Short-pulse Radiation Research Articles

Expansion and Spectral Softening of the Dust-scattering Rings of GRB 221009A

An expanding X-ray halo or rings appear when short pulses of X-ray radiation from a background source are scattered by clouds of dust in the Milky Way. We study the X-ray rings of the brightest gamma-ray burst (GRB) 221009A, detected by the Swift X-Ray Telescope. The rings center on the GRB position, and their angular radii increase with time. We identify five major expanding rings, and our modeling of their expansion history suggests that they are scattered off from five dusty clouds at distances of 0.4–13 kpc from the observer. Given an assumed prompt X-ray fluence of this GRB, the fluxes of those rings suggest that these clouds have dust grain column densities of 107∼8 cm−2. More interestingly, our time-dependent spectral analysis of these rings shows that they all experience spectral softening, i.e., getting softer as they expand, with spectral indices ranging from 2.2 to 5, consistent with what the dust-scattering model predicts.

Liquid crystal wave plate operating close to 18 THz.

Controlling the properties of mid- and far-infrared radiation can provide a means to transiently alter the properties of materials for novel applications. However, a limited number of optical elements are available to control its polarization state. Here we show that a 15-µm thick liquid crystal cell containing 8CB (4-octyl-4'-cyanobiphenyl) in the ordered, smectic A phase can be used as a phase retarder or wave plate. This was tested using the bright, short-pulsed (∼1 ps) radiation centered at 16.5 µm (18.15 THz) that is emitted by a free electron laser at high repetition rate (13 MHz). These results demonstrate a possible tool for the exploration of the mid- and far-infrared range and could be used to develop novel metamaterials or extend multidimensional spectroscopy to this portion of the electromagnetic spectrum.

Superradiance and solids: Reduced description method

Spontaneous ordering in a system of excited emitters with a powerful short radiation pulse predicted by Dicke attracted the great attention of scientists for decades as a bright example of the nontrivial behavior of a nonequilibrium system. The Bogolyubov reduced description method has some advantages and provides new possibilities in the theoretical investigation of the Dicke process. The paper presents the authors’ results of modeling such processes concerning both optical ones in the presence of crystal lattice influence and acoustic superradiance, which is possible in solids. The right choice of reduced description parameters allows the account of atom motions (phonons), cavity influence, and excitations in the emitter system (excitons) in the electromagnetic radiation process. The mathematical analogy between the Dicke system and a spin system in a magnetic field opens the way to applying the reduced description technique to acoustic phenomena previously investigated with the boson variable elimination method. Such a new approach to superradiance in crystals with paramagnetic impurities and with competing mechanisms of relaxation (Wagner model) is outlined. Acoustic superradiance is discussed in connection with the problem of structural phase transitions.

Ratiometric Fluorescent Detection of Ultrasound-Regulated ATP Release: An Ultrasound-Resistant Cu,N-Doped Carbon Nanosphere.

Focused ultrasound, as a protocol of cancer therapy, might induce extracellular adenosine triphosphate (ATP) release, which could enhance cancer immunotherapy and be monitored as a therapeutic marker. To achieve an ATP-detecting probe resistant to ultrasound irradiation, we constructed a Cu/N-doped carbon nanosphere (CNS), which has two fluorescence (FL) emissions at 438 and 578 nm to detect ultrasound-regulated ATP release. The addition of ATP to Cu/N-doped CNS was conducted to recover the FL intensity at 438 nm, where ATP enhanced the FL intensity probably via intramolecular charge transfer (ICT) primarily and hydrogen-bond-induced emission (HBIE) secondarily. The ratiometric probe was sensitive to detect micro ATP (0.2-0.6 μM) with the limit of detection (LOD) of 0.068 μM. The detection of ultrasound-regulated ATP release by Cu,N-CNS/RhB showed that ATP release was enhanced by the long-pulsed ultrasound irradiation at 1.1 MHz (+37%, p < 0.01) and reduced by the short-pulsed ultrasound irradiation at 5 MHz (-78%, p < 0.001). Moreover, no significant difference in ATP release was detected between the control group and the dual-frequency ultrasound irradiation group (+4%). It is consistent with the results of ATP detection by the ATP-kit. Besides, all-ATP detection was developed to prove that the CNS had ultrasound-resistant properties, which means it could bear the irradiation of focused ultrasound in different patterns and detect all-ATP in real time. In the study, the ultrasound-resistant probe has the advantages of simple preparation, high specificity, low limit of detection, good biocompatibility, and cell imaging ability. It has great potential to act as a multifunctional ultrasound theranostic agent for simultaneous ultrasound therapy, ATP detection, and monitoring.

