Short-wavelength Radiation Research Articles

Photoluminescence emission spectra of Makrofol® DE 1-1 upon irradiation with ultraviolet radiation

Photoluminescence (PL) emission spectra of Makrofol® DE 1-1 (bisphenol-A based polycarbonate) upon irradiation with ultraviolet radiation of different wavelengths were investigated. The absorption-and attenuation coefficient measurements revealed that the Makrofol® DE 1-1 is characterized by high absorbance in the energy range 6.53–4.43eV but for a lower energy than 4.43eV, it is approximately transparent. Makrofol® DE 1-1 samples were irradiated with ultraviolet radiation of wavelength in the range from 250 (4.28eV) to 400 (3.10eV) nm in step of 10nm and the corresponding photoluminescence (PL) emission spectra were measured with a spectrofluorometer. It is found that the integrated counts and the peak height of the photoluminescence emission (PL) bands are strongly correlated with the ultraviolet radiation wavelength. They are increased at the ultraviolet radiation wavelength 280nm and have maximum at 290nm, thereafter they decrease and diminish at 360nm of ultraviolet wavelength. The position of the PL emission band peak was red shifted starting from 300nm, which increased with the increase the ultraviolet radiation wavelength. The PL bandwidth increases linearly with the increase of the ultraviolet radiation wavelength. When Makrofol® DE 1-1 is irradiated with ultraviolet radiation of short wavelength (UVC), the photoluminescence emission spectra peaks also occur in the UVC but of a relatively longer wavelength. The current new findings should be considered carefully when using Makrofol® DE 1-1 in medical applications related to ultraviolet radiation.

Design and optimization of spectral beamsplitter for hybrid thermoelectric-photovoltaic concentrated solar energy devices

The design and optimization of a thin-film multilayer spectral beamsplitter for hybrid thermoelectric-photovoltaic (TE-PV) solar energy devices are considered. In the configuration being studied the concentrated solar radiation is either transmitted through the beamsplitter onto a thermoelectric generator, or reflected onto a photovoltaic cell. The role of the beamsplitter is to reflect (transmit) those parts of the solar spectrum that can be converted most efficiently in the PV cell (TE generator). Beamsplitters are designed for maximizing the output of the hybrid system taking into account the spectral efficiency of realistic solar cells based on amorphous or microcrystalline silicon, efficiencies of the thermoelectric generator of either 4% or 8%, and the AM1.5 solar spectrum. The beamsplitter is constructed using thin-film layers of SiO2 and Si3N4 deposited on N-BK7 glass. The layer thicknesses are optimized for maximizing the efficiency of the hybrid system. The total achievable efficiency versus the number of layers used in the beamsplitter is studied considering from app. 20 to app. 200 layers. For an amorphous solar cell the relative increase in hybrid system efficiency above the single solar cell efficiency is 21.4%. Designs are made assuming that solar radiation is incident on the beamsplitter at an angle of 45°. However, the efficiency is found to only change slightly if the angle is varied from 35° to 55°. Finally, it is also found that efficient beamsplitters cannot be constructed for the reverse configuration with the TE and PV elements interchanged since efficient reflection of the long-wavelength radiation relevant for the TE generator is not possible without also having reflection of shorter-wavelength radiation that would be converted more efficiently in the PV cell.

Exploring the limits to energy scaling and distant-target delivery of high-intensity midinfrared pulses

We numerically investigate the scaling behavior of midinfrared filaments at extremely high input energies. It is shown that, given sufficient power, kilometer-scale, low-loss atmospheric filamentation is attainable by prechirping the pulse. Fully resolved four-dimensional ($xyzt$) simulations show that, while in a spatially imperfect beam the modulation instability can lead to multiple hot-spot formation, the individual filaments are still stabilized by the recently proposed mechanism that relies on the temporal walk-off of short-wavelength radiation.

Different Narrow-Band Light Ranges Alter Plant Secondary Metabolism and Plant Defense Response to Aphids.

