Vol 80, No 4 (2016)

The results from experiments on the laser irradiation of metallic targets of the copper group immersed in liquid are reported. Comparative studies of the formation of colloids during the laser irradiation of targets with varying (from moderate to ultrahigh) radiation intensities are conducted. The dependence of the size of obtained particles on laser irradiation conditions (pulse duration and radiation intensity) is revealed.

The formation of porous matrix structures (scaffolds) from biocompatible polymers and their composites with finely dispersed hydroxyapatite via air pressure–aided 3D printing and digital light processing (DLP) is studied. A triblock copolymer (polyethylene glycol/poly-ε-caprolactone/polyethylene glycol) and polyethylene glycol diacrylate served as raw polymer materials. The internal structure and surface morphology of the resulting scaffolds and the correspondence of their architectonics to the initial 3D virtual models are analyzed by means of optical and scanning electron microscopy.

A technique for the stereolithographic manufacturing of plastic casts of the costochondral complex is developed using computer tomography scans of real patients for preoperative simulations of the laser thermoplastics of children’s funnel and keeled chests.

The microstructure of a clad layer produced via selective laser cladding with coaxial metal powder injection is studied numerically. The Johnson–Mehl–Avrami–Kolmogorov equation for condensed systems with inhomogeneous rates of nucleation is used to model the phase change kinetics. The impact of the substrate boundary along with interconnected heat transfer and phase change processes on the final microstructure of a built-up layer is demonstrated. The qualitative difference between the behavior of the temperature on the built-up layer’s surface and at the depth of the substrate is established, revealing the inhomogeneous microstructure of the final layer.

Aspects of steel sheet perforation are studied experimentally. Calculations show that the mechanisms of thin sheet perforation change as the focal spot size is increased at a constant laser power. If the spot is small, the melt is removed and the film is disrupted by steel boiling in the spot center. With larger spots, the melt is removed by the force of gravity. The hole diameter grows along with the focal spot size and sheet thickness and is reduced upon an increase in laser power.

Forms of the condensed phase created under the action of a high-power CO₂ laser pulse (power, 4 J/pulse; λ = 10.6 μm; pulse duration, 1.5 μs) on optical sapphire (Al₂O₃) solid targets are investigated. The ablation products emitted from the laser crater and the particles formed in the space above the surface of the target are collected using witness samples oriented in a predetermined manner with respect to the laser crater. Forms of the condensed phase are studied via electron microscopy and atomic force microscopy. Conclusions are drawn as to the mechanisms of formation of particles with different shapes and structures, including Al₂O₃ vacuum hollow microspheres (hollow bubbles).

A spectroscopic prism coupler is created for measuring refractive indices n_f and thicknesses H_f of dielectric films. The operating principle of the device is based on the simultaneous resonance excitation of several waveguide modes in a film by a focused TE or TM polarized light beam in the geometry of frustrated total internal reflection. Calculations of n_f and H_f are performed using measured angular positions θ_m of dark m-lines in the cross section of the specularly reflected beam. Using obtained angles θ_m, we can calculate effective refractive indices β_m of modes. By solving a set of nonlinear dispersion equations for the modes of a planar waveguide, we can calculate refractive index n_f and thickness H_f of a film. The proposed prism coupler has no moving parts and allows us to measure the optical parameters of films 0.5–10 μm thick in the 400–1100 nm range of wavelengths. The device can also be used as a spectroscopic refractometer for measuring the refractive indices of bulk media. The device is used to measure refractive index and thickness of a SiO film and the refractive index of TF4 glass.

A criterion for selecting the best ranges for measuring the reflectivity of a prism coupler, based on minimizing the error in reconstructing the parameters of thin films using the least-square method, is proposed. The effectiveness of the criterion is demonstrated by solving the inverse optical problem for a SiO_x film deposited on a silicon substrate as an example.

A new noncontact technique is proposed for determining the parameters of nanosized metal coatings (absorption coefficients, refractive indices, and thicknesses). It is based on processing the measured angular dependence of the energy reflection coefficient of a polarized laser beam reflected by a thin-film structure surface. Features of determining the parameters of films on silicon substrates have been considered.

The results from calculations and preliminary experimental investigations of a solid-state laser manufactured in the form of a plate 15 × 10 × 0.3 mm in size and made of YAG:Yb³⁺ crystal with two-side diode edge pumping with a total power of 600 W at a wavelength of 940 nm are presented. Both stable and hybrid stable–unstable resonators are used in the experiment.

Electric collector investigations of the singleand multi-shot femtosecond laser ablation of optical-quality surfaces of different materials, including aluminum, copper, titanium, silicon, and graphite, show that the emission of erosion plasma is significantly lower than the energy density of laser ablation of these materials and replaces the dominant electron emission at lower energy densities. I–V characteristics and cumulative dependences of the collector signal are studied in the emission mode. The observed dependences of the electron and plasma emission signals on the laser pulse energy density are discussed.

In vitro perforation of gelatin-based biomodels and myocardium tissue by powerful CO₂ and YAG:Er laser pulses is considered. Features of the thermal and shock-wave effects on the walls of the laser channel are investigated. Patterns of laser channeling in gelatin by a single YAG:Er laser pulse were studied.

Prospects for using upconversion nanoparticles as markers for tumor optical imaging are discussed. Using a model of epidermoid Lewis lung carcinoma engrafted in mice, luminescent signals from nanoparticles delivered into the tumor tissue are registered in vivo.

A THz transistor based on a metamorphic nanoheterostructure with generation frequency f_max = 0.63 THz and a zigzag-shaped gate L_g = 46 nm long is developed. A series of low-temperature GaAs structures are produced, and photoconductive antennas with generation frequencies above 1.5–2 THz are developed on their basis.

Born’s criterion of crystal stability with respect to small variations of homogeneous deformations is formulated in a quasi-harmonic approximation. It is shown that the third-order Landau potential with respect to a tensor’s components of Lagrangian deformation is sufficient for predicting the critical pressure at which the cubic structure becomes unstable. The accuracy of prediction is no worse than that of the available experimental data.