Output Radiation Research Articles

Nonlinear spectral tunability of pulsed fiber laser with semiconductor optical amplifier

We examine spectral properties of radiation in the pulsed fiber lasers using the semiconductor optical amplifier (SOA) as the gain medium. The complex light dynamics that result from the interplay between the fiber propagation effects in the cavity, the nonlinear effects in the SOA and spectral filtering, shift the generated radiation from the central wavelength of the filter. The resulting wavelength of the output radiation depends on the SOA pump power and the bandwidth of the intracavity filter. This offers the possibility of a spectral tunability of the generated pulses through nonlinear dynamics rather than the conventional use of a tunable filter.

Hardware implementation of dynamic radiation therapy verification

The effectiveness of the use of modern technologies and methods of radiation treatment depends on the means of quality control of the operational parameters of the radiotherapy equipment. The development of technical means for verification of the radiation therapy plan, allowing accurate assessment of the three-dimensional dose distribution in the target, is a priority task when introducing innovative methods of radiation treatment. The aim of the work is to develop tools for assessing the three-dimensional dose distribution of radiation therapy plans with intensity modulation using the magnitude of the absolute radiation dose. The authors analyzed the existing technical means and methods for verifying radiation therapy plans on medical linear electron accelerators, and also identified their shortcomings. It is shown that these techniques for verifying the three-dimensional dose distribution do not give an accurate idea of the absolute values of the radiation dose in the target. A system and a method are proposed that allows improving the accuracy of the verification of the radiation therapy plan by using the obtained cross-calibration coefficient determined taking into account the value of the radiation output of the medical linear accelerator immediately at the time of the implementation of both this procedure and the radiation therapy session, as well as a method for verifying the plan radiation therapy with their use.

Quality control test of fixed x-ray units at Bir hospital and National trauma center

One of the important goals of the use of X-rays is to diagnose a disease and its extent and minimizing the adverse effect. In diagnostic X-ray, there is an important issue concerning the quality of the image and the exposure of radiation to the patient. Regular practice of quality control in diagnostic X-ray is essential to provide good quality images, decrease hazard to patients, and enhance the appropriate diagnosis. Quality control tests were carried out at six fixed X-ray units at National Academy of Medical Sciences, Bir Hospital and National Trauma Center. Parameters like kVp accuracy, timer accuracy, Reproducibility of kV, time and dose, variable mA and radiation output Linearity with the acceptance limits were checked. Radiation leakage, spatial resolution, contrast resolution and field alignment tests were also carried out. Quality control tests of kVp dose, dose rate, HVL, mAs, beam alignment and leakage radiation shows mixed results. The measured values were within limit in four X-ray units. Until now we do not have any regulations in Nepal on acceptance testing of x-ray units after installation. The need for quality assurance of X-ray needs to be taken to avert detrimental effects to patients and staff. Institutes must introduce a mandatory system for acceptance tests of X-ray when installed and alongside regular quality control programs.

Toward Miniaturized Undulators with L10 Phase FePt Micromagnet Array

Undulators In article number 2100701, Ozan Akdogan and co-workers synthesize a sub-mm undulator prototype with a period ranging from 250 μm to 10 mm using L10 ordered FePt micro magnets developed by utilizing photolithography. Room temperature coercivity of the structures reaches up to 1.4 Tesla. Simulations yield output radiation with 0.52 nm wavelength and 0.7 Giga-Watt peak power. The synthesized FePt micromagnets could be utilized in next-generation miniaturized undulators.

Variability of the Sun’s Luminosity Places Constraints on the Thermal Equilibrium of the Convection Zone

Luminosity, which is the total amount of radiant energy emitted by an object, is one of the most critical quantities in astrophysics for characterizing stars. Equally important is the temporal evolution of a star’s luminosity because of its intimate connection with the stellar energy budget, large-scale convective motion, and heat storage in the stellar interior. The Sun’s luminosity and its variation have not been measured to date because current observations of the solar radiative output have been restricted to vantage points near the Earth. Here, we model the solar luminosity by extending a semiempirical total solar irradiance (TSI) model that uses solar-surface magnetism to reconstruct solar irradiance over the entire 4π solid angle around the Sun. This model was constrained by comparing its output to the irradiance in the Earth’s direction with the measured TSI. Comparing the solar luminosity to the TSI on timescales from days to solar cycles for cycles 23 and 24, we find poor agreement on short timescales (<solar rotation). This is not unexpected due to the Earth-centric viewing geometry and short-term irradiance dependence on surface features on the Earth-facing solar disk. On longer timescales, however, we find good agreement between the luminosity model and the TSI, which suggests that the extrapolation of luminosities to multicycle timescales based on TSI reconstructions may be possible. We show that the solar luminosity is not constant but varies in phase with the solar cycle. This variation has an amplitude of 0.14% from minimum to maximum for Solar Cycle 23. Considering the energetics in the solar convection zone, it is therefore obvious that a steady-state input from the radiative zone at the solar minimum level would lead to a gradual reduction in the energy content in the convection zone over multicentury timescales. We show that the luminosity at the base of the convection zone should be approximately 0.032% higher than that at the solar surface during solar minimum to maintain net energy equilibrium through the solar cycle. These different energy-input scenarios place constraints on the long-term evolution of the TSI and its impact on the solar forcing of climate variability. These results highlight the convection zone’s role as an energy reservoir on solar-cycle timescales and set constraints for dynamo models intending to understand the long-term evolution of the Sun and solar analogs.

