New System for Ultra-Fast Flashes

Experimental setup for the generation of ultrashort laser light pulses. (Source: Politec. Milano)

An international research team consisting of the Institute of Photonics and Nano­technology of the CNR (CNR-IFN), the Politecnico di Milano, the DESY in Hamburg and the Massa­chusetts Institute of Techno­logy has managed to synthesise optical waveforms by means of the synchronised overlap of different light pulses. These light pulses, which can be sculpted according to the user’s wishes, will be used to study atomic and molecular processes.

One of the laser’s many excep­tional properties is that it allows the user to generate incredibly short flashes of light, up to a duration of just a few femto­seconds. These pulses, thanks to their extremely short duration, allow us to study ultra-fast pheno­mena, such as the processes underlying vision and photo­synthesis, and can, thanks to their extremely high intensity, modify atoms and molecules in order to create new states of matter. As such, controlling the properties and the temporal profile of these pulses is of utmost scientific and techno­logical importance, and has been the object of intense study since the 1980s.

The scientists has managed to synthesise genuine optical waveforms by controlling the electrical field of the light with an extremely high degree of precision, much less than a femto­second. The synthesis of these waveforms is based on the synchro­nised overlap of different light pulses. “It’s like directing an orchestra. Each pulse is a musical instrument, called upon to produce its own sound; coherent synthesis is the perfect execution of a piece of music. This orchestra could poten­tially produce an infinite multitude of waveforms – that is, melodies. As such, the coherent synthesis achieved in these experi­ments is a very promising approach for the generation of laser light pulses of any shape and duration,” explains Cristian Manzoni, researcher at the CNR-IFN and the Poli­tecnico.

Many years of work went into the experi­ment. “We built the first prototype right in the labora­tories of the Politecnico di Milano,” adds Giulio Cerullo from the Department of Physics at the Politecnico di Milano. “It was like a little ensemble, but from that first experiment, published in 2012, came the idea to put together the large orchestra we have now. The experi­mental apparatus was recon­structed and expanded at the labora­tories in Hamburg”. The waveforms that can now be synthesised will increase the oppor­tunities to control the way light interacts with matter, especially at high inten­sities.

In this case, the electro­magnetic field of the light is so strong that it can counteract the forces that bind electrons to nuclei; the light can temporarily remove electrons from the atom and cause them to orbit along brand new tra­jectories. For example, it has been demons­trated that when the electron moves propelled by such short and intense waveforms, it generates even shorter light pulses lasting just a few attoseconds. These are the shortest arti­ficial events that man has ever been capable of creating. This research is laying the foun­dations for the study of new atomic and molecular mechanisms, in that it will allow us to examine nature through light pulses that are sculpted according to the user’s wish. (Source: Politec. Milano)

Reference: G. M. Rossi et al.: Sub-cycle millijoule-level parametric waveform synthesizer for attosecond science, Nat. Phot., online 13 July 2020; DOI: 10.1038/s41566-020-0659-0

Link: Ultrafast Optics, Center for Free-Electron Laser Science, Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany

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