Amplification Of Radiation Research Articles

Mesoporous Photonic-Crystal Films for Amplification and Filtering of Electromagnetic Radiation

We consider optical properties of mesoporous aluminum-oxide-based photonic crystal films, derive the dispersion relation for electromagnetic waves, obtain the effective refractive index of the photonic crystal, and determine group velocities and effective masses of photons and polaritons in the mesoporous media. We compare the reflection spectra calculated with the experimental results. We discuss the potential for using mesoporous photonic-crystal films as amplifiers of electromagnetic radiation, high-efficiency selective mirrors, and optical filters.

Generation of auroral kilometric radiation by a finite-size source in a dipole magnetic field

Generation, amplification, and propagation of auroral kilometric radiation in a narrow three-dimensional plasma cavity in which a weakly relativistic electron beam propagates is studied in the geometrical optics approximation. It is shown that the waves that start with a group velocity directed earthward and have optimal relation between the wave vector components determining the linear growth rate and the wave residence time inside the amplification region undergo the largest amplification. Taking into account the longitudinal velocity of fast electrons results in the shift of the instability domain toward wave vectors directed to the Earth and leads to a change in the dispersion relation, due to which favorable conditions are created for the generation of waves with frequencies above the cutoff frequency for the cold background plasma at the wave generation altitude. The amplification factor for these waves is lower than for waves that have the same wave vectors but are excited by the electron beams with lower velocities along the magnetic field. For waves excited at frequencies below the cutoff frequency of the background plasma at the generation altitude, the amplification factor increases with increasing longitudinal electron velocity, because these waves reside for a longer time in the amplification region.

Parametric amplification of broadband radiation of a cw superluminescent diode under picosecond pumping

It is proposed to use cw superluminescent diodes with a spectral width of about 300 and high spatial coherence as seed radiation sources in parametric amplifiers with picosecond pumping in order to form broadband picosecond pulses. A two-cascade parametric amplifier based on (BBO) crystals is pumped by pulses of the second harmonic of an Nd : YAG laser. For a superluminescent diode spectral width of (centre wavelength ), the spectral width of picosecond pulses at the parametric amplifier output is . At a total pump energy of for BBO crystals, the energy of the enhanced emission of the superluminescent diode is found to be .

Amplification of Electromagnetic Pulses by Photoionized Plasma

We consider the conditions of aperiodic instability appearance in photoionized plasma produced at the impact of a pulse of circularly polarized radiation on the gas. We show the possibility of electromagnetic radiation amplification under reflection by photoionized plasma. We give a comparative analysis of amplification patterns taking place in hydrodynamic and kinetic description of the photoelectrons dynamics.

Terahertz radiation generation process in the medium based on the array of the noninteracting nanotubes

Consideration of periodically alternating arrays of noninteracting carbon nanotubes with the metal type of conductivity as elements of the quantum layer heterostructures (quantum wells), which will play the role of the active field, is suggested. From the earlier obtained results based on the models of the elementary cell, it follows that the system in the neighborhood of the Dirac points at the presence of the longitudinal electric field will have equidistant spectrum. The eigenvalues of the energies do not depending on the longitudinal electric field. The two-component eigenfunctions do not depend on the longitudinal electric field. The amplification of the generation terahertz radiation by the analogy with the cascade lasers in the multilevel medium, based on the system of the noninteracting metallic carbon, is considered. If concentration of the nanotubes is 107 cm−2 then the output power per unit area will be about \(Q \sim n_{0} k_{0} \hbar \omega J_{k} /e \approx 8\;{\text {W}}/{\text {cm}}^{2}\). The wavelength of the terahertz radiation is 65 µm.

