Transmission Of Laser Radiation Research Articles

Transmission of KrF laser radiation through hollow rough ceramic capillaries

Waveguide properties of the hollow rough ceramic capillaries were measured in experiments with the discharge-pumped KrF laser. Capillaries had inner diameter 1 mm, the length up to 34 cm with wall irregularities ∼5 μm in height and ∼100 μm in length along the capillary axes. Due to wall roughness the measured capillary transmittance appeared to be much less than the geometrical one in a perfect capillary with a smooth wall. It was shown that rough-wall capillaries transform radiation distribution along the channel and produce near-diffraction limited output radiation, even if the input multimode laser beam have a divergence tenfold higher than the diffraction one.

Understanding the coaxial optical coherence tomography signal during the laser welding of hidden T-joints

In the case of “hidden” T-joints, the nonvisible web sheet is welded through the face sheet. Positioning tolerances and movement due to the distortion of the web sheet represent the main challenges to maintain on track during laser beam welding. This study investigated the assumption that keyhole monitoring based on optical coherence tomography (OCT) could be utilized for seam tracking by detecting critical misalignments between the laser beam and the web sheet position. It hereby analyzed whether an emerging misalignment between the laser beam and the web sheet could be discerned in the OCT data before the laser beam misses the web sheet and penetrated only the face sheet. This prediction represents a key requirement for the industrial use of this approach. To this end, this study investigated the welding of hidden T-joints with angular and parallel offsets of the laser path relative to the web sheet centerline while recording with OCT. The interface zone between the web and face sheets was recorded by a high-speed camera to detect the transmission of laser radiation through a lower keyhole opening. It was shown that a lower keyhole opening, in combination with transmitted radiation, was advantageous for the reliable detection of an emerging misalignment. This lower keyhole opening can occur lateral to the web sheet prior to a misalignment, therefore enabling a prediction of spot misalignments via OCT. The welding parameter dependent maximum distance of the laser spot edge to the web sheet edge at detection was 0.1 mm in this study.

Development of the selective micropulse individual retinal therapy depends on age and type on the Fitzpatrick scale.

To develop a selective micropulse individual retinal therapy (SMIRT) based on the age and appearance type of the patient, to derive a formula for calculating power, and evaluate clinical efficacy for the treatment of central serous chorioretinopathy (CSCR). 73 patients (aged 30-65years) with acute CSCR and types 1-4 on the Fitzpatrick scale were divided into 2 groups. In the first group (33 patients), the testing of the micropulse mode (50µs, 2.4%, 10ms, 100µm, 0.4-1.9W) on the Navilas 577s laser system defined as selective by computer modeling was performed. A logistic regression function based on probability damage detection (PDD) of the 1584 laser spots from power, age, and type on the Fitzpatrick scale was constructed. PDD is the probability of detecting the laser spots using the autofluorescence method. The second group was divided into 4 subgroups of 10 eyes each. Groups 2.1, 2.2, and 2.3 were treated without preliminary testing. The power for Groups 2.1, 2.2, and 2.3 was obtained with the inverse PDD function, so that PDD was 50%, 70%, and 90%, respectively. Control group 2.4 went without treatment. The transmission and absorption coefficients of laser radiation of the eye depend on the age and the Fitzpatrick scale type. In Groups 2.1-2.3, complete resorption of subretinal fluid was observed 3months after CSCR treatment in 5 (P < 0.35), 8 (P < 0.023), and 10 eyes (P < 0.0008) out of 10, respectively. The developed SMIRT is effective for CSCR treatment with PDD 90%.

