Parameters Of Laser Radiation Research Articles

Modification of gas-thermal coatings by laser radiation

The results of the researches which determine the dependence of gas-thermal coating porosity on the laser radiation parameters are given in the article. It determines such operational characteristics as thermocyclic and corrosion stability. In order to solve the problem, at the first stage the based on analytic dependences effect of a laser radiation to surface layers of gas-coating is described. The discontinuity of coating was taken into account, what was explained by presence of open and closes pores. It was shown that it’s necessary to produce the temperature range of “point of fusion — boiling point” on the surface of coating for the decrease of coating porosity as the action of laser radiation. The increase of the temperature above this range which is generated by the rise of the radiation rate results to evaporating of coating surface layers leading to its complete elimination in the thermal affect zone. At the second stage the experimental researches were realized. They consisted in the laser treatment of two types gas-thermal coating with a preliminary evaporation. The coatings which are based on the metal lic (PN-85-U-15) and non-metallic (Al2O3) components were analyzed. The quantitative assessment of porosity modification were realized by means of the based on Visual Studio 2008 program. This image processing program allows to compare the microstructure of the occupied by pores and coating material areas pixel-by-pixel. It has been established that the action of laser radiation leads to reduction of average porosity of gas-thermal coating. This reduction is: — the porosity in the initial position for coating of a PN 85-U-15-based alloy is 17 %; after the laser treatment it’s 5...8 %; — the porosity in the initial position for ceramic coating of Al2O3 is 24,5 %; after the laser treatment it’s 15...18 %.

Direct Laser Writing and Investigation of Optofluidic Elements inside Nanoporous Silicate Matrix

The paper demonstrates direct laser writing by femtosecond laser pulses (λ = 1030 nm, tau = 220 fs, v = 200 kHz) of functional optofluidic elements inside a nanoporous silicate matrix (NPSM). The influence of focused laser pulses led to the compaction of the nanoporous frame, which made it possible to fabricate barriers for the isolation of nanoporous cells and channel optical waveguides. The writing of microchannels in the mode of decompression of a nanoporous matrix with subsequent purification of debris area in distilled water under the action of ultrasound is also demonstrated. For each type of elements, the dependences of geometric characteristics on the energy parameters of laser radiation are established. The methods of testing the elements were also developed --- checking the permeability of the barrier, the entering of laser radiation into channel waveguides. Keywords: Direct laser writing, femtosecond laser pulses, barriers, waveguide, microchannel, porous silicate matrix, nanopores.

Импульсная проводимость в Ag-Pd-резисторах, индуцированная импульсами лазера

Pulsed EMF in resistive thick-film Ag - Pd elements is experimentally studied when their surface is irradiated with a laser beam. The dependences of the pulsed EMF on the coordinate of the action of the laser beam on the film surface are obtained. It is shown that applying a constant bias voltage to a thick-film resistive element can significantly increase the amplitude of unipolar EMF pulses induced by laser pulses. It was found that the amplitude and frequency of the EMF signals depend, respectively, on the power and frequency of laser pulses. It is shown that by the value of the pulsed EMF it is possible to control the parameters of the high-power laser radiation incident on the surface in real time. The design of a receiver for recording the parameters of laser radiation based on an Ag - Pd sensitive element has been developed. The sensitivity of the device for measuring the power and pulse repetition rate is estimated.

Pulse Conductivity in Ag-Pd Resistors Induced by Laser Pulses

Pulsed EMF in resistive thick-film Ag-Pd elements is experimentally studied when their surface is irradiated with a laser beam. The dependences of the pulsed EMF on the coordinate of the action of the laser beam on the film surface are obtained. It is shown that applying a constant bias voltage to a thick-film resistive element can significantly increase the amplitude of unipolar EMF pulses induced by laser pulses. It was found that the amplitude and frequency of the EMF signals depend, respectively, on the power and frequency of laser pulses. It is shown that by the value of the pulsed EMF it is possible to control the parameters of the high-power laser radiation incident on the surface in real time. The design of a receiver for recording the parameters of laser radiation based on an Ag-Pd sensitive element has been developed. The sensitivity of the device for measuring the power and pulse repetition rate is estimated. Keywords: measurement of laser parameters, thick-film resistor, thermo EMF.

