Monochromatic Laser Radiation Research Articles

Optical microcavity formation and ultrafast control using half-cycle attosecond pulses in two- and three-level media

Light induced population difference gratings have numerous applications in modern optics. The conventional approach of creating them by using monochromatic laser radiation makes it virtually impossible to rapidly control their properties. In recent years, there has been active discussion about using ultra-short light pulses to control such gratings. We show the possibility of ultrafast control of population difference structures, such as dynamic microresonators and Bragg-like grating formations, by the collision of extremely short light pulses in a resonant medium. This work focuses on changes in microcavity properties based on the different parameters, such as the atomic density of the medium, the form of the pulses, and whether the medium is two- or three-level.

Comparative Study of Single Crystal and Polymeric Pyroelectric Detectors in the 0.9-2.0 THz Range Using Monochromatic Laser Radiation of the NovoFEL.

The development of efficient and reliable sensors operating at room temperature is essential to advance the application of terahertz (THz) science and technology. Pyroelectric THz detectors are among the best candidates, taking into account their variety, outstanding performance, ease of fabrication, and robustness. In this work, we compare the performance of six different detectors, based on either LaTiO3 crystal or different polymeric films, using monochromatic radiation of the Novosibirsk Free Electron Laser facility (NovoFEL) in the frequency range of 0.9-2.0 THz. The main characteristics, including noise equivalent power and frequency response, were determined for all of them. Possible reasons for the differences in the obtained characteristics are discussed on the basis of the main physicochemical characteristics and optical properties of the sensitive area. At least three detectors showed sufficient sensitivity to monitor the shape and duration of the THz macropulses utilizing only a small fraction of the THz radiation from the primary beam. This capability is crucial for accurate characterization of THz radiation during the main experiment at various specialized endstations at synchrotrons and free electron lasers. As an example of such characterization, the typical stability of the average NovoFEL radiation power at the beamline of the electron paramagnetic resonance endstation was investigated.

Interplay of Kekulé distortions and laser fields in graphene

We study the interplay between a Kekulé patterned distortion in monolayer graphene and a monochromatic laser irradiation, focusing in the long wavelength approximation of its Landau level structure. Exploiting the symmetries of the system, we calculate in the static regime an exact analytical solution for the energy spectrum and its eigenstates, which in turn allows us to find close expressions for the polarizations in the valley and pseudospin degrees of freedom. We find that due to the valley-momentum coupling, the valley polarization exhibits a distinct magnetic response for the two K-valley components. Owing to that, the introduction of the radiation field mixes the Landau levels, and it is shown that by tuning the system to resonance leads to a larger valley-polarization response as compared to the non-resonant scenario.

Guidelines for improving laser targeting device in military

The invention of the laser can rightfully be considered one of the most significant discoveries of the 20th century. At the very beginning of the development of this technology, they already predicted a completely universal applicability, from the very beginning the prospect of solving various problems was visible, even though some tasks were not even visible on the horizon at that time. Monochromatic laser radiation can be obtained in principle at any wavelength, both in the form of a continuous wave with a certain frequency and in the form of short pulses lasting up to fractions of a femtosecond. Focusing on the studied sample, the laser beam is subjected to nonlinear optical effects, which allows researchers to perform spectroscopy by changing the frequency of light, as well as to perform coherent analysis of processes by controlling the polarization of the laser beam. Lasers were initially limited more to scientific research and military applications. The report examines the use of laser targeting. Today there are several areas in which the introduction of laser technology in the military industry follows: air, ground and underground location, communications, navigation systems, rifles, missile defense systems. In the report let’s present some of the applications of lasers, as well as protection of them

Energy Transfer and Restructuring in Amorphous Solid Water upon Consecutive Irradiation.

