Characteristics of a multi-keV monochromatic point x-ray source based on vacuum diode with laser-produced plasma as cathode

Temporal, spatial and spectral characteristics of a multi-keV monochromatic point x-ray source based on vacuum diode with laser-produced plasma as cathode are presented. Electrons from a laser-produced aluminium plasma were accelerated towards a conical point tip titanium anode to generate K-shell x-ray radiation. Approximately 10₁₀ photons/pulse were generated in x-ray pulses of ∼18 to ∼28 ns duration from a source of ∼300 μm diameter, athυ = 4.51 keV (K _α emission of titanium), with a brightness of ∼10²⁰ photons/cm²/s/sr. This was sufficient to record single-shot x-ray radiographs of physical objects on a DEF-5 x-ray film kept at a distance of up to ∼10 cm.     

Formation of a plane layer of plasma under irradiation by a soft X-ray source

We investigate theoretically the formation of a plasma in a plane layer of polymer foam (density ρ = 0.002 g/cm³ and thickness 800 μm) under the action of an external source of soft X-ray radiation under the conditions of PHELIX experiments. The incident flux is assumed to have a Planck’s distribution over the spectrum with T _rad = 20–40 eV. In numerical calculations, the flux of incident X-ray radiation and the spectral constants of the target substance are varied. The action of an external X-ray radiation source on a low-density foam substance with a density of 2 mg/cm³ causes a plasma to be formed with relatively homogeneous profiles of density and temperature T = 15–35 eV. Absorption of externalradiation energy is distributed in the volume. The plasma temperature increases with increase in the external energy, and the energy passed through the plasma also increases. The results prove to be sensitive to the values of optical constants used in numeral simulation. The spectral flux of external radiation passed through the plasma is chosen as a criterion of correctness of the optical constants used in the calculations. In future experiments using the PHELIX facility, we plan to investigate the slowing-down of an ion beam in a plasma formed as a result of indirect heating of low-density polymer triacetate cellulose (TAC) foam with densities ρ = 0.001–0.01 g/cm³ under the action of a pulse of X-ray radiation, into which the laser radiation is preliminarily transformed.     

Microwave energy channeling in plasma waveguides created by a high-power UV laser in the atmosphere

The grazing mode of microwave propagation in a hollow plasma waveguide formed by ionization of atmospheric air with a small easily ionized additive by strong UV pulses of the Garpun KrF laser (λ = 248 nm, the pulse duration and energy are ∼70 ns and ∼50 J) was experimentally demonstrated for the first time. The annular laser beam produced a hollow tube ∼10 cm in diameter with an electron density of ∼10¹² cm⁻³ in a plasma wall ∼1 cm thick, over whichmicrowave radiation with λ _mw ∼ 8 mm was transmitted to a distance of 60 m. Themicrowave signal transmitted by the waveguide was amplified by a factor of 6 in comparison with propagation in free space.     

Optical characteristics of a transverse discharge in neon at atmospheric pressure

We present the results of investigation into radiation of a pulsed transverse discharge in neon at a pressure of 10–200 kPa. Survey spectra of plasma radiation, time characteristics of radiation, and the effect of small impurities of water vapors and air on the optical characteristics of a neon plasma were studied. We show that at a pressure of residual gases at a level of 10 Pa intense OH*, NO*, and N _* ² bands are observed in radiation of the plasma of a nanosecond transverse discharge in Ne against the background of continuous plasma radiation, and in the spectral region with λ>400 nm radiation was observed on the H_β 486.1 nm and NeI 585.3 nm lines, and (when P≥100 kPa) on the line at the 3s–3p-transitions of a Ne atom. The radiation intensity of the third continuum of neon increases with pressure and with energy contribution to plasma, with its maximum being located in the VUV spectral region (λ _max <200 nm). To whom correspondence should be adressed. Uzhgorod State University, 46, Pidgirna St., Uzhgorod, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 1, pp. 5–10, January–February, 1999.     

Radiation processes in impulse cesium plasma of high pressure

Dependence of spectral and energy characteristics of cesium plasma radiation on electric power P _L has been found. It is shown that with P _L growth metal vapor pressure increases; transformation of spectral structure of radiation manifested in disappearance of individual lines and increase of steady monotone takes place. Redistribution of average radiation power in individual spectral ranges is observed.     