Прямая лазерная запись и исследование оптофлюидных элементов внутри нанопористой силикатной матрицы

The paper demonstrates direct laser writing by femtosecond laser pulses (λ = 1030 nm, τ = 220 fs, v = 200 kHz) of functional optofluidic elements inside a nanoporous silicate matrix (NPSM). The influence of focused laser pulses led to the compaction of the nanoporous frame, which made it possible to fabricate barriers for the isolation of nanoporous cells and channel optical waveguides. The writing of microchannels in the mode of decompression of a nanoporous matrix with subsequent purification of area of debris in distilled water under the action of ultrasound is also demonstrated. For each type of elements, the dependences of geometric characteristics on the energy parameters of laser radiation are established. The methods of testing the elements were also developed - checking the permeability of the barrier, the entering of laser radiation into channel waveguides.

Laser processing of fused silica for fabricating microfluidic elements

The paper discusses the action of the power and the scanning speed of CO2-laser radiation on the surface of fused silica for the manufacture of microchannels and microreservoirs for microfluidics tasks is investigated. The dependences of the size and the roughness of microstructures on of laser radiation parameters is established. The depth of microfluidic elements reaches 45 μm with a roughness of < 40 nm. The velocity of liquid propagation (up to 15 mm/s) is estimated for the microchannels fabricated. The wettability of microreservoirs is evaluated, with the wetting angle reaching 64± 7o. The fabricated elements have a high transmission (T≥ 0.8) in the visible spectral range. Keywords: CO2-laser, microchannel fused silica, microfluidics.

Selection of laser processing parameters for hot stamping tools based on mathematical planning of the experiment

The results of experimental studies to determine the influence of the technological parameters of laser processing of 3Kh3M3F die steel on the service life of the working tool of a hot-stamping machine designed for hot stamping of rolling bearing rings are presented. Development of a mathematical model of the tool's resistance to laser radiation parameters was carried out by the method of mathematical planning of the experiment using a full factorial experiment. Durability of the die tool N (in thousand forgings) was chosen as an optimization criterion, while dimensionless (generalized) parameters of the speed V* and power P* of laser processing, as well as the overlap coefficient of laser tracks S* were proposed to use as factors. The obtained mathematical model of the resistance of laser-hardened die tools for hot deformation is used for the development and optimization of laser quenching modes without melting the surface of the ejectors in order to increase their thermal fatigue strength. Due to the fact that dimensionless factors containing the thermophysical characteristics of the die tool material are used in the planning of the experiment, the developed mathematical model can be used to assess the operational resistance of other heat-resistant tool steels of the martensite class.

Vulnerabilities in the quantum key distribution system induced under a pulsed laser attack

Quantum communication protocols are considered secure provided that all devices included in the system are fully characterized, and side channels are closed. However, as a result of laser radiation exposure, it is possible to change quantum communication systems components’ characteristics. This leads to vulnerabilities appearing in the quantum key distribution system. In this paper, we consider the effect of pulsed laser radiation on fiber-optic isolators used in quantum communication systems. Isolators protect the source of the system from attacking optical radiation coming from the “eavesdropping” side via the quantum channel. Lowering the isolation factor can bring the entire system out of a secure state. This gives an eavesdropper access to information about the secret key. The scenario of the most probable attack to the source of the quantum key distribution system via a pulsed laser was simulated. The experimental setup provided exposure of fiber isolators with pulsed laser radiation at a wavelength of 1064 nm (within the transparency window of the isolators) with a mean power up to 840 mW in four different pulse generation modes. The isolation factor and throughput of tested samples were monitored using a laser diode with a wavelength of 1550 nm and average power of 10.5 mW. Spectrally selective splitters were used to separate the lasers. It is shown that the isolation factor (isolator attenuation in the direction from the quantum channel to the system) at a wavelength of 1550 nm decreases from the initial value of 59.1 dB to 24.5 dB. The throughput (in the direction from the system to the quantum channel) at the same wavelength decreases from 0.6 dB to 1.2–12.3 dB or remains the same, depending on the acting pulsed laser radiation parameters. Temperature monitoring showed that the temperature of the isolator body changes insignificantly when exposed to pulsed radiation. The obtained effects of changing the isolation coefficient and throughput can be explained by the presence of nonlinear effects in the magneto-optical crystal of the isolator. The results of the work can be applicable in the practical evaluation of quantum communication systems security, in particular, the security evaluation of quantum key distribution systems. The results can be used to prepare the standards for certification procedures for assessing the security of quantum communication systems. The work gives recommendations for enhancing signal source unit security in quantum communication systems. Namely, as countermeasures to protect against the effects of pulsed laser radiation, it is proposed to set optical fuses with a limited threshold power, detectors for monitoring input optical radiation power, and narrow-band optical filters at the entrance of the quantum communication system.