PM2.5 Air Pollution Prediction through Deep Learning Using Multisource Meteorological, Wildfire, and Heat Data

Air pollution is a lethal global threat. To mitigate the effects of air pollution, we must first understand it, find its patterns and correlations, and predict it in advance. Air pollution is highly dependent on spatial and temporal correlations of prior meteorological, wildfire, and pollution structures. We use the advanced deep predictive Convolutional LSTM (ConvLSTM) model paired with the cutting-edge Graph Convolutional Network (GCN) architecture to predict spatiotemporal hourly PM2.5 across the Los Angeles area over time. Our deep-learning model does not use atmospheric physics or chemical mechanism data, but rather multisource imagery and sensor data. We use high-resolution remote-sensing satellite imagery from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument onboard the NASA Terra+Aqua satellites and remote-sensing data from the Tropospheric Monitoring Instrument (TROPOMI), a multispectral imaging spectrometer onboard the Sentinel-5P satellite. We use the highly correlated Fire Radiative Power data product from the MODIS instrument which provides valuable information about the radiant heat output and effects of wildfires on atmospheric air pollutants. The input data we use in our deep-learning model is representative of the major sources of ground-level PM2.5 and thus we can predict hourly PM2.5 at unparalleled accuracies. Our RMSE and NRMSE scores over various site locations and predictive time frames show significant improvement over existing research in predicting PM2.5 using spatiotemporal deep predictive algorithms.

Impact of Accumulated Dust on Performance of Two Types of Photovoltaic Cells: Evidence from the South of Jordan

This paper examines the impact of accumulated dust on two types of photovoltaic (PV) cells in the performance of solar panels facility located in the southern part of Jordan between January to August 2020. To determine the performance of the solar PV panel system, two elements have been considered: sun radiation total efficiency and output power generated from the two types of the PV panel. Results of the study revealed that the mass of dust accumulated on the polycrystalline panel accumulated faster than on the cadmium telluride panel at a rate of 10.5 g/m2 for polycrystalline panels and 8.4g/m2 for cadmium telluride panel. Furthermore, results indicated that the projected drop in the efficiency of washed and unwashed polycrystalline panels decreased monthly by 5% and 16% respectively, while the efficiency of washed and unwashed cadmium telluride panels decreased monthly by 5% and 11.5% respectively. In the same context, results indicated that the wind speed, concentration rate, and relative humidity increased by 3%, 5%, and 8% respectively whereas the ambient temperature decreased by 4% monthly. On the other hand, the size and charge of accumulated dust on the cadmium telluride panel surface were larger than the size and charge of dust on the polycrystalline panel surface with a high percent of (Si) and low percent of (Ca) and (Fe). This research contributes to the literature by providing empirical evidence for the impact of accumulated dust on PV panels applied on a dusty-weather such as the one in the southern part of Jordan.

Deep reinforcement learning for self-tuning laser source of dissipative solitons

Increasing complexity of modern laser systems, mostly originated from the nonlinear dynamics of radiation, makes control of their operation more and more challenging, calling for development of new approaches in laser engineering. Machine learning methods, providing proven tools for identification, control, and data analytics of various complex systems, have been recently applied to mode-locked fiber lasers with the special focus on three key areas: self-starting, system optimization and characterization. However, the development of the machine learning algorithms for a particular laser system, while being an interesting research problem, is a demanding task requiring arduous efforts and tuning a large number of hyper-parameters in the laboratory arrangements. It is not obvious that this learning can be smoothly transferred to systems that differ from the specific laser used for the algorithm development by design or by varying environmental parameters. Here we demonstrate that a deep reinforcement learning (DRL) approach, based on trials and errors and sequential decisions, can be successfully used for control of the generation of dissipative solitons in mode-locked fiber laser system. We have shown the capability of deep Q-learning algorithm to generalize knowledge about the laser system in order to find conditions for stable pulse generation. Region of stable generation was transformed by changing the pumping power of the laser cavity, while tunable spectral filter was used as a control tool. Deep Q-learning algorithm is suited to learn the trajectory of adjusting spectral filter parameters to stable pulsed regime relying on the state of output radiation. Our results confirm the potential of deep reinforcement learning algorithm to control a nonlinear laser system with a feed-back. We also demonstrate that fiber mode-locked laser systems generating data at high speed present a fruitful photonic test-beds for various machine learning concepts based on large datasets.