Output characteristics and parameters of the plasma from a gas-discharge low-pressure ultraviolet source using helium-iodine and xenon-iodine mixtures

The output characteristics and parameters of the plasma of a powerful gas-discharge source of UV radiation are studied. The UV source uses He-I₂ and Xe-I₂ mixtures and is excited by a longitudinal glow discharge. The pressure of the gas mixtures is varied from 100 to 1500 Pa, and the discharge power falls into the range 15–250 W. The source (lamp) emits in the spectral interval 200–390 nm, which covers the spectral line of the iodine atom at 206.2 nm, the spectral band of XeI(B-X) with a maximum at 253 nm, and the spectral band of with a maximum at 342 nm. For He(Xe)-I₂ mixtures at a pressure of 800–1000 Pa (this pressure range is near-optimal according to our experimental data), the electron energy distribution functions and the electron kinetic coefficients as functions of parameter E/N (E is the electric field strength, and N is the particle concentration in the discharge) are calculated. The calculated plasma parameters are used in the qualitative analysis of key electronic processes in the plasma of an exciplex halogen UV source and will be subsequently employed in numerical simulation of the process kinetics and output characteristics of a UV source based on helium-iodine or xenon-iodine mixtures.     

Reaction48Ca (p,n)48Sc fromE p =1.885 to 5.1 MeV

The total (p, n) reaction cross section for⁴⁸Ca has been measured as a function of proton energy in the energy range 1.885 to 5.100 MeV with an overall resolution of ∼ 2 keV and in ∼ 5 keV energy steps. The fluctutions in fine resolution data have been analysed to determine the average coherence width 〈Γ〉. The excitation function averaged over large energy intervals has been analyzed in terms of the optical model. The isobaric analogue resonances atE _p ∼ 1.95 and 4 MeV have been shape-analyzed to extract the proton partial width and the spectroscopic factorS _n . A comparison of the gross structures observed in ∼ 55 keV averaged excitation function with the predictions of Izumo’s partial equilibrium model has also been made.     

Excitation of X rays by electrons accelerated in air in the wake wave of a laser pulse

The characteristics of X rays of a laser plasma generated in the interaction of a femtosecond pulse with solid targets in an air atmosphere have been investigated. It has been shown that the mechanism for the generation of X rays in the interaction of short intense laser pulses with solid targets in a gas atmosphere is attributed to the generation of fast electrons in the region of the filamentation of a laser pulse. It has been proven experimentally that under such conditions, the solid target irradiated by laser radiation of even a low density of about 10¹⁵ W/cm² very efficiently emits ∼10-keV photons. It has been shown theoretically that the maximum energy of accelerated electrons can reach ɛ_max ∼ 100–200 keV under these conditions. This means that the proposed method can provide characteristic radiation with the energy of photons much higher than 10 keV.     

Effect of ionizing irradiation on the mechanism of current passage in TlInSe<Subscript>2</Subscript> single crystals

The temperature dependence of the electrical conductivity and current-voltage characteristics of γ-irradiated TlInSe₂ single crystals with an electrical resistivity of ∼10⁸ Ω cm have been investigated. It has been established that the anomalies of the conductivity observed in weak electric fields and at low dozes of irradiation are related to the decomposition of neutral complexes containing an interstitial cation atom. In strong electric fields, a thermal-field ionization of traps occurs. The main mechanism of radiation defect formation is the formation of complexes [V _In⁻In _i ⁺], [V _Se⁻Se _i ⁻], and others with the structural defects characteristic of unirradiated crystals. The activation energy, trap concentrations, and the potential well shape near the traps have been determined.     

Plasma parameters in the upgraded Trimyx-M Galathea

Results are presented from measurements of the plasma parameters in the upgraded Trimyx-M Galathea. After the barrier magnetic field and the energy of the injected hydrogen plasma bunch were increased to B _bar ∼ 0.1 T and W ₀ ≈ 200 J, respectively, the following plasma parameters were achieved: the density n ∼ 5 × 10¹³ cm⁻³, the plasma confinement time τ* = 800–900 μs, the elergy of the confined plasma W ₁ ∼ 100 J, the ratio of the plasma pressure to the barrier magnetic pressure β ₀ ∼ 0.2, the electron temperature T _e ∼ 20 eV, and the ion temperature T _i ∼ 2T _e . The maximum time during which the plasma density decreased e-fold, τ _p , was found to be 300 μs at B _bar = 0.1 T, which agrees with the classical transport model.     

