A study of molybdenum radiation from alcator A

Radiation emitted by molybdenum impurity ions in the Alcator A tokamak has been investigated. A grazing incidence monochromator photometrically calibrated against synchrotron radiation was used to determine absolute brightnesses of emission lines and the role of molybdenum radiative losses in the plasma discharge power balance. At line average electron densities of 3 × 10¹⁴ cm^?3, molybdenum radiation from the central (0–3 cm) region was equal to ～17% of the local ohmic heating power, implying radiation from molybdenum ions does not dominate the power loss from the central part of the plasma. The temporal behavior of molybdenum ions injected by the laser blow off technique at $\text{n}{}_{\mathrm{e}}\text{= 3 × 10}{}^{14}\text{cm}{}^{\mathrm{?3}}$ indicated that the molybdenum ion confinement time was finite in conflict with neoclassical theory. At lower densities (1–2 × 10¹⁴ cm^?3) the radiation from intrinsic molybdenum increased faster than the electron density during the discharge, indicating a buildup of molybdenum ions in the plasma.     

Reflectance measurements on laser-produced plasmas at 0.26 μm

Total and specular reflection from planar Al-targets was measured with a frequency-quadrupled (λ = 0.26 μm) Nd-YAG laser. The intensity on target was 4 × 10¹³ W/cm² with pulse duration 20 ps. Total absorption for near normal incidence was 80%, very little dependence on intensity and pulse duration was found. By varying the polarization and angle of incidence (0°–80°) the characteristic behaviour of resonance absorption was observed.     

Degree of conversion and temperature increase of a composite resin light cured with an argon laser and blue LED

Different light sources and power densities used on the photoactivation process may provide changes in the degree of conversion (DC%) and temperature (T) of the composite resins. Thus, the purpose of this study was to evaluate the DC (%) and T (°C) of the microhybrid composite resin (Filtek? Z-250, 3M/ESPE) photoactivated with one argon laser and one LED (light-emitting diode) with different power densities. For the KBr pellet technique, the composite resin was placed into a metallic mould (2-mm thickness, 4-mm diameter) and photoactivated as follows: a continuous argon laser (CW) and LED LCUs with power density values of 100, 400, 700, and 1000 mW/cm² for 20 s. The measurements for DC (%) were made in a FTIR spectrometer Bomen (model MB 102, Quebec, Canada). Spectroscopy (FTIR) spectra for both uncured and cured samples were analyzed using an accessory of the reflectance diffusion. The measurements were recorded in absorbance operating under the following conditions: 32 scans, 4 cm^?1 resolution, 300 to 4000-cm^?1 wavelength. The percentage of unreacted carbon double bonds (% C=C) was determined from the ratio of absorbance intensities of aliphatic C=C (peak at 1638 cm^?1) against an internal standard before and after the curing of the specimen: aromatic C-C (peak at 1608 cm^?1). For T (°C), the samples were created in a metallic mould (2-mm thickness, 4-mm diameter) and photoactivated for 20 s. The thermocouple was attached to the multimeter allowing temperature readings. The DC (%) and T (°C) were submitted to ANOVA and Tukey’s test (p < 0.05). The degree of conversion values varied from 35.0 to 50.0% (100 to 1000 mW/cm²) for an argon laser and from 41.0 to 49% (100 to 1000 mW/cm²) for an LED. The temperature change values varied from 1.1 to 13.1 °C (100 to 1000 mW/cm²) for an argon laser and from 1.9 to 15.0 °C (100 to 1000 mW/cm²) for an LED. The power densities showed a significant effect on the degree of conversion and changes the temperature for both lightcuring units.     

Laser-induced photoprocesses in solutions and films of the CdSe/ZnS nanoparticles

The photophysical properties of solutions and films with relatively high concentrations of CdSe/ZnS nanoparticles are studied in the presence of the visible laser irradiation in a wide range of power densities. The short-wavelength wing detected in the photoluminescence spectra of the solutions of quantum dots is due to the selective laser excitation of small-size nanoparticles. A comprehensive analysis of the anti-Stokes photoluminescence of the nanoparticles in solutions and films indicates the thermal mechanism of this phenomenon. The dimensional quantization effect, narrow spectra, and a relatively high luminescence yield are retained in the films with a high nanoparticle concentration. The luminescence spectra of the films remain unchanged when the laser flux density increases to 1 × 10⁶ W/cm². The effect of the laser radiation on the nanoparticle films is studied at the flux densities exceeding the damage threshold (5 × 10⁶–1 × 10⁹ W/cm²).     