Generation of Ultrashort Pulses in XUV and X-ray FELs via an Excessive Reverse Undulator Taper

The pulse duration in short-pulse schemes for Self-Amplified Spontaneous Emission Free Electron Lasers (SASE FELs) is limited by the FEL coherence time. A recently proposed concept allows to overcome the coherence time barrier and to obtain much shorter pulses. When the lasing part of an electron bunch is much shorter than the coherence time, one can suppress the radiation in the long main undulator while preserving microbunching within that short lasing slice. Then, a short radiation pulse is produced in a relatively short radiator. A possible suppression method, an excessive reverse undulator taper, is discussed and illustrated numerically in this paper. We also performed the first experimental tests of this method at the soft X-ray FEL user facility FLASH. The measured pulse duration approaches 1 fs (FWHM) at the wavelength of 5 nm.

High power balanced TEM horn antenna for ultra wide band radiator

AbstractA balanced transverse electromagnetic (TEM) horn type antenna is designed and developed for a 120 kV, 66 Ω high power ultra wideband (UWB) radiator. This antenna consists of a coaxial to parallel plate unzipper BALUN followed by an exponentially tapered TEM horn structure. Analysis of this antenna in time and frequency domain is performed using CST Microwave Studio. This antenna is having a power handling capacity of 1000 MW, with percentage bandwidth of 167%. This antenna has a gain of ~10 dB at 1 GHz frequency. Return loss performance of better than −10 dB is observed in 150 MHz to 1 GHz frequency range. Effective radiation of short pulses (&lt;5 ns) with very fast rise time (300–500 ps) has been demonstrated using this high‐power antenna. Practical results at 220 MW power are presented in this article. Directional performance of this antenna is practically established through peak power patterns in horizontal and vertical plane.

ASYMMETRY OF THE OPTICAL TRANSMISSION SPECTRA OF A PULSED DISCHARGE WITH AN EXTENDED HOLLOW CATHODE DURING AT RESONANCE INTERACTION OF SHORT POLYCHROMATIC LASER PULSES WITH EXCITED NEON ATOMS

The processes of resonant interaction of short pulses of polychromatic radiation of a dye laser with plasma of a nanosecond discharge in neon with an extended hollow cathode are experimentally studied. During the propagation of laser radiation inside the cathode cavity near the spectral absorption line of Ne I with a wavelength of 650.6 nm, the formation of asymmetric optical transmission spectra of the plasma of the dispersion type are detected, while during the propagation of laser radiation in the region between the electrodes, symmetric transmission spectra of the classical kind are formed.

A New Approach to Formation and Directed Radiation of Powerful Short Radio Pulses

This article details a new method for formation and directional radiation of short high-power electromagnetic (EM) pulses, which is based on a wave analog of the Smith–Purcell effect. The presented device cycles through two stages. At the stage of energy accumulation, a slow wave of an open guiding structure interacts with a periodic chain of storage resonators and excites high-Q free field oscillations in each resonator of this chain. The phase of oscillations inside the storage resonators differs by a constant value, and the amplitude increases with time. At the radiation stage, the chain of storage resonators is opened to radiation (as it usually happens in active compressors of EM pulses), and short powerful pulses burst out into free space in strictly defined directions. The proposed design is considered in detail for the simplest model of a device. The results obtained during its rigorous electrodynamic analysis look rather promising; the continuation of this work can contribute to solving a number of urgent problems of physics and technology of millimeter and submillimeter waves.

