Characteristics Of Laser Radiation Research Articles

Low-threshold random lasers based on the DCM-DEG gain system with graphene nanosheets.

In this article, low-threshold random lasers based on DCM-DEG (DD) gain system with graphene nanosheets are studied. The experiment results show that the threshold of random lasers reduces rapidly when an appropriate amount of graphene nanosheets is added in DD solution. Meanwhile, the quantity and quality of random lasing modes raise significantly. We discussed the potential reasons why the graphene nanosheets can strengthen the sample's random lasing. And, the influence of the graphene nanosheet concentration on the radiation characteristics of random lasers is further studied. When the concentration of graphene nanosheets is 0.088wt%, the lasing threshold of DD samples with graphene nanosheets (GDD) is only about 31.8% of the lasing threshold of DD samples, and the quality of random lasing modes is five times higher than that of the DD sample. To further reduce the lasing threshold, the gold (Au) nanoparticles are added in the mixed solution to form the GDD solution with Au nanoparticles (GGDD). The results show that the lasing threshold of the GGDD sample is about 7.73 µJ/pulse, which is 5.2% of the lasing threshold of the DD sample. This experiment provides a new method to study low-threshold and high-quality random lasers based on graphene.

Оптические и лазерные характеристики Yb:YSAG-керамики

The optical and generation characteristics of 8.3(3) at. % Yb:YSAG ceramics (Y2,55Yb0,25Sc1,00Al4,2O12) made by solid solution powder sintering. Lasing was obtained on the basis of Yb:YSAG ceramics and the characteristics of laser radiation were studied at different transmittances of the output mirror of the resonator. The maximum generation power was 1.8 W at 3.6 W of absorbed pumping in the quasi-cw generation mode. The maximum differential efficiency was 57% for a mirror with a transmittance of 14.5%.

Average and statistical properties of coherent radiation from steady-state microbunching.

A promising accelerator light source mechanism called steady-state microbunching (SSMB) is being actively studied. With the combination of strong coherent radiation from microbunching and high repetition rate of a storage ring, high-average-power narrow-band radiation can be anticipated from an SSMB storage ring, with wavelengths ranging from THz to soft X-ray. Such a novel light source could provide new opportunities for accelerator photon science like high-resolution angle-resolved photoemission spectroscopy and industrial applications like extreme ultraviolet (EUV) lithography. In this paper, a theoretical and numerical study of the average and statistical properties of coherent radiation from SSMB are presented. The results show that 1 kW average-power quasi-continuous-wave EUV radiation can be obtained from an SSMB ring provided that an average current of 1 A and a microbunch train with bunch length of 3 nm can be formed at the radiator which is assumed to be an undulator. Together with the narrow-band feature, the EUV photon flux can reach 6 × 1015 photons s-1 within a 0.1 meV energy bandwidth, which is three orders of magnitude higher than that in a conventional synchrotron source and is appealing for fundamental condensed matter physics and other research. In this theoretical investigation, we have generalized the definition and derivation of the transverse form factor of an electron beam which can quantify the impact of its transverse size on coherent radiation. In particular, it has been shown that the narrow-band feature of SSMB radiation is strongly correlated with the finite transverse electron beam size. Considering the pointlike nature of electrons and quantum nature of radiation, the coherent radiation fluctuates from microbunch to microbunch, or for a single microbunch from turn to turn. Some important results concerning the statistical properties of SSMB radiation are presented, with a brief discussion on its potential applications, for example the beam diagnostics. The presented work is of value for the development of SSMB to better serve potential synchrotron radiation users. In addition, this also sheds light on understanding the radiation characteristics of free-electron lasers, coherent harmonic generation, etc.

Optically guided spatially modulated Laser generation doped with rhodamine 6G dye in the polymer (PVS) layer

The article is a continuation of a previous work in which optically controlled spatially modulated laser generation by means of a cholesteric liquid crystal laser layer was studied. In this work, a layer of polyvinyl alcohol doped with rhodamine 6G dye is used. The mentioned has been studied Laser radiation characteristics of the structure.