Generation of phase - matched coherent point source in plasma media by propagated X-ray laser seeded beam

There is a significant interest in developing the coherent table-top X-ray lasers. Advent of plasma-based transient collisional excitation x-ray laser and particular, injection of coherent seeded beam, especially high-order harmonics, has tremendously improved the spatial coherence of such lasers, what allowed them to be the same widely used as synchrotron sources. Here we report experimental founding of unknown interference structure in a spatial profile of the output beam of the two-stage plasma X-ray laser. That allowed us experimental and theoretical discovering a new phenomenon consisted in a generation of phase-matched coherent point source in a laser plasma media by propagated X-ray laser seeded beam. This phenomenon could extend the applications of such x-ray lasers. For explanation of the observed phenomenon a new method of solving the standard system of Maxwell-Bloch equations has been developed. It was found that the interference pattern in the output laser beam was formed due to an emergence of phase-matched coherent virtual point source in the XRL amplifier and could be treated as the first observation of mirage phenomenon, analogous to the optical mirage, but in X-rays. The obtained results bring new comprehension into the physical nature of amplification of X-ray radiation in laser-induced plasma amplifiers and opening new opportunities for X-ray interferometry, holography and other applications, which requiring multiple rigidly phased sources of coherent radiation.

XUV lasing during strong-field-assisted transient absorption in molecules

Using ab-initio non-Born-Oppenheimer simulations, we demonstrate amplification of XUV radiation in a high-harmonic generation type process using the example of the hydrogen molecular ion. A small fraction of the molecules is pumped to a dissociative Rydberg state from which IR-assisted XUV amplification is observed. We show that starting at sufficiently high IR driving field intensities the ground state molecules become quasi-transparent for XUV radiation, while due to stabilization gain from Rydberg states is maintained, thus leading to lasing from strongly driven Rydberg states. Further increase of the IR intensity even leads to gain by initially unexcited molecules, which are quickly excited by the driving IR pulse.

Propagation and amplification of microwave radiation in a plasma channel created in gas by a high-power femtosecond UV laser pulse

The time evolution of a nonequilibrium plasma channel created in a noble gas by a high-power femtosecond KrF laser pulse is investigated. It is shown that such a channel possesses specific electrodynamic properties and can be used as a waveguide for efficient transportation and amplification of microwave pulses. The propagation of microwave radiation in a plasma waveguide is analyzed by self-consistently solving (i) the Boltzmann kinetic equation for the electron energy distribution function at different spatial points and (ii) the wave equation in the parabolic approximation for a microwave pulse transported along the plasma channel.

Variability in solar irradiance observed at two contrasting Antarctic sites

The features of erythemally weighted (EW) and short-wave downwelling (SWD) solar irradiances, observed during the spring–summer months of 2007–2011 at Johann Gregor Mendel (63°48′S, 57°53′W, 7m a.s.l.) and Dome Concordia (75°06′S, 123°21′E, 3233m a.s.l.) stations, placed at the Antarctic coastal region and on the interior plateau respectively, have been analysed and compared to each other. The EW and SWD spectral components have been presented by the corresponding daily integrated values and were examined taking into account the different geographic positions and different environmental conditions at both sites. The results indicate that at Mendel station the surface solar irradiance is strongly affected by the changes in the cloud cover, aerosols and albedo that cause a decrease in EW between 20% and 35%, and from 0% to 50% in SWD component, which contributions are slightly lower than the seasonal SWD variations evaluated to be about 71%. On the contrary, the changes in the cloud cover features at Concordia station produce only a 5% reduction of the solar irradiance, whilst the seasonal oscillations of 94% turn out to be the predominant mode. The present analysis leads to the conclusion that the variations in the ozone column cause an average decrease of about 46% in EW irradiance with respect to the value found in the case of minimum ozone content at each of the stations. In addition, the ratio between EW and SWD spectral components can be used to achieve a realistic assessment of the radiation amplification factor that quantifies the relationship between the atmospheric ozone and the surface UV irradiance.

Large polarization squeezing in non-degenerate parametric amplification of coherent radiation

Polarization squeezing is shown to occur in non-degenerate parametric amplification of coherent light and the degree of squeezing at interaction time $T$ can be as large as $1-e^{-2T}$. This gives $86.4\%$ polarization squeezing for $T=1$ and $98.2\%$ for $T=2$. One simple case when this occurs is on taking initially plane polarized light having equal amplitudes in the two modes that finally has equal intensities of two circular polarizations. This suggest the experimental settings of parameters to achieve this extent of polarization squeezing in coherent light.