Interstellar and cometary ices play an important role in the formation of planetary systems around young stars. Their main constituent is amorphous solid water (ASW). Although ASW is widely studied, vibrational energy dissipation and structural changes due to vibrational excitation are less well understood. The hydrogen-bonding network is likely a crucial component in this. Here, we present experimental results on hydrogen-bonding changes in ASW induced by the intense, nearly monochromatic mid-IR free-electron laser (FEL) radiation of the FELIX-2 beamline at the HFML-FELIX facility at the Radboud University in Nijmegen, The Netherlands. Structural changes in ASW are monitored by reflection-absorption infrared spectroscopy and depend on the irradiation history of the ice. The experiments show that FEL irradiation can induce changes in the local neighborhood of the excited molecules due to energy transfer. Molecular dynamics simulations confirm this picture: vibrationally excited molecules can reorient for a more optimal tetrahedral surrounding without breaking existing hydrogen bonds. The vibrational energy can transfer through the hydrogen-bonding network to water molecules that have the same vibrational frequency. We hence expect a reduced energy dissipation in amorphous material with respect to crystalline material due to the inhomogeneity in vibrational frequencies as well as the presence of specific hydrogen-bonding defect sites, which can also hamper the energy transfer.

Design, Construction and Characterization of Sealed Tube Medium Power CO2 Laser System

A low-cost medium-power carbon dioxide (CO2) laser system is designed, constructed, and characterized to produce coherent, monochromatic laser radiation in the infrared region. The laser cavity is simulated and designed by using ZEMAX optic studio. A switch-mode high-tension pump source is designed and constructed using a flyback transformer and simulated using NI Multisim to study the voltage behavior at different node points. A prototype cooling system/chiller is designed and built using thermo-electric coolers (TEC) to remove the excess heat produced during laser action. Various parameters, such as pumping mechanism, chiller stability, efficiency, output power, and current at different applied voltages, are studied. The chiller efficiency at different output powers of the laser is analyzed, which clearly shows that the chiller’s cooling rate is good enough to compensate for the heat generated by the laser system. The center wavelength of the carbon dioxide laser is 10.6 μm with an FWHM of 1.2 nm simulated in the ZEMAX optic studio. The output beam penetration through salt rock (NaCl), wood, and acrylic sheet (PMMA) at various output powers is analyzed to measure the penetration depth rate of the CO2 laser.

Interference of areas of subcycle light pulses

Progress in reducing the duration of light pulses (down to one cycle of field oscillations or less), achieved in the last decades, has made it possible to experimentally observe and study a number of atomic-scale phenomena that occur at ultrafast times. Their study and observation are unavailable with conventional sources of monochromatic laser radiation. When using few- or subcycle pulses, a number of well-known phenomena in optics, which are well studied when using long monochromatic radiation sources, either lose their meaning, or their underlying physical mechanisms require revision. For example, the direct interference of subcycle pulses with their direct overlap is not possible due to their short duration. This note addresses the interference phenomenon, when a pair of subcycle pulses act on a medium, while do not simultaneously overlap inside it. In this case, it is not the pulses themselves that interfere in the medium, but the probability amplitudes of the bound states of the medium. Therefore the result of their impact on the medium can be interpreted as the interference of the areas of pulses—electric pulse areas (integral of the electric field strength over time) and envelope areas (integral of the slowly varying envelope of the electric field strength over time).

Electron Dynamics and Thomson Scattering for Ultra-Intense Lasers: Elliptically Polarized and OAM Beams

We investigated the classical nonlinear Thomson scattering (TS), from a single relativistic electron, generated by either: (a) an incoming plane wave monochromatic laser radiation and general elliptical polarization or (b) incoming radiations with intrinsic orbital angular momentum (OAM). Both (a) and (b) propagate along the z direction, with wave vector k0, frequency ω0, and initial phase φ0≠0 and have any intensity. Item (a) enables obtaining general electron TS Doppler frequencies and other quantities, for fusion plasmas. We explored the possibility of approximating nonlinear TS with OAM beams (Item (b)) by means of nonlinear TS with plane wave beams (Item (a)). For Item (a), a general explicit solution of the Lorentz relativistic equation and the subsequent TS are given in terms of ζ=ω0t−k0z (t denoting time). In particular, it includes the cases for linear and circular polarizations and φ0≠0 for fusion plasmas, thereby extending previous studies for φ0=0. The explicit solutions give rise to very efficient computations of electron TS Doppler frequencies, periods of trajectories, and drift velocities, and the comparisons with ab initio numerical solutions (for Item (a)) yield an excellent match. The approximate approach, using explicit solutions for Item (a), towards TS OAM (employing ab initio numerical computations for Item (b)), extending previously reported ones) yields a quite satisfactory agreement over time spans including several optical cycles, for a wide range of laser intensities, polarizations, and electron energies. The role of φ0≠0 was analyzed. A simple quantitative criterion to predict whether the agreement between the two approaches (a) and (b) would be observed over a given time span is discussed.

