Radiation Power Density Research Articles

Observation of photobleaching in Ge-deficient Ge16.8Se83.2 chalcogenide thin film with prolonged irradiation

We presented the unusual result of photobleaching (PB) in Ge-deficient Ge16.8Se83.2 thin films with continuous irradiation with 560 nm laser for 12000 s, which is contradicted with the previous reports that the PB only occurs in GexSe100-x films with x > 30. Observation of the dynamics variations of the photo-induced effects indicated that, photodarkening (PD) appears almost instantaneously upon light irradiation, saturates faster in a shorter time scale, and then photobleaching (PB) becomes dominant. Moreover, both PD and PB process accelerates with increasing irradiation power density. Raman spectra provided the evidence on the change of the photostructure of the samples, e.g. the structural transformation from Ge(Se1/2)4 edge-sharing (ES) to corner-sharing (CS) tetrahedral and homopolar Ge-Ge and Se-Se bonds to heteropolar Ge-Se bonds.

PHOTODYNAMIC THERAPY FOR SQUAMOUS CELL SKIN CANCER OF THE CHEEK (CASE REPORT)

The results of the clinical observation of a female patient with squamous cell carcinoma of the cheek skin treated by the method of photodynamic therapy (PDT) using the photosensitizer of fotoditazin are represented. The patient had single course of PDT. Fotoditazin was injected in a dose of 0.8 mg/kg of body weight as a single intravenous infusion in 0.9% sodium chloride. The irradiation was performed once, 2.5 h after injection of the photosensitizer (power density of laser irradiation – 200-300 mW/cm 2 , light dose of a single session of 300-350 J/ cm 2 ). There were no side effects after photosensitizer injection and after irradiation. The result of the treatment was defined as partial tumor regression. For nowadays the follow-up period is 2 months. The repeated course of PDT is scheduled.

In‐Situ Observation of Nanoparticle Formation Under Different Power of Microwave Irradiation

AbstractMicrowave technology has emerged as one of the useful methods for nanoparticle synthesis. Despite many studies on this area, its underlying mechanism has not been clearly understood. In this study, in‐situ observation of nanoparticle growth was carried out and the profiles and behaviors of produced bubbles and particles under microwave effect were reported. Sizes of bubble and nanoparticle particle were measured during and after microwave irradiation using a DLS apparatus and behavior of particle growth and superheating effect were observed. From the experimental data, it is apparent that the maximum bubble sizes were greatly influenced by the irradiation power and solute concentration. Particle number density, which is related to the initial solute concentration, is also an important factor for the bubble size produced during the irradiation. Finally, through in‐situ observation of superheating effect, the behavior was frequently caused by the irradiation at higher power. To prevent superheating effect, influencing factors such as the irradiation power and number density should be controlled to ensure a stable operation of particle formation process.

Spectral properties and anti-Stokes luminescence of TeO2–BaF2:Ho3+, Ho3+/Yb3+ ceramics and glass excited by 1.9-μm radiation of a Tm:LiYF4 laser

We demonstrate the up-conversion of Tm:LiYF4 infrared (IR) laser radiation with 1908-nm wavelength into visible light with a spectral maximum at 650 nm by ceramics with a composition of (100 − x)TeO2−xBaF2 − 1 wt % HoF3−yYbF3, where x = 20, 30, or 40 mol % and y = 0 or 0.5 wt %. The samples of 60TeO2−40BaF2 − 1 wt % HoF3 − 0.5 wt % YbF3 exhibited anti-Stokes luminescence at a threshold radiation power density of 1.0−1.5 W cm−2.

Phase-Imposing Initiation of Cherenkov Superradiance Emission by an Ultrashort-Seed Microwave Pulse.

For the first time, we demonstrate experimentally the possibility of Cherenkov superradiant generation with a phase imposed by an ultrashort seed microwave pulse. The phases of seed and initiated Ka-band microwave pulses were correlated with the accuracy of 0.5-0.7rad for the power ratio down to -35 dB. Characteristics of such a process were determined in the frame of a basic theoretical model that describes both spontaneous and stimulated emission of an electron beam moving in corrugated waveguides. The obtained results open up opportunities of reaching extremely high radiation power density in phased arrays of short-pulse coherently operating microwave generators.

