We report the results of detailed X-ray spectroscopic diagnostics of a high-temperature laser-produced plasma of iron: the electron temperature is measured, and the absolute intensities of lines in the spectrum are determined. The plasma is generated by focusing laser radiation (0.53 μm, 2.3 J, 2 ns) onto a solid target. The spectra are recorded using an absolutely calibrated focusing crystal spectrometer. Using satellite lines near the resonance line of the [He]-like Fe XXV ion (wavelength λ = 1.85 Å), the electron temperature (Te = 1250 eV) is measured and the absolute intensities of lines of various ionization stages (from the [He]-like Fe XXV ion to the [O]-like Fe XIX ion) are determined.
We report a study of the dependence of the optimized reflection coefficient in forward four-wave mixing on the spatial orientation of bismuth titanate. The formation of three holographic gratings with a phase–amplitude structure is examined during the interaction of light waves in a photorefractive crystal. Calculations are performed taking into account the anisotropy of the linear electro-optical, photoelastic, and inverse piezoelectric effects, as well as the optical activity, linear absorption, and circular dichroism of the crystal. It is shown that the efficiency of phase-conjugation diffraction in bismuth titanate depends markedly on the crystal sample cut. It is found that when using a Bi12TiO20 crystal with a (111) cut, the reflection coefficient reaches 95
We report an experimental study of the spatial distribution of radiation from an Nd:YLF laser operating under conditions of nonuniform longitudinal diode pumping and frequency degeneracy of the cavity modes. The laser beam behind the cavity output mirror is narrowed to the size of a narrow pump beam, allowing the formation of a beam with a radius significantly smaller than that of the cavity zero mode without additional optical elements. By focusing a frequency-degenerate beam using a lens, multiple focusing regions can be achieved.
We report a comprehensive study of Hall effects during the sub-Alfvén expansion of a spherical plasma cloud into a magnetized background plasma in the weakly magnetized ion regime. A laboratory experiment on the KI-1 large-scale laser-plasma facility and kinetic numerical simulations using the IPIC3D hybrid code demonstrate that the Hall effects are suppressed with increasing background plasma concentration, yielding good agreement between the experiment and simulations. This is evident in the nature and rate of magnetic field re-penetration into the displaced volume during the diamagnetic cavity collapse phase.
Phase-change materials are widely employed in nanotechnology and microelectronics due to their ability to reversibly switch between amorphous and crystalline states, thereby altering their electrical and optical properties. The ternary compound Ge2Sb2Te5, the most studied and widely used phase-change material, consists of two binary tellurides, GeTe and Sb2Te3, each of which is itself a promising phase-change compound. This paper investigates the modification of thin amorphous GeTe and Sb2Te3 films by continuous-wave laser beams with different spatial structures, including Hermite–Gaussian modes HG00 and HG01, vector beams, and an optical vortex. The irradiated regions are analyzed based on brightness assessments of optical images and Raman spectroscopy, making it possible to conclude that beams with an annular intensity profile are promising for forming an optimal heating profile and achieving more uniform crystallization compared with HG00. For all beam types, laser-induced structural transformation significantly manifested in the Raman spectra, are accompanied by a pronounced change in optical contrast (reflectivity) for germanium telluride, whereas considerably smaller changes are abserved for antimony telluride.
The possibility of generating nitrogen-vacancy (NV) centers in diamond under prolonged exposure of the crystal surface to nanosecond UV pulses (193 nm and 248 nm, 20 ns) is demonstrated for the first time. The graphitization threshold (33 J/cm2) of a CVD diamond crystal was determined for the KrF laser, and the rates of surface nanoablation (photo-oxidative) etching developing below this threshold were measured. The dependencies of the NV center photoluminescence signal intensity on the number of laser pulses and energy density under KrF laser exposure were investigated. A 17-fold enhancement of the NV0 line intensity was obtained after laser exposure at a wavelength of 248 nm with an energy density of 25 J/cm2.
Analytical expressions are derived for calculating the light pressure force acting on a chiral spherical particle of arbitrary size relative to the wavelength in an evanescent field generated by total internal reflection of an electromagnetic wave incident at a planar interface between two dielectric media, while neglecting reflection of the particle-scattered field from the interface. The expressions are used to analyze the Cartesian components of the light pressure force as functions of particle size and the angle of incidence at the interface between right- and left-handed circularly polarized waves interacting with chiral spheres composed of dielectric materials and a negative-index metamaterials. In the context of the solved problem, it is demonstrated that the force of light pressure may differ significantly for incident waves of opposite circular polarizations, especially under force resonance conditions, which can be used to sort chiral particles in corresponding evanescent fields.