Method for determining the energy characteristics of laser radiation for controlling an unmanned aerial vehicle via an atmospheric optical channel

Method for determining the energy characteristics of laser radiation for controlling an unmanned aerial vehicle via an atmospheric optical channel

Pulsed RF excitation inductive discharge CO-=SUB=-2-=/SUB=- laser with the radiation energy of 1 J and high efficiency

An efficient pulsed gas-discharge inductive CO2-laser with a radiation energy of 1.05 J has been developed for the first time. In this case, the pulse duration of the laser radiation was about 10 msec. The maximum efficiency of 21.1% was obtained at a radiation energy of 340 mJ. HF current pulses propagated along the inductor conductor and, thus, an inductive discharge was formed to create a population inversion at the infrared (IR) transitions of CO2* molecules. The temporal and energy characteristics of the radiation of the inductive CO2-laser depending on the duration of the pump pulse are investigated. The spatial characteristics and spectrum of the radiation of the developed laser are estimated. The divergence of the laser radiation was 0.52 mrad. The cross-sectional dimension of the laser output beam was about 35 mm in diameter. Keywords: inductive discharge in a mixture of gases, high-frequency modulation of the pump voltage, population inversion, output characteristics of laser radiation.

Investigation of spatial and temporal characteristics of turbulent-distorted laser radiation during its dynamic phase correction in an adaptive optical system

We report the results of the analysis of experiments on dynamic phase correction of laser radiation distorted by a turbulent airflow in an adaptive optical system (AOS) with a Shack–Hartmann wavefront sensor (WFS). A field-programmable gate array is used as the main AOS control element, which provides a closed loop AOS bandwidth of up to 2000 Hz. The WFS is used to estimate the characteristic bandwidth of the generated turbulence ν turb. Changes in the spatial and temporal spectra of the laser radiation phase, as well as the quality of the beam during its dynamic phase correction at various AOS frequencies, are analysed. It is shown experimentally and by calculation that to ensure a high efficiency of the wavefront correction, the AOS frequency should be at least 20 times higher than ν turb.

Влияние неоднородностей разрядной плазмы на характеристики излучения KrF-лазера

Влияние неоднородностей разрядной плазмы на характеристики излучения KrF-лазера

Optomechanical interaction in fibre lasers with micro-optomechanical resonance structures

We report the results of studies of fibre lasers with passive modulators based on light-excited micro-optomechanical resonance structures (micro-oscillators). It is shown that in fibre lasers based on active fibres doped with rare-earth elements (Er, Er/Yb, Yb, Nd), the optomechanical interaction of laser radiation with micro-oscillators of various types (fibre-optic, microvolume) leads to self-oscillations of the characteristics of laser radiation at frequencies of relaxation oscillations and intermode beats synchronised with the frequencies of elastic eigenoscillations of micro-oscillators. It is found that in an ultra-long erbium – ytterbium fibre laser with a nonlinear mirror based on a microcantilever, laser photothermal excitation of the second mode of elastic transverse oscillations of the microcantilever makes it possible to perform passive mode locking exclusively due to Q-switching of the laser cavity. Pulsed lasing with a controlled repetition rate (∼76 kHz), a pulse duration of 2 – 5 μs and an output energy of 0.1 μJ per pulse is implemented. Based on a simplified physical model of the indicated fibre lasers with micro-oscillators, we have developed an approximate mathematical model describing the regimes of passive mode locking of fibre lasers with micro-oscillators that play the role of mirrors with a nonlinear reflection coefficient in the laser cavity. The prospects for the development and application of the considered laser systems are discussed.

Methods for Substantiating the Spatial Characteristics of the Laser Beam of Telecommunication Systems when Getting into Communication with Airborne Control Objects

Based on the method of functional conversion of random variables, a method has been developed for estimating the density of distribution of fluctuating radiation intensity of a transmitting laser at the input of the receiver, which allows to optimize the divergence angle when getting into communication, taking into account the accuracy of laser beam aiming and the fluctuation characteristics of laser radiation

Combined magnetron-laser deposition of titanium oxide thin-film plasmonic structures with silver nanoparticles

In this work, we consider a method for producing film structures, which are a dielectric matrix with nanosized metal particles in it. The technique is implemented by the simultaneous use of magnetron sputtering and pulsed laser deposition. As a dielectric matrix, TiO2 films formed by magnetron sputtering are used. Metallic Ag particles were deposited from an erosive laser stream. The conditions for the implementation of the technique are presented: the relative position of the magnetron, laser target, and substrate; characteristics of laser radiation; magnetron discharge parameters; pressure and composition of the gaseous medium. Using the methods of spectrophotometry, scanning electron microscopy and atomic force microscopy, the optical and structural characteristics of coatings are determined. The coating thickness was determined, the prevailing particle size and their surface density were estimated. A significant effect of the frequency of laser pulses on the absorption and transmission of the plasmon surface resonance band, as well as the presence in the film structure of small-sized particles of the cathode material of the magnetron sputter, is established.