Light of different wavelengths affects various physiological processes in plants. Short-wavelength radiation (like UV) can activate defense pathways in plants and enhance the biosynthesis of secondary metabolites (such as flavonoids and glucosinolates) responsible for resistance against certain herbivorous insects. The intensity of light-induced, metabolite-based resistance is plant- and insect species-specific and depends on herbivore feeding guild and specialization. In this study, broccoli (Brassica oleracea var. italica) plants were grown for 4weeks in a climate chamber under conventional fluorescent tubes and were additionally treated with UV-B (310nm), UV-A (365 or 385nm), or violet (420nm) lightgenerated with UV-B tubes or light-emitting diodes (LEDs). The objective was to determine the influence of narrow bandwidths of light (from UV-B to violet) on plant secondary metabolism and on the performance of the cabbage aphid Brevicoryne brassicae (a specialist) and the green peach aphid Myzus persicae (a generalist). Among flavonol glycosides, specific quercetin and kaempferol glycosides increased markedly under UV-B, while among glucosinolates only 4-methoxy-3-indolylmethyl showed a 2-fold increase in plants exposed to UV-B and UV-A. The concentration of 3-indolylmethyl glucosinolate in broccoli plants increased with UV-B treatment. Brevicoryne brassicae adult weights and fecundity were lower on UV-B treated plants compared to UV-A or violet light-treated plants. Adult weights and fecundity of M. persicae were increased under UV-B and UV-A treatments. When specific light wavelengths are used to induce metabolic changes in plants, the specificity of the induced effects on herbivores should be considered.

Changes in the optical absorption induced in the Bi12TiO20:Al crystal by exposition to short- and long-wavelength radiation

The impurity absorption model is used to describe the experimentally observed reversible changes in the optical absorption spectrum induced in the Bi12TiO20:Al crystal by subsequent exposition to short-wavelength radiation with λi, = 532 nm and longer-wavelength radiation with λn changing from 588 to 1064 nm. The model takes into account the photoinduced transitions between two metastable states of a deep defect center leading to the change of its position in the crystal lattice under conditions of strong lattice relaxation.

Ultrashort high-brightness pulses from storage rings

The brightness of short-wavelength radiation from accelerator-based sources can be increased by coherent emission in which the radiation intensity scales with the number of contributing electrons squared. This requires a microbunched longitudinal electron distribution, which is the case in free-electron lasers. The brightness of light sources based on electron storage rings was steadily improved, but could profit further from coherent emission. The modulation of the electron energy by a continuous-wave laser field may provide steady-state microbunching in the infrared regime. For shorter wavelengths, the energy modulation can be converted into a temporary density modulation by a dispersive chicane. One particular goal is coherent emission from a very short “slice” within an electron bunch in order to produce ultrashort radiation pulses with high brightness.

Theory of electromagnetic insertion devices and the corresponding synchrotron radiation

Permanent magnet insertion devices (IDs), which are the main radiation generating devices in synchrotron light sources and free-electron lasers, use a time-invariant but space-periodic magnetic field to wiggle relativistic electrons for short-wavelength radiation generation. Recently, a high power microwave based undulator has also been successfully demonstrated at SLAC which promises the advantage of dynamic tunability of radiation spectrum and polarization. Such IDs employ transverse elecromagnetic fields which are periodic in both space and time to undulate the electrons. In this paper we develop a detailed theory of the principle of electromagnetic IDs from first principles for both linear and circular polarization modes. The electromagnetic equivalent definitions of undulator period (${\ensuremath{\lambda}}_{u}$) and undulator deflection parameter ($K$) are derived. In the inertial frame where the average momentum of the electron is zero, we obtain the figure-8-like trajectory for the linear polarization mode and the circular trajectory for the circular polarization mode. The corresponding radiation spectra and the intensity of harmonics is also calculated.

Nanoemulsions containing a synthetic chalcone: Photodegradation, in vitro release, and interaction studies

