A Nanoscale Laser Made of Gold

Experiments with extremely short light flashes led to the new nanolaser. (Picture: U. Oldenburg)

Tiny particles composed of metals and semi­conductors could serve as light sources in components of future optical computers, as they are able to precisely localize and extremely amplify incident laser light. A team from Germany and Sweden led by Christoph Lienau and Jin-Hui Zhong from the University of Oldenburg has now explained for the first time how this process works.

For their study, the team produced hybrid nano­materials that combine the optical properties of metals and semi­conductors. The starting point of the study were sponge-like gold particles with a diameter of several nanometers and pores with a size of around ten nanometers. The material scientists Dong Wang and Peter Schaaf from the Technical University of Ilmenau fabri­cated these nanosponges and further used advanced nano­fabrication techniques to coat the sponges and infiltrate their tiny pores with a thin layer of the semi­conductor zinc oxide.

The particles are capable of changing the colour of an optical light beam. For example, if they are irradiated with the light of a red laser, they might emit blue laser light, which has a shorter wavelength. The emitted colour depends on the properties of the material. “Creating such nonlinear optical materials with nanoscale dimen­sions is one of the grand challenges in current optics research,” Lienau reports. In future optical computers, which might use light instead of electrons for calcu­lations, such nano­particles could serve as tiny light sources. “You could call such particles nano­lasers,” adds Zhong, who worked together with Jan Vogelsang from Lund University. Possible applications include ultrafast optical switches or transistors.

In order to elucidate how nano­materials convert light of one colour into another, team members led by Anne L’Huillier and Anders Mikkelsen from Lund University in Sweden used a special micro­scopic method, ultrafast photo­emission electron micro­scopy. Combining extremely short flashes of light with an electron microscope, they were able to directly show that light is effi­ciently concen­trated in the nanopores – an important prerequisite for its future application.

Erich Runge, a physicist from the Technical University of Ilmenau, simulated the properties of the material with theoretical models. As the team reports, nano­particles composed of metals and semi­conductors probably offer new oppor­tunities for adjusting the properties of the emitted light. “Our study provides fundamental new insights into how hybrid metal-semi­conductor nano­structures amplify light,” says Zhong. In addition, the obser­vations could help develop materials with even better optical properties.

The research group “Ultrafast Nano-Optics” at the Univer­sity of Oldenburg headed by Christoph Lienau specializes in studying processes in the nanoworld with parti­cularly high spatial and temporal resolution. The physicists have already achieved several signi­ficant breakthroughs in this field. Only recently, they deve­loped a metallic superlens made of gold with previously unattained optical resolution. (Source: U. Oldenburg)

Reference: J.-H. Zhong et al.: Nonlinear plasmon-exciton coupling enhances sum-frequency generation from a hybrid metal/semiconductor nanostructure, Nat. Commun. 11, 1464 (2020); DOI: 10.1038/s41467-020-15232-w

Link: Ultrafast Nano-Optics (C. Lienau), University Oldenburg, Oldenburg, Germany

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