Microwave Radiation Associated with Lightning Initiation Events of Negative Cloud-to-Ground Flashes

In this paper, we examined the initiation events of ten negative cloud-to-ground (CG) flashes detected close to measurement stations on 12 November (CG-1 to CG-5) and 24 November (CG-6 to CG-10), 2019. All CG flashes were accompanied by microwave and very-high frequency (VHF) radiation pulses. We recorded all the CG flashes from two measurement stations (ST1 and ST2), which are separated by 13.3 km and consist of fast and slow antenna (FA and SA) sensors, a magnetic field (B-field) sensor, a VHF sensor (60 MHz), and a microwave sensor (~1 GHz). The key finding is that all of the microwave radiation pulses detected before the onset of initial electric field changes (IECs) preceded all VHF radiation pulses with an average lead time of 1.53 µs, ranging between 0.3 and 3.0 µs (for all CG flashes within reversal distance). A total of 50%, 17%, and 33% CG flashes were initiated by a single radiation pulse, two radiation pulses, and three radiation pulses, respectively, and were followed by IECs. Some VHF pulses are classified as short VHF radiation pulses (pulse duration less than 0.5 µs). The average duration from the first microwave and VHF pulses to the onset of IECs were 53.4 µs and 32.78 µs, respectively. The VHF radiation pulses detected before the IECs are suggested to be emitted by short-length positive streamers. Because the microwave radiation pulses were detected earlier (average lead time of 1.53 µs) than VHF radiation pulses, it is most likely that the microwave pulses were emitted by an electron avalanche process.

Effect of short-pulsed ion irradiation on the optical and electrical properties of titanium nitride films deposited by reactive magnetron sputtering

The effect of short-pulsed irradiation with 220 keV carbon ions for fluences of 2.2 × 1013 – 2.1 × 1015 cm−2 on the optical and electrical properties of titanium nitride films deposited by reactive magnetron sputtering on silicon and steel substrates has been studied. Relationships are obtained between the irradiation conditions and the parameters of interband absorption. A relationship has been established between the concentration of defects before and after irradiation, the degree of overlap of their levels and changes in the optical and electrical properties of the films. Reasons of high radiation resistance of the films are discussed.The optical and electrical properties of the films change during irradiation in two stages.The first stage is related to the annihilation of defects, the second stage is associated with their accumulation.Irradiation of filmssignificantly slows down the rate of oxidation of their surface layers and stabilizes the electrical properties.

Analysis of Combination Frequencies Arising from the Ionization of Gases by Multicolor Femtosecond Pulses

Ionization-induced multiwave mixing is attracting much interest nowadays due to the possibility of generating short pulses of secondary radiation over a very wide spectral range, from terahertz to far ultraviolet. This paper presents an analytical method for calculating the amplitudes of arbitrary spectral components of free electron currents arising under the action of multicolor ionizing laser pulses. We show that this method can be used to obtain the dependences of characteristics of a frequency-tunable third harmonic of the intense component of a three-color pulse obtained in an optical parametric generator. The obtained results are in good agreement with quantum mechanical calculations.

2H,13C-Cholesterol for Dynamics and Structural Studies of Biological Membranes.

We present a cost-effective means of 2H and 13C enrichment of cholesterol. This method exploits the metabolism of 2H,13C-acetate into acetyl-CoA, the first substrate in the mevalonate pathway. We show that growing the cholesterol producing strain RH6827 of Saccharomyces cerevisiae in 2H,13C-acetate-enriched minimal media produces a skip-labeled pattern of deuteration. We characterize this cholesterol labeling pattern by mass spectrometry and solid-state nuclear magnetic resonance spectroscopy. It is confirmed that most 2H nuclei retain their original 2H–13C bonds from acetate throughout the biosynthetic pathway. We then quantify the changes in 13C chemical shifts brought by deuteration and the impact upon 13C–13C spin diffusion. Finally, using adiabatic rotor echo short pulse irradiation cross-polarization (RESPIRATIONCP), we acquire the 2H–13C correlation spectra to site specifically quantify cholesterol dynamics in two model membranes as a function of temperature. These measurements show that cholesterol acyl chains at physiological temperatures in mixtures of 1-palmitoyl-2-oleoylphosphatidylcholine (POPC), sphingomyelin, and cholesterol are more dynamic than cholesterol in POPC. However, this overall change in motion is not uniform across the cholesterol molecule. This result establishes that this cholesterol labeling pattern will have great utility in reporting on cholesterol dynamics and orientation in a variety of environments and with different membrane bilayer components, as well as monitoring the mevalonate pathway product interactions within the bilayer. Finally, the flexibility and universality of acetate labeling will allow this technique to be widely applied to a large range of lipids and other natural products.