Abstract Two different nanoemulsions containing a synthetic chalcone (SC) were prepared and characterized with respect to SC release and photodegradation profiles using Franz diffusion cells and a short-wavelength ultraviolet radiation (UVC) light chamber, respectively. In order to explain the differences observed in the behavior of these two formulations, the interactions between the SC and the components of the nanocarriers were investigated by Differential Scanning Calorimetry (DSC), Nuclear Magnetic Resonance (NMR) and Fourier Transform Infrared (FTIR) techniques. DSC and NMR measurements showed that SC seems to interact with the polysorbate 20 and medium chain triglycerides groups in the formulation composed by soy lecithin and polysorbate 20 (LP20). On the other hand, the interaction of SC with the formulation composed by sorbitan monooleate and polysorbate 80 (SP80) seems to affect the sorbitan monooleate and medium chain triglycerides groups. FTIR findings showed that SC decreases the mobility of the methylene group and displaces phosphate one in the LP20 system. In the SP80 formulation, it was observed that SC displaces the methylene chains groups, increasing the mobility of the carbonyl group. Our results indicate that the system structural arrangement might influence the SC release profile and photodegradation, since LP20 presented lower fluidity, thereby lower amount of SC released and higher photostability, whereas the opposite behavior was observed for SP80.

Two-beam based two-stage EEHG-FEL for coherent hard X-ray generation

The ability to generate stable and coherent short wavelength radiation is a great promise of the externally seeded free-electron laser. However, the frequency up-conversion efficiency is limited to a small number in a single stage setup. In this paper, we propose a new scheme to produce coherent hard X-ray FEL with two-beam based two-stage echo-enabled harmonic generation configuration. Electron beams with quite different properties are separately used in each stage and a monochromator is adopted to purify the radiation from first stage for seeding the second stage. Three-dimensional start-to-end simulations have been performed with realistic parameters to show the feasibility of the proposed scheme.

Spectroscopic studies of non-thermal plasma jet at atmospheric pressure formed in low-current nonsteady-state plasmatron for biomedical applications

The optical and electrophysical characteristics of the nonequilibrium low-temperature plasma formed by a low-current nonsteady-state plasmatron are experimentally investigated in the present work. It is demonstrated that experimental data on the optical diagnostics of the plasma jet can provide a basis for the construction of a self-consistent physical and mathematical plasma model and for the creation of plasma sources with controllable electrophysical parameters intended for the generation of the required concentration of active particles. Results of spectroscopic diagnostics of plasma of the low-current nonsteady-state plasmatron confirm that the given source is efficient for the generation of charged particles and short-wavelength radiation—important plasma components for biomedical problems of an increase in the efficiency of treatment of biological tissues by charged particles. Measurement of the spatial distribution of the plasma jet potential by the probe method has demonstrated that a negative space charge is formed in the plasma jet possibly due to the formation of electronegative oxygen ions.

Solar Irradiance Changes and Phytoplankton Productivity in Earth's Ocean Following Astrophysical Ionizing Radiation Events.

Two atmospheric responses to simulated astrophysical ionizing radiation events significant to life on Earth are production of odd-nitrogen species, especially NO2, and subsequent depletion of stratospheric ozone. Ozone depletion increases incident short-wavelength ultraviolet radiation (UVB, 280-315 nm) and longer (>600 nm) wavelengths of photosynthetically available radiation (PAR, 400-700 nm). On the other hand, the NO2 haze decreases atmospheric transmission in the long-wavelength UVA (315-400 nm) and short-wavelength PAR. Here, we use the results of previous simulations of incident spectral irradiance following an ionizing radiation event to predict changes in terran productivity focusing on photosynthesis of marine phytoplankton. The prediction is based on a spectral model of photosynthetic response, which was developed for the dominant genera in central regions of the ocean (Synechococcus and Prochlorococcus), and on remote-sensing-based observations of spectral water transparency, temperature, wind speed, and mixed layer depth. Predicted productivity declined after a simulated ionizing event, but the effect integrated over the water column was small. For integrations taking into account the full depth range of PAR transmission (down to 0.1% of utilizable PAR), the decrease was at most 2-3% (depending on strain), with larger effects (5-7%) for integrations just to the depth of the surface mixed layer. The deeper integrations were most affected by the decreased utilizable PAR at depth due to the NO2 haze, whereas shallower integrations were most affected by the increased surface UV. Several factors tended to dampen the magnitude of productivity responses relative to increases in surface-damaging radiation, for example, most inhibition in the modeled strains is caused by UVA and PAR, and the greatest relative increase in damaging exposure is predicted to occur in the winter when UV and productivity are low.