Cherenkov terahertz radiation from graphene surface plasmon polaritons excited by an electron beam

We demonstrate a mechanism of efficiently transforming surface plasmon polaritons (SPPs) into Cherenkov terahertz (THz) radiation. In a structure where multilayer graphene is deposited on a dielectric substrate with a buffer layer, the energy of the SPPs can be significantly enhanced. The dispersion of SPPs crosses the light line of the substrate if the buffer layer has a low permittivity relative to the substrate. As a result, the SPPs can be readily transformed into radiation without the need of wavevector compensation. Compared to the radiation from structures without graphene, the radiation power density is enhanced by nearly three orders of magnitude due to the field enhancement of SPPs. Our results could provide a promising way for developing room temperature, tunable, coherent, and intense THz radiation sources to cover the entire THz regime.

The influence of a powerful stream of deuterium ions and deuterium plasma on the structural state of the surface layer of titanium

The effect of a high-power pulsed flow of deuterium ions and deuterium plasma generated in a plasma focus setup on the surface structure of a Ti plate was investigated. It was established that, depending on the radiation-thermal conditions on the surface, three zones with different surface morphology, structure, and defects were formed in the surface layer irradiated. The peculiarities of the surface damage in the center of the irradiated region of the Ti target exposed to the most severe radiation (power density of the ion and plasma flows of q i ≈ 1011–1012 and q p ≈ 109–1010 W/cm2, respectively) were studied, as well as those for the peripheral region exposed to softer radiation.

A comparative study of the processes of generation of singlet oxygen upon irradiation of aqueous preparations on the basis of chlorin e6 and coproporphyrin III

The photosensitizing ability of an agent based on chlorin e6 (Photoditazin), which is used for photodynamic diagnosis and therapy, is compared with that of a new preparation on the basis of coproporphyrin III in the environment of a phosphate buffer and a simulated biological environment (albumin solution). The efficiency of singlet-oxygen production was estimated by EPR spectroscopy and spectroscopy in the UV and visible ranges with the use of “chemical traps” of singlet oxygen. By irradiating drugs with LED emission centered at λmax = 520 nm, we determined the quantum yield of singlet-oxygen production in a buffer solution; the obtained values are 0.60 and 0.37 for chlorine and coproporphyrin, respectively. The steady-state concentration of singlet oxygen upon irradiation of solutions of the studied photosensitizers with concentrations of 12–43 μМ and the density of radiation power within the 6–96 W/cm2 region was found to be in the region of 1010–1011 molecules/cm3. It is shown that the introduction into the solution of egg albumin (0.1%) reduces the sensitizing properties of the two drugs by two to three times, while the efficiencies of the preparations with respect to singlet-oxygen production become almost identical (0.19 and 0.17).

Frequency dependent power and energy flux density equations of the electromagnetic wave

The calculation of the power and energy of the electromagnetic wave is important for numerous applications. There are some equations to compute the power and energy density of the electromagnetic wave radiation. For instance, the Poynting vector is frequently used to calculate the power density. However those including the Poynting vector are not perfect to represent the actual values because the equations are frequency independent. In the present study we have derived the frequency-dependent equations to calculate the power and energy flux density of the electromagnetic wave by help of the classical electromagnetic theories. It is seems that the Poynting vector with a certain electric and magnetic fields is correct only for a specific frequency. However our equations are perfect to calculate the values of the power and energy flux density for all frequencies of the electromagnetic radiation. The equations may help to develop the applications of the electromagnetic wave radiation.

A Compact Quasi-Isotropic Shorted Patch Antenna

A compact shorted patch antenna with quasi-isotropic radiation pattern is proposed in this paper. The antenna consists of a radiating patch, a small ground plane that has the same dimensions with the top patch, and a metallic sidewall which connects the former two. A coaxial probe is used to feed the antenna and excite its fundamental TEM mode, whose magnetic field generates surface electric current on the shorted sidewall and electric field generates surface magnetic current on the open-ended aperture. Due to the inherent properties of the electric and magnetic fields, the corresponding currents are found not only perpendicular but also quadrature with each other, and, therefore, the patch antenna can provide a quasi-isotropic radiation pattern without involving complex feeding circuit. To verify the theory, a prototype operating at 2.4-GHz WLAN band was designed, fabricated, and measured. Reasonable agreement between the calculated, simulated, and measured results is obtained. It has been shown that the difference between the maximum and minimum radiation power densities is ~2 dB over the entire spherical radiating surface, and the difference can be further reduced to ~0.9 dB by using a lower profile.