Effect of Battery Discharge on the Output from Budget Light-Curing Units

Abstract Objectives The manufacturers of budget light-curing units (LCUs) often claim to provide high-quality units that are equivalent to LCUs from major manufacturers. This study investigated the effects of battery discharge on the light output from different budget LCUs compared to a major manufacturer. Materials and Methods Two brands of budget LCUs (LY-A180 and LED-CL) were compared to a control LCU from a major manufacturer (3M). The LCUs were fully charged, and their light outputs were measured over one battery discharge cycle using repeated 10-second exposures at a 0-mm distance. Statistical Analysis Data were analyzed using one-way analysis of variance and Bonferroni post-hoc test. Results The budget LCUs delivered fluctuating light output values. In their first exposure, the budget LCUs delivered between 205 and 444 mW power, an irradiance between 533 and 1154 mW/cm2, and a radiant exposure between 5.3 and 11.5 J/cm2. As the number of exposures increased, their light output decreased between 24 and 81%, while the control LCU showed only a 4.9% decrease in power and irradiance. The light outputs from the budget LCUs were significantly less than the control LCU, and they were significantly from each other. Conclusion The budget LCUs tested could not maintain their power, irradiance, and radiant exposure output values as the battery discharged. This supports the recommendation that clinicians should be very cautious when using budget LCUs in their clinical practice.

Development of Powerful Spatially Extended W-Band Cherenkov Maser of Planar Geometry With Two-Dimensional Distributed Feedback

A powerful spatially extended planar Cherenkov maser project operating in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${W}$ </tex-math></inline-formula> -band is under development in collaboration between Budker Institute of Nuclear Physics of the Russian Academy of Sciences (BINP RAS) (Novosibirsk) and Institute of Applied Physics of the Russian Academy of Sciences (IAP RAS) (Nizhny Novgorod). The ELMI accelerator (1 MeV/5–7 kA/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3~\mu \text{s}$ </tex-math></inline-formula> ) forms a sheet electron beam with the transverse size (width) of up to 18 cm, which serves to drive the oscillator. The electrodynamic system of this Cherenkov maser is based on doubly periodical structure, which combines the properties of a slow wave system that realizes conditions for an effective Cherenkov interaction with a high-current rectilinear sheet electron beam and a high- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q}$ </tex-math></inline-formula> resonator that implements the mechanism of two-dimensional distributed feedback and provides selective excitation of the operating mode in the strongly oversized interaction space. In this article, the crucial elements and design parameters of the oscillator are discussed, and the results of simulations are presented to demonstrate the possibility of achieving a stable narrow-band generation regime for a transverse system size reaching about 50 wavelengths and a gigawatt output power level. To provide a single-directed output of radiation, a planar Bragg reflector is elaborated for installation at the cathode side of the interaction space. A mode converter formed by a slowly tapered waveguide section for transformation of the radiated wavebeam into a Gaussian-type wavebeam was designed to be installed at the oscillator output. In the electron-optical experiments, the formation of a large-width sheet electron beam with parameters acceptable to drive designed <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${W}$ </tex-math></inline-formula> -band Cherenkov maser is demonstrated.

Two-dimensional displacement sensors with angstrom-scale resolution based on optical slot antenna arrays

Optical displacement sensing with high resolution and noncontact detection plays an important role in nanometrology, nanofabrication, and super-resolution microscopy. However, displacement sensing along an arbitrary direction in a two-dimensional (2D) plane with angstrom-level precision remains challenging. Here, we propose a 2D displacement sensor composed of eight optical slot antennas. A tightly focused laser beam is illuminated upon the antennas. The amplitudes and phases of the output radiation of the antennas are controlled by geometries. The intensity distribution of the output far-field radiation, which strongly depends on the relative position between the focal spot of the incident light and the antennas, was used to retrieve the 2D coordinates of any location in a plane. A resolution as high as 0.88 nm was obtained. We also show a method for improving displacement sensitivity by designing the destructive interference among the radiation of the antennas. The angstrom-scale resolution and arbitrary point localization, along with the nanoscale size, pave the way for the development of high-performance sensing, integrated photonic circuits, and on-chip signal processing.