ОБ ИСПОЛЬЗОВАНИИ БИСТАТИЧЕСКИХ ПОДВОДНЫХ ОПТИЧЕСКИХ СИСТЕМ СВЯЗИ

Atmospheric and underwater optical communication lines have much in common due to variable conditions for the transmission of laser radiation along the path of the communication line, both in time and in space. The passage of a laser beam through a cloudy medium is accompanied by a decrease in the radiation intensity and an increase in the intensity of the scattered flux, which forms illumination, the intensity of which decreases with distance from the laser beam. As a rule, at the scales of distances at which the radiation of the optical range decays by several orders of magnitude, water in natural systems is homogeneous. The analysis shows that water in natural reservoirs is a light-attenuating medium both due to attenuation on dispersed particles and due to scattering on nanobubbles. The article analyzes the capabilities of atmospheric and underwater optical communication systems (POS). The results of modeling bistatic PIC in a reservoir containing particles with a diameter of 0.8 ?m and a concentration of 2 х 107 cm-3 are presented. It was shown that the parameters of the bistatic PIC pulses are significantly affected by nanobubbles in water. In natural reservoirs, the use of systems with direct line of sight is preferable. It has been shown that bistatic PICs, in which the scattering region is located on the side of the receiver unit relative to the transmitter - receiver line, have the greatest energy potential and minimal intersymbol interference. In natural reservoirs, it is possible to use such bistatic PICs for communication with a frequency of less than 20 MHz at distances of not more than 20 m. As a scattering region in bistatic PIC, you can use the bottom of the reservoir, the surface of the water or the region of water with a higher turbidity than the rest of the reservoir.

Free-electron Auger quenching of the Fe2+ excited state in ZnSe

The influence of free electrons in Fe2+: ZnSe crystals on the nonlinear transmission of high-power laser radiation with a wavelength of 2940 nm at room and low temperatures is experimentally found. Fe2+ : ZnSe samples additionally doped with Al are used. The transmission of an Al : Fe : ZnSe sample with electron conduction in a strong (peak intensity about 4.6 MW cm−2) field is almost the same as in a weak field both at low and room temperatures. The absence of an increase in the transmission of this sample under the action of high-power radiation is explained by increasing absorption saturation intensity of Fe2+ at this wavelength due a decrease in the lifetime of the excited state of Fe2+. The decrease in the lifetime is related to the well-known Auger quenching of impurity luminescence in semiconductors by free electrons.

CO laser line wavenumbers and absorption of their radiation by gaseous nitrogen oxides

In the article, new Dunham coefficients of the CO molecule in the X1Σ+ state are determined on the basis of the energy data for high vibrational–rotational levels. A comparison of the predicted values of the vibrational terms and the centers of vibrational–rotational transitions with experimental data for different sets of Dunham coefficients showed the reliability of the coefficients found. The centers of CO laser lines formed by transitions from high-energy vibrational–rotational levels are calculated. Modeling of the absorption spectral characteristics of NO, N2O, and NO2 is carried out. It is confirmed that the emission spectrum of a CO laser within a wide spectral region significantly depends on a number of factors (for example, characteristics of laser optical elements, mechanisms of broadening, and shifts of the working levels of laser transitions), which leads to variations in the values of the centers and widths of the laser lines and, as a consequence, to different values of transmission of CO laser radiation by gaseous compounds on the same laser lines.

Remote detector of hazardous substances based on a tunable 13С16О2 laser

A description of the developed prototype of a remote detector of hazardous substance vapors based on a tunable 13С16О2 laser is given. Results of test measurements of laser radiation transmission of organic liquid vapors (acetone, ammonia, ethanol, gasoline) are presented. The remote detection of acetone and ammonia vapors at distances up to 100 m is experimentally implemented.

Interaction of high-power laser radiation with low-density polymer aerogels**Presented at the ECLIM 2016 conference (Moscow, 18 – 23 September 2016).

The interaction of high-power subnanosecond laser pulses with low-density targets of cellulose triacetate polymer is considered. An Nd-glass laser setup provides a focal spot intensity of over 1014 W cm−2. An investigation is made of absorption of laser radiation, laser-to-X-ray energy conversion, spectra of ions emitted from the plasma, transmission of laser radiation through the target and plasma, as well as volume heating of the target material. It is experimentally determined that the laser energy conversion efficiency to X-rays with photon energies of a few Kiloelectronvolts decreases with increasing target material density. With the use of targets of density 10 mg cm−3 this efficiency is two times lower in comparison to 2 mg cm−3 density targets. The duration and amplitude of laser pulses transmitted through the target decreases with increasing column target density (the product of target material density and its thickness). The spectra of ions emitted from low-density target plasmas are recorded using ion collectors positioned at different angles relative to the direction of laser beam propagation as well as a high-resolution Thomson mass spectrometer. The ion flux and ion energies are found to increase with increasing target material density. The peak of the ion energy spectrum is shifted towards higher energies with increasing laser radiation intensity.