Features of the Growth Dynamics of Plasma Jets in Laser-Induced Vacuum Discharges with High Rates of Current Rise

An experimental study of the dynamics of formation of plasma jets and ion beams in laser-induced low-voltage discharges with high rates of current rise has been performed. It has been found that for given discharge characteristics (energy store voltage, discharge current, current rise rate, and discharge gap spacing) there exist optimum initial conditions, determined by the characteristics of the laser radiation, that provide stable single pinching of the cathode plasma jet at its maximum compression. Increasing the ion density and decreasing the temperature of the foreplasma by reducing the laser radiation power density at the cathode due to an increase in laser pulse duration improves the stability of the plasma pinching at a lower energy input.

Design of a low-cost equipment for optical hyperthermia

A laser equipment is presented which has been specifically designed for optical hyperthermia. Such specificity in the design has allowed implementation at costs significantly lower than other options currently available in the market. The developed equipment includes a 808nm laser whose output power is up to 500mW. It also incorporates additional devices that help the user in calibrating the system and supervising it while functioning. The performance of a prototype is tested by running two hyperthermia experiments: one involving gold nanorods, and the other using gold nanostars. The specific set-up of this prototype has allowed laser irradiation with radiated power densities up to 4W/cm2.

Investigation of terahertz radiation influence on rat glial cells.

We studied an influence of continuous terahertz (THz) radiation (0.12 - 0.18 THz, average power density of 3.2 mW/cm2) on a rat glial cell line. A dose-dependent cytotoxic effect of THz radiation is demonstrated. After 1 minute of THz radiation exposure a relative number of apoptotic cells increased in 1.5 times, after 3 minutes it doubled. This result confirms the concept of biological hazard of intense THz radiation. Diagnostic applications of THz radiation can be restricted by the radiation power density and exposure time.

Impact of subthreshold laser defect accumulation on the optical stability of crystals

Optoacoustic means are used to study the kinetics of laser damage accumulation in potassium chloride crystals. This approach allows us to observe the accumulation of changes in KCl crystals when it is irradiated by a series of laser pulses of subthreshold intensity in a variety of actions (alloying, applying an external electric field, UV illumination). Number of laser pulses N cr required to destroy a specimen at the same density of radiation power depends on density power I as N ~ I −4. Results are explained by the formation and accumulation of structural defects during photochemical reactions under the action of laser radiation.

Dynamic of Nanopowder Production During Laser Target Evaporation

The paper presents the results of research focusing on the processes occurring when powerful laser radiation interacts with refractory oxide targets. To visualize formation of the nanoparticle cloud and large fragments, the authors used laser illumination and laser monitor methods. Image analysis allowed studying the dynamic of cloud formation from nanoparticles and determining the nature of its interaction with surrounding air. It was established that it is possible to mostly avoid the formation and ejection of a multitude of drops from the crater, if the target is evaporated by fiber laser radiation pulses with duration of no more than 200 μs. With pulse duration of 120 μs, peak power of 600 W and radiation power density of 0.4 MW/cm2, mass nanoparticle output was 30 mass%, which is 1.4 more than when the target is affected by continuous radiation of the same power.

Laser-Driven Hybridization of a Surface Plasmon Resonance Collective Mode in a Monolayer of Silver Nanoparticles

Laser-driven hybridization of a collective surface plasmon mode of a monolayer of silver nanoparticles has been studied as a function of irradiation power density. Two collective surface plasmon modes were identified in the spectra, namely, T- and P-modes, associated with the induced particle dipoles parallel and perpendicular to the plane of the layer. The P-mode was in resonance with the laser irradiation wavelength (488 nm). The magnitude, spectral position, and bandwidth of the two modes depend significantly differently on the laser power density. The laser-driven changes of the T-mode were attributed to the thermal effects caused by laser heating of the sample. Meanwhile, the spectral behavior of the P-mode is governed by resonant excitation by an Ar laser.

Study on fatigue damage characteristics of deformable mirrors under thermal-mechanical coupling effect.

