Wave Laser Research Articles

Anomalous hot electron generation from two-plasmon decay instability driven by broadband laser pulses with intensity modulations

We investigate the hot electrons generated from two-plasmon decay (TPD) instability driven by laser pulses with intensity modulated by a frequency Δω m using theoretical and numerical approaches. Our primary focus lies on scenarios where Δω m is on the same order of the TPD growth rate γ 0 ( Δωm∼γ0 ), corresponding to moderate laser frequency bandwidths for TPD mitigation. With Δω m conveniently modeled by a basic two-color scheme of the laser wave fields in fully-kinetic particle-in-cell simulations, we demonstrate that the energies of TPD modes and hot electrons exhibit intermittent evolution at the frequency Δω m , particularly when Δωm∼γ0 . With the dynamic TPD behavior, the overall ratio of hot electron energy to the incident laser energy, fhot , changes significantly with Δω m . While fhot drops notably with increasing Δω m at large Δω m limit as expected, it goes anomalously beyond the hot electron energy ratio for a single-frequency incident laser pulse with the same average intensity when Δω m falls below a specific threshold frequency Δω c . This anomaly arises from the pronounced sensitivity of fhot to variations in laser intensity. We find this threshold frequency Δω c primarily depends on γ 0 and the collisional damping rate of plasma waves, with relatively lower sensitivity to the density scale length. We develop a scaling model characterizing the relation of Δω c and laser plasma conditions, enabling the potential extention of our findings to more complex and realistic scenarios.

Interference mechanism of plasma self-organization in transparent dielectrics under the intense femtosecond laser pulse exposure

A new mechanism of plasma self-organization in transparent dielectrics with wide bandgap exposed to the intense tightly focused laser radiation was revealed, which causes the generation of 3D periodic ring structures with subwavelength period both along the laser pulse propagation and in the radial direction. The mechanism involves formation of dense plasma burst in the pre-focal region that provides efficient scattering of the incident wave. The interference of a plane incident laser wave in the focal region and a divergent reflected one will form the standing wave pattern with local minima and maxima of laser field both in the direction of the incident wave propagation and perpendicular to it producing the ring patterns of effective ionization regions in the dielectric volume. Analytical and numerical simulations of the process of laser wave scattering on a near-spherical plasma object with dimensions both smaller and larger than the laser radiation wavelength are performed to verify the proposed model.

Optical Rogue Waves in Fiber Lasers

Optical Rogue Waves in Fiber Lasers

Generation and real-time dynamics of vector square waves

The study delves into the characteristics and dynamics of vector square waves in an erbium-doped fiber laser employing a nonlinear optical loop mirror (NOLM). Through experimental investigation, the laser's operational modes, namely stable and periodic pulsating states, are achieved by manipulating polarization controllers (PCs). Within these states, the generation of two square waves with distinct peak power is observed. The vector properties of the pulses are authenticated using a polarized beam splitter (PBS). Furthermore, meticulous adjustment of the PCs reveals phenomena such as multi-pulse periodic breathing and prolonged fluctuations in pulse intensity.

The orbital angular momentum of radiation from relativistic electrons in the laser wave field with linear polarization

The paper reports the results of calculations of the generation of twisted photons by relativistic electrons in the laser wave field with linear polarization. It is shown that in this case the probability of radiation of twisted photons obeys the selection rule that n + m is an even number. The radiation of the probability of detecting a twisted photon is numerically investigated depending on various parameters: photon energy, helicity and the cone opening of the twisted photon. In general, the radiation of twisted photons by electrons in the laser wave field with linear polarization is a mixture of twisted photons at the total angular momentum of the photons; however, we have found conditions when generation of twisted photons will be an almost pure source of twisted photons.

Achieving high power continuous wave and short pulses of semiconductor laser for use in photodynamic therapy: theoretical work

Achieving high power continuous wave and short pulses of semiconductor laser for use in photodynamic therapy: theoretical work

Highly Stable and Reversible Coloration of Oxide Nanoparticles Film by Ultrafast‐CW Laser Induced Band Engineering

