The acceleration of electrons in a laser plasma excited by subterawatt femtosecond pulses in gas-cluster targets of different types has been experimentally studied. The laser–plasma interaction was investigated under different target pumping conditions. A possibility of generating a narrowly directed beam of electron bunches with average electron energy up to 90 keV under excitation of a gas-cluster jet, containing nanoscale sulfur hexafluoride molecular clusters, by laser pulses of subrelativistic intensity (up to 1016–1017 W/cm2) was experimentally demonstrated for the first time. The main characteristics of the pulsed electron beam generated under optimal jet excitation conditions have been measured, and the generation of THz radiation, accompanying the electron acceleration, has been investigated as well.
An improved optical ultramicroscope is described to be used for visualizing single nanoparticles (NPs) sized over 5–10 nm in aqueous solutions and determining their hydrodynamic radii. The ultramicroscope is based on detection of Brownian motion trajectories of NPs using the elastic light scattering signals of two—laser and nonlaser—sources and their subsequent analysis for determining individual hydrodynamic radii of the detected NPs. The actual capabilities of the developed microscope in studying NPs of a different nature, including biological ones, are demonstrated. The analysis results for silver and silicon dioxide (SiO2) NPs obtained using the developed microscope are compared to those obtained using a transmission electron microscope and a dynamic light scattering microscope (DLS). The developed microscope is shown to hold promise in medical diagnosis applications. Advantages of using a nonlaser source of bright incoherent radiation for analysis of submicron particles larger than 100 nm are demonstrated.
The formation of stable birefringent micromodifications (voxels) in silica glass by single ultrashort laser pulses with a flat-top intensity profile has been studied experimentally and theoretically as a function of the focusing numerical aperture. It is experimentally shown that birefringence is formed in a voxel if the focusing numerical aperture is higher than 0.5, while lower-aperture focusing gives rise to voxels without birefringence. The slow axis of birefringence is predominantly oriented along the polarization of the incident light, and the azimuthal dispersion of the axis direction decreases with increasing numerical aperture.
Piezothermoelasticity and wave interaction studies play a vital role in the development of functional devices such as transducers and sensors, which are widely used in energy harvesting and structural health monitoring. Motivated by these applications, this paper investigates the reflection of plane waves at the boundary of a piezothermoelastic half-space for a traction free surface. A particular focus on the influence of initial stress is examined. Four reflected wave modes such as quasi-longitudinal (qP), quasi-shear vertical (qSV), electrical-acoustic (EA), and thermal (T) are considered. By apply the boundary conditions, a coupled system of linear algebraic equations is obtained. This is solved to express the corresponding amplitude ratios explicitly as functions of the angle of incidence. These expressions are solved by using appropriate mathematical tools, and numerical simulations are conducted for a piezothermoelastic material, such as barium titanate (BaTiO3). The study compares results under two thermoelastic theories: Lord and Shulman (LS) and Green and Lindsay (GL). More energy shifts into the qP wave, while the qSV wave becomes weaker, which helps when a clear qP signal is needed in practical devices. The effects of initial stress on wave behavior are demonstrate graphically and it provides a valuable intuition for smart material design and wave-based sensing technologies.
The electronic band structure, origin of energy states, spectral dependences of optical functions at different polarizations of incident light and partial densities of states projected onto atoms have been studied for TlInS2 crystals of hexagonal modification using ab initio calculations. The linear and nonlinear optical properties of this compound were experimentally investigated in the range of photon energies from 0.7 to 6.5 eV by spectral ellipsometry. The experimentally found spectral dependences of the imaginary and real parts of the dielectric function; optical conductivity; refractive indices; and extinction and absorption coefficients are in good agreement with the calculation results. The nonlinear refractive index, as well as the first- and third-order nonlinear susceptibilities, were calculated; the found values indicate good prospects of integrating the compound under study into various nonlinear optical systems.