Method development to secure the stability of the parameters of pulsed and continuous radiation in laser systems with semiconductor pumping

The necessity of increasing the stability of the parameters of pulsed and cw laser radiation when operating at peak powers is substantiated. Particular attention is paid to the parameters of pulsed laser radiation in systems with semiconductor pumping. The main requirement in this case is the repeatability of the parameters of the output pulses with high accuracy. This condition is ensured by the stability of the diode supply drivers, especially at peak powers, which are required for scientific research. It was found that even a short-term excess (about 1 ms) of the upper range of the permissible current leads to damage to the laser diode, which instantly degrades the parameters of laser radiation. The developed technique can significantly reduce the likelihood of these phenomena and increase the reliability of the laser.

Model the structure of nano-modified aluminium alloy with the addition of boron carbide

Nanocomposite thin films based on Al-Si alloy with the addition of boron carbide (B4C) particles are widely used in various fields of modern high-tech industry. For their synthesis, the method of laser nanomodification was used, which made it possible to obtain samples with a dendritic structure. The parameters of laser radiation were selected on the basis of preliminary modeling of the temperature field of the system. To describe the ensemble of nanodendrites on the surface, we used modeling of their structure in variable phase field and temperature for the initial stages, as well as the approximation of diffusion-limited aggregation and fractal Brownian motion for subsequent time intervals. The model showed satisfactory adequacy, estimated on the basis of the ratio of fractal dimensions of experimental and model structures. The proposed approach can be useful for predicting the structure of nanomodified aluminum alloys with various additions.

The laser radiation parameters control method based on the digital video system registration

The paper describes a method of a beam radiation parameters analysis. Such analysis bases on the laser beam registration in the plane of a diffusely reflecting screen and digital processing of the registered image. The algorithm of the laser beam spatial parameters determination is presented and realized programmatically. The experiment was carried out using a digital high-speed video system and a solid-state pulsed periodic laser based on a Cr3+: BeAl2O4 alexandrite crystal. A comparison of the proposed method with a standardized method based on the registration of radiation by a matrix photodetector is presented. The development of measure methods of the laser radiation parameters is necessary due to the appearance of new sources of laser radiation and their use in various applications.

Sub-ns-pulsed laser cleaning of an archaeological bone from the Sierra de Atapuerca, Spain: a case study

Controlled laser irradiation parameters using recently developed sub-nanosecond pulsed laser technology with emission wavelength in the near Infrared regime (1064 nm) have been assessed on a Pleistocene bone from the archaeological site of Sierra de Atapuerca, Spain. Burst pulse mode was employed to explore contaminant removal efficiency, while at the same time, assessing the degree of damage produced to the underlying original substrate surface. The surface morphology and composition of the deteriorated bone have been characterized, along with the effects of laser irradiation at 1064 nm, using Optical Microscopy (OM), Scanning Electron Microscopy–with Energy Dispersive X-ray Spectrometry (SEM–EDS), and X-ray Photoelectron Spectroscopy (XPS). The most effective laser cleaning parameters in burst mode have been identified in order to optimize the emission parameters of the laser, thus localizing its interaction within the outermost layers of contaminants and degradation products, avoiding damage to the underlying original bone surface. Hence, threshold cleaning and substrate damage values have been determined for this new sub-ns laser, paving the way to safer laser cleaning procedures that may be useful for the effective conservation of bone archaeological artifacts.