In a wavefront correction process, both the mechanical effect and the irradiation of a high-power continuous-wave laser distort the deformable mirror (DM) surface, which inevitably speeds up the fatigue damage of the DM. By utilizing the stress analysis model for the fatigue damage of the DM, the fatigue damage effects are analyzed quantitatively on the consideration of thermal-mechanical coupling effects, and the fatigue life prediction model has further been proposed based on the S-N curve and Miner cumulative damage theory. On this basis, thermal-mechanical conditions have been analyzed, and the influence of laser parameters on the fatigue life of the DM has also been discussed in detail. The results indicate that the increasing of maximum temperature rise of the DM leads to the increasing of stress, and further brings about the decreasing of the fatigue life. Meanwhile, the position at the rear surface of the DM subjected to the maximum stress always presents the minimum fatigue life. Furthermore, the laser irradiation makes the DM more easily damaged when the DM is correcting a distorted wavefront, and the fatigue life decreases with the increasing of irradiation time and power density for a given peak and valley (PV) value of the corrected wavefront. Additionally, the fatigue life also decreases with the increasing of power density and the decreasing of spot radius for a certain total irradiation. On the other hand, for the given laser parameters, the influence of the mechanical effect on fatigue life is gradually apparent with increasing PV value of the corrected wavefront, and when the PV value is more than 2λ, the mechanical effect instead of the thermal effect becomes the key factor for fatigue damage of the DM.

Analysis of excitation mechanisms of Ho3+ upconversion luminescence in Ho3+:LiYbF4 (0.2 at %) crystal via photographs of its longitudinal cross sections and via spectral and kinetic characteristics

The results of a complex analysis of the excitation mechanisms of the up conversion luminescence of Ho3+:LiYbF4 (0.2 at %) crystal are presented. The spatial distribution of the upconversion luminescence intensity is studied by the photographs of longitudinal cross sections at different positions of the laser beam waist with respect to the sample. The surface power density of the pump laser diode radiation (0.755 W, λ = 933 nm) was changed by focusing the beam (similar to Z-scanning). The dependences of the longitudinal luminescence cross sections, as well as of the spectral and kinetic characteristics of Ho3+ and Yb3+ luminescence, on the position of the laser beam waist are determined. It is found that there exist two different mechanisms of the population of the energy levels of Ho3+ ions from which green and red luminescence occur, namely, cooperative sensitization of luminescence and absorption of induced photon groups (JETP Letters, 102 (5), 279 (2015)). It is shown that the contributions of these mechanisms vary both in time and over the crystal volume. All the observed spatial, spectral, and temporal specific features of the upconversion luminescence of Ho3+:LiYbF4 (0.2 at %) crystal are qualitatively explained.

Photoinduced toxicity of PrF3 and LaF3 nanoparticles

PrF3 and LaF3 nanoparticles were synthesized by the hydrothermal method. The size distribution of these nanoparticles in the colloidal solution produced was studied by photon correlation spectroscopy. The mean diameter of the nanoparticles was 42 ± 1 nm. During the study of the toxicity of the nanoparticles, the mixture of a colloidal solution of the nanoparticles with cells to be studied was irradiated by 30-mW continuous lasers at wavelengths of 532 and 473 nm. The concentration of salmonella cells in normal saline was 106 cell/mL, while that of nanoparticles was 0.1 g/L. The cell survival percentage was 39, 34, and 20% for the irradiation times of 5, 10, and 15 min, respectively, at an optimal laser radiation power density of 0.4 W/cm at a wavelength of 532 nm. It was ascertained that LaF3 nanoparticles do not possess the property of photoinduced toxicity and the apoptosing effect. Moreover, the property of photoinduced toxicity is not shared by microparticles, in contrast to nanoparticles.

Conversion of two-micron radiation into visible light using glass and ceramics based on ZBLAN: Но3+ and ZBLAN: Ho3+ + Yb3+

Visualization of infrared radiation of Tm:YLF-laser at the wavelength of 1908 nm has been investigated in the glass and ceramics samples with compositions of 53ZrF4 · 20 BaF2 · 1HoF3 · 3YbF3 · 3AlF3 · 20NaF and 53ZrF4 · 20BaF2 · 3LaF3 · 1HoF3 · 3AlF3 · 20NaF (mol %). In luminescence spectra of ZBLAN samples doped with Но3+, the bands at the wavelengths of 480, 540, and 650 nm were observed, which correspond to 5F3 → 5I8, 5S2, 5F4 → 5I8, and 5F5 → 5I8 electron transitions in Но3+ ions with the maximum intensity of the red band (650 nm). Occupancy of the 5S2 and 5F4 levels in the ZBLAN: 1% Но3+ samples is related to the sequential absorption of the exciting radiation quanta. The level of 5F5 is filled mainly due to the ionic interaction. Additional doping with the Yb3+ ions led to the change of the luminescence color to green and a decrease in the threshold radiation power density of the Tm:YLF-laser in ceramic samples up to 2 W/cm2.