Model of the spectral dependence of changes in the polarization state of laser radiation in magneto-optical crystal in the presence of multiple reflections from its faces

In this work we investigated the phenomena in the Faraday rotator that can affect the polarization state of transmitting laser radiation. We have found that multiple reflections of radiation from the faces of the terbium gallium garnet (TGG) crystal can cause deterioration of radiation extinction ratio and, therefore, isolation properties of Faraday cell. We were able to calculate the impact of this factor on polarization extinction ratio of monochromatic and quasimonochromatic laser radiation transmitting through the crystal.

Внутридопплеровские резонансы затухания свободной поляризации в ультратонких газовых ячейках

The linear-optical effect of the free polarization decay (FPD) in an ultrathin gas cell, the internal thickness of which is less than or of the order of the wavelength of the exciting monochromatic laser radiation, transmitted orthogonally to the plane-parallel walls of this cell, is theoretically investigated. The considered coherent FPD signal is emitted immediately after an abrupt interruption of such a relatively weak stationary radiation. Sub-Doppler resonances arising at the central frequencies of the studied quantum transitions in the spectra of the intensity and energy of the FPD as a result of the transit-time relaxation of atoms in the gas cell are established and analyzed. A significant dependence of these resonances and the dynamics of the FPD on the ratio of the inner thickness of the ultrathin cell to the wavelength of the exciting monochromatic radiation is shown. The narrow, high-contrast sub-Doppler resonances of the FPD detected and investigated in the linear-optical regime can be used in ultrahigh-resolution atomic (molecular) spectroscopy, as well as references for compact frequency standards.

IMPLEMENTATION OF INTERNAL-RESONANCE LASER SPECROSCOPY IN THE EXAMINATION OF THE ELECTROPHYSICAL CHARACTERISTICS OF BLOOD ELEMENTS

The suggested model for assessment of the refractive index and the size of blood constituents might turn out to be more informative and precise than the existing models, which utilize non-resonance methods. This approach provides for the discovery of a correlation between the electrophysical parameters of blood cells and their biological properties. Evaluation of the incident and scattered monochromatic laser radiation is given as a key of understanding optical characteristics of bio-matter. The suggested model for assessment of the refractive index and the size of blood constituents might turn out to be more informative and precise than the existing models, which utilize non-resonance methods. This approach provides for the discovery of a correlation between the electrophysical parameters of blood cells and their biological properties. Evaluation of the incident and scattered monochromatic laser radiation is given as a key of understanding optical characteristics of bio-matter.

Photoinduced polarization enhancement on biased bilayer graphene in the Landau level regime

We investigate the charge carrier dynamics in bilayer graphene subject to monochromatic laser irradiation within the Landau level quantization regime. Even though the radiation field does not lift the energy degeneracy of the lowest Landau levels (LLs), it nevertheless has a strong effect on the photoinduced pseudospin polarization response for higher LLs (). Our results show that the photoinduced bandgaps lead to a finite response of the averaged pseudospin polarization with nontrivial oscillating behavior. It is shown that the contribution from these higher LL transitions turns out to be crucial to achieve an enhanced photoinduced polarization in radiated bilayer graphene. The experimental feasibility of our findings is also discussed.