Length of formation of processes in a constant external field at high energies

The complex time method is used to show that length l _C of formation of processes involving emission of photons and production of pairs in a constant external field can be determined correctly and that the resultant values of l _C have not only qualitative, but also quantitative meaning. Analysis based on the complex time method makes it possible to express the amplitudes of processes in the form of rapidly converging integrals. It is found that the radiation formation length for low-energy (soft) photons decreases upon an increase in the radiation frequency in accordance with the familiar law l _C ∼ ω^−1/3, while for higher frequencies, this dependence changes to l _C ∼ ω^−1/2. The formulas derived for l _C make it possible to indicate the accuracy with which this quantity can be treated as the radiation formation length.     

RF exciplex halogen source of UV radiation on an argon-xenon-chlorine mixture

An exciplex halogen source of UV radiation that is excited by an rf transverse discharge is studied experimentally. The active medium of the source is an Ar-Xe-Cl₂ mixture kept at a low pressure (100–1000 Pa), and its working spectral range is 220–450 nm. The radiation spectrum contains 235 nm XeCl(D-X), 257 nm Cl₂(D′-A′), 306 nm XeCl(B-X), 390 nm XeCl(C-A), and 430 nm XeCl(B-A) lines. The results of optimization of the UV power as a function of the pressure, Ar-Xe-Cl₂ mixture composition, and excitation power are reported.     

Study of opto-mechanical characteristics of interaction of ultrashort laser pulses with polymer materials

The opto-mechanical characteristics, such as the specific mechanical recoil momentum, the specific impulse, and the energy efficiency, of the laser ablation of flat polymer targets ((C₂F₄) _n , (CH₂O) _n ) have been determined experimentally for the first time for the case of excitation with femtosecond pulses (τ ∼ 45–70 fs) of UV-IR (λ ∼ 266, 400, 800 nm) laser radiation (I ₀ up to 10¹⁵ W/cm²) under normal atmospheric and vacuum (p ∼ 10⁻⁴ mbar) conditions. The efficiency of mechanical recoil momentum generation is analyzed for various regimes of the laser irradiation.     

Electrical and optical characteristics of inert-gas plasmas in spatially nonuniform electrode systems

The characteristics of unipolar and bipolar corona discharges in mixtures He/Ar/Kr, He/Ar/Xe, and He/Kr/Xe at atmosphere pressures in electrode systems of the point-plane and point-grid type distributed along the length. It is shown that bipolar corona discharges can be used in the preionization systems of high-pressure inert-gas-atom lasers. The spectral characteristics of the plasma are investigated, and the dependence of the relative intensity of the radiation in the lines Ar(4s-4p), Kr(5s-5p), and Xe(6s-6p) on the composition and pressure of the working mixtures and on the value of the corona discharge current are determined. Zh. Tekh. Fiz. 67, 15–18 (November 1997)     

Synchrotron radiation interference in front of the silicon absorption edge for silicon-on-insulator structures

The synchrotron radiation (SR) interference phenomenon has been for the first time observed in a strained silicon nanolayer deposited on a dielectric SiO₂ layer (∼150 nm) on Si (100) single crystalline substrates (silicon-on-insulator (SOI) structures). Strong oscillations of spectra intensity depending on photon energy have been detected in the energy range preceding the elementary silicon Si L _2,3 absorption edge (≤100 eV) at grazing angles of SR smaller than 21° in the X-ray photoeffect quantum yield structure. The phase of the spectra oscillation structure is reversed for small variations of grazing angle in the 4°–21° range. The silicon nanolayer thickness (∼180 nm) has been estimated in the three-layer, Si nanolayer-SiO₂-Si substrate structure with the use of neighbor maxima positions of ultrasoft X-ray radiation interference in XANES (X-ray absorption near edge structure) spectra. A decrease in the crystal lattice parameter of a strained silicon layer along the normal to substrate has been determined by X-ray diffraction. An increase in the Si-Si interatomic distances in the strained silicon nanolayer lattice of SOI structure has been found using ultrasoft X-ray emission spectroscopy data.     

Investigation of Rb <Emphasis Type="Italic">D</Emphasis><Subscript>1</Subscript> atomic lines in strong magnetic fields by fluorescence from a half-wave-thick cell

It has been experimentally demonstrated that the use of the effect of significant narrowing of the fluorescence spectrum from a nanocell that contains a column of atomic Rb vapor with a thickness of L = 0.5λ (where λ = 794 nm is the wavelength of laser radiation, whose frequency is resonant with the atomic transition of the D ₁ line of Rb) and the application of narrowband diode lasers allow the spectral separation and investigation of changes in probabilities of optical atomic transitions between levels of the hyperfine structure of the D ₁ line of ⁸⁷Rb and ⁸⁵Rb atoms in external magnetic fields of 10–2500 Gs (for example, for one of transitions, the probability increases ∼17 times). Small column thicknesses (∼390 nm) allow the application of permanent magnets, which facilitates significantly the creation of strong magnetic fields. Experimental results are in a good agreement with the theoretical values. The advantages of this method over other existing methods are noted. The results obtained show that a magnetometer with a local spatial resolution of ∼390 nm can be created based on a nanocell with the column thickness L = 0.5λ. This result is important for mapping strongly inhomogeneous magnetic fields.     