グラフェンのテラヘルツオプトエレクトロニクス

Graphene has attracted considerable attention due to its extraordinary carrier transport, optoelectronic, and plasmonic properties originated from its gapless and linear energy spectra enabling various functionalities with extremely high quantum efficiencies that could never be obtained in any existing materials. This paper reviews recent advances in graphene optoelectronics particularly focused on the physics and device functionalities in the terahertz (THz) electromagnetic spectral range. Optical response of graphene is characterized by its optical conductivity and nonequilibrium carrier energy relaxation dynamics, enabling amplification of THz radiation when it is optically or electrically pumped. Current-injection THz lasing has been realized very recently. Graphene plasmon polaritons can greatly enhance the THz light and graphene matter interaction, enabling giant enhancement in detector responsivity as well as amplifier/laser gain. Graphene-based van der Waals heterostructures could give more interesting and energy-efficient functionalities.

The comparative analysis of observational series of total ozone content and UV-B radiation in boreal forest zones

Results of the comparative analysis of observational series of the total ozone content and UV radiation of the 300–315-nm wavelength band at stations located in boreal forest zones of midlatitudes of Russia and Canada (Northern Hemisphere, 50° N and higher) are presented. It is shown that the ozonosphere is a primary modulator of the biologically active part of UV-B radiation in this climatic zone. Radiation amplification factors of solar UV-B spectral region are determined. It is shown that 20% of total ozone depletion increases more than twofold the dose of the short-wave part of solar UV-B radiation relative to its climatic normal.

E-beam sustained plasma as a medium for the amplification of electromagnetic radiation in the subterahertz frequency band

It is demonstrated that low-temperature weakly-ionized nonequilibrium plasma created by a high-energy electron beam in gases (gas mixtures) with the Ramsauer minimum in a transport cross section and the effective attachment of slow electrons can be used as a medium for the amplification of electromagnetic radiation in the subterahertz frequency band. An analysis of the electron energy distribution function (EEDF) in a Xe : F2 mixture is performed. An energy interval with a growing EEDF is found to exist in such a mixture. Such an interval provides the existence of the population inversion of the electron spectrum in the continuum and is responsible for the positive value of a gain factor for microwave radiation. A gain factor depending on amplified radiation frequency and plasma parameters is analysed.

Abstract C147: Radiosensitization using gold nanoparticles for effectively targeting molecular pathways in cancer radiation therapy

