In real-time, scientists observed that helium nanodroplets respond ultrafast after being excited by XUV radiation (extreme ultraviolet radiation). Researchers now have new opportunities for thoroughly examining the basic characteristics of matter thanks to lasers that produce intense, brief XUV and X-ray bursts. Nanometer-sized material samples are of special interest in many of these experiments.
Some researchers transport and study embedded molecules and molecular nanostructures in helium droplets no bigger than a few nanometers. Helium particles have exceptional qualities that make them perfect for this use. They are regarded as superfluids because they travel without resistance at a temperature of just 0.37 K. Additionally, helium droplets are typically totally transparent to IR and visible light and inert to the chemical reactions of the embedded molecules.
The study aimed to determine how a single superfluid droplet responds to being immediately impacted by a powerful XUV laser pulse. The team used FERMI (Trieste, Italy), the world’s first and only seeded free-electron laser that produces intense XUV pulses at their chosen frequency.
The researchers found three fundamental reaction steps, supported by model calculations: A single excited helium atom is released from a bubble that ultimately bursts at the surface of the droplets after a very quick localization of electrons, the population of metastable states, and bubble formation.
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