On the method of calculating the energy density of laser radiation in a metal surface modification

Today, modification of metal surfaces using laser radiation (laser ablation) is one of the most common processing methods in various scientific studies. At the same time, there is no unified approach to estimating the energy of laser radiation impact on the metal surface, which significantly complicates the comparison of the results of studies performed at different parameters of laser radiation. In the present work, a universal method of calculating the energy density of laser radiation impact on the surface is presented. The formation of relief with identical geometric characteristics at different parameters of laser radiation, but with the same energy density of radiation effect on the surface being modified, was experimentally confirmed.

Droplets generation conducting during laser-plasma treating of metals in electric field

Evolution of plasma plume generation on the surface of metal irradiated by laser beam with the mean radiation flux density ~ 106 W/cm2 in the external electric field with different polarity and field strength from 0 to 106 V/m was experimentally investigated. It is shown that the mean size of metal droplets carried out from the irradiated zone of target becomes materially (in several times) smaller when of the external electric field strength amplitude grow, independently to its polarity. It is essential that the mentioned differences (at the considered parameters of laser radiation) are observed only at the initial stage of the laser plume development, because after the steam-plasma cloud reaches the electrode an electric breakdown (short-circuit) occurs, and the external field in the interelectrode gap disappears. Electric breakdown leads to the spasmodic increase of electron density and temperature of plasma and to effective absorption of laser radiation by plasma torch (shielding of the target). In consequence of shielding droplets generation happens only during electric field existence. This explains decrease by several times of the characteristic size of the target substance droplets in spite of short duration of electric field existence.

Change in the coherence of light scattering from the surface of apples and their transpiration during storage

The potential possibility of using coherent optics for non-destructive testing to modify the microstructure of the surface of apples under the influence of chemical factors was studied. The model objects included solar and shade sides of fruits of Antonovka Common variety, untreated (control) and treated with diphenylamine (DPA). The amplitude-phase parameters of laser radiation reflected from the fruit surface were evaluated using a polarization shearing interferometer. It was experimentally shown that by the intensity and degree of coherence of the reflected laser radiation of the surface of apples, it is possible to register the anatomical and morphological characteristics of their tissues. It was revealed that after two months of storage, the spatial coherence of light scattering of the shadow side of an apple is higher than that of the solar, and the surface of apples treated with diphenylamine has a higher coherence of light scattering of the surface of both the solar and shadow sides. It was shown that the transpiration of apples treated with diphenylamine exceeds the transpiration of control apples.

Polarization stability of the single-mode laser diodes radiation applied in radiation scattering study complexes

Key features of semiconductor lasers and its serially manufacturing technology modernization have greatly expanded of its using at applied studies at last 20 years. But there is set of factors restricting such lasers application in a number of optical-electronic measuring complexes. Particularly in particle image velocimetry (PIV) and laser Doppler velocimetry (LDV) complexes commonly the gas and solid-state lasers is used due to more stability of spectral, energy and polarization characteristics of radiation then semiconductor lasers have. However gradual introduction of the serially manufacturing laser diodes into such systems picking up the pace that certainly characterizes the progress of reaching the required stability of its output laser radiation parameters. In laser measurement systems where medium investigation carried out by analyzing of scattering radiation in it the probe radiation polarization is often important. So the using in such systems the laser diodes as sources of radiation need to be followed by stability monitoring of its polarization characteristics which may be violated both by the outer factors and by natural degradation of inner laser diode structure. This work is devoted to the issues of monitoring the radiation polarization characteristics of the serially manufacturing single-mode laser diodes.

