Предпороговые эффекты при воздействии ультрафиолетовых лазерных импульсов на медь и ее сплавы

The prethreshold processes on the surface of copper and its alloys are investigated. In the absence of obvious traces of melting, while preserving the metal in a condensed state, under a nanosecond ultraviolet laser radiation energy density of 0.1–1.0 J/cm2, manifestations of high-temperature plastic deformation were observed. These are sliding and cracking along grain boundaries, within which crystallographic slipping was observed. A microprotrusion was formed on the surface of the irradiated zone, which was outwardly similar the distribution of laser radiation in the spot. The height of the microprotrusion reached 1 µm, and sometimes even more. An increase in the number of impacting impulses led to the accumulation of damage. The data obtained are in many ways similar to the acoustoplastic, electroplastic, and magnetoplastic effects. By analogy, we consider it possible to call the discovered effect optoplastic.

Laser hardening of metallic materials

The surface microstructure of metallic materials formed under the effect of laser radiation is characterized by high degree of nonequilibrium, has layered structure consisting of the main three zones formed from the fused material, the heat-affected zone and the tempering zone. As the laser radiation energy increases, the size of the modified layer increases, and the coverage width of the melting zone and heat-affected zone is determined by the maximum penetration depth of the melting and polymorphic transformation isotherms. The distribution of microhardness over the depth depending on the laser radiation energy is exponential or extreme, and the microhardness is usually maximum in the heat-affected zone. As the laser energy increases, the microhardness of the hardened surfaces changes with extreme dependence. Laser hardening of metallic materials is the result of two competing hardening and softening processes. As result of mathematical processing of experimental results, empirical equations for the distribution of microhardness over the depth of laser-hardened surface layers of various steels and ARMCO-iron are obtained. Empirical equations consist of two terms, the first of which describes the processes of hardening, and the second — softening. The obtained equations allow optimizing the laser hardening modes and predicting the hardened layer depth.

SOLAR PUMPED LASER BASED ON COMPOSITE TITANIUMSAPPHIRE ACTIVE MEDIUM

On the basis of the active element of Ti3+:Al2O3, the possibility of converting solar energy into laser radiation energy is investigated. By the computer simulations, it was shown the possibility of reducing the threshold pump power by choosing the optimal geometry of the crystal parameters for end-pumping scheme of concentrated solar radiation.

HIGHLY EFFICIENT Nd:Cr:GSGG LASER WITH SIDE-PUMPING BY SOLAR RADIATION

The possibility of achieving high efficiency of converting solar energy into laser radiation energy on the basis of the active element Nd: Cr: GSGG in the form of a thin slab allowing providing an effective heat output during side pumping by concentrated solar radiation at the focus of a parabolic concentrator with a diameter of 1 m2 is considered. The study was carried out by computer simulation of the laser system.

Новый люминофор ИК-диапазона на основе германата Sr-=SUB=-3-=/SUB=-La-=SUB=-2-=/SUB=-(Ge-=SUB=-3-=/SUB=-O-=SUB=-9-=/SUB=-)-=SUB=-2-=/SUB=- : Nd-=SUP=-3+-=/SUP=-, Ho-=SUP=-3+-=/SUP=-

Cyclogermanate Sr_3La_2(Ge_3O_9)_2, isostructural to silicate Sr_3Er_2(Si_3O_9)_2, activated by neodymium and holmium is obtained for the first time by the precursor method. Ion Nd^3+ in the structure of Sr_3La_2(Ge_3O_9)_2 is a sensitizer of the infrared luminescence of Ho^3+. Excitation by radiation with a wavelength of 808 nm leads to a series of emission lines in the luminescence spectra of Sr_3La_2- x Nd_ x (Ge_3O_9)_2 : Ho^3+ in the short-wave and middle-IR ranges (1.0–3.4 μm). The highest intensity of lines at 2.1 and 2.7 μm, associated with the ^5 I _7 → ^5 I _8 and ^5 I _6 → ^5 I _7 transitions in the Ho^3+ ion, is found for compositions containing traces of holmium. Based on the analysis of the concentration dependences of the luminescence intensity, an optimal composition of the phosphor is determined, which ensures the maximum efficiency of conversion of laser radiation energy. The data obtained are interpreted in the assumption of cross-relaxation energy transfer from Nd^3+ to Ho^3+.

Magnetic Assisted Laser Percussion Drilling

In this paper, feasibility of laser percussion drilling on highly reflective materials i.e., Al5052 using an assisting magnetic field was explored. During the laser percussion drilling, the Lorentz force generated by the assisting magnetic field affects the laser-induced plasma and results in significant influence of the laser percussion drilling. The magnetic field simulation was performed to investigate the field strength of the circular hollow permanent magnet. The influences of magnetic field and the laser radiation energy on the penetration depth and inlet diameter were examined.