Abstract The use of nanoparticles with high atomic (Z) number have been known to attenuate X-rays and gold nanoparticles (GNPs) have established themselves as potent radiosensitizer to significantly enhance Radiotherapy (RT) treatment. The understanding of the biochemical pathways accompanying GNPs radiation amplification can provide information on the molecular pathways relevant to therapeutic efficacy and thus will pave the way for designing novel therapeutic platforms by targeting these pathways. However, there are significant limitations in the ability to deliver sufficiently potent concentration of GNPs to tumor cells and currently there is very limited understanding of the biology of the radiosensitization using GNPs. Thus, to improve the efficacy of radiosensitization and subsequently study the impact of radiosensitization on biochemical pathways, we have fabricated a new generation of targeted GNPs formulation. These ultrasmall 2-3 nm gold nanoparticles were functionalized with hetero-bifunctional PEG, imaging agent- AlexaFlour 647 and targeting peptide- RGD. The in vitro studies showed a robust uptake of these GNPs in different cancer cells lines and clonogenic survival assays have demonstrated a 2.8-fold cell kill enhancement with X-rays in HeLa cell line. To evaluate that these GNPs are targeted to the tumor site, we have injected these nanoparticles via different routes in two different tumor animal models and studied the uptake using in vivo optical imaging. The imaging studies showed highly specific tumor uptake in tumor endothelial cells in orthotopic pancreatic tumor mice model injected intravenously with RGD targeted GNPs. The administration of same RGD targeted GNPs formulation via inhalation/instillation (INH) route as opposed to customary intravenous (i.v) route was studied in transgenic lung cancer mice model. Fluorescence imaging and ex-vivo electron microcopy results showed a significantly higher concentration of GNPs (4.7 times) in the lung tumors of mice when using INH delivery compared to i.v. approach. Further, to understand the radiobiology of GNPs in vitro, we have studied the protein expression of γH2aX and RAD51 using western blots. The studies involving the radiation induced alterations in presence of GNPs to study the impact on cell cycle and DNA damage/repair are currently underway. The studies will help identify the specific pathways that are critical to GNP radiotherapy which can be targeted subsequently to further boost the efficacy of GNP radiotherapy. This work is supported by ARMY/ W81XWH-12-1-0154, NSF DGE 0965843, HHS/5U54CA151881-02, NCI R03CA164645, NCI1 K01CA17247801, the Electronics Materials Research Institute at Northeastern University, and Brigham and Women's Hospital. Citation Format: Rajiv Kumar, Jodi Belz, Ilanchezhian Shanmugam, Wilfred Ngwa, Ross Berbeco, Mike Makrigiorgos, Srinivas Sridhar. Radiosensitization using gold nanoparticles for effectively targeting molecular pathways in cancer radiation therapy. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr C147.

Sensitivity of UV Erythemal Radiation to Total Ozone Changes under Different Sky Conditions: Results for Granada, Spain.

This study focuses on the analysis of the sensitivity of UV erythemal radiation (UVER) to variations in the total ozone column (TOC) under different sky conditions at Granada (southeastern Spain). The sensitivity is studied both in relative terms by means of the Radiation Amplification Factor (RAF) and in absolute terms using the Ozone Efficiency (OE). These two variables are determined for diverse sky conditions characterized by the cloud cover information given by a sky camera (in oktas) and the cloud optical depth (COD) estimated from global solar radiation measurements. As expected, in absolute terms, the TOC variations cause substantially smaller UVER changes during completely overcast situations than during cloud-free cases. For instance, the OE (SZA = 30°, TOC = 290 DU) decreases from 0.68 mW m(-2) per unit of TOC (0 oktas) to 0.50 mW m(-2) per unit of TOC (8 oktas). However, the opposite is observed when the analysis is performed in relative terms. Thus, the RAF (determined for SZA cases below 80°) increases from 1.1 for cloud-free cases (0 oktas) to 1.4 for completely overcast situations (8 oktas). This opposite behavior is also found when both RAF and OE are analyzed as functions of COD. Thus, while the OE strongly decreases with increasing COD, the RAF increases as COD increases.

Superradiant amplification of terahertz radiation by plasmons in inverted graphene with a planar distributed Bragg resonator

It is shown theoretically that stimulated generation of terahertz radiation by plasmons in graphene with a planar distributed Bragg resonator is possible at two different frequencies for each plasmon mode. This behavior may be attributed to the superradiance of the collective plasmon mode, which is associated with superlinear increase in the radiative damping of the plasmons with increase in pumping power. As a result, the curves of the radiative damping and the plasmon gain as a function of the pumping power intersect at two points corresponding to different generation conditions.

Leaky unstable modes and electromagnetic radiation amplification by an anisotropic plasma slab

The interaction between electromagnetic radiation and a photoionized plasma slab with an anisotropic electron velocity distribution is studied. It is shown that the fields of leaky modes are amplified due to the development of aperiodic instability in the slab, which leads to an increase in both the reflected and transmitted fields. The transmitted field can significantly increase only if the slab thickness does not exceed the ratio of the speed of light to the electron plasma frequency, whereas there is no upper bound on the slab thickness for the reflected signal to be amplified.