Specific features of radiation flux formation in diode-pumped lasers and amplifiers with active elements made of Nd : YAG ceramics

The spatial, temporal, and spectral characteristics of the output radiation of diode-pumped laser systems and optical amplifiers with active elements made of Nd : YAG ceramics are studied. It is shown that the divergence of radiation in the subthreshold regime has the form of concentric nested cones emerging from the active element (AE) faces at angles of 2 – 4 °. A model explaining the experimentally observed phenomenon is proposed based on the mechanism of scattering of the generated beam from the granular structure of the optical ceramics. Analysis of the divergence pattern makes it possible to estimate the grain size and the optical quality of ceramics. The output beam divergence in the lasing regime is determined mainly by the cavity parameters and does not exceed several milliradians. The scattering events in this case serve as sources of additional optical losses. Luminescence enhancement and parasitic oscillations in the AE volume restrict the possibility of using Nd : YAG ceramics for fabricating AEs of high-power optical amplifiers.

Demystifying the CT Radiation Dose Sheet.

The radiation dose sheet generated by the CT scanner is a form that displays important information about an examination. It functions as a road map for the examination, detailing what CT examinations were performed and what parameters were used to perform them. One essential element of the radiation dose sheet, the volume CT dose index (CTDIvol), is a commonly used radiation dose index that is displayed on most CT scanners. The CTDIvol is used for quality control and is helpful for comparing the radiation output among different protocols and different scanners. The dose-length product (DLP) is a radiation dose index that builds on the CTDIvol by incorporation of the scan length. The DLP is combined with a conversion coefficient and used to determine the effective dose from the CT examination. Determining the effective dose is a way to estimate the whole-body radiation dose, even if the CT examination is confined to a smaller part of the body. In addition to these values, other data about the study from the CT scanner manufacturer, including the tube voltage and tube current-time product, usually are displayed on CT scanners. These values are major determinants of the image quality and radiation dose. The radiation dose sheet is a useful tool for radiologists, technologists, and physicists, allowing them to comprehend the technical details of a CT examination. The authors describe the components of the radiation dose sheet, the relationships of these components with one another, and the contributions of these components to the radiation dose. ©RSNA, 2022.

Investigation of a widely-tunable subnanosecond BBO-based optical parametric amplifier

We report an experimental realization of a subnanosecond optical parametric amplifier (OPA) system in a beta barium borate (BBO) crystal pumped by the third harmonic of a passively Q-switched Nd:YAG microlaser system and seeded by the continuum generated in a photonic crystal fibre (PCF). It yields broadband continuous signal wavelength tunability in the visible spectrum range from 470 to 660 nm and the idler wavelength from 768 to 1450 nm. Besides the experimental data, the numerical simulation results of the BBO optical parametric amplifier are presented. The maximum output power of the subnanosecond BBO OPA is limited by laser induced damage in the BBO crystal by the pump radiation and seed radiation spectral power density. We also notice and discuss the effect of seed radiation on BBO OPA output radiation characteristics. The numerical simulations qualitatively agree with the experimental data.

Linearly polarized 2044-nm pulsed laser generation in Ho:YAG active medium

We demonstrated the efficient generation of a linearly polarized Ho:YAG laser pumped by a thulium fiber laser. Independent of the pumping power and without utilizing any dispersive optical element, the output radiation remained stable with a high degree of linear polarization. The output with 2044 nm wavelength and 0.12 nm bandwidth was measured. In the free-running generation, with respect to the incident pump power, we recorded more than 9 W of output power with 59% slope efficiency. In addition, in the pulsed generation, we obtained more than 2.2 mJ pulses with 50 ns time duration, and 44 kW peak power.

Experimental Demonstration of Dark‐State Metasurface Laser with Controllable Radiative Coupling

AbstractLasing at the nanoscale using plasmonic nanoparticles offers the prospect of strong field concentration, hence strong light−matter interactions, low lasing thresholds, and ultrafast operation. However plasmonic nanoparticles suffer from high dissipative and radiative losses, the latter being rigidly tied to the shape of the nanoparticles and symmetry of their localized plasmon resonant modes. To overcome this limitation, recent theoretical work proposes using direct lasing into dark surface states to construct lasers that conceptually allow for independent implementation of the lasing state and its coherent radiation output. Here, lasing in dark resonant states of a metasurface laser and controllable coherent outcoupling of radiation with the aid of a tightly coupled, weakly radiative metasurface are demonstrated experimentally. The laser is implemented using a thin, low‐loss dielectric film supporting surface mode‐like dark dielectric bound states and the coupling metasurface is composed of small non‐resonant scatterers that controllably but weakly perturb the dark mode and turn it partially bright. Distinct far‐field signatures that can be observed experimentally for both dark and bright lasing are identified and demonstrated. The scalability of this design, here implemented for lasing in the near‐infrared, enables large‐aperture ultra‐thin coherent light sources with controllable emission from the infrared to the visible.

