For the first time in the history of science, physicists from the LOA (Laboratoire d’Optique Appliquee) in France have created a so-called relativistic plasma mirror, a laser-light-induced region inside which free plasma electrons move at nearly the same speed. your light. And the most remarkable thing in this case is that this plasma mirror “updates” at a fairly high speed – about a thousand times per second.

When a very intense pulse of laser light ionizes the surface of a material target, it creates a dense cloud of plasma that becomes completely opaque, even if the target was previously completely transparent. Laser light is simply reflected from such a plasma mirror. However, during such reflection, a process called surface high harmonic generation (SHGG) occurs, which “intensifies” the laser light pulses, making them even shorter and more intense, which is of interest to some fields of science and technology.

However, the “fragile nature” of the SHHG process dictates a number of stringent requirements for laser parameters, such as the spatio-temporal quality of the pulse and temporal contrast, as well as a large peak power that must be measured in terawatts. ie thousands of gigawatts. And that is why all previous experiments in this direction were performed with a low (less than 10 times per second) generation-update frequency of the plasma mirror.

For this, French scientists have developed a new terawatt class laser that can produce pulses lasting less than 4 femtoseconds, thousands of times per second. At the same time, all other parameters of the laser also meet the requirements of the SHHG process. At most, scientists have applied a new technology in which two pulses are used to create or maintain a plasma mirror. The first pulse creates a plasma cloud and contributes to its expansion. The main light pulse follows with a short delay, allowing control of the plasma density gradient, which determines many parameters of the plasma mirror.

In the next stages of their research, the French scientists plan to tackle the problem of refocusing the radiation reflected from a plasma mirror;