Photodynamic therapy of the experimental tumors of different morphological types with liposomal boronated chlorin е6

The article summarizes the results of studies of the effectiveness of photodynamic therapy using a new domestic photosensitizer liposomal borated chlorin e6 (LBC) after its parenteral administration (intraperitoneal and intravenous). Antitumor efficacy was evaluated in rats with M-1 sarcoma and PC-1 alveolar liver cancer and mice with B16 melanoma and Ehrlich’s carcinoma, which were transplanted subcutaneously into the thigh area of the animals. The aim of the study was to determine the optimal regimes of photodynamic therapy that would allow achieving the maximum antitumor effect up to 21 days after the photodynamic therapy. The therapy was carried out under the control of the accumulation of the photosensitizer in the tumor and surrounding tissues of the thigh by selecting the doses of the drug and the parameters of laser radiation (energy density and power density). The effectiveness of therapy was assessed by the inhibition of tumor growth, by the percentage of animals with complete tumor regression, by the absolute growth rate in animals with continued tumor growth compared to controls. The results of our studies have shown that the domestic photosensitizer liposomal borated chlorin e6 has high antitumor activity in vivo. In an experimental study of the photosensitizer under certain PDT modes, the maximum antitumor effect (complete tumor regression in 100% of animals) was obtained up to 21 days after PDT in all tumor models used.

Транспупиллярная лазерная термотерапия ретинобластомы

The review article presents the literature data concerning the history of the use of thermotherapy in the treatment of intraocular tumors, in particular, retinoblastoma (Rb). The article describes the historical aspects of the use of transpupillary thermotherapy (TTT) and the possibility of using this method in the treatment of RB nowadays. The analysis of Russian and foreign publications on the main parameters of laser radiation and the multiplicity of TTT was carried out. The efficacy of TTT as an independent method of Rb treatment has been demonstrated. The frequency of the main complications of TTT in Rb is presented. Key words: ophthalmology, retinoblastoma, transpupillary thermotherapy, laser treatment, pediatric oncology.

Laser nitriding of Zr-based metallic glass: An investigation by orthogonal experiments

Laser nitriding is a useful method to improve the surface hardness of materials, and it has been newly introduced to harden the surface of Zr-based metallic glass (MG). However, the currently achieved improvement in surface hardness is only 15.7%. To explore the potential of laser nitriding of Zr-based MG, orthogonal experiments were designed and performed in this study. By nanosecond pulsed laser irradiation in nitrogen atmosphere, the effects of laser parameters (average laser power, scanning speed, overlap rate and number of irradiation cycle) on the surface hardness of Zr-based MG were systematically investigated. The experimental results showed the highest surface hardness reached 18.21 GPa (Meyer's hardness) by orthogonal design, which is about 2 times higher than that of the as-cast MG. Furthermore, the laser affecting layer consisting of nitride phase reached tens of microns. The obtained results demonstrated that significant improvement in surface hardness could be achieved by selecting appropriate laser irradiation parameters, which would be beneficial to the engineering applications of MGs as surface contact materials. • The potential of laser nitriding on improving the hardness of Zr-based MG was investigated by orthogonal experiments. • The achieved highest hardness was almost three times of the hardness of the as-cast MG surface. • The effects of laser parameters on the surface hardness were comparatively studied. • The characteristics of shear bands and serrated flows of the laser nitrided MG surfaces were changed.

Nitrogen assisted formation of large-area ripples on Ti6Al4V surface by nanosecond pulse laser irradiation

Ti6Al4V is one of the most widely used titanium alloys due to its excellent mechanical, physical, and chemical properties. Laser surface texturing is a promising method to endow new functions of material surfaces; however, direct generation of laser-induced periodic surface structure (LIPSS) on the Ti6Al4V surface by nanosecond laser is rarely reported. In this study, by nanosecond laser irradiation in nitrogen atmosphere, the ripples (a typical LIPSS) were directly fabricated on the Ti6Al4V surface. By single-line laser scanning, the effects of laser irradiation parameters including the laser power and repetition frequency on the formation and evolution of the ripples were systematically investigated, followed by optimizing the laser irradiation parameters to achieve the large-area regular and clear ripples with relatively good surface quality as well. Furthermore, by performing contrast experiments in argon atmosphere, the role of nitrogen atmosphere on the formation of ripples was confirmed. Accordingly, formation mechanism of the ripples was discussed. Finally, the effects of the formed ripples on the surface color and wettability were preliminarily characterized to demonstrate the potential applications of surface ripples. This paper provides a nitrogen assisted method to fabricate large-area ripples on the Ti6Al4V surface by nanosecond laser irradiation.