3.8 ?滋m和1.55 ?滋m激光辐射在雾中传输特性的数值计算

3.8 ?滋m和1.55 ?滋m激光辐射在雾中传输特性的数值计算

Mid-infrared laser filaments in the atmosphere.

Filamentation of ultrashort laser pulses in the atmosphere offers unique opportunities for long-range transmission of high-power laser radiation and standoff detection. With the critical power of self-focusing scaling as the laser wavelength squared, the quest for longer-wavelength drivers, which would radically increase the peak power and, hence, the laser energy in a single filament, has been ongoing over two decades, during which time the available laser sources limited filamentation experiments in the atmosphere to the near-infrared and visible ranges. Here, we demonstrate filamentation of ultrashort mid-infrared pulses in the atmosphere for the first time. We show that, with the spectrum of a femtosecond laser driver centered at 3.9 μm, right at the edge of the atmospheric transmission window, radiation energies above 20 mJ and peak powers in excess of 200 GW can be transmitted through the atmosphere in a single filament. Our studies reveal unique properties of mid-infrared filaments, where the generation of powerful mid-infrared supercontinuum is accompanied by unusual scenarios of optical harmonic generation, giving rise to remarkably broad radiation spectra, stretching from the visible to the mid-infrared.

Nonlinear optical properties of polyvinylcarbazole composites with graphene

The study has focused on polyvinylcarbazole (PVK) composites with graphene. It has been shown that there is a noticeable nonadditive shoulder on the long-wavelength edge of the optical absorption of PVK in these samples, which can be attributed to the formation of a charge-transfer complex between PVK as a donor and graphene as an acceptor. The formation of the complex causes a significant nonlinear optical effect in the PVK/graphene composite. The revealed increase in both the nonlinearity coefficient with increasing laser intensity and the cross section with increasing incident energy density is due to the formation of the graphene−· radical anion, an additional species contributing to nonlinear absorption, with an increase in the radiation energy density. Nonlinear optical properties of PVK composites with graphene isolated from a solution in tetrachloroethane after 1.5-h centrifugation (sample 1) have been considered. It has been suggested that a significant decrease in optical transmission of laser radiation by the composite TOA = 0.4 at an energy density at focus of 502 J/cm2 is due to the formation of the PVK/graphene charge-transfer complex responsible for the nonadditive shoulder on the long-wavelength optical absorption edge of PVK. During photoexcitation of graphene in the PVK/graphene composites at a laser wavelength of 1064 nm, mobile holes are generated in PVK, indicating the formation of graphene−· radical anions as a result of charge transfer from PVK to photoexcited graphene. The observed increase in both β with an increase in the laser radiation intensity and the cross section (σexc — σ0) with an increase in the incident energy density may be due to either the contribution of nonlinear transitions (S0 → S2, S0 → S1 → S2, T1 → T2) or the formation of the additional species, the graphene-· radical anions, participating in nonlinear absorption by increasing the energy density at the focus (Ffoc, J/cm2).

Nonlinear transmission of CO2 laser radiation by graphene

The nonlinear transmission of multilayer (∼12 layers) graphene at the wavelength λ ∼ 10 μm is measured for the first time. The absorption saturation intensity in graphene (∼330 kWcm-2) and the ablation threshold of its outer layers (∼1 MW cm-2,0.11 J cm-2) under action of a CO2 laser pulse with a duration of 70 — 85 ns at λ = 10.55 μm are determined. The residual absorption of graphene at its partial saturation was 48 % of the initial value. This is significantly smaller than the value measured previously for samples with a close number of layers at λ = 1.55 μm (92.3 % — 93.8 %). It is shown that the ablation threshold of two graphene layers adjacent to the BaF2 substrate (after successive ablation of outer layers) exceeds 0.27 J cm-2.