Nonthermal Microwave Emission Features under the Plasma Ohmic Heating and Low-hybrid Current Drive in the FT - 2 Tokamak

Study of behavior of accelerated electrons (AE) in the ohmically heated (OH) plasma and low-hybrid current drive (LHCD) in tokamak has the practical interest especially for estimations of AE radiation energy losses and solving of the non-inductive CD problem for the ITER. Studies based on measurements of non-thermal microwave radiation (MR) intensity and hard X-ray (HXR) spectra are conducted in the FT-2 tokamak having large local magnetic ripples under LHCD in the omically heated (OH) plasma with the fan instability excited. The paper presents experimental data first obtained in such conditions witnessing about some AE behavior features. Nature of MR abnormal intensity and short giant flashes together with the fast additional electron heating in the plasma core are discussed. The first high additional fast electron heating was registered together with the synchrotron radiation (SR) intensity increase. It was accompanied by short MR spikes observed in the narrow frequency range (53 ÷ 78) GHz. They arise owing to the AE transverse energy and pitch angle increase under each crossing the cyclotron auto-resonance region and SR maser gain. It is proposed the heating mechanism owing to absorption of SR and Bernstein waves arising at linear transformation the extraordinary component of intensive MR spikes in the black plasma layers. It was found that the non-thermal MR of abnormal intensity arising during OH in the frequency range (10 ÷ 40) GHz is due to the fan instability development and the substantial local magnetic ripples. MR is accompanied by short giant flashes having a narrow frequency spectrum. Together with the SR growth the less intensive MR flashes appear in the range (57 ÷ 75) GHz. In our case it becomes possible the maser amplification of both SR and collective radiation. Appearance of the giant flashes may be initiated under transition of the maser - amplifier into the self - excitation regime, when low-frequency quasi- coherent MR flashes are generated.

Characterisation of <i>J</i>(O<sup>1</sup>D) at Cape Grim 2000–2005

Abstract. Estimates of the rate of production of excited oxygen atoms due to the photolysis of ozone (J(O1D)) have been derived from radiation measurements carried out at Cape Grim, Tasmania (40.6° S, 144.7° E). The individual measurements have a total uncertainty of 16 % (1σ). These estimates agree well with model estimates of clear-sky photolysis rates. Observations spanning 2000–2005 have been used to quantify the impact of season, clouds and ozone column amount. The annual cycle of J(O1D) has been investigated via monthly means. These means show an interannual variation (monthly standard deviation) of 9 %, but in midsummer and midwinter this reduces to 3–5 %. Variations in solar zenith angle and total column ozone explain 86 % of the observed variability in the measured photolysis rates. The impact of total column ozone, expressed as a radiation amplification factor (RAF), is found to be ~ 1.53, in agreement with model estimates. This ozone dependence explains 20 % of the variation observed at medium solar zenith angles (30–50°). The impact of clouds results in a median reduction of 30 % in J(O1D) for the same solar zenith angle range. Including estimates of cloudiness derived from long-wave radiation measurements resulted in a statistically significant fit to observations, but the quality of the fit did not increase significantly as measured by the adjusted R2.

Optical amplification using surface plasmon resonance with total internal reflection

The surface plasmon enhanced optical amplification is proposed, designed and simulated in Kretschmann geometry formed by a 500μm thick, 10mm long and 5mm wide BK7 parallel slab and 29nm thin gold layer which is sandwiched between the said parallel slab and 20nm thin GaAs layer. This GaAs layer is pumped by 1319nm higher order Gaussian beam of a Nd:YAG laser, which passes through a cylindrical lens thereby generating a high aspect ratio elliptical cross section to attain intensity dependent negative extinction coefficient on that 3mm long strip of irradiated GaAs. The negative extinction coefficient of GaAs layer facilitates the amplification of the incident optical radiation at 1550nm within the communication window. Here the incident pulsed optical radiation of 5mW is amplified to 274MW through external pumping and surface plasmon resonance phenomenon by total internal reflection with three bounces along the length of said BK7 parallel slab considering the Goos–Hänchen shift at the slab-Au layer interface and slab-air interface.