Influence of micro- and macro-processes on the high-order harmonic generation in laser-produced plasma

We compare the resonance-induced enhancement of single harmonic and the quasi-phase-matching-induced enhancement of the group of harmonics during propagation of the tunable mid-infrared femtosecond pulses through the perforated laser-produced indium plasma. We show that the enhancement of harmonics using the macro-process of quasi-phase-matching is comparable with the one using micro-process of resonantly enhanced harmonic. These studies show that joint implementation of the two methods of the increase of harmonic yield could be a useful tool for generation of strong short-wavelength radiation in different spectral regions. We compare these effects in indium, as well as in other plasmas.

Towards graphene plasmon-based free-electron infrared to X-ray sources

Rapid progress in nanofabrication methods has fuelled a quest for ultra-compact photonic integrated systems and nanoscale light sources. The prospect of small-footprint, high-quality emitters of short-wavelength radiation is especially exciting due to the importance of extreme-ultraviolet and X-ray radiation as research and diagnostic tools in medicine, engineering and the natural sciences. Here, we propose a highly directional, tunable and monochromatic radiation source based on electrons interacting with graphene plasmons. Our complementary analytical theory and ab initio simulations demonstrate that the high momentum of the strongly confined graphene plasmons enables the generation of high-frequency radiation from relatively low-energy electrons, bypassing the need for lengthy electron acceleration stages or extreme laser intensities. For instance, highly directional 20 keV photons could be generated in a table-top design using electrons from conventional radiofrequency electron guns. The conductive nature and high damage threshold of graphene make it especially suitable for this application. Our electron–plasmon scattering theory is readily extended to other systems in which free electrons interact with surface waves. Scientists theoretically show infrared to X-ray sources that can be implemented on-chip by scattering high-energy electrons with graphene plasmons and predict that they are capable of producing tunable radiation.

Spectral Sensitivity of Thermally Modified and Unmodified Wood

The chemical structure of wood changes significantly during thermal modification, significantly influencing the behaviour of wood during weathering. In this study, the effect of different wavelength ranges on thermally modified and unmodified aspen (Populus tremula L.) wood during solar irradiation was investigated. Irradiation was performed by exposing wood to natural solar irradiation under filters transmitting different wavelength ranges. For both woods, the magnitude of characteristic change (discolouration, changes in reflectance, and chemical composition) clearly depended on the solar wavelength bands, but the trends of the changes differed. For unmodified wood, the magnitude of the characteristic changes increased as the portion of short-wavelength radiation in the light increased. However, UV radiation was not found to be the dominant factor influencing changes in thermally modified wood during solar irradiation. The colour and chemical structure of thermally modified wood changed substantially for all studied irradiation conditions.

Coulomb frustration of the multiphoton ionization of metallic clusters under intense EUV FEL evidenced by ion spectrometry

Free electron laser light sources delivering high intensity pulses of short wavelength radiation are opening novel possibilities for the investigation of matter at the nanoscale and for the discovery and understanding of new physical processes occurring at the exotic transient states they make accessible. Strong ionization of atomic constituents of a nano-sized sample is a representative example of such processes and the understanding of ionization dynamics is crucial for a realistic description of the experiments. We report here on multiple ionization experiments on free clusters of titanium, a high cohesive energy metal. The time of flight ion spectra reveal a saturation of the cluster ionization at ∼1016 photons per pulse per cm2. Our results also show a clear lack of any explosion process, opposite to what is observed for a rare-gas cluster under similar conditions. A simple and generalized multi-step ionization model including Coulomb frustration of the photoemission process effectively reproduces with a good agreement the main features of the experimental observation and points to an interpretation of the data involving a substantial energy deposition into the cluster through electronic system heating upon scattering events within photoemission.

History of Synchrotron Radiation

Although natural synchrotron radiation from charged particles spiraling around magnetic-field lines in space is as old as the stars—for example, the light we see from the Crab Nebula—short-wavelength synchrotron radiation generated by relativistic electrons in circular accelerators is a modern phenomenon. The first observation—literally, since it was visible light that was seen—came at the General Electric Research Laboratory in Schenectady, New York, on April 24, 1947. In the 68 years since, synchrotron radiation has become a premier research tool for the study of matter in all its varied manifestations, as facilities around the world constantly evolved to provide this light in ever more useful forms.