Generalizations of the R-Matrix Method to the Treatment of the Interaction of Short-Pulse Electromagnetic Radiation with Atoms

Since its initial development in the 1970s by Phil Burke and his collaborators, the R-matrix theory and associated computer codes have become the method of choice for the calculation of accurate data for general electron–atom/ion/molecule collision and photoionization processes. The use of a non-orthogonal set of orbitals based on B-splines, now called the B-spline R-matrix (BSR) approach, was pioneered by Zatsarinny. It has considerably extended the flexibility of the approach and improved particularly the treatment of complex many-electron atomic and ionic targets, for which accurate data are needed in many modelling applications for processes involving low-temperature plasmas. Both the original R-matrix approach and the BSR method have been extended to the interaction of short, intense electromagnetic (EM) radiation with atoms and molecules. Here, we provide an overview of the theoretical tools that were required to facilitate the extension of the theory to the time domain. As an example of a practical application, we show results for two-photon ionization of argon by intense short-pulse extreme ultraviolet radiation.

Применение неохлаждаемых микроболометров для регистрации импульсного терагерцового и инфракрасного излучения

Analytical relations for temperature response of the bolometer to periodic radiation pulses are obtained. It is theoretically shown and experimentally confirmed by the example of infrared bolometers that when detecting short radiation pulses, in contrast to the case of constant radiation, increasing the thermal conductivity of the bolometer and, accordingly, decreasing its thermal relaxation time, it is possible to significantly increase the response rate of the receiver, practically without reducing its sensitivity. The possibility of effective registration of pulsed terahertz radiation by microbolometers with a resistively coupled, thermally non-isolated antenna is considered. It is shown that such bolometers, which have increased thermal conductivity and, accordingly, reduced sensitivity to continuous-wave radiation, can be highly effective when detecting pulsed radiation with a duration shorter than the thermal relaxation time of the bolometer. On their basis, uncooled matrix detectors of pulsed terahertz radiation, characterized by a minimum detectable energy of less than 110-12 J and a frame rate of up to 1000 Hz, can be developed.

Application of uncooled microbolometers for detecting pulsed terahertz and infrared radiation

Analytical relations for temperature response of the bolometer to periodic radiation pulses are obtained. It is theoretically shown and experimentally confirmed by the example of infrared bolometers that when detecting short radiation pulses, in contrast to the case of constant radiation, increasing the thermal conductivity of the bolometer and, accordingly, decreasing its thermal relaxation time, it is possible to significantly increase the response rate of the receiver, practically without reducing its sensitivity. The possibility of effective registration of pulsed terahertz radiation by microbolometers with a resistively coupled, thermally non-isolated antenna is considered. It is shown that such bolometers, which have increased thermal conductivity and, accordingly, reduced sensitivity to continuous-wave radiation, can be highly effective when detecting pulsed radiation with a duration shorter than the thermal relaxation time of the bolometer. On their basis, uncooled matrix detectors of pulsed terahertz radiation, characterized by a minimum detectable energy of less than 1·10-12 J and a frame rate of up to 1000 Hz, can be developed. Keywords: microbolometer, pulsed terahertz radiation, antenna.

