Intrinsic symmetry relations are obtained for components of optical susceptibility tensors of a nonabsorbing linear medium with the nth-order frequency dispersion (n = 1, 2, ...) and time-varying optical characteristics. They are used to find analytical expressions for all components of the energy–momentum tensor of the electromagnetic field of the waves propagating in the medium. In the case of the second- and higher-order frequency dispersion, formulas for electromagnetic field energy and momentum densities have, apart from the known additional terms, new terms involving time derivatives of medium optical susceptibility components.
Cubically nonlinear properties of a LiNa5Mo9O30 crystal were studied under ultrafast laser excitation at a wavelength of 1030 nm with a peak power (>4 MW) exceeding the critical power of self-focusing Pcr. Transient stimulated Raman scattering (SRS) in LiNa5Mo9O30 was observed in competition with nonlinear effects associated with a nonlinear refractive index n2. This competition was controlled by adjusting the external chirp of the pump pulses. A new fast method for measuring the nonlinear refractive index of Raman media using a change in the chirping of the pump pulse is proposed and compared with a known fast method using a change in the energy of the pump pulse. The proposed technique enabled measurement of n2 = (6.5 ± 1.7) × 10–16 cm2/W and Pcr = 1.4 ± 0.4 MW at 1030 nm for LiNa5Mo9O30 with twice the accuracy of the previous method. Raman conversion into the Stokes wavelength occurred with an optical efficiency of up to 9
The paper presents a new method of emission spectroscopy in the far infrared range. This method does not require heating or other excitation of the sample; that is, it allows recording the spectrum of intrinsic radiation. The spectra of lactose monohydrate, liquid water, and water vapor were recorded at room temperature. Emission bands corresponding to phonon vibrations of the crystal lattice of lactose monohydrate and rotational transitions of water molecules in the gas phase are recorded. For liquid water, the emission spectrum was recorded in the range of 7–200 cm–1, and the potential for extension to the mid-infrared range was noted. A method has been developed for expressing the spectra of intrinsic radiation in absolute units of spectral radiosity. Spectroscopy of intrinsic radiation is as informative as absorption spectroscopy and does not require the use of a radiation source. This may be especially in demand for spectral analysis of radiation-sensitive samples.
Hybrid master oscillator power amplifier laser systems have been proposed and experimentally implemented for laser amplification of ultrashort radiation pulses from a crystalline Raman generator operating in a highly transient regime on dual Raman modes with Stokes radiation wavelengths of 1.06 and 1.14 μm (frequency shifts 327 and 887 cm–1, respectively). Experimental optimization of laser amplification has been carried out when controlling both the chirp of the pump pulse of the Raman generator and the polarization of the amplified laser radiation. The ultrashort pulses of the SrMoO4 Raman generator with a wavelength of 1.06 μm were amplified in a regime of small-signal gain up to output energy of 200 μJ with a pulse duration of 2.2 ps in a system of two double-pass Nd3+:CaMoO4 crystal laser amplifiers (the amplification linewidth of 3 nm) with lamp pumping at the radiation polarization parallel to the Nd3+:CaMoO4 crystal optical axis. The adjustment of the rotation angle of the input radiation led, during the amplification, to the formation of double-wave radiation with wavelengths of 1061 and 1067 nm with each linewidth of 1.7 nm at a frequency difference of 1.6 THz, which is important for terahertz applications. The radiation of the same Raman generator with a wavelength of 1.14 μm was amplified in a regime of saturated gain up to 200–250 μJ, which is close to the amplifier stored energy, in an ultra-wideband (160 nm) double-pass laser amplifier based on a F_2^ - :LiF crystal with nanosecond laser pumping at optimization of chirping the pump pulse of the Raman generator. For the Raman generator pumped with a transform-limited pulse (0.25 ps), the spectrum width of the amplified radiation at 1.14 μm was the widest: 52 nm with output energy of amplified radiation of 200 μJ and the pulse duration of 0.8 ps with a compression capability of down to 40 fs.
The effect of high γ-radiation doses on thermoluminescent properties of BGO single crystals is studied. It is shown that exposure to high γ-radiation doses results in formation of centers with deep trapping levels in the crystals. The high thermal stability of these centers indicates their structural origin. The nature of the centers is determined.