Transmission of multiwave laser radiation to the investigated volume through dense aerosol layers

This paper presents calculation results for the transmission of laser radiation through aerosol. It is shown that due to intermode beats, laser radiation can reach the investigated volume with smller losses than incoherent radiation.

Demonstration of a waveguide regime for a silica hollow - core microstructured optical fiber with a negative curvature of the core boundary in the spectral region &gt; 35 μm

We present a numerical and experimental demonstration of a waveguide regime in a broad band spectral range for the hollow core microstructured optical fibers (HC MOFs) made of silica with a negative curvature of the core boundary. It is shown that HC MOFs with the cladding consisting only of one row of silica capillaries allows to guide light from the near to mid infrared despite of high material losses of silica in this spectral region. Such result can be obtained by a special arrangement of cladding capillaries which leads to a change in the sign of the core boundary curvature. The change in the sign of the core boundary curvature leads to a loss of simplicity of boundary conditions for core modes and to "localization" and limitation of their interaction with the cladding material in space. Such HC MOFs made of different materials can be potential candidates for solving problem of ultra high power transmission including transmission of CO and CO2 laser radiation.

降雨对532 nm和1064 nm激光传输的衰减特性研究

降雨对532 nm和1064 nm激光传输的衰减特性研究

降雨对532 nm和1064 nm激光传输的衰减特性研究

降雨对532 nm和1064 nm激光传输的衰减特性研究

降雨对532 nm和1064 nm激光传输的衰减特性研究

降雨对532 nm和1064 nm激光传输的衰减特性研究

Visualization of the simulation results for multi-dimensional interaction of laser radiation with a photonic crystal

The article describes a software interface for the visualization of multidimensional time-dependent intensity distribution of laser radiation propagating in a photonic crystal. The intensity distribution is displayed in a three-dimensional space in color, which makes it possible to model the fourth dimension. The program constructs different sections of the intensity distribution, charts the evolution of the surface with a given intensity increment, and writes avi files. It allows viewing selected regions with different levels of detail and if necessary interpolates the computation results to achieve the required smoothness of the intensity distribution. The software has been validated and tested for the problem of transmission of laser radiation through a photonic crystal formed by polymer-filled spheres.

Analysis of Low-Level Laser Radiation Transmission in Occlusive Dressings

The purpose of this study is to analyze the power transmitted by low-level laser therapy (LLLT) into occlusive dressings using different wavelengths for the treatment of cutaneous lesions. LLLT has been largely used to treat several cutaneous lesions commonly associated with occlusive dressings to accelerate the healing process. Radiation transmission was measured by a digital power analyzer connected to a laser emitter with wavelengths of 660, 830, and 904 nm and mean levels of 30, 30, 6.5 mW, respectively, previously calculated. Thirteen different occlusive dressings were analyzed and interposed between the laser emitter and the power analyzer sensor, with 15 measurements made for each dressing. Statistics were provided by the analysis of variance (ANOVA), followed by Student's t-test (p < 0.05). The power transmitted ranged between 98.6% and 0%, depending on the material and wavelength. The dressings tested were BioFill, Hydrofilm, Confeel Plus 3533, Confeel 3218, DuoDERM Extra Thin, Hydrocoll, Micropore Nexcare, CIEX tape, Emplasto Sábia, CombiDERM, Band-aid, Actisorb Plus, in addition to polyvinylchloride (PVC) film, and transmitted power higher than 40% of the incident power, independently from the wavelength indicated for the association with LLLT. The results showed that LLLT transmission depends on the occlusive dressing material and the wavelength irradiated.

Aerogel foil plasma: Forward scattering, back scattering, and transmission of laser radiation

AbstractExperimental results obtained with “Kanal-2” facility under the study of powerful laser pulse interaction with the low density microstructure media are presented and discussed in this paper. Forward scattering, back scattering, and transmission of laser radiation by aerogel foil plasma have been investigated. The temporal, spectral, and energy characteristics of both the radiation scattering in the direction of heating radiation beam and the back scattering radiation were studied; the directional diagrams of forward and back scattering radiation were obtained for ω0 and 2ω0 frequencies. Analysis of intensity redistribution on the heating beam cross-section after passing through a polymer microstructure target was carried out.