Effect of Reflection Asymmetry on the Output of the Parametric X-Ray Radiation of Electrons in Crystals

Effect of Reflection Asymmetry on the Output of the Parametric X-Ray Radiation of Electrons in Crystals

THz Radiation From a TM₅₁ Mode Sheet Beam Extended Interaction Oscillator With Low Injection

This article designs and studies a low-injection sheet beam extended interaction oscillator (EIO) circuit that uses TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">51</sub> - <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\pi $ </tex-math></inline-formula> mode operation. Through the combination of theoretical analysis and particle-in-cell (PIC) simulation, the mode characteristics and output characteristics of the circuit are studied. Theory and dispersion analyses on the designed EIO demonstrated that the special circuit structure and the optimized cutoff frequency effectively suppress nonoperating lower order modes. Only TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">51</sub> - <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\pi $ </tex-math></inline-formula> mode can support effective beam–wave interaction in the designed EIO, which has a benefit of increasing the frequency and size of miniaturized devices. The designed EIO can achieve high-frequency microwave radiation output with higher energy under low injection (low current density and low voltage). At a certain surface loss, when an electron beam with 1 A and 19.6 kV is injected, the 0.36-terahertz (THz) radiation power of 200 W is achieved. The slow wave structure has been presented. The designed circuit structure can be applied to high-frequency THz radiation source devices.

Toward Miniaturized Undulators with L10 Phase FePt Micromagnet Array

An undulator is a required part for building free‐electron lasers (FELs) upon which a large body of the literature has expressed interest for the applications in various areas such as the defense industry, material science, and medicine. The current state of the art of X‐FEL uses an undulator period down to 3 cm, which creates an output radiation wavelength down to 1.5 A using ≈14 GeV e‐beam. By developing a mm/sub‐mm period undulator (i.e., a period of 300 μm), it is possible to obtain the same output radiation wavelength with a much less e‐beam energy of ≈1.4 GeV. Thus, compact XFELs could become a reality. In this work, FePt thin films and micromagnets are synthesized by the sputtering deposition technique, and their properties are studied. The X‐ray diffraction (XRD) pattern indicated that the crystal structure transformed from face‐centered cubic (FCC) to L10 face‐centered tetragonal (FCT) phase upon annealing. Room temperature coercivity of the structures reached up to 1.4 Tesla. Undulator prototype is developed and the performance tests are done using Genesis simulation. Simulations yield output radiation with 0.52 nm wavelength and 0.7 GW peak power. Synthesized FePt micromagnets could be utilized in next‐generation miniaturized undulators.

Optical alignment and radiative flux characterization of a multi-source high-flux solar simulator

High-flux solar simulators are research-grade sources of artificial radiation mimicking optical characteristics of concentrating solar systems. They allow for experimental evaluation of high-temperature solar thermal devices and materials under controlled and reproducible conditions. In this study, we demonstrate the application of close-range photogrammetry in tandem with radiometry to optically align radiation modules of a multi-source high-flux solar simulator and to characterize its radiative output. The photogrammetric setup consists of photogrammetry targets, a digital camera and photogrammetry software. The radiometric measurements are conducted using mobile Lambertian targets, a heat flux gauge, and a complementary metal-oxide semi-conductor camera equipped with neutral density filters. An iterative procedure for adjusting lamp positions allows obtaining optical configurations of radiative modules meeting experimental requirements of high and ultra-high temperature solar thermal and thermochemical research. Close-range photogrammetry is demonstrated to be a convenient and effective method to obtain the as-built geometric configuration of the solar simulator setup. We report characteristics of an example radiative module configuration for a subset of six radiation modules. The peak and mean radiative fluxes over a 60-mm diameter flat target located in the focal plane are 3080kWm−2 and 1135kWm−2, respectively. The mean aiming error, defined as the average distance between theoretical and actual aiming points in the focal plane, is reduced from 37.20mm to 4.50mm for the pre- and post-alignment configurations, respectively.