Physics of Wave Phenomena最新文献

The study of the scattering of structured light beams is of great interest to the researchers owing to their unique characteristics and potential applications in many fields. So, in this manuscript, the electromagnetic wave scattering for a non-diffracting focused Airy beam by a homogenous spherical particle is inspected within the domain of the generalized Lorenz–Mie theory (GLMT) and plane wave spectrum method. Incident electromagnetic fields of Airy beams are expanded by employing the beam shape coefficients (BSCs), whose mathematical expressions are derived by implementing the vector angular spectrum decomposition method (VASDM) and using the spherical vector wave functions (SVWFs). The undetermined expansion coefficients regarding scattered fields can be calculated by considering the boundary conditions (BCs) on the surface of the homogeneous spherical particle. The scattered intensities for the far-field/far-zone are numerically analyzed, and results depict that the Airy beam configuration parameters, such as attenuation factor, transverse scale parameter, center coordinates, and particle radius, strongly influence the far-field scattered intensities.

A Nafion–CdSe/CdS/ZnS colloidal nanocrystals molecular complex with the specific luminescence spectrum is produced by diffusion of colloidal CdSe/CdS/ZnS nanocrystals with the size of 8.8 ± 0.2 nm into a proton exchange membrane. Characteristic lines of the Cd, Zn, and C atoms are observed in the emission spectrum of the membrane with embedded CdSe/CdS/ZnS nanocrystals. The luminescence spectrum of the membrane with nanocrystals has additional intensity peaks that do not coincide with the spectral lines of the solvent and the membrane itself. The luminescence lines of the membrane with implanted nanocrystals have a higher intensity than the secondary emission peaks of the neat nanocrystals. Two additional absorption peaks are detected at the wavelengths of 415 and 490 nm. A new IR transmission peak at the wavenumber of 4676 cm^–1 (2138.5 nm) is found in the membrane kept in the toluene solution with nanocrystals.

The results of the experiments on modeling the processes occurring during endovenous laser coagulation (EVLC, EVLA) using laser radiation with wavelengths λ = 1.55 and 1.94 µm are presented. The application of blood plasma, which is transparent in the visible range and similar to blood in thermophysical properties and absorption coefficient at the selected wavelengths, made it possible to study these processes in detail using video filming. The experiments were carried out using fibers with end and radial radiation output, which are most often used in phlebological practice for EVLC. The results obtained on the vein model showed the following. (i) Heating of the venous wall is mainly due to convection and boiling of the liquid. When a radial fiber is used, additional heating may occur as a result of the direct action of laser irradiation due to the Moses effect. (ii) For laser radiation with λ = 1.94 µm, effective heat transfer begins at lower power levels as compared to λ = 1.55 µm. (iii) Heat transfer in EVLC occurs asymmetrically, predominantly upward. The exception is direct heating by laser radiation due to the Moses effect, which sometimes occurs when using a fiber with a radial output (iv) Periodic events of explosive boiling help to clean the radiation output area from adhered coagulate particles, which cause undesirable carbonization. The intensity of this process increases with increasing radiation power and its absorption coefficient. The results obtained may help to improve the EVLC technology.

We report on the multiwavelength generation in an Er/Yb-doped fiber ring laser with a cavity length of 301 m. Passive mode locking is implemented by nonlinear polarization rotation. Depending on the adjustment of the polarization controller, the laser operated in a mode-locking regime with emission at one, two, or three wavelengths. At certain orientation angles of the polarization controller, the emission was accompanied by long-period pulsations. It is revealed that the emission at several wavelengths is associated with the nonlinear polarization rotation mechanism, which acts as an intracavity spectral filter and restricts mode competition. Long-period pulsations are formed due to the increase in the intracavity losses caused by a change in the orientation angles of the polarization controller paddle. The experimental results may contribute to the development of pulsed fiber laser sources with long cavities.

