Science Technology

The new technology can efficiently generate X-ray laser pulse, and the luminous efficiency is greatly increased to 80%

Recently, a group of researchers from TU Wien announced the development of a new, simpler and more effective X-ray laser pulse generation technology.
In daily scenes, X-ray films used to check broken legs in hospitals are easy to make. However, in industrial application scenarios, a completely different kind of X-ray radiation is required – that is, the shortest and high-energy X-ray laser pulse as possible. For example, they are used for the production of nanostructures and electronic components, but also for real-time monitoring of chemical reactions.
It is difficult to generate intense and ultra-short wave X-ray pulse in the nanometer wavelength range, but now Vienna University of Technology has developed a new and simpler method: it does not use titanium sapphire laser, but uses ytterbium laser. The key technique is that light changes its properties through gas.
The new technology can efficiently generate X-ray laser pulse, and the luminous efficiency is greatly increased to 80%
(Image source: TU Wien)
Long-wavelength conversion produces short-wavelength shock beam
The wavelength of the laser beam depends on the material that produces the laser beam: in the atoms or molecules involved, the electrons change from one state to another with lower energy. This causes the photon to be emitted – its wavelength depends on how much energy the electron loses in the process of state change. In this way, different colors of laser can be produced – from red to purple.
However, in order to produce a laser beam with smaller wavelength, special techniques must be adopted: first, produce a laser beam with longer wavelength and emit it to the atom. An electron is stripped from the atom and accelerated in the electric field of the laser. Then it turns back and collides with the original atom again, producing short-wave X-ray. This technology is called “high harmonic generation”.
Paolo Carpeggiani, of the Institute of Photonics at Vienna University of Technology, explained: “At first glance, this situation seems counterintuitive. Because scientists have previously proved that the larger the wavelength of the original laser beam, the smaller the wavelength you can finally reach. However, the generation efficiency of X-ray radiation will also decrease in the process: if you want to generate very short wave radiation, its intensity will become very low.”
Substitute ytterbium for titanium sapphire and gas for crystal
Up to now, this technology almost always uses a titanium sapphire laser, and then uses a special crystal to increase its radiation wavelength in order to generate the shortest X-ray radiation through high harmonic generation.
However, the research team of Vienna University of Technology has developed a simpler and more powerful method: they use ytterbium laser. Ytterbium lasers are simpler, cheaper and more powerful than titanium sapphire lasers, but so far, their performance in X-ray generation is much lower.
The key breakthrough of the Vienna University of Technology team is that they have increased the wavelength of ytterbium laser radiation for the first time – not through crystals as usual, but through molecular gases. This has greatly improved the luminous efficiency from 20% to about 80%.