Air and Metal Vias Combined Metamaterial-Based Lens for Radiation Performance Enhancement of Short-Pulse Tapered Slot Antenna

A post-wall-structured tapered slot antenna (PWTSA) loaded with an embedded metamaterial-based lens (metalens) is proposed and investigated for short-pulse applications. The proposed embedded metalens consists of not only a metallic delay lens, but also an airy acceleration region surrounding the lens, which is different from the conventional metalenses used in various tapered slot antennas and can exhibit a small equivalent permittivity. Therefore, the embedded metalens has a large usable range of permittivity and does not increase the size of the original prototype PWTSA. The post-wall structure and metalens of the proposed antenna can help it achieve a comprehensive and balanced performance, including a high fidelity, low cross-polarization, stable main-lobe direction and gain enhancement. The simulated and measured results show that without any increase in antenna size, the proposed antenna enhances the realized gain by 6.4 dB over the frequency range from 9 to 26 GHz and achieves a stable radiation with the offset of the main-lobe direction being confined to 2° up to 24.9 GHz. Furthermore, the cross-polarization levels are less than −20 dB and the fidelity is kept high for the short-pulse radiation with the frequency spectrum up to 30 GHz.

Corona and polio viruses are sensitive to short pulses of W-band gyrotron radiation.

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic has raised the need of versatile means for virus decontamination. Millimeter waves are used in biochemical research in dynamic nuclear polarization enhanced nuclear magnetic resonance (DNP/NMR) spectroscopy. However, their efficiency in object decontamination for viruses has not been tested yet. Here we report the high efficiency of 95 GHz waves in killing both coronavirus 229E and poliovirus. An exposure of 2 s to 95 GHz waves reduced the titer of these viruses by 99.98% and 99.375%, respectively, and formed holes in the envelope of 229E virions as detected by scanning electron microscopy (SEM) analysis. The ability of 95 GHz waves to reduce the coronavirus titer to a range of limited infective dose of SARS-CoV-2 for humans and animal models along with precise focusing capabilities for these waves suggest 95 GHz waves as an effective way to decontaminate objects.

An inverted relativistic magnetron with virtual cathode based on bidirectional electron beams

An improved L-band inverted relativistic magnetron powered by a virtual cathode is presented. An extra emitter is introduced at the end of a slow-wave structure to reduce the desired π mode start-oscillation time, which is critical when short radiation pulses are required. Electrons produced by both upstream and downstream emitters are injected into the interacting space simultaneously, and the rapid increase in electron density in this region accelerates the establishment of a virtual cathode. Furthermore, the additional emitter provides more charged particles for beam–wave interaction, so that the amplitude of output power can be improved. The particle-in-cell simulation demonstrates that a power conversion efficiency of 76.5% could be obtained for a diode voltage of 500 kV and guiding magnetic field of 0.165 T. Compared with the same slow-wave structure powered by a single beam, the output microwave power is increased from 1.1 to 3.1 GW and the startup time is shortened from 53 to 29 ns.

May oxygen depletion explain the FLASH effect? A chemical track structure analysis

Background and purposeRecent observations in animal models show that ultra-high dose rate (“FLASH”) radiation treatment significantly reduces normal tissue toxicity maintaining an equivalent tumor control. The dependence of this “FLASH” effect on target oxygenation has led to the assumption that oxygen “depletion” could be its major driving force. Materials and MethodsIn a bottom-up approach starting from the chemical track evolution of 1 MeV electrons in oxygenated water simulated with the TRAX-CHEM Monte Carlo code, we determine the oxygen consumption and radiolytic reactive oxygen species production following a short radiation pulse. Based on these values, the effective dose weighted by oxygen enhancement ratio (OER) or the in vitro cell survival under dynamic oxygen pressure is calculated and compared to that of conventional exposures, at constant OER. ResultsWe find an excellent agreement of our Monte Carlo predictions with the experimental value for radiolytic oxygen removal from oxygenated water. However, the application of the present model to published radiobiological experiment conditions shows that oxygen depletion can only have a negligible impact on radiosensitivity through oxygen enhancement, especially at typical experimental oxygenations where a FLASH effect has been observed. ConclusionWe show that the magnitude and dependence of the “oxygen depletion” hypothesis are not consistent with the observed biological effects of FLASH irradiation. While oxygenation plays an undoubted role in mediating the FLASH effect, we conclude that state-of-the-art radiation chemistry models do not support oxygen depletion and radiation-induced transient hypoxia as the main mechanism.

Electromagnetically Induced Transparency of Weak and Powerful Short Laser Radiation Pulses

Electromagnetically Induced Transparency of Weak and Powerful Short Laser Radiation Pulses