Optimization of Temperature Dependence of Heteronanolaser Threshold Current with Account for the Thickness and Dielectric Properties of the Heterostructure Waveguide Nano-Layer Material

An exact problem of the electromagnetic wave propagation in a multilayer heteronanostructure with complex values of the dielectric constant (permittivity) is solved. The contribution to the refractive index of an additive to the dielectric constant due to the injected carriers is taken into account. A heterostructure based on a nanosystem used for the manufacture of lasers in the range 0.94–1.14 μm is considered. The methods and approaches used are also applicable for optimizing multilayer structures based on other solid solutions and those with several quantum wells. Based on the calculations of the temperature dependence of the radiation characteristics of injection lasers based on heteronanostructures, it was shown that the anomalous behavior of the temperature dependence of the threshold current is associated with a weakening of the waveguide properties of their active region. In accordance with the calculation results, the heteronanotructures parameters of injection lasers were optimized with respect to the thickness and dielectric properties of the waveguide nanolayer material, which made it possible to significantly reduce the temperature dependence of their radiative characteristics.

Analysis of characteristics of paraxial vector Gaussian beams affecting the formation of microstructures in an azopolymer

The paper considers paraxial Gaussian laser beams with different polarization states and their characteristics, such as the Poynting vector, gradient force, and force density, which are important for evaluating the effects of radiation on matter. An analysis of the considered characteristics of laser radiation from the point of view of the formation of photoinduced microrelief in an azopolymer film is carried out.

Influence of laser wavelength and laser energy on depth profiling of easel painting samples

The depth-resolved analysis by means of the laser-induced breakdown spectroscopy (LIBS) is a useful tool in the investigation of multi-layered structures of paintings. The LIBS technique is considered micro-destructive, as it is associated with the formation of the ablation crater. It is important to optimize the laser pulse parameters to minimize the crater size and also to avoid some possible side effects of the laser radiation, such as the material redeposition and the light- or heat-induced pigment discoloration. In the present work, mock-up painting samples were used to investigate the influence of laser radiation characteristics on the ablation process. The first LIBS set-up contains a Nd:YAG laser at the second harmonic frequency (laser wavelength 532 nm, pulse duration ~ 10 ns) and the second set-up is comprised of a modified laser-ablation system equipped with a Nd:YAG laser at the fourth harmonic frequency (laser wavelength 266 nm, pulse duration ~ 5 ns). The influence of different laser wavelengths and different laser energies on the properties of the craters was examined. The effects caused by the laser-ablation process were described.

Parameters of Laser Diodes Radiation in Different Temperature Intervals

The article deals with experimental studies that have been carried out in order to examine the radiation characteristics of commercially available semiconductor laser diodes and to analyze the reasons that cause changes in the characteristics of laser radiation. The need for such studies is connected with the search for expanding the possibilities of using semiconductor lasers in various appliances and devices operating in different conditions. The article presents experimental study results of the features of laser diodes emission spectra made on the basis of AlGaInP solid quadruple solution in the temperature range (50-300) K. The influence of temperature on the characteristics of the radiation spectrum was studied. The temperature was stabilized in a Cryomech ST15 closed-cycle vacuum helium cryostat. The radiation spectrum was investigated using a MDR-23 monochromator with a CCD detector installed. It is shown that the spectral characteristics of the emission spectrum (the predominance of stimulated or induced radiation, the wavelength of the radiation) depend on the operating temperature of the laser diode. Information is obtained that in the temperature range (50-300) K certain processes take place in the semiconductor laser diode material that lead to a change in the width of the forbidden band by approximately (4.2-4.5) % of the value corresponding to a temperature of 50 K. Data is given that the the temperature coefficient value of the change in the forbidden band width varies in absolute magnitude in 2-3 times within the investigated temperature interval. The authors propose an experimental method for determining the ionization energies of exciton levels localized in the region of the p-n junction of a laser diode. This method can find practical application for quality control of material in the manufacture of semiconductor lasers. The advantage of the proposed method is that it provides information on the exciton spectrum of a laser diode material in the narrow zone of the p-n junction in which laser radiation is formed.