Time lags of the flickering in cataclysmic variables as a function of wavelength

Flickering is a ubiquitous phenomenon in cataclysmic variables (CVs). Although the underlying light source is one of the main contributors to the optical radiation, the mechanism leading to flickering is not understood as yet. The present study aims to contribute to the set of boundary conditions, defined by observations, which must be met by physical models that describe the flickering. In particular, time lags in the occurrence of flickering events at different wavelengths over the optical range are examined. To this end, the cross-correlation functions (CCFs) of numerous light curves of a sample of CVs are analysed that were observed simultaneously or quasi-simultaneously in different bands of various photometric systems. Deviations of the maxima of the CCFs from zero time-shift indicate a dependence of the flickering activity on the wavelength in the sense that flickering flares reach their maxima slightly earlier in the blue range than in the red. While the available observational material does not permit detecting this individually in all observed systems, the ensemble of all data clearly shows this effect. Particularly instructive are the cases of V603 Aql and TT Ari, where time lags of 15.1 sec and 4.3 sec, respectively, are observed between the U and R bands. In principle this can be understood if during the development of a flickering flare the radiation characteristics of the light source responsible for flickering change such that in the early phases of a flare more short-wavelength radiation is emitted, and later on, the peak of the emission shifts to the red. Respective scenarios are discussed and shown to be in qualitative and quantitative agreement with observations.

Linking high harmonics from gases and solids.

When intense light interacts with an atomic gas, recollision between an ionizing electron and its parent ion creates high-order harmonics of the fundamental laser frequency. This sub-cycle effect generates coherent soft X-rays and attosecond pulses, and provides a means to image molecular orbitals. Recently, high harmonics have been generated from bulk crystals, but what mechanism dominates the emission remains uncertain. To resolve this issue, we adapt measurement methods from gas-phase research to solid zinc oxide driven by mid-infrared laser fields of 0.25 volts per ångström. We find that when we alter the generation process with a second-harmonic beam, the modified harmonic spectrum bears the signature of a generalized recollision between an electron and its associated hole. In addition, we find that solid-state high harmonics are perturbed by fields so weak that they are present in conventional electronic circuits, thus opening a route to integrate electronics with attosecond and high-harmonic technology. Future experiments will permit the band structure of a solid to be tomographically reconstructed.

Using the transit of Venus to probe the upper planetary atmosphere.

During a planetary transit, atoms with high atomic number absorb short-wavelength radiation in the upper atmosphere, and the planet should appear larger during a primary transit observed in high-energy bands than in the optical band. Here we measure the radius of Venus with subpixel accuracy during the transit in 2012 observed in the optical, ultraviolet and soft X-rays with Hinode and Solar Dynamics Observatory missions. We find that, while Venus's optical radius is about 80 km larger than the solid body radius (the top of clouds and haze), the radius increases further by >70 km in the extreme ultraviolet and soft X-rays. This measures the altitude of the densest ion layers of Venus's ionosphere (CO2 and CO), useful for planning missions in situ, and a benchmark case for detecting transits of exoplanets in high-energy bands with future missions, such as the ESA Athena.

Heat transfer in microcellular polystyrene/multi-walled carbon nanotube nanocomposite foams

We report the heat-transfer characteristics of polystyrene (PS)/multi-walled carbon nanotube (MWCNT) nanocomposite foams with a large expansion ratio (18-fold) and a microcellular cell size (5μm) that have never been achieved before. These PS/MWCNT foams exhibited excellent thermal insulation performance even without insulation gas. The 5μm-sized cells in these PS/MWCNT foams are small enough to induce Knudsen effect, and also lead to a distinct radiation behavior that has never been reported; that is, because of the unique synergy of the small cells and the MWCNTs, the short wavelength radiation below the cell size is 100% blocked while the long wavelength radiation over the cell size is strongly attenuated. We made an in-depth analysis of the heat transfer through the PS/MWCNT foams using models. Adding 2wt% MWCNTs into the PS matrix, 86% of the radiative thermal conductivity was effectively blocked, and the radiative contribution was reduced to 3.5% of the total thermal conductivity. However, the MWCNTs increased the solid conductivity of the PS/MWCNT foams due to their inherently high thermal conductivity. So, a compromised content of 1wt% MWCNTs was added to optimize solid conduction and radiation, and thereby to minimize the total thermal conductivity to 32.8mW/mK.