γ-irradiation effect on transparent conducting ZnO:Ga films

Transparent and conducting pure and Ga-doped ZnO films prepared by e-beam evaporation in vacuum were irradiated at room temperature by Co⁶⁰ radiation source with the γ-photon average energy of 1.25 MeV and with different doses up to ∼600 kGy. The energy band gap E _g, electrical resistivity, carrier density as well as the structure parameters of pure and doped ZnO films versus the impurity content and γ-doses were determined in order to estimate the radiation-induced degradation effect on ZnO-based films used as transparent electrodes for electro-optical device applications.     

Dynamics of plasma formation during quasicontinuous laser irradiation of metals in high-pressure nitrogen atmospheres

This is a study of target destruction and the dynamics of surface plasma formation during the interaction of quasicontinuous laser radiation (λ = 1.06 μm, q = 1–7 MW/cm², τ ∼ 1.5 msec) with D16T duraluminum and bismuth in nitrogen atmospheres at pressures p = 1–20 atm. High speed photography and spectroscopy of the erosion plasma flare are used to determine the onset time for vaporization of the target, as well as the times of appearance of erosion and nitrogen plasmas for different gas pressures and laser energy fluxes q. The emergence of the plasma front from the vapor zone into the surrounding nitrogen is detected experimentally and the properties of the nitrogen plasma are studied.     

Luminescence and lasing properties of neodymium- and uranium-activated inorganic laser liquids

An attempt was made to describe and show the possibilities of new inorganic neodynium- and uranium-activated laser liquids: SO₂-GaCl₃-NdCl₄; SO₂Cl₂-GaCl₃-NdCl₃-UO₂Cl₂; POCl₂-MCl_n-NdCl₃-UO₂Cl₂ for development and synthesis of direct nuclear reaction-excited lasers. Luminescence data presented in the work were used to calculate the luminescence parameters of the laser liquids such as oscillator strengths f, probability of spontaneous radiation A, intermultiplet luminescence branching coefficient β, cross-section for induced radiation σ, luminescence decay time τ, quantum yield η, and others. It is shown that the oscillator strengths of the normal absorption bands of Na³⁺, which play the main part in the pumping processes, exceed the oscillator strengths of Na³⁺ for aqueous and many other nonaqueous systems. In the luminescence excitation spectra of the Na³⁺ ion, bands are isolated in the range 400–1000 nm atλ _rec =1.06 μm. With excitation, luminescence occurs through the⁴F_3/2→⁴I_{9/2,11/2.13/2} channels. Luminescence spectral data are related to the lasing parameters. The threshold lasing energy is∼18 J/cm³. For a resonator with mirros h₁=100% and h₂=20, 40, 56, and 80%, the lasing energy is∼20–120 MJ/cm³ in the pumping energy range 18–180 J/cm³. The differential efficiency is ∼0.2% The substantial angular radiation divergence (θ∼4·10⁻² rad) and strong thermostatic distortions that occur in the active element (dn/dT≈−1.9·10⁻⁴K⁻¹) are a disadvantage of laser liquids. It is shown that operation of neodymium- and uranium-activated inorganic liquid lasers is stable under the present conditions. A. I. Gertsen Russian State Pedagogical University, Moika Embankment, 48, St. Petersburg, 191186, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 5, pp. 607–619, September–October, 1997.     

Measurement of cross-section of excitation transfer from 3s2 to 4s1 and 5s1 energy levels of neon

Collision induced non-radiative transitions in neon plasma have been studied using high intra-cavity radiation field of a 633 nm He-Ne laser. The transitions, induced from 3s ₂ energy level to 4s₁ and 5s₁ groups of energy levels, have been detected as changes in intensities of the spectral lines originating from these energy levels. From these intensity measurements, the quantities governing the transitions i.e. (i)S ₃ ^e /S _3RT , the ratio of the probabilities of electronic deexcitation to the total radiative deexcitation of energy level 3 (ii) 〈r ₂₃ ^e v _e〉, rate of excitation transfer per particle and (iii)S ₂₃ ^e , the total probability for excitation transfer from level 2 to level 3 at a certain value of electron density have been calculated.