AbstractColoration in oxides meets the challenge in achieving high stability and repeatability simultaneously. In this work, reversible coloration of TiO2 nanoparticles (NPs) film is demonstrated by alternate ultrafast (UF) laser and continuous wave (CW) laser irradiation. Under UF laser irradiation, oxygen vacancies are introduced in the TiO2 lattice, which lead to the bandgap reduction (2.73 to 1.50 eV) and surface blackening. The blackened area can achieve high resolution with size down to ≈1.1 µm. This coloration in TiO2 also shows excellent thermal stability that color fading is negligible even after thermal annealing at 700 K for 2 h in air. The generated high temperature by CW irradiation is known to be beneficial for the O2 dissociation on defected TiO2, thus promoting the internal oxygen diffusion to eliminate the vacancies. The energy band structure of TiO2 can be recovered accordingly, and decoloration is achieved. TiO2‐NPs film shows stable microstructures with barely changed optical properties after 12 cycles of coloration–decoloration process. This band engineering‐induced reversible coloration can also be applicable for broad oxides, e.g., ZnO, HfO2, and Ga2O3. Such highly stable and reversible coloration is promising in high‐performance micro/nano‐devices development for color display and optical encryption.

Patient-Reported Outcomes and Higher Order Aberrations Following Topography-Guided Femtosecond Laser-Assisted In Situ Keratomileusis.

To examine patient-reported outcomes and higher order aberrations following topography-guided laser-assisted in situ keratomileusis (LASIK). This was a prospective, nonrandomized observational study at a single academic center. Sixty eyes from 30 patients underwent bilateral topography-guided femtosecond LASIK for correction of myopia using the VisuMax 500 femtosecond laser (Zeiss; Oberkochen, Germany) and Allegretto Wave Eye-Q 400 Hz Excimer Laser (Alcon/Wavelight; Erlangen, Germany) with the Contoura topography system (Alcon; Geneva, Switzerland) for topography-modified refraction. The main outcomes of this study were higher order aberrations (HOAs) and results from the Patient-Reported Outcomes with LASIK questionnaire. There was a small, significant increase in HOA root mean square, spherical aberration, and coma at 1, 3, 6, and 12 months following topography-guided LASIK (all P < 0.05), but no change in trefoil. In addition, self-reported worry related to vision (P < 0.001) and ability to perform activities (P < 0.001) significantly improved after surgery. The prevalence of double images, glare, halos, or starbursts decreased from 73% preoperatively to 56%, and no participants reported "very" or "extremely" bothersome visual symptoms after 12 months. Dry eye symptoms per Ocular Surface Disease Index score decreased significantly at 6 (P = 0.01) and 12 (P = 0.002) months after surgery. There was a 100% satisfaction rate with visual outcomes and duration of time to improvement in vision following the procedure. Although there was an increase in HOAs following topography-guided LASIK, there were significant improvements in the presence of double images, glare, halos, and starbursts and vision-related quality-of-life metrics. Overall satisfaction rates in this study were high.

Stimulated magneto-optics with different detunings for plasma local diagnostics

The polarization plane stimulated rotation angle of a probe signal in an intense laser field in plasma is calculated for arbitrary detunings of intense and weak laser waves compared with the resonant transition frequency of the medium. Estimates of the residual gas local density in a cesium plasma have been found based on the Faraday, Cotton–Mouton effects and on the effect of stimulated rotation of the polarization plane of the probe signal in an intense laser field. It is shown that the rotation in the medium has a complex structure consisting of the sum of only the influence of the magnetic field, only the influence of the intense laser field and the interfering part of the magnetic and intense laser fields.

Emission behaviors from ZnO microwire pumped CsPbBr3 perovskite microwire.

Perovskite semiconductor materials have attracted significant attention in the fields of photovoltaics and luminescence due to their excellent photoelectric properties, such as high carrier mobility, high absorption coefficient, and high fluorescence quantum yield. In particular, low-dimensional metal-halide perovskite microcrystalline materials have been reported to exhibit low-dimensional lasing phenomena and laser devices due to their high gain and widely tunable bandgap. In this Letter, one-dimensional (1-D) ZnO microwires with their ultraviolet lasing emissions are utilized as an excitation source to pump CsPbBr3 microwire on hybrid ZnO-CsPbBr3 microscale structures. At higher excitation, the amplified spontaneous emission (ASE) behaviors from CsPbBr3 microwire are realized with ultralow threshold by indirect pumping from the ZnO lasing emission for the first time, to the best of our knowledge. In comparison, the ASE behaviors from the CsPbBr3 microwire directly pumped by Nd:YAG Q-switched laser and continuous wave laser are also performed at room temperature. There are also no multimode lasing behaviors observed. The paper provides a new method to achieve a low threshold on-chip microlaser by a high-quality perovskite micro-nano structure.

Bio-thermal response during laser haemorrhoidoplasty: an exclusive analytical and numerical approach for theoretical investigation.

