Well, it had an interesting start...

From the description, the device made by the Chinese team is for a free-electron laser what a transistor was for an amplifying vacuum tube.

A free-electron laser is also a kind of vacuum tube, and one that is extremely large and expensive.

The new kind of free-electron laser, uses the free electrons from a solid-state metal wire instead of using free electrons from vacuum, so it can be much smaller, much cheaper and much more reliable, exactly like a solid-state transistor is in comparison with a vacuum pentode or triode.

Without access to complete text, it is not known in which wavelength range the metal wire can act as a laser and which is the energy efficiency.

Nevertheless, it could revolutionize the use of free-electron lasers. Such a laser has a much more limited domain of applications than a transistor, so it will not have a similar impact, even if it is a similar kind of invention.

The traditional free-electron lasers have the advantage that they can be designed to produce light of a desired frequency, while most other kinds of lasers are constrained to produce only certain frequencies from the spectra of various kinds of atoms, ions, molecules or solid crystals.

It would be interesting to know if this new kind of free-electron laser can also be designed to produce light of any desired frequency (within a certain range).

Thanks for the explanation! Could this be used for holograms for less money like hobos? What are some other applications? Better laser cutters?

After browsing through the full text, thanks to the link provided by another poster, the conclusion is that such solid-state free-electron lasers might be realizable only in the far infrared, at frequencies much lower than those of visible light, unlike the vacuum free-electron lasers, which can produce even ultraviolet light.

These can still have many useful applications, but holograms are not one of them, because their output will not be visible.

Laser cutters are also another excluded application, because such lasers will have a low electrical energy to light energy conversion efficiency. The reason is that these solid-state free-electron lasers, like also most other laser types except the laser diodes and some of the gas lasers, use another laser as their energy source, so the efficiencies of the 2 lasers are multiplied. Actually the pumping laser needs almost certainly to be pumped itself by a laser diode. Therefore the total efficiency will be the product of the efficiencies of 3 lasers, so it will be low.

More likely applications would be in communications, Lidar, imaging through materials that are opaque for visible light, chemical analysis, maybe influencing certain chemical reactions.

The fact that solid-state free-electron lasers should work only in the far infrared is actually expected, because high frequencies, like those of visible or ultraviolet light require a large energy difference between the energy of the electrons before and after emitting the laser light. When the electrons are free before and after emission, that means that the pumping source must accelerate them, providing the energy difference.

In vacuum, a free electron can be accelerated to any energy, e.g. up to levels enabling the emission of X-rays when the electrons lose the accumulated energy, but in a metal a free electron that is accelerated too much will either collide with the lattice of atoms, losing the energy, or it might even exit the metal and be lost, like in the photoemissive electrodes that were used in the earliest video cameras.

Is there a way to shift light frequency outside of the laser? That could open up more applications.

Full paper is here https://europepmc.org/article/ppr/ppr485152

https://web.archive.org/web/20220421175228/https://assets.re...

"Coherent Surface Plasmon Polariton Amplification via Free Electron Pumping" (2022) Ye Tian, Dongdong Zhang, Yushan Zeng, Yafeng Bai, Zhongpeng Li, and 1 more https://doi.org/10.21203/rs.3.rs-1572967/v1

Abstract: Surface plasmonic with its unique confinement of light is expected to be a cornerstone for future compact radiation sources and integrated photonics devices. The energy transfer between light and matter is a defining aspect that underlies recent studies on optical surface-wave-mediated spontaneous emissions. But coherent stimulated emission, being omnipresent in every laser system, remains to be realized and revealed in the optical near fields unambiguously and dynamically. Here, we present the coherent amplification of Terahertz surface plasmon polaritons via free electron stimulated emission. We demonstrate the evolutionary amplification process with a frequency redshift and lasts over 1-mm interaction length. The complementary theoretical analysis predicts a 100-order surface wave growth when a properly phase-matched electron bunch is used, which lays the ground for a stimulated surface wave light source and may facilitate capable means for matter manipulation, especially in the Terahertz band.

Polariton: https://en.wikipedia.org/wiki/Polariton

Surface plasmon polaritons : https://en.wikipedia.org/wiki/Surface_plasmon_polaritons :

[...] Application of SPPs enables subwavelength optics in microscopy and photolithography beyond the diffraction limit. It also enables the first steady-state micro-mechanical measurement of a fundamental property of light itself: the momentum of a photon in a dielectric medium. Other applications are photonic data storage, light generation, and bio-photonics.[2][3][4][5]

This looks ripe for some cutting edge table-top physics!