Recently employees of the RAS Institute of Physics named after P. Lebedev in cooperation with the scientists of Moscow and Belgorod State Universities, RAS Institute of General Physics named after A. Prokhorov, as well as students of a number of Moscow higher education institutions produced unidimensional nanostructures with a period of up to 90 nm, based on the method of multi-impulse exposure of a solid material surface to femtosecond laser radiation. It was for the first time that the physicists overcame 100-nanometer "psychological" barrier separating nano- and micro-technologies. In addition, the length of laser radiation wave was 8 times more than the period of produced nanostructures. The scientists of the RAS Institute of Physics Andrei Ionin, Dr. Sc. (Phys. & Math.), Sergei Kudryashov and Leonid Seleznev, both Cands. Sc. (Phys. & Math.) gave details of the work under consideration to Vasily Yanchilin, a correspondent of the Poisk newspaper.

As a rule, minimally possible "nanostructures" are produced by means of molecular and atomic assembly using tunnel microscope. But this process takes too much time to "assemble" any, even nanosize, structure. The authors of the work under consideration decided to act otherwise—they began to change properties of a large (several mm²) material surface directly on a nanolevel using femtosecond laser Start-248M, designed especially for this purpose by the Research and Development Company Avesta-Project, located in the town of Troitsk (Moscow Region) and engaged in manufacture of innovative spectroscopic equipment.

Super-high-speed impulse duration of the said unit at appropriate focusing ensures a rather high local (in time and space) intensity of the effect of light radiation on the solid target material. As a result of the so-called soft noninvasive laser ablation (removal), there takes place its "scorching" from the surface, which in this case has a positive effect. The process itself takes from a couple of minutes to several hours (depending on the material). But nanostructures are created almost "blindly", therefore, it is necessary to visualize them using microscopic methods, for example, by means of scanning electronic microscopes with a high magnification level, which allow to see details of around 20nm in size.

According to physicists, these studies are fundamental; at the moment they cannot foresee discoveries that are in store for us: 100 nm is a starting point when paradoxal laws of the quantum world take effect, and characteristics of materials with nanostructures on the surface can be cardinally different from usual ones. Scientists are only making first steps in their studies, having attracted many specialists in material science.

The first results were obtained after femtosecond laser processing of silicon, which enabled to increase the material absorption index. Then, in order to produce surface structures, scientists started to aluminum, nickel, aurum, ferrum, graphite, superconducting ceramics and, finally, titanium. In addition, the formation mechanism of the latter turned out to be most interesting: titanium structures became smaller and smaller with an increase of the energy density of laser impulses. This is really intriguing, as other materials demonstrated an opposite effect (which was confirmed by foreign research groups).

Reduction of the period of forming nanostructures with an increase of the energy density of femtosecond radiation on a dry titanium surface (when registered in the water medium, it was even smaller—about 90 nm) is

of great interest. The fact is that titanium is one of the main materials for aerospace machinery and medical implants, and nanomodification of its surface can significantly change not only its current properties, but also add to it new unusual characteristics.

Employees of the RAS Institute of Physics together with technologists of Smolensk Production Amalgamation Kristall have also found out: femtosecond laser impulses can be used to mark natural super-pure mono-crystalline diamonds, having created inside them a graphite structure of less than 10 µm—the logo of the manufacturer or an individual number of the stone. It is invisible with a naked eye, but can be easily read if examined under a microscope.

Finally, ophthalmologists have long been performing operations on eyes to correct eyesight* using excimer lasers. New technologies based on femtosecond quantum generators have made these operations more effective and safe. Such equipment can be focused at any required depth. It creates microscopic bubbles in the layers of cornea, then carefully and accurately carries out exfoliation of its flap and is detached by an insignificant mechanical action. Employees of the laboratory of gas lasers of the RAS Institute of Physics in cooperation with the colleagues of the RAS Central Clinical Hospital have already got first positive results in creation of thin flaps on the sclera by means of femtosecond laser impulses, where malignant tumors are often formed. The results of this works have been published in a scientific magazine and highly appreciated by specialists.

* See: I. Shcherbakov, "Laser Physics in Medicine", in this issue of the magazine. —Ed.

V. Yanchilin. Dishevelled by Laser. — "Poisk", No. 21, 2010

Prepared by Marina KHALIZEVA