Researchers can now precisely measure the appearance and damping of the plasmonic field

An international research team led by Universität Hamburg, DESY and Stanford University, e.g. have developed a new approach to characterize the electric field of arbitrary plasmonic samples such as gold nanoparticles. Plasmonic materials are of particular interest due to their extraordinary efficiency in absorbing light, which is important for renewable energy and other technologies. In the journal Nano Letters, the researchers report on their study, which will advance the fields of nanoplasmonics and nanophotonics with their promising technology platforms.

An ultra-short laser pulse (blue) excites plasmonic gold nanorods, leading to characteristic changes in the transmitted electric field (yellow). Sampling this field allows us to infer the plasmonic field of the nanoparticle.

Localized surface plasmons are discrete excitations of electrons in nanoscale metals such as gold or silver, where mobile electrons in the metal oscillate cooperatively with the photo-electric field. It condenses optical energy, which enables applications in photonics and energy conversion, for example in photosynthesis. To advance such applications, it is essential to understand the details of plasmon drive and damping. However, a problem for the development of relevant experiments is that the processes take place on very short time scales (within a few femtoseconds).

The attosecond community, including lead authors Matthias Kling and Francesca Galleri, has developed tools to measure the oscillating electric field of ultrashort laser pulses. In one of these field sampling methods, an intense laser pulse is focused in air between two electrodes, producing a measurable current. The intense pulse is overlaid with a weak signal pulse that is then characterized. The signal pulse modulates the ionization rate and consequently the generated current. Screening the delay between the two pulses provides a time-dependent signal proportional to the electric field of the signal pulse.

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„We used this configuration for the first time to characterize the signal field emerging from a shock-excited plasmonic model,” says Francesca Galleri, lead scientist at DESY, professor of physics at the University of Hamburg and spokeswoman for the Cluster of Excellence „CUI: Material”. This allowed them to detect the appearance of the plasmon and its rapid decay, which they confirmed with electrodynamic model calculations.

„Our approach can be used to characterize arbitrary plasmonic patterns under ambient conditions and in remote regions,” says CUI scientist Prof. Holger Lange. In addition, precise characterization of the laser field emitted from nanoplasmonic materials can be a new tool to improve the design of phase-patterned devices for ultrashort laser pulses.

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