Haemorrhoidal disease is identified by declension of the inflamed and bleeding of vascular tissues of the anal canal. Traditionally, haemorrhoids are associated with chronicconstipation and the most common symptoms are irritation in anus region, pain and discomfort, swelling around anus, tender lumps around the anus and rectal bleeding (depending upon the grade of haemorrhoid). Among the several conventional treatment procedures (commonly mentioned as, rubber band litigation, sclerotherapy and electrotherapy), laser haemorrhoidoplasty is an out-patient and less-invasive laparoscopic procedure. From literature survey it has been observed that an exclusive theoretical model depicting the impact of 1064nm wavelength laser wave on living tissues subjected to haemorrhoid therapy is not available. This research work is a pioneering attempt to develop a theoretical study attributing specifically on laser therapy of haemorrhoid treatment based on Pennes' biological heat transfer model. The corresponding mathematical model has been solved by analytical method to establish thermal response of tissue during the treatment and also the same has been solved a numerical approach based on finite difference method to validate the feasibility of former method due to unavailability of any theoretical model. Impact of variation of blood perfusion term, laser pulse time and optical penetration depth on temperature response of skin tissue is captured. The tissue temperature decreases along with time of laser exposure with increasing the blood perfusion rate as it carries away large amount of heat. With the increase in laser pulse time, tissue temperature declines due to shorter pulse time resulting in higher energy consumed by electrons. The research outcome is successfully validated with less than 1% of error observed between the appointed analytical and numerical scheme.

Analytical study of linear optical properties of metal nanoparticle trimers: the impact of dipole-dipole interaction on different modes of configuration

In this study, we theoretically investigate the linear properties of a metal nanoparticle (MNP) trimer. Three identical spherical nanoparticles (NPs) whose centers are equidistantly oriented on a same straight line are considered. Using the solid core approximation for NPs and considering interaction between particles through induced electric dipoles, the motion equation of each NP conduction electrons is analytically solved. Some appropriately approximated expressions are derived for the permittivity of each NP based on a Drude-like model, allowing the clear observation of the contribution of inter-particle interaction. Depending on the orientation of the trimer axis and incident laser beam geometry (i.e., orientation of electromagnetic (EM) fields and wave vector of laser beam), three different configurations or modes are considered. The extinction efficiency of each NP as a function of wavelength is plotted, revealing that when the laser electric field is perpendicular to the symmetry axis of the trimer, it increases compared to the case of non-interactional single NP, and its plasmon resonance peak experiences a red shift. For other cases where the electric field of the laser beam is parallel to the trimer axis, the extinction efficiency of each NP decreases, and its peak shifts to the blue. In all cases, the effect of interaction on the optical properties of the middle NP is greater than on the other NPs.

Controlling the time shape of terahertz pulses from two-color plasma by combining wavelength dispersion and laser chirp

Using a two-color plasma in air or gas allows for the generation of ultra-broadband and highly intense terahertz (THz) pulses. Precisely controlling the shape of THz pulses, particularly the carrier envelope phase, is crucial for a wide range of technological and scientific applications. Recent research has revealed that the phase difference between the fundamental laser wave and its second harmonic influences the shape of the emitted THz pulse. However, the combined impact of laser chirp and the air-dispersion-induced phase difference between the two colors has not been explored in detail. This study aims to fill this gap. The results show that both of these factors have a significant impact on the THz waveform and emitted pulse energy. Positive and negative chirps lead to distinct effects on the pulse shape. A positively chirped pump laser produces a THz waveform with a negative monopolar shape, while a negatively chirped pump laser results in a positive THz pulse shape. Additionally, our findings indicate that the relationship between THz pulse energy and chirp changes with variations in the specific phase difference between the first and second harmonics. These results underscore the importance of carefully tuning both parameters to achieve maximum generation efficiency for a given waveform.

Theoretical study of influence of laser pulse chirp on terahertz emission characteristics of gas induced by two-color laser field