The current–voltage and emission characteristics of a two-photon quantum cascade laser operating at frequencies of 3.1–3.9 THz and employing a resonant-phonon active-region design are measured in magnetic fields up to 11.5 T at liquid-helium temperature. Near resonant magnetic fields corresponding to the intersection of the zero Landau level associated with the upper laser state and the nth (n = 1–3) Landau levels associated with the lower laser state, the emission intensity is found to decrease, leading to complete suppression of lasing due to the onset of resonant scattering from the upper laser state by interface roughness, impurities, and acoustic phonons. In strong magnetic fields (ℏωc > ℏω), where the cyclotron frequency exceeds the laser frequency, a several-fold reduction in the threshold current is demonstrated due to the nullification of electron states and the suppression of parasitic scattering processes.
The photocatalytic properties of palladium nanoparticles synthesized by laser-induced forward transfer are investigated using the degradation of the brilliant green dye under various irradiation conditions. The experiments are performed both under UV irradiation and in the absence of light.
The effect of waveguide layer thickness on basic characteristics of high-power superluminescent diodes (SLDs) emitting in the 800–900 nm spectral range has been investigated. These were based on separate-confinement heterostructures within the system of AlGaAs/GaAs/InGaAs materials fabricated by the metalorganic chemical vapor deposition (MOCVD) method. The catastrophic optical damage (COD) threshold is shown to increase with increasing waveguide layer thickness, while the far-field divergence and differential quantum efficiency remain at acceptable levels. It is demonstrated that the maximum optical output power of SLDs can reach 500 mW in continuous-wave (CW) mode while maintaining a single-transverse-mode regime.
The nonlinear optical properties of thin (50 μm) films of composites of PbS colloidal quantum dots (3.5‒4.0 nm in size), passivated with oleylamine and oleic acid, and the polymer poly(2-dimethylamino)ethyl methacrylate (PbS) are studied using the Z-scan method in the field of 70 ps pulses of the first harmonic (1064 nm) of an Nd3+:YAG laser. Nonlinear absorption and refraction are observed upon transition from the colloidal solution to the polymer composite, along with as an increase in photostability. The observed features of the nonlinear optical response are explained by the interaction between the composite components and the formation of local structural defect states.
Anomalous behavior of pair spatiotemporal correlators of the velocity field in a stationary turbulent Navier‒Stokes flow generated numerically in a cubic domain with periodic boundary conditions has been discovered. It is shown that the temporal decay of the correlations at all scales (including viscous ones) decreases inversely proportional to the time shift, even at times much larger than the integral time, where exponential decay would normally be expected. If this dependence persists at even larger time shifts, beyond those achieved in the present simulations, the discovered anomaly implies that the correlation time diverges logarithmically and is therefore infinite. The correlation time calculated over a sufficiently large but finite observation time exhibits linear scaling associated with the so-called “sweeping effect.”
Doping semiconductors with metal atoms is widely employed in microelectronic devices. However, conventional techniques often require thermal or chemical postprocessing and are limited to a narrow range of compatible materials. This work demonstrates a flexible approach for laser-induced forward transfer (LIFT)-based superdoping of silicon using femtosecond laser pulses. Thin silver films are used to evaluate the doping level and spatial distribution of impurities, as well as the laser-induced structural modifications of the crystal lattice after multipulse irradiation. The samples are characterized by energy-dispersive X-ray spectroscopy, Raman spectroscopy, and a noninvasive optical pump‒terahertz probe technique for measuring the lifetime of nonequilibrium charge carriers. The proposed method is promising for the microalloying of multilayer substrates.
This paper investigates the polarized photoluminescence and orientation order of luminescent centers in mechanically stressed polyurethane containing a fluorescent dye. The azimuthal dependence of the recorded luminescence intensity is expanded over the polarization azimuth as part of a dipole model. The observed modulation is shown to be described by a sum of a finite number of Fourier harmonics. This formulation enables the introduction of a minimal “4 + 2” experimental setup sufficient to calculate the degree of linear polarization (DoLP) and to extract the scalar order parameter (S) and the director orientation field. To quantitatively correlate the optical maps with the mechanical stress field, a local Landau-type relationship is proposed, wherein the deviatoric part of the stress tensor determines the order parameter.
