Researchers realize multiphoton electron emission with non-classical light

Strong-field quantum optics is a rapidly emerging research topic, combining elements of nonlinear photoemission, rooted in strong-field physics, with the established domain of quantum optics. Although the distribution of light particles (i.e. photons) has been extensively documented both in classical and non-classical light sources, the impact of such distributions on photoemission processes remains poorly understood.

Researchers from the Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) and the Max Planck Institute for the Science of Light recently attempted to fill this gap in the literature by investigating light-matter interactions with a non-classical light source. Their article, published in Natural physicsshows that photon statistics from the driving light source are imprinted on the electron number statistics of emitted electrons from metal needle tips, an observation that could have interesting implications for the future development of optical devices.

“The field of strong field physics is now highly developed, as evidenced by the 2023 Nobel Prize in Physics,” Jonas Heimerl, co-author of the paper and researcher at FAU, told Phys.org. ‘This physics is not limited to atoms, but also takes place on metal surfaces such as metal needle points. Similarly developed and even more diverse is the field of quantum optics. One aspect of this area is generating light with non-classical light statistics, such as clear pressed vacuum.”

The primary goal of Heimerl and his collaborators’ latest research was to understand how quantum light from non-classical light sources interacts with matter. It is striking that the interactions between quantum light and matter have so far only been investigated using classical light sources.

“Our neighbor, Professor Maria Chekhova, is a leading expert in the field of generating clear pressed vacuum, a special form of non-classical light,” Peter Hommelhoff, co-author of the paper and researcher at FAU, told Phys .org. “We therefore collaborated with her and our long-time partner Ido Kaminer from the Technion in Israel to investigate electron emission driven by non-classical light.”

Heimerl, Hommelhoff and their research group at FAU conducted their experiments in close collaboration with Chekhova, a researcher with extensive expertise in quantum optics. Chekhova is best known for her work in the field of clear pressed vacuum generation, a technique that involves the use of nonlinear optical processes to generate clear pressed vacuum, a form of non-classical light.

“In our experiment, we used this non-classical light source to initiate a photoemission process from a metal needle tip that is only a few tens of nanometers in size,” Heimerl explains. “Think of it as the well-known photoelectric effect that Einstein studied, but now with a light source that exhibits extreme intensities and extreme fluctuations within each laser pulse.”

For each generated laser pulse, the researchers counted the number of electrons, for both classical and non-classical light sources. Interestingly, they found that the number of electrons can be directly affected by the driving light.

“Our findings could be of enormous importance, especially for electron imaging applications, for example when it comes to imaging biological molecules,” Heimerl said.

Biological molecules are known to be very sensitive to damage and reducing the dose of electrons used to image these molecules could reduce the risk of such damage. Heimerl et al.’s paper suggests that it is possible to modulate the number of electrons to meet the needs of specific applications.

“Before we can tackle this, however, we need to show that we can also imprint a different photon distribution on electrons, namely one with less noise, which may be difficult to achieve,” Hommelhoff said.

The findings of this recent work could soon open new avenues for research focusing on high-field quantum optics. At the same time, they could serve as the basis for new devices, including sensors and strong-field optics that use the interaction between quantum light and electrons.

“We think this is just the beginning of exploring experimental research in this area,” Heimerl added. “A lot of theoretical work is already underway, some of it led by our co-author Ido Kaminer. One observable thing we haven’t explored yet, but which contains a lot of information, is the energy of the electron, which could shed even more light on the light-matter interaction.”

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