The temperature dependences of the velocity and attenuation coefficient of longitudinal acoustic waves in pure and neodymium-doped yttrium–aluminum garnet (YAG) crystals have been studied in the temperature range of 290–450 K using the Williams–Lamb ultrasonic method at a frequency of 30 MHz. The temperature coefficients of the elastic constants c_11^' and c_44^' in these crystals were determined. It is shown that the attenuation of acoustic waves significantly changes in the investigated temperature range, especially in doped YAG crystals. It is found that, in the case of longitudinal acoustic waves, the maximum deviation of the energy flux from the wave vector is 0.8° for pure crystals and 2.8° for neodymium-doped crystals. Based on the measured values of the velocity and attenuation of acoustic waves, the real and imaginary components of the elasticity tensor were determined; this data make it possible to determine the velocity and attenuation coefficient of acoustic waves along any arbitrary direction in crystals.
The influence of ultrasonic dispersion power on the morphology, texture characteristics, and phase composition of CaSn(OH)6 samples synthesized by salt coprecipitation has been studied. The samples were characterized using X-ray diffraction analysis, scanning electron microscopy, and low-temperature nitrogen adsorption. The specific surface area of the samples is found to depend nonlinearly on the radiation power. Linear interpolation and Voigt fitting [1] were used to determine the linear sizes of crystallites according to the Scherrer principle [2]. The Keller–Miksis model [3] was used to calculate the critical bubble size at different impact powers and determine the “hot point” temperature at the instant of bubble collapse. It is shown that ultrasonic processing with a power density of 33 W/cm2 provides the highest collapse temperature at the smallest sizes of cavitation bubble (548 µm); in this case, the CaSn(OH)6 phase undergoes decomposition with the formation of calcium hydroxide Ca(OH)2 and amorphous tin oxide SnO2.
The design of next-generation acoustic devices, whether for biosensing, telecommunications, or advanced wave control, increasingly relies on the precise exploitation of resonance phenomena. These phenomena enable highly controlled manipulation of the transmission frequency, laying the groundwork for high-resolution selective filtering functions. In this work, we conduct an in-depth theoretical and numerical study of an innovative acoustic filtering system comprising four asymmetric resonators arranged in series and parallel, and coupled to a main waveguide. Using the transfer matrix method, we analyze the system’s spectral response in detail. Our results highlight the appearance of Fano-type resonances, as well as the phenomenon of acoustic induced transparency (AIT), resulting from destructive and constructive interference between the different resonance paths. The study of the associated quality factors of resonance peaks allows us to quantify the fineness of these resonances and their sensitivity to variations in the geometric parameters of the system. This sensitivity offers great flexibility in frequency control, a key element in the development of compact, efficient, and reconfigurable devices. The observed performance highlights the potential of our system for applications in the fields of medical acoustics, environmental detection, acoustic signal processing, and the development of highly selective smart sensors.
The expansion and collapse dynamics of a laser-induced bubble in water, gasoline, and engine oil has been investigated for the first time. The properties of the laser plasma generated inside a bubble for in situ chemical analysis using double-pulse laser-induced breakdown spectrometry (LIBS) were determined. It was found that laser-induced bubble expansion is independent of the liquid nature, whereas the bubble collapse dynamics in water, gasoline, and oil differed in both rates and stability. It was demonstrated that, using double-pulse LIBS, one can record atomic and ionic emission lines in laser plasma, in contrast to the single-pulse laser-induced breakdown in the liquid bulk. The influence of the bubble formation stage on the properties (temperature and electron density) of the laser plasma induced by the second laser pulse in the bubble was investigated, and the optimal time for recording emission lines of the chemical elements of interest was chosen.
Molybdenum disulfide (MoS2), a prototypical two-dimensional transition metal dichalcogenide (TMD), has attracted substantial interest for its tunable properties and broad technological potential. This review presents a comprehensive comparison between monolayer and bulk MoS2, highlighting key differences in their structural, optical, electrical, mechanical, and bio-interactive properties. The transition from bulk to monolayer induces a transformation from an indirect to a direct bandgap, significantly enhancing photoluminescence, charge mobility, and surface sensitivity features critical for next-generation electronic, optoelectronic, and biosensing devices. We also explore state-of-the-art synthesis strategies, including top-down and bottom-up approaches, that enable the scalable production of high-quality monolayer MoS2. By synthesizing insights from recent theoretical and experimental advances, this article elucidates why monolayer MoS2 consistently outperforms its bulk counterpart in functional applications ranging from strain sensors and photodetectors to non-invasive biosensors for prenatal diagnostics. The review not only maps the current landscape but also outlines future directions, positioning monolayer MoS2 as a cornerstone material for advanced technologies.