Multiple charge states of titanium ions in laser produced plasma

An intense laser radiation (10¹² to 10¹¹ W/cm⁻²) focused on the solid target creates a hot (≥1 keV) and dense plasma having high ionization state. The multiple charged ions with high current densities produced during laser matter interaction have potential application in accelerators as an ion source. This paper presents generation and detection of highly stripped titanium ions (Ti) in laser produced plasma. An Nd:glass laser (KAMETRON) delivering 50 J energy (λ=0.53 μm) in 2.5 ns was focused onto a titanium target to produce plasma. This plasma was allowed to drift across a space of ∼3 m through a diagnostic hole in the focusing mirror before ions are finally detected with the help of electrostatic ion analyzer. Maximum current density was detected for the charge states of +16 and +17 of Ti ions for laser intensity of ∼10¹¹ W/cm⁻².     

Generation of fast ions in femto-and picosecond laser plasmas at low intensities of the heating radiation

X-ray spectra from Teflon targets irradiated by laser pulses with a duration of 60 fs to 1 ps have been investigated experimentally. It is shown that, when the contrast of the laser pulse is sufficiently low, the effect of self-focusing of the main laser pulse in the plasma produced by the prepulse can significantly enhance the generation efficiency of fast particles. In this case, ions with energies as high as ～1 MeV are observed at relatively low laser intensities, q _las ≈ (4–6) × 10¹⁶ W/cm².     

Ionenlaser hoher Leistung

Investigations on ion lasers with large bored tubes (7 ... 15 mm I.D.) without additional axial magnetic field are performed. An axial magnetic field is shown to be not necessary to achieve high laser power. By absence of additional magnetic fields the laser construction is considerably simplified. Experimental criterions for maximum laser power are derived by means of a previously published theoretical paper. 120 W total power summed up over the 4p-4s Argon II transitions in the visible part of the spectrum, and 1.5 W ultraviolet power in Argon (3638 Å, 3511 Å) and Krypton (3507 Å) are obtained in continuous mode operation. High inversion densities of 7 · 10⁹ cm^?3 give rise to non-resonant laser oscillations. By multipass amplification the spontaneous emission is amplified up to 20 W/cm², having a beam divergence of about 10^?4 rad. All results are pointing out the influence of radiation trapping effects on the laser power to be smaller than estimated and measured by other authors using conditions deviating from our optimum conditions for maximum laser power.     

Observation of highly ionised species in plasma produced by picosecond laser pulses

Results are presented which show that in the case of the light elements highly ionised species can be detected in laser produced plasmas using a normal incidence spectrograph, the plasmas being formed by picosecond pulses from a high power Nd: glass laser. In particular hydrogenic ions of carbon, oxygen and fluorine have been observed when the incident laser flux density onto a solid target was about 3×10¹⁴W/cm².     

Nonlinear rotation of the polarization of the intense femtosecond laser radiation in BaF<Subscript>2</Subscript>

The dependence of the polarization plane rotation angle in the BaF₂ crystal on the intensity of the femtosecond laser radiation with 0.62 μm wavelength in the ω = ω + ω ? ω process on cubical nonlinearity χ⁽³⁾ is investigated. An anomalous increase in the efficiency of the cross-polarized radiation generation at I > 2 × 10¹² W cm² is observed for the first time. The 10% efficiency of the orthogonal component generation at the ～3 × 10¹² W cm² intensity is obtained.     