Finite-Element Modeling in the Technology of Hardening Laser Processing of a Metal-Cutting Tool

A problem on heating of a cutting tool by triangularly shaped pulsed laser radiation has been solved numerically in a three-dimensional formulation by the finite-element method. The developed model takes account of the influence of both the geometry of the tool and the spatial and temporal characteristics of laser radiation on the formation of a temperature field in the laser-processing zone. A study has been made of the temperature distribution on the front face of the tool and over the depth of the laser-impingement point for different positions of the center of a laser-processing spot relative to the major cutting edge. For different tool angles, the regularities of formation of a temperature field during the hardening by pulsed laser radiation have been established; processing regimes (energy density, the multiplicity of processing, and the position of the center of the laser-processing spot relative to the tool’s cutting edges) that ensure the best parameters of the laser-impingement point (maximum hardening depth and the hardening-zone length) have been determined. A procedure to select technological parameters for the process of hardening of the cutting tool has been developed.

INTRACAVITY LARGE-SCALE HETEROGENEITY AND THEIR INFLUENCE ON RADIATION PARAMETERS OF POWERFUL LASERS

Large‑scale inhomogeneities occur in the optical resonator of a high‑power laser due to uneven redistribution of heat and errors in the alignment of the circuit. Such inhomogeneities can significantly affect the characteristics of laser radiation. The paper analyzes the effect of large‑scale phase inhomogeneities associated with the separation and thermal deformation of unstable resonator mirrors on the parameters of the laser radiation – the power and angular divergence. The numerical simulation of the unstable resonator in the di‑fractional approximation is carried out, on the basis of which the quantitative effect of phase aberrations such as optical wedge (separation) and spherical lens (thermodeformation) on the power and divergence of laser radiation depending on the main characteristics of the unstable resonator‑the Fresnel number and the magnification coefficient is determined. The results of experimental studies of the effect of separation on the radiation parameters of a 100‑kilowatt CO2 gas‑dynamic laser are presented. The results of the work should be taken into account in the structural‑parametric optimization of the resonator.

Ensuring the Uniformity of Measurements of Spatial-Energy Characteristics of Pulsed Laser Radiation

The structure and principle of creation of a standard for the spatial-power characteristics of pulsed laser radiation are examined, and problems solved with its aid are enumerated. Measurement results of spatial-energy characteristics (beam width, angle of divergence, centroid coordinates) of pulsed laser radiation are presented. Errors of conversion of the units of width and angle of divergence of the laser beam, as well as the total error of the standard, are estimated.

Влияние поляризационных характеристик пробного излучения на сигнал оптически детектируемого магнитного резонанса в магнитометрических и гироскопических квантовых датчиках

The influence of polarization characteristics of probe laser radiation in quantum sensors, i.e. magnetometers that use the electron paramagnetic resonance, and gyroscopes that use both the electron and nuclear magnetic resonances, on the amplitude of the magnetic resonance signal is considered. The relations between the magnitude of the magnetic resonance signal and the parameters of the elements of the optical scheme of the sensor are derived using the Stokes – Muller formalism and experimentally verified; It is shown that the main destructive effect on the signal in a standard two-beam scheme is exerted by phase delays introduced by both metal and dielectric mirrors. Methods for compensating for this destructive influence have been proposed and tested.

알루미나의 Nd:YAG 파이버 레이저 드릴링 특성

The mechanical drilling of micro holes is considered a difficult endeavor, due to the high hardness and brittleness of alumina plates found during the drilling process. In this work, an alumina plate with a 4mm thickness is drilled with the use of a continuous-wave Nd:YAG fiber laser. As can be seen, there is minimum required power density to ablate the alumina plate. As shown in this study, the hole diameter and straightness are not constant with the hole depth recorded, which is presumably due to the recondensation of vaporized alumina, and the characteristics of irregular laser radiation. The oxygen pressure, power density, focal position, and laser on time (duration) are chosen as the control parameters. To understand the influence of control parameters, the orthogonal arrays table in Taguchi method is applied, and the micro holes are evaluated based on the use of geometrical factors. Through the review of a sensitivity and interaction analysis, the appropriate duration and oxygen pressure are identified as the major parameters governing the geometrical quality of drilled holes in this study.