Cyclotron-resonance-induced photogalvanic effect in surface states of 200-nm-thick strained HgTe films

We report on the study of magneto-photogalvanic and magnetotransport phenomena in 200 nm partially strained HgTe films. This thickness is slightly larger than the estimated critical thickness of lattice relaxation leaving the film partially relaxed with the value of the energy gap close to zero. We show that illumination of HgTe films with monochromatic terahertz laser radiation results in a giant resonant photocurrent caused by the cyclotron resonance in the surface states. The resonant photocurrent is also detected in the reference fully strained 80 nm HgTe films previously shown to be fully gapped 3D topological insulators. We show that the resonance positions in both types of films almost coincide demonstrating the existence of topologically protected surface states in thick HgTe films. The conclusion is supported by magnetotransport experiments.

Лазерный контроль среднего объемно-поверхностного диаметра частиц для оценки параметров аэрозольного загрязнения атмосферы

Aerosol air pollution is one of the most dynamic factors of the environmenal technogenic transformation. The danger degree of the aerosol particles increases in air with their sizes reduction therefore the dust disperse composition has the great hygienic value and in the working zone air and the dust disperse composition at the enterprise border — on health of the population of these territories are the important characteristic for its It has led to the introduction of new ecological standards for mass concentration of the particles with a diameter less than 10 μ (PM10) and particles with a diameter less than 2,5 μ (PM2,5). impact assessment on health of the enterprise employees and the population of near territories. The laser methods using for the assessment of parameters of aerosol emissions and extent of their impact on the environment have been introduced in this article. The modified spectral transparency method is the best of all and suitable for determination of the average size and concentration of disperse particles. The physical model of this method is based on interaction of monochromatic laser radiation with the polydisperse aerosol by Mie’s theories and maintaining invariancy of the average factor of the extinction efficiency concerning the type of the of particles size distribution function with using of the concept of particles average volume and superficial diameter. The optical density measurement of the disperse aerosol is performed at the same time, on several wavelengths, and the average factors of the extinction efficiency for these laser radiation wavelengths can be derived from the experimental data. This method has rather simple hardware realization and allow to diagnose flows of high optical density (that is characteristic of technogenic aero disperse flows).

Dichromatic and monochromatic laser radiation effects on antibiotic resistance, biofilm formation, and division rate of Pantoea agglomerans

Since infection is a common cause of delayed wound healing, it is important to understand the effect of low-level laser therapy (LLLT) in bacterial mechanisms. In this study we evaluated the effects of LLLT on antibiotic resistance, division rate, and biofilm formation of Pantoea agglomerans. P. agglomerans samples were isolated from human pressure injuries in humans and cultures were exposed to low-level monochromatic and simultaneous dichromatic laser radiation to study the susceptibility of an antimicrobial to ampicillin and piperacillin + tazobactam, quantification of areas of bacterial colonies, and biofilm formation of bacterial cells. Fluence, wavelength, and emission mode were used in the therapeutic protocols for wound healing. The data showed no changes in the areas of the colonies, but dichromatic laser radiation decreased biofilm formation, while a monochromatic red laser at low dose increased biofilm formation and infrared at high dose decreased antibiotic resistance to ampicillin. LLLT modulates antibiotic resistance and biofilm formation of P. agglomerans, but these depend on the laser irradiation parameters, since dichromatic laser radiation induces biological effects that differ from those induced by monochromatic laser radiation. Thus, simultaneous dichromatic low-level red and infrared lasers could be a new option for the treatment of infected wounds, reducing biofilm formation, without altering antibiotic resistance and the division rate of P. agglomerans cultures.

Fluorescence in a Quantum System with Violated Symmetry

The model of a single multilevel one-electron atom with violated symmetry such that its transition dipole-moment operator has constant diagonal matrix elements, among which not all are pairwise equal to each other, has been studied. It has been shown that the expression for the far electromagnetic field of such an atom does not contain any appreciable contributions from the diagonal matrix elements of the transition dipole moment in an explicit form; thus, these matrix elements have an effect on fluorescence via the time dependence of non-diagonal matrix elements due to quantum non-linear processes of higher orders. It has also been demonstrated that a two-level quantum system, whose transition dipole operator has constant unequal diagonal matrix elements, can continuously fluoresce under excitation with monochromatic laser radiation at a much lower frequency than the frequency of the exciting radiation. The possibility of the experimental detection and practical application of this effect are discussed.

