# Synopsis: Drilling for tunable photons in a nanohole

The demonstration of photon emission as free-electrons pass through a nanoscale grating could pave the way for a new generation of on-chip tunable light sources.

When free electrons interact with a periodic structured environment, such as the surface of a metal grating, they emit photons [1]. The same principle guides the operation of the free-electron laser, whereby a beam of relativistic electrons passes through a spatially periodic transverse magnetic field, generating tunable, coherent, high-power radiation [2].

Writing in Physical Review Letters, Giorgio Adamo and colleagues from the University of Southampton in the UK, and collaborators in Taiwan and Spain, take the concept of tunable light sources into the realm of the nanoscale. Adamo et al. fire an electron beam through a $700$-$\text{nm}$-diameter hole in a stack of alternating silica and gold layers, each $200\phantom{\rule{0.333em}{0ex}}\text{nm}$ thick. As the electrons travel through the periodically layered structure, they emit near-infrared photons whose frequency can be tuned by adjusting the electron energies in the $20$$40$ $\text{keV}$ range. The tunability of this “light well,” together with its compact size, makes this device potentially interesting as an on-chip light source for nanophotonic circuits, or in optical memory and display applications. Scaling the concept from the $\text{THz}$ range to the $\text{UV}$ appears within reach by varying the periodicity of the structure.

At this proof-of-concept stage there are caveats: The emitted light is incoherent and the photon conversion process is hampered by losses, with only $2$$4$ photons emitted per 100 000 electrons at maximum intensity. If the technical challenges presented in this demonstration can be surpassed, Adamo et al.’s results could pave the way for a new generation of on-chip tunable light sources. – Manolis Antonoyiannakis

[1] S. J. Smith and E. M. Purcell, Phys. Rev. 92, 1069 (1953).

[2] L. R. Elias et al., Phys. Rev. Lett. 36, 717 (1976); D. A. G. Deacon et al., Phys. Rev. Lett. 38, 892 (1977).

### Announcements

More Announcements »

Optics

Optics

## Next Synopsis

Atomic and Molecular Physics

## Related Articles

Metamaterials

### Synopsis: Enter the Metacage

An array of equally spaced nanowires, dubbed a metacage, could block optical radiation from entering or escaping a region of arbitrary shape. Read More »

Optics

### Viewpoint: Sharing Heat in the Near Field

The maximum amount of radiative heat that can be transferred between two objects of any shape has been calculated for separations of less than the thermal wavelength. Read More »

Quantum Physics

### Synopsis: Quantum Rocking Motion in Molecular Rotors

A type of quantum oscillation—known to occur for electrons in a crystal—has now been observed in a gas of molecular rotors that are spun around by laser pulses. Read More »