With the development of terahertz (THz) wave research, the demand for controllable THz sources is increasing. How to obtain the regulated THz waves has been one of the research hotspots and key problem in the field of THz science. There have been researches in which the resulting THz wave is modulated by changing the wavelength, relative phase, energy, or chirp of the laser produced by a two-color laser. In this work, we establish a three-dimensional theoretical model of THz wave generation and subsequent propagation induced by two-color laser. And we investigate the influence of chirp modulation of different laser on THz wave by chirp modulation of the fundamental wave (FW) and the second harmonic wave (SHW) of two-color laser, including THz wave amplitude, THz wave center frequency and spectrum width, and analyze the physical mechanism of related phenomena. At the same time, the effects of different orders of magnitudes of laser chirp parameters (femtosecond and picosecond) and initial phase of laser pulse on THz wave parameters are also studied. The results are shown below. 1) In the two-color laser, the chirp of FW mainly affects the shape of THz wave when the initial phase is unchanged. The chirp modulation of SHW can cause the amplitude of THz wave to change significantly, and affect the center frequency and spectrum width of THz waves. 2) In the case of laser pulse width of femtosecond order, 40 fs is taken as an example. When the chirp parameter is of femtosecond magnitude, the chirp parameter has a great influence on the THz wave generation efficiency of two-color laser filament. At the picosecond magnitude, the chirp parameter has a weak effect on the THz wave energy and mainly affects the phase of the THz wave. 3) The initial phase of the two-color laser can aid in chirp modulation of THz wave to optimize the energy generated. 4) The initial phase of two-color laser can assist in the process of chirped laser modulation of terahertz waves to optimize the energy generated. Our research shows that the chirp modulation, as a controllable parameter, has multiple regulation effect on the properties of radiated THz waves. The related research results provide a new idea and basis for studying the generation and regulation of THz waves.

Современные тренды эстетической гинекологии

Aim. To conduct a systematic analysis of the data available in modern literature on modern methods used in aesthetic gynecology. Key points. In the world of modern medicine and cosmetology, new methods and technologies are constantly appearing, aimed at improving the quality of life and well-being of patients. A new branch of medicine – aesthetic gynecology – is gaining great popularity. This review examines its current areas: plastic surgery and thread lifting, injection methods (use of fillers and PRP, carbon dioxide, autologous fat), laser and radio wave technologies, and the use of high-intensity focused ultrasound (HUFU). Conclusion. Modern methods of aesthetic gynecology, based on the latest scientific achievements, make it possible to solve many medical problems associated with disorders of the urogenital tract. As this field evolves, one of the most important issues is the development of standardized procedures for safe practice. Long-term studies are required to establish the results of these methods and confirm the effectiveness of new approaches in the field of aesthetic gynecology. Key words: fillers, laser technologies, thread lifting, HUFU.

In English

When metal nanoparticles (MNPs) are illuminated with a monochromatic laser wave, the frequency of which is far from the plasmon frequency (the frequency of plasmon resonances), under certain conditions (depending on the frequency of the wave, its polarization, the size and shape of the MNPs), absorption of light by MNPs can be dominated by magnetic absorption (absorption caused by the magnetic component of the electromagnetic field of the light (laser) wave). This work is focused on studying the features of absorption caused by the influence of the magnetic component of laser radiation. This issue is rather poorly studied for MNPs of non-spherical shape. Therefore, how the shape of the particle manifests itself in its absorption of laser radiation (laser pulses) is one of the goals of our research. In this work, we will study the features of magnetic absorption of light (laser radiation) depending on the shape of the particles. In this paper, we will investigate the influence of spheroidal MNPs on this process. Calculations will be carried out using the kinetic equation method, because we will consider the case when the size of the MNP is smaller than the length of free path of the electron in the MNP. Note that the kinetic approach makes it possible to obtain correct results for the case when the size of the particle is greater than the length of the free path. For non-spherical MNPs, we have developed a theory that makes it possible to calculate the energy of magnetic absorption by a particle when it is irradiated with laser pulses. The dependence of magnetic absorption on the ratio of the radii of curvature of spheroidal MNPs and the vector of the magnetic field of an electromagnetic (laser) wave was constructed and theoretically investigated. An interesting result is the absorption of energy by a spheroidal MNP as its disco similarity increases. We now use to estimate the relative contributions of electric We and magnetic Wm absorption to the total absorption. For example, let us take a gold MNP’s, then ωp ≈ 5·1015 s–1, ν ≈ 1013 s–1, R = 3·10–6 sm, ω ≈ 2·1014 s–1 (carbon dioxide laser), ε' ≈ –600, ε'' ≈ 30 we received the next ratio We/Wm ≈ 2. We can see that for the given set of parameters magnetic absorption is twice as large as electric. Obviously, for different parameters of the particle and a different frequency range electric absorption can be either larger or smaller than magnetic absorption. Hence, when studying the dependence of optical absorption by MNP’s on particle form, we must allow for both electric and magnetic absorption. For an asymmetric MNP’s (for example ellipsoidal particles), apart from everything else, the ratio of the electric and magnetic contributions to absorption (as fixed frequency) is strongly dependent on the degree of particle asymmetric and wave polarization.

