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Streaking of 43-attosecond soft-X-ray pulses generated by a passively CEP-stable mid-infrared driver

October 30, 2017

The world's shortest laser pulse

What is the advantage of being able to observe the reaction steps now with even higher resolution? "The faster a charge transfer can take place, the more efficiently a reaction can proceed", says Prof. Wörner. The human eye for example is very efficient when it comes to converting photons into nerve signals. In rhodopsin, a visual pigment in the retina, the photosensitive molecule retinal is prearranged in such a way that its structure can change extremely fast through the absorption of only a single photon. This enables the visual process even in twilight. A much slower reaction would render vision impossible, because the energy of the photon would be converted to heat in only a few picoseconds.

Attosecond spectroscopy could contribute to the development of more efficient solar cells since it is now for the first time possible to follow the process of excitation through sunlight up to the generation of electricity step by step. A detailed understanding of the charge transfer pathway could help optimizing the efficiency of the next generation of photosensitive elements.

Attosecond laser spectroscopy is not only suitable for mere observation, Prof. Wörner explains. Chemical reactions can also be directly manipulated: Using a laser pulse can alter the course of a reaction – even chemical bonds can be broken by stopping the charge shift at a certain location in the molecule. Such targeted interventions in chemical reactions have not been possible until now, since the time scale of electron movement in molecules was previously unreached. The group of Prof. Wörner is already working on the next generation of even shorter laser pulses. These will make it possible to record even more detailed images, and thanks to a wider X-ray spectrum even more elements can be probed than before. Soon it will be possible to follow the migration of electrons in more complex molecules with an even higher time resolution.

Figure 1: Experimental realization of the attosecond streak camera with a mid-IR driver. Isolated attosecond pulses are created through high-harmonic generation in a high-pressure gas cell filled with neon or argon. The residual mid-IR pulse is separated from the attosecond soft-X-ray pulse by means of a perforated mirror. Broadband reflection of the SXR super-continuum is achieved through grazing-incidence reflection on 3 flat mirrors coated with diamond-like carbon and one gold-coated toroidal mirror that focuses the SXR beam into the interaction region of a photoelectron time-of-flight spectrometer. A 100-nm Zr foil acts as a high-pass filter and simultaneously compensates the attochirp. Recombination of mid-IR and SXR pulses is achieved with another perforated mirror that focuses the mid-IR beam to the same spot.

Reference:  Gaumnitz, T., A. Jain, Y. Pertot, M. Huppert, I. Jordan, F. Ardana-Lamas and H. J. Wörner (2017). Streaking of 43-attosecond soft-X-ray pulses generated by a passively CEP-stable mid-infrared driver. Optics Express 25: 27506-27518. (10.1364/OE.25.027506) Gaumnitz-2017 (4.96 MB).

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