Energy scale calibration of the KEDR tagging system

The KEDR detector tagging system is a symmetric focusing magnetic spectrometer of small-angle electrons born in the interaction region of the VEPP-4M collider. Using this system, which is designed for studying the two-photon processes, the scattered electrons and positrons energy is measured with a resolution of ΔE/E0= 0.03–0.6% where E0 is the beam energy. Two different methods are employed for calibrating the tagging system energy scale: the first one involves the electron/positron tagging by the energy of the singlebremsstrahlung photon measured in the BGO calorimeter, and the second one is based on the determination of the recoil electrons spectrum edge in the Compton backscattering of monochromatic laser radiation. The technical implementation and the present status of the calibration system are discussed in this paper.

Intense laser field effects on the third-harmonic generation in a quantum pseudodot system

In this research, we present the effects of high-frequency intense laser field on the third-harmonic generation associated with intersubband transitions in a two-dimensional quantum pseudodot system subjected to an uniform external magnetic field. Non-resonant monochromatic laser radiation with circular polarization is considered within the framework of high-frequency Floquet approach. On the basis of the compact-density matrix approach and an iterative method, the third-harmonic generation coefficient is calculated. The results presented for a GaAs quantum dot show that: (i) the position and magnitude of the resonant peak of third-harmonic generation depend strongly on magnetic field, the chemical potential and zero-point of pseudoharmonic potential; (ii) the strength of intense laser field modifies the confinement potential which results in considerable changes in the nonlinear optical response of the system.

Photo-assisted electron emission from illuminated monolayer graphene

We establish a formalism to address co-existing and complementing thermionic and photoelectric emission from a monolayer graphene sheet illuminated via monochromatic laser radiation and operating at a finite temperature. Taking into account the two dimensional Fermi-Dirac statistics as is applicable for a graphene sheet, the electron energy redistribution due to thermal agitation via laser irradiation, and Fowler's approach of the electron emission, along with Born's approximation to evaluate the tunneling probability, the expressions for the photoelectric and thermionic emission flux have been derived. The cumulative emission flux is observed to be sensitive to the parametric tuning of the laser and material specifications. Based on the parametric analysis, the photoemission flux is noticed to dominate over its coexisting counterpart thermionic emission flux for smaller values of the material work function, surface temperature, and laser wavelength; the analytical estimates are in reasonably good agreement with the recent experimental observations [Massicotte et al., Nat. Commun. 7, 12174 (2016)]. The results evince the efficient utilization of a graphene layer as a photo-thermionic emitter.

Dichromatic and monochromatic laser radiation effects on survival and morphology of Pantoea agglomerans

Despite the beneficial effects of low-level lasers on wound healing, their application for treatment of infected injuries is controversial because low-level lasers could stimulate bacterial growth exacerbating the infectious process. Thus, the aim of this work was to evaluate in vitro effects of low-level lasers on survival, morphology and cell aggregation of Pantoea agglomerans. P. agglomerans samples were isolated from human pressure injuries and cultures were exposed to low-level monochromatic and simultaneous dichromatic laser radiation to study the survival, cell aggregation, filamentation and morphology of bacterial cells in exponential and stationary growth phases. Fluence, wavelength and emission mode were those used in therapeutic protocols for wound healing. Data show no changes in morphology and cell aggregation, but dichromatic laser radiation decreased bacterial survival in exponential growth phase and monochromatic red and infrared lasers increased bacterial survival at the same fluence. Simultaneous dichromatic laser radiation induces biological effects that differ from those induced by monochromatic laser radiation and simultaneous dichromatic laser could be the option for treatment of infected pressure injuries by Pantoea agglomerans.