The geometric accuracy of refractive elements is crucial for the optimal focusing performance of compound refractive X-ray lenses. Achieving precise control of lens geometry during two-photon polymerization direct laser writing (TPP DLW) iremains challenging due to the complex dependence of the fabrication process on printing parameters and the limited availability of non-destructive methods for internal structural characterization. This work addresses the fabrication of arrays of three-dimensional polymer parabolic lenses with curvature radii at the apex of the parabola R = 2 and 5 μm from a PETA/4Met-BAC photocomposition at laser powers ranging from 4 to 9 mW, and the investigation of their morphology by confocal laser scanning microscopy (CLSM). It is shown that CLSM enables nondestructive three-dimensional analysis of the structures and accurate assessment of geometric deviations caused by polymer shrinkage. All structures exhibited isotropic shrinkage, the magnitude of which depended on both the design radius of curvature and the laser power. For lenses with R = 5 μm, the shrinkage ranged from 5.3 to 6.0
The nonlinear absorption of femtosecond laser pulses (λ = 1030 and 515 nm, τ = 300 fs) in KU-1 (Eg = 7.6 eV) and KV (Eg = 4.6 eV) fused silica samples is studied using the open-aperture Z-scan method. The βn coefficients for 2-, 4-, and 7-photon absorption processes are determined within the framework of a model that takes into account multiphoton absorption and avalanche ionization. It is shown that the role of avalanche ionization increases with increasing order of the multiphoton process and is not manifested in two-photon absorption. The results are consistent with calculations based on the Keldysh theory.
Methods for correcting the trajectory of a cryogenic fuel target (CFT) during its injection into the laser focus of an inertial confinement fusion (ICF) facility are studied. One of the approaches involves the use of various electrostatic fields. In our case, the field source is an electrode in the form of a charged needle (U = 500 V). A successful series of experiments is conducted in a test vacuum chamber (P = 10‒5 Torr, T = 300 K) using glass and polystyrene microspheres (diameter Ø = 0.7–2.0 mm, wall thickness Δ = 10‒15 μm) as surrogate targets. In addition, free-falling microspheres (Ø = 2.0 mm, Δ = 20 μm) are delivered to a special holder located at a given point inside the test chamber. Stable microsphere positioning on the holder is achieved using a charged needle integrated with the holder. The results may find practical application in the development and optimization of advanced systems for high-precision injection delivery of CFTs to the laser focus of existing ICF facilities.
This study employed the Monte Carlo method to simulate the production of 64Cu using a low-energy proton cyclotron, which is essential for identifying cost-effective production strategies. Two target materials, 64Ni and 68Zn metals, were considered. The SRIM code was used to calculate the proton ranges in these two target materials. Based on the available experimental cross‑section data and the physical models embedded in PHITS, the effects of target material type, target thickness, and incident angle of the proton beam on the target surface on the production yield of 64Cu and associated impurities were also analyzed using the PHITS software. The results indicated that proton-induced reactions on 64Ni and 68Zn targets can achieve desirable yields of 64Cu within incident proton energy ranges of 12 → 9 MeV (for 64Ni target) and 28 → 25 MeV (for 68Zn target), respectively. Appropriately reducing the incident angle of the proton beam on the target surface can improve the utilization efficiency of the proton beam. Consequently, under the same target thickness, the yield of 64Cu is increased while the impurity yields remain relatively stable. Furthermore, as the incident angle decreases, the optimal target thickness required to achieve the maximum 64Cu yield is correspondingly reduced.
Solutions to the Vlasov kinetic equation for a distribution function with sharp boundaries have been obtained in the form of nonlinear periodic waves. It is demonstrated that the wave amplitude is bounded; furthermore, waves exhibiting maximum amplitude feature sharpening at the wave crest.
Magnetic monopoles g+ and g‒ are likely the primary components of dark matter, which, immediately after their birth, form g+g‒ atoms. These atoms are characterized by an annihilation energy of 2.4 GeV and Lyman-series transition energies of 1.8, 2.1, and 2.25 GeV corresponding to Lyα, Lyβ, and Lyγ lines, respectively. The gamma-ray excess observed in the galactic center by the Fermi observatory in the range of 1‒8 GeV with a maximum near 2.4 GeV indicates the presence of magnetic atoms. On galactic scales, magnetic atoms are dark matter. In addition, dark matter must necessarily include familons and light Goldstone bosons with energies ≪ 1 eV, formed during phase transitions accompanying the cooling of the Universe. The emergence of a new research field—the astrophysics of magnetic atoms—is anticipated, along with the presence of such monsters as g+e‒, g‒e+, g+μ‒, g‒μ+, g+τ‒, and g‒τ+.
