains.
Ultraviolet spectroscopy plays a pivotal role in scrutinizing electronic transitions in atoms and rovibronic transitions in molecules. Beyond its conventional applications, such studies serve as crucibles for testing fundamental physics, quantum-electrodynamics theory, and the determination of essential constants. The precision offered by ultraviolet spectroscopy is indispensable in the realms of optical clocks, high-resolution spectroscopy for atmospheric chemistry and astrophysics, and the cutting-edge field of strong-field physics.
The cornerstone of this breakthrough is the successful implementation of high-resolution linear-absorption dual-comb spectroscopy in the ultraviolet spectral range. Dual-comb spectroscopy, renowned for its precision in infrared linear absorption studies, relies on the interference patterns generated by two frequency combs with slightly different repetition frequencies. These combs, akin to rulers of laser lines, provide unparalleled precision, overcoming geometric limitations associated with traditional spectrometers.
What sets this achievement apart is the transcendence of dual-comb spectroscopy into low-light conditions. Typically requiring intense laser beams, the researchers demonstrated its efficacy at power levels over a million times weaker than conventionally used. Employing two distinct experimental setups with different frequency-comb generators, the team introduced a photon-level interferometer that harnessed the statistical power of photon counting, achieving a signal-to-noise ratio at the fundamental limit.
Addressing the challenges of generating ultraviolet frequency combs and constructing dual-comb interferometers with extended coherence times, the researchers showcased meticulous control over the mutual coherence of comb lasers. With femtowatt power per comb line, they achieved optimal counting statistics over durations exceeding one hour, a testament to their mastery of low-light interferometry.
The implications of this breakthrough extend far beyond the confines of the laboratory. The prospect of dual-comb spectroscopy at short wavelengths opens avenues for precise vacuum- and extreme-ultraviolet molecular spectroscopy across broad spectral spans. Currently limited in resolution and accuracy, broadband extreme-UV spectroscopy stands to benefit from this innovation, potentially transforming our understanding of molecular dynamics at the most fundamental levels.
Bingxin Xu, the post-doctoral scientist spearheading these experiments, emphasizes the innovative approach's potential to overcome challenges in nonlinear frequency conversion efficiency. This not only solidifies the foundation for extending dual-comb spectroscopy to shorter wavelengths but also positions it as a realistic goal. Nathalie Picqué envisions a future where ultraviolet dual-comb spectroscopy, once deemed challenging, becomes a potent tool in precision spectroscopy, biomedical sensing, and environmental atmospheric sounding, unlocking novel applications that were once deemed beyond reach.
The findings are published in the journal Nature.
Source: Max Planck Society