Absorption of CO laser radiation by NO

Absorption of CO i.r. laser radiation by NO has been studied over the temperature range 300°–4000°K using a grating-tunable CO laser in conjunction with a room-temperature absorption cell and a shock tube. The CO laser line with strongest absorption at elevated temperatures was determined to be the V = 7 → 6, J = 12 → 13 line at 1935.4817 cm^-1, which is nearly coincident with the ²Π_{$\text{3}\text{2}$}V = 0 → 1, J = 37/2 → 39/2 transition in NO. The absorption cell measurements (300°K) were used to infer the position of the NO absorption line (a Λ-doublet at 1935.492 and 1935.497 cm^-1) as well as collision-broadening parameters in pure NO and NO dilute in foreign gases: 2γ° (collision-broadened full width at half maximum in cm^-1 atm^-1 at 300°K) = 0.110, NO-NO; 0.072, NO in Ar; 0.069, NO in Kr; 0.109, NO in N₂. Calculations of the NO absorption coefficient at 1935.4817 cm^-1 are presented for a range of conditions applicable to current studies in combustion and NO_x kinetics. Shock tube measurements (630°–4000°K) supporting these calculations are also reported.     

CW CO2-laser annealing of arsenic implanted silicon

CW CO₂-laser annealing of arsenic implanted silicon was investigated in comparison with thermal annealing. Ion channeling, ellipsometry, and Hall effect measurements were performed to characterize the annealed layers and a correlation among the different methods was made. The laser annealing was done with power densities of 100 to 640 W cm⁻² for 1 to 20 s. It was found that the lattice disorder produced during implantation can be completely annealed out by laser annealing with a power density of 500 W cm⁻² and the arsenic atoms are brought on lattice sites up to 96±2%. The maximum sheet carrier concentration of 6×10¹⁵ cm⁻² was obtained for 1×10¹⁶ cm⁻² implantation after laser annealing, which was up to 33% higher than that after thermal annealing at 600 to 900°C for 30 min.     

Impact of subthreshold laser defect accumulation on the optical stability of crystals

Optoacoustic means are used to study the kinetics of laser damage accumulation in potassium chloride crystals. This approach allows us to observe the accumulation of changes in KCl crystals when it is irradiated by a series of laser pulses of subthreshold intensity in a variety of actions (alloying, applying an external electric field, UV illumination). Number of laser pulses N _cr required to destroy a specimen at the same density of radiation power depends on density power I as N ~ I ^?4. Results are explained by the formation and accumulation of structural defects during photochemical reactions under the action of laser radiation.     

Generation of narrowband tunable VUV radiation at the Lyman-α wavelength

Tunable narrowband VUV radiation has been generated at the Lyman-α wavelength $\text{λ =}\text{1216}\text{\&}\text{A}\text{ring}$; by frequency tripling in krypton the frequency-doubled output of a powerful dye laser system which is excited with the second harmonic of a Nd-YAG laser. 5 ns long UV dye laser pulses ($\text{λ =}\text{3646}\text{A}\text{?}$) of 1.8 MW peak power yielded VUV light pulses of 2.2 W (5.4 × 19⁹ photons/pulse). The bandwidth of the dye laser radiation could be narrowed to 8.7 × 10^-3cm^-1 (4.6 × 10^-3 Å). The expected bandwidth of the VUV is less than 5.2 × 10^-2cm^-1 (7 × 10^-4 Å). The tunable VUV radiation is used for the recording of the absorption spectra of the Lyman-α resonance transitions in atomic hydrogen and deuterium with doppler-limited resolution.     

Features of the energy distribution of secondary particles upon the ion bombardment of graphite

The secondary emission of carbon atoms from the (0001) plane of graphite nanocrystallites bombarded with argon ions with energies of 1 and 10 keV and the incidence angle α = 45° is investigated. The unusual oscillating energy distributions of secondary C⁺ ions with main maxima E _max in the range of 40–60 eV and peaks corresponding to the energies E ₁ ≈ 20, 30, 70, 80, and 100 eV have been revealed. The C⁺ ion yield decreases, the energy spectrum increases, and the maximum E _max shifts to larger energies E ₁ with increasing emission angle (with respect to the normal to the surface). The secondary-ion emission from the (0001) face of graphite is numerically simulated with allowance for the charge exchange of secondary ions to obtain a qualitative explanation of the observed results.     