Tricomi–Gaussian beams (TGBs) belong to the class of non-diffracting Tricomi light beams with finite cross-section and finite energy. So, in this work, a theoretical investigation of propagation characteristics of TGB in a strongly nonlocal nonlinear medium (SNNM) has been conducted. SNNM is well-known for its nonlinear optical response at a specific location, and it can be affected by an electromagnetic field that extends across a large spatial region. The propagation problem is addressed by expressing the TGB fields in SNNM with the help of the extended Huygens–Fresnel diffraction integral formula and the optical ABCD matrix system. To analyze its propagation dynamics, the effects of different configuration parameters of TGB, such as topological charge, waist radius, and propagation distance, are meticulously examined. The diverse cases like as on-axis, off-axis, and asymmetrical Bessel Gaussian beams can be achieved as special cases by appropriately selecting the complex beam parameters of TGB. This work will be helpful to study and analyze the electromagnetic radiation force, scattering and propagation, optical manipulation, computer-generated holography, light–matter interaction, and optical tweezers and sensors.
The long (multimicrosecond) delay of irradiated material ejection after exposure of metals to an intense subnanosecond pulse during laser ablation observed in 2003 is experimentally investigated. However, though afterward mentioned many times, this result has never been repeated, and its initial explanation is still unsatisfactory. In this work, the long delays in ejection of a material under exposure of metal targets (aluminum, copper, lead) to a laser pulse with the duration of 70 ps, wavelength of 0.527 µm, and intensity I ≈ 1013 W/cm2 are confirmed using the two-beam time-of-flight method. It is stressed that the explanation of this effect based on the notion of a delayed phase explosion alone is insufficient and that cavitation phenomena subsequently arising in the melt layer should be taken into account.
We report the development of a stimulated Raman scattering (SRS) converter capable of generating 10-ps pulses at several wavelengths simultaneously. For the first time, two-color SRS generation is demonstrated on O–H and C–H stretching vibrations in water–acetone and water–ethanol cascade systems. The SRS converter is pumped by 60-ps pulses of the Nd3+:YAP laser second harmonic in an unfocused beam (in traveling-wave mode). The spectral overlap of the generation bands indicates preamplification of the acetone Stokes component by SRS generation in water. The achieved results demonstrate the feasibility of creating multifrequency SRS converters operating in a traveling wave mode based on a combination of liquid gain media. These converters are promising for application in spectroscopy, chemical analysis, and as biharmonic sources for resonant pumping of nanoscale objects, such as viruses.
The possibility of precise local etching of monolayer graphene on sapphire using nanoablation by nanosecond 532-nm laser pulses under normal conditions in air has been demonstrated for the first time. The multipulse local removal of graphene was investigated by atomic force microscopy in combination with Raman spectroscopy, according to the specially developed technique, which makes it possible to implement multipulse laser impact and monitor in situ the nanorelief and surface structure before and after laser irradiation. All modes of low-intensity laser irradiation with energy density in the range of 0.85 ≤ Е ≤ 1.55 J/cm2 had the following features: (i) formation of craters ≈1 nm deep (i.e., through holes in a graphene film, whose diameter depends on the number of pulses and energy density) and (ii) the absence of any explicit signs of thermally induced etching in the Raman spectra of graphene. The mechanism of multipulse low-intensity laser etching of graphene, caused by photostimulated weakening of covalent bonds between carbon atoms and increase in the reactivity of these atoms to oxidation in the presence of ambient oxygen and an aqueous adsorbate, is discussed.
