Strong and ultra-short wave X-ray pulse is difficult to generate in the nanometer wavelength range, but at present, TU Wien (Technical University of Vienna, Austria) has developed a new and simpler method. The starting point of this method is not a titanium sapphire laser, but a ytterbium laser. The key trick is that light is sent through a gas to change its properties.
The wavelength of the laser beam depends on the material that produces it. In the relevant atoms or molecules, the electrons change from one state to another with lower energy. This causes a photon to be emitted - its wavelength depends on how much energy the electron loses during its state change. In this way, different laser colors from red to purple can be generated.
However, in order to create a laser beam with smaller wavelength, special techniques must be adopted. First, a long-wavelength laser beam is created and directed at the atom. An electron is pulled off the atom and accelerated in the electric field of the laser. Then it turns back and collides with the atom from which it comes again -- thus producing short-wave X-ray. This technology is called "high order harmonic generation".
Paul Capejani of the Institute of Photonics at Vienna University of Technology said: "At first glance, this situation seems a little counterintuitive, but it turns out that the larger the wavelength of the original laser beam, the smaller the wavelength you can finally achieve." However, in the process, the efficiency of X-ray radiation will also decline: if the purpose is to produce very short wave radiation, its intensity will become very low.
Substitute ytterbium for titanium and gas for crystal
So far, this technology almost always uses a titanium sapphire laser, and then uses a special crystal to increase its radiation wavelength, so as to generate the shortest possible X-ray radiation through higher harmonics. The University of Vienna team has now developed a simpler and more powerful method. They used a ytterbium laser. The ytterbium laser is simpler, cheaper and more powerful than the titanium sapphire laser. But until now, their performance in X-ray production is still much lower.
"At the University of Vienna, researchers first increased the radiation wavelength of the ytterbium laser, not through the crystal as usual, but through the molecular gas." Paolo Carpeggiani said, "This has greatly improved the efficiency, from 20% in the past to about 80% now."
Source: OFweek