Mößbauereffekt in Eisenstilben und FeCl2·H2O

Using Mößbauer effect measurements in the temperature range between 3 °K and 310 °K the magnetic fields at the nucleus in iron-stilbene, FeCl₂·H₂O and FeCl₃ are determined to beH _T=0=(250±10) kOe, (252±18) kOe and (468±10) kOe; a Néel-temperature ofT _N=(23±1) °K is measured for iron-stilbene. The electric quadrupole splittings atT=0 °K for iron-stilbene and FeCl₂ ·H ₂ O, ΔE=(+2.52±0.02) mm/sec and (+2.50±0.05) mm/sec, yield electric field gradients at the iron nucleus ofq _z=+9.7·10¹⁷ V/cm² and +9.6·10¹⁷ V/cm², whereq _z⊥H; Debyetemperatures of θ=162 °K and 188 °K are obtained. The energy of the excited 3d-electron levels in iron-stilbene is estimated to Δ₁=309 cm^?1 and Δ₂=618cm^?1 as deduced from the temperature dependence ofΔE. In contrast to the suggestion ofEuler andWillstaedt bivalence of the iron in ironstilbene is found; its composition is shown to be 4(FeCl₂ ·H ₂O)·stilbene.     

Second-harmonic conversion of neodymium glass laser radiation with controlled spatial coherence

The experimental results on the second optical harmonic conversion of neodymium glass laser radiation with controlled spatial coherence in a nonlinear KDP crystal are presented. The conversion efficiency is studied depending on the radiation power density on the crystal and the crystal rotation angle in the principal optical plane with respect to the radiation propagation direction. The experiments were performed in the radiation power density range I = 0.2–3 GW/cm² for the number of cavity transverse modes N = 100–1000, radiation divergence 2ч = 0.5–3.5 mrad, spectrum width of 26 Å, and pulse duration of 2.5 ns.     

Short wavelength X-ray emission generated by highly excited cluster beams

X-ray radiation is studied for large clusters consisting of 10⁷–10¹⁰ atoms and irradiated by an intense laser pulse with an intensity ranged from (10¹⁴ up to 10¹⁸ W/cm²). The model is developed for such a laser plasma that includes the radiative transitions and the processes of excitation and quenching of multicharged ions of this plasma by electron impact. Due to interaction of a radiating multicharged ion with a surrounding plasma, spectral lines of emission are broaden and neighboring spectral lines are overlapped. As a result, the spectrum of radiation of multicharged ions is transformed into a continuous spectral band. The model under consideration includes important plasma processes including dielectronic recombination, spontaneous radiation, excitation, quenching and ionization of multicharged ions by electron impact. On the basis of the model developed the X-ray spectrum and spectral power are evaluated. In the range of laser intensities under consideration a laser plasma formed contains multicharged ions with charges Z = 26?36 that corresponds to the 3d-electron shell in the xenon case.     

Investigation of 4H-SiC epitaxial layers implanted by Al ions

4H-SiC epitaxial layers 26 μm thick with N _d ?N _a = 1 × 10¹⁵ cm^?3 grown by the CVD method on 4H-SiC commercial wafers were implanted by Al ions with energy of 100 keV and a dose of 5 × 10¹⁶ cm^?2. To produce the p ⁺?n junction, a rapid thermal annealing for 15 s at 1700°C was used. The obtained samples were studied by the local cathodoluminescence, X-ray diffractometry, and transmission electron microscopy. It was established that under specified conditions of implantation, the width of a region with a high content of radiation defects exceeded by two orders of magnitude, the depth of the projective range of Al ions and was equal to 40 μm. This result is explained by the combined contribution of the radiation enhanced defect diffusion and long-range action effect. A short-term high-temperature annealing resulted in the recrystallization of the specimen surface layer and enhancement of CVD layer structure.     

Sputtering of highly oriented pyrolytic graphite with 30 keV Argon ions

The influence of the incidence angle of 30 keV Ar⁺ ions, ion fluence and target temperature on the sputtering yield and surface microgeometry of highly oriented pyrolytic graphite (UPV-1T) samples was experimentally studied. It was found that at fluences more than 5 × 10¹⁹ ion cm^?2 the sputtering yield at room temperature in the range of the ion incidence angle from 0° to 80° is twice as small as the corresponding experimental data for both polycrystalline graphite and glassy carbon. The analysis of ion-induced relief permits us to suppose the topographical suppression mechanism of highly oriented pyrolytic graphite sputtering.