The energy flux deviation and anisotropy of acoustic wave attenuation in NaCl1−xBrx crystals has been investigated in the frequency range of 30–1200 MHz at room temperature. It is shown that the degree of change in the acoustic attenuation coefficient with increasing bromine content is caused by two factors: decrease in the relaxation time of thermal phonons and increase in the effective Grüneisen constant. All real and imaginary components of the elasticity tensor are determined based on experimental velocity and attenuation coefficient values. The anisotropy of the phase and group velocities of acoustic waves is analyzed, and special directions, along which pure and ordinary acoustic waves propagate, are revealed. A cross-section of the surface of acoustic-wave attenuation coefficient by the (110) plane is constructed for NaCl0.7Br0.3 crystals. It is shown that the highest attenuation anisotropy is observed for quasi-transverse acoustic waves, for which the attenuation coefficients along the [110] and [001] directions differ by an order of magnitude.
The results of studying the impact of laser pulses with different temporal shapes on a metallic material (structural steel) produced by selective laser melting are reported for the first time. The influence of the conventional and complex temporal shapes of laser pulses with identical energies and durations on initiation of dominant material destruction mechanisms and the effect of recoil pressure are investigated using mathematical modeling. The model allows for the nonlinear depth distribution of porosity characteristic of additive metallic materials. It is shown that pulses of complex temporal shape, which combine a long high-energy pulse and a short high-intensity pulse, cause an increase in the recoil pressure much higher than the increase in the capillary pressure. The increase in the recoil pressure in the laser interaction zone initiates an increase in the volume of the removed material and increases the laser processing speed in additive manufacturing of items. The results demonstrate the potential of using laser pulses of complex temporal shape for postprocessing of metallic materials produced on the basis of additive technologies.
Adsorption of molecular oxygen on the Ag(111) surface at room temperature has been studied using scanning tunneling microscopy (STM), Auger-electron spectroscopy (AES), temperature programmed desorption (TPD), and density functional theory (DFT). In the early stage of adsorption, the STM images show formation of a disordered phase in the form of dark spots (local oxide (Ag6O6) rings. Further O2 dosing leads to the formation of a set of bright objects 5–8 Å in size, which were associated with CO2 molecules stabilized on the surface due to the presence of H2O molecules. Heating of the system to temperatures above 423 K led to partial desorption of silver dioxide molecules and formation of ordered striped ( 8 × 2√(3) ) and hexagonal (3 × 3) phases. According to the DFT calculations, the (3 × 3) phase can be interpreted as surface high-temperature silver carbonate (Ag2CO3), adsorbed on Ag(111). Small areas with the (3 × 3) phase can be seen in STM images even after heating to 540 K, which indicates higher temperature stability of surface carbonates on Ag(111) than it was believed previously.
The problem of estimating the distance to a sound source in an underwater waveguide from sound field measurements using a vertical receiving array is considered. In recent years, methods for solving this problem using an artificial neural network, to the input of which a sample correlation matrix of the recorded field is applied, have been developed. The inevitable inaccuracy of the mathematical model of environment makes it possible to train the network on only short paths using the so-called synthetic data, i.e., data of theoretical calculation. This paper considers an alternative approach, where input data are set by the distribution of recorded field intensity in the depth–arrival angle plane. This distribution, constructed using the coherent state method borrowed from the quantum theory, is less sensitive to the environment model inaccuracies than the initial field recorded by the array and the correlation matrix of the field. It is shown by numerical simulation that the use of the aforementioned distribution may expand the range of distances for which the network can be trained on synthetic data.
A fiber-optic interferometer sensitive to variations in the constant magnetic field is presented. A magnetostrictive material is used as its sensitive element. The sensor is based on the Fabry–Perot interferometer with the length determined using a unique signal processing algorithm, which allows the measurement accuracy to be improved by two orders of magnitude. Advantages of the sensor are a high dynamic range, small size, and standard components. The working range of the sensor is B ⩽ 50 mT and the dynamic range is 84 dB. Recommendations are given for increasing the system sensitivity and the measurement accuracy.
In this study, nanosized aluminum (Al) thin films with different thicknesses were deposited on soda lime glass (SLG) substrates using the thermal sputtering technique for optoelectronic applications. Their optical properties were characterized using spectroscopic ellipsometry, a nondestructive method for analyzing film thickness, roughness, and optical constants. The results revealed that variations in film thickness significantly affected the refractive index and extinction coefficient. These changes were closely related to the microstructural differences and surface conditions. The findings highlight the potential of Al thin films for use in photonic and electronic devices, such as photodetectors and reflective coatings. This work provides valuable insight into the design of materials with tailored optical behavior.
