Shortest Ultraviolet Laser Pulse Ever

The 1.9-femtosecond UV flash is made via up-conversion of infrared light in a gas cell. (Source: Calegari group, DESY)

Researchers at the Center for Free-Electron Laser Science (CFEL) at DESY in Hamburg have generated a 1.9-femtosecond ultra­violet laser light pulse – setting a record for ultra­violet laser pulses with the shortest duration. The experi­ments outshine the previous record of 2.8 femto­seconds, set in 2010.

The 1.9-femtosecond pulse has been generated in the labora­tory of Francesca Calegari, leading scientist at DESY and head of the atto­second science group at the Center for Free-Electron Laser Science, a cooperation of DESY, Hamburg Uni­versity and Max Planck Society. It covers the very relevant spectral region between 210 and 340 nanometers, corre­sponding to the UVB and UVC energy ranges. UVB radiation contained in the solar emission partially penetrates our atmo­sphere, thus triggering a number of bio­chemically relevant processes including damage of the DNA, leading to skin cancer. These processes are often based on ultrafast mechanisms that require extremely short light pulses to be captured in real time.

Generating ultra­short UV pulses has always been a challenge due to the high dispersion of light in this spectral region in air and in materials that are used for their generation. The approach used by the team of Calegari is frequency upcon­version of 5-femto­second infrared pulses in a high-pressure laser-fabricated gas cell located in vacuum. This method allows for the shortest pulse duration to be preserved. “Reaching the sub-2-femto­second barrier represents an exciting result,” says Calegari. “By further opti­mizing the geometry for the pulse generation we could even push the duration down to atto­seconds, a duration that is typically achieved at higher photon energies.”

The research conducted in the team of Calegari, in colla­boration with the Institute of Photonics and Nano­technology (IFN-CNR, Milano, Italy) and Poli­tecnico di Milano (Milano, Italy), has been financed by the European Starting Grant STARLIGHT (Steering atto­second electron dynamics in biomolecules by UV/XUV light pulses) and it opens new important perspec­tives for ultrafast molecular spectro­scopy, as a promising tool to reach a deeper under­standing of the first instants of UV induced photo­chemical reactions and bio-damage effects. (Source: CFEL / DESY)

Reference: M. Galli et al.: Generation of deep ultraviolet sub-2-fs pulses, Opt. Lett. 44, 1308 (2019); DOI: 10.1364/OL.44.001308

Link: Attosecond Science, Center for Free-Electron Laser Science (CFEL), DESY, Hamburg, Germany

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