Nonlinear inverse bremsstrahlung absorption in magnetized laser-fusion plasma

The nonlinear inverse bremsstrahlung absorption (NLIBA) in magnetized plasma has been investigated within the framework of relativistic kinetic theory. Collisions are described by an improved Krook collision term that accounts for relativistic effects and the Landau microscopic collision form. The non-linearity considered in this paper arises from the anisotropy in electron momentum space in the plasma that is heated by an intense laser pulse. The absorption is explicitly expressed, under reasonable approximations, as a function of the plasma, laser pulse, and magnetic field parameters. Numerical treatment of the model equations shows that absorption increases with laser intensity but decreases with plasma temperature and laser wavelength. It has been shown that the polarization of the laser wave has a significant influence on absorption for high-intense magnetic fields used in magneto-inertial fusion (MIF) experiments. Nonlinear effects clearly reduce absorption for laser intensities comparable to the characteristic intensity, I0=me2c3ε0ωL2/e2, where me is the electron mass, c is the speed of light in vacuum, ɛ0 is the electric permittivity of free space, ωL is the laser wave frequency, and e is the elementary electric charge. Within the intensity I ≪ I0 and laser wavelength in the micro-meter range (λ ∼ μm), relativistic effects appear in the third order of absorption. These findings allow for the optimization of laser pulse parameters to achieve efficient absorption in MIF experiments.

Performance analysis of the RoFSO system over a log-normal turbulent link

Abstract This study provides a comprehensive analysis of the design and performance evaluation of a radio over free space transmission link using Optisystem v.20 software. The research focuses on the integration of four transmission channels through the use of a multiplexer to achieve a transfer rate of 40 Gbps over a distance of 2 km, with each channel carrying 10 Gbps of data. This is achieved by modulating data on 20 GHz radio frequency signals, which are subsequently transmitted via laser waves at different frequencies. The performance of the proposed communication is assessed by evaluating its behavior in the presence of different levels of atmospheric turbulence, classified as light, medium, and strong. This analysis involves calculating based on metrics such as the Q-factor, bit error rate (BER), and log values (BER). The results showed that the Q factor decreased by (4.7) under the influence of a strong disturbance, while in contrast, it decreased by (0.2) under the influence of a weak disturbance. The results also indicated a minimum log BER (at −7.96) for the wavelength (193.3 THz) at 1.5 km. Besides, the best frequency for data transfer was (193.1 THz), followed by (193.4 THz).

Influence of fusion welding processes on microstructure and mechanical properties of dissimilar metal (AISI 304 SS-Copper) weldment

Dissimilar metal welding of AISI 304 stainless steel (304 SS) and commercially pure copper (CP copper) has been taken up to understand the influence of the different fusion welding processes on microstructure and mechanical properties of the weldment. The fusion welding processes specifically involve continuous wave CO2 laser, pulsed wave Nd: YAG laser and pulsed wave tungsten inert gas (P-TIG) welding. The primary objective of the present work is to develop a successful weld between two dissimilar metals without using any filler material by different fusion welding processes. An overall comparison of the results obtained from different sets of analyses is represented. The optical image of the top surface of the weld revealed that the no spatter formation during CO2 laser and P-TIG welding process, whereas minimal spatter for Nd: YAG laser. In comparison to laser processes, the weld face formed by P-TIG welding was much wider. However, 100 % penetration was achieved with all three types of welding. The average widths of heat affected zone (HAZ) found to be 10 µm and 23 µm for CO2 and Nd:YAG laser respectively. The way the microstructure changes at the fusion zone was the same in all cases. For example, copper channels form, dendrites grow epitaxially, etc. SEM pictures indicate the Cu tubular channels observed more often for P-TIG welding. The microhardness distribution in the weld zone was found to be larger than that of copper and close to that of 304 SS. The acceptable ultimate tensile stress (UTS) for dissimilar metal welding of SS-Cu couples was found 275 MPa, 278 MPa and 195 MPa for CO2 laser, P-TIG and Nd:YAG laser respectively.

On the status of channeling radiation and laser based radiation sources

A unified description of channeling radiation (CR) in oriented crystals (OC) and radiation in the field of an intense plane wave (laser radiation sources – LRS) is proposed in terms of two Lorentz-invariant parameters. The case of planar positron channeling (quasi-channeling) and linearly polarized laser wave is considered in detail up to TeV energies. The crucial difference between LRS and CR is that in the former case both invariants are independent, while in channeling they are linearly related to each other. This leads to a strong limitation on the range of possible values of these invariants in OC. On the other hand, OC make it possible to study QED processes in strong non-uniform external fields.