A duality lemma is derived that relates power cross-flows to their corresponding functions of sources in an absorbing medium. This lemma allows simplifying the description of energy exchange between arbitrarily chosen volumes in a dissipative medium containing radiation sources and scatterers. To illustrate the use of the lemma, derivation of the optical theorem for a scatterer in a lossy medium is considered. It is shown that local power flows are naturally divided into dissipative ones (i.e., drains associated with medium absorption), energy ones, which describe interaction of extrinsic and scatterer-induced currents with the electromagnetic field, and interference ones, which arise from superposition of the incident-wave and scattered-wave fields.

The generation of supercontinuum (SC) in highly nonlinear fibers pumped by noise-like pulses with linear frequency modulation is demonstrated. The zero-dispersion wavelength λ_zwd of the nonlinear waveguides varied in the range of 1.48–2.3 µm. A fiber ring laser with passive mode locking based on nonlinear polarization rotation was used as the pulse source, generating linear frequency modulation noise-like pulses with an optical spectrum width of 15 nm at the −3 dB level. During amplification, the energy of noise-like pulses reached 277 nJ. Supercontinuum generation with an optical spectrum covering the range from 1104 to 2123 nm was obtained at the output of a 3-meter-long highly nonlinear fiber with a zero-dispersion wavelength of 1.48 µm.

Shock impact is found to affect the properties of droplets of synthesized colloidal nanoparticles falling on a solid surface. Luminescence of droplets, caused by their impact with a solid surface, is detected. It is established that the luminescence intensity increases with increasing the droplet fall height, nanoparticle concentration, and concentration of molecular oxygen dissolved in the liquid. It is revealed that the reactive oxygen species generation under a shock impact is enhanced by the presence of nanoparticles in the solution.

The results of temperature and concentration experimental studies of the intensity ratio in the scattered light fine structure components (Landau–Placzek ratio) in γ-picoline aqueous solutions are presented. A significant increase in the Landau–Placzek ratio is revealed in a narrow concentration range near the so-called specific point. The specific point corresponds to the polar organic solvent concentration at which formation of molecular aggregates of water and organic component occurs. The sizes of these aggregates were estimated in experiments on measuring the adiabatic compressibility and on dynamic light scattering; the results of measurements according to these independent techniques are in very good agreement. It is concluded that the technique based on measuring the adiabatic compressibility in the gigahertz range of sound frequencies is efficient for estimating the sizes of spatial inhomogeneities at the specific point.

We study various coherent optical properties, e.g., two-photon electromagnetically induced transparency (EIT) and three-photon electromagnetically induced transparency and absorption (TPEIT/TPEIA), in a four-level ladder (Ξ)-type system of ⁸⁷Rb atoms, where the probe and control fields are Gaussian-shaped laser beams and the pump field is structured laser beam. Additionally, the generated four-wave mixing (FWM) signal has been studied. Interestingly, it is found that the generated FWM signal is spatially structured along with the azimuthal phase, which carries the orbital angular momentum (OAM) of light. It is also observed that the coherent optical responses (EIT, TPEIT/TPEIA, and FWM signals) can be manipulated by utilizing the OAM number of the pump beam as a control knob.

The LiGaSe₂ and LiGaS₂ crystals with antireflection microstructures are comparatively tested as frequency down-converters into the mid-infrared range (4874 nm) in a two-stage optical parametric oscillator with a single cavity under intracavity pumping with a Nd:YLF laser with a wavelength of 1047 nm and a pulse duration of 25 ns. The first stage of optical parametric oscillation in the KTiOAsO₄ crystal produces two-micron radiation with wavelengths of 1724 and 2668 nm at a pulse energy of up to 2 mJ. In the second stage of conversion, the LiGaS₂ crystal with antireflection microstructures compared to LiGaSe₂ with antireflection microstructures proves to be more efficient despite the lower effective nonlinearity coefficient, which can be explained by the higher optical quality of the crystal. The energy of the radiation pulse with a wavelength of 4874 nm reaches the level of 100 nJ.