Spectroscopic diagnostics of a laser erosion plasma formed from CuSbS<Subscript>2</Subscript> polycrystals

The spectra and dynamics of emission from regions of a laser plasma torch located at different distances from a polycrystalline CuSbS₂ target irradiated by a neodymium laser (W=(3–5)×10⁸ W/cm², ?=20 ns, f=12 Hz, 73x03BB;=1.06μm) were investigated. The emission data were used to estimate the average temperature (≤0.82 eV) and the electron density ((1.82?1.92)×10¹⁶ cm^?3) in the laser torch and the recombination times of ions (t _r(S²⁺)=15 ns, t _r(Cu⁺)=65?85 ns), as well as to analyze the efficiency of filling of excited atomic levels. A model describing the target destruction and the evolution of the processes accompanying spread of the laser plasma is proposed.     

Electron temperature and concentration in the laser erosion plasma of lead and gallium

Time-averaged values of the electron temperature and concentration at distances of 1 and 7 mm from a target have been determined from the emission characteristics of the laser erosion plasma of lead and gallium. The plasma was produced in a vacuum (3–12 Pa) as the corresponding target was exposed to radiation of a neodymium laser (τ = 20 ns, λ = 1.06 μm, f = 12 Hz, W = 10⁸–10⁹ W/cm²). The energy distribution of excited atomic states has been analyzed. The time dependence of the electron temperature at a distance of 7 mm from the target is presented.     

Plasma-volume generation of H<Superscript>−</Superscript> ions in a low-voltage xenon-hydrogen discharge. II

A low-voltage xenon-hydrogen discharge is considered theoretically at an interelectrode distance of L = 1 cm and cathode emission current densities of j _s = 2–20 A/cm². Basic parameters of the discharge plasma, in particular, the total hydrogen and xenon densities, are optimized to attain the maximum possible density of negative hydrogen ions \(N_{H^ - } (L)\) at the plasma-anode boundary. The distributions of the plasma parameters over the discharge gap are calculated for optimized regimes. According to calculations, at intermediate cathode emission current densities (j _s ≈ 5–10 A/cm²) in optimized discharge regimes, the density of negative hydrogen ions in the anode region of the plasma is \(N_{H^ - } (L)\) ≈ (1.5–2.5) × 10¹² cm^?3 and the total plasma pressure is p ₀ = 0.5–0.6 Torr.     

Optimization of soft x-ray line emission from laser-produced carbon plasma with laser intensity

Absolute measurement for He-α resonance (1s^{2 1}S₀?1s2p¹ P ₁, at 40.2 Å) line emission from a laser-produced carbon plasma has been studied as a function of laser intensity. The optimum laser intensity is found to be ≈1.3×10¹² W/cm² for the maximum emission of 3.2 × 10¹³ photons sr^?1 pulse^?1. Since this line lies in the water window spectral region, it has potential application in x-ray microscopic imaging of biological sample in wet condition. Theoretical calculation using corona model for the emission of this line is also carried out with appropriate ionization and radiative recombination rate coefficients     

Plasma satellites of X-ray lines of ions in a picosecond laser plasma

We present the results of our measurements of the spectra for multicharged ions in a plasma produced by moderately intense (about 10¹⁷Wcm^?2) picosecond laser pulses. They suggest the existence of intense plasma oscillations with a frequency appreciably lower than the frequency of the laser radiation. The observed spectrum for the plasma satellites of the Lyman Ly_α doublet of the hydrogenic F IX ion in a dense plasma was modeled theoretically. The resulting doublet profile was shown to have a complex structure that depends non-trivially both on the plasma density and on the frequency and amplitude of the plasma oscillations. The positions of the satellites and their separations allowed them to be associated with intense electrostatic oscillations with an amplitude of (4–6)×10⁸Vcm^?1 and a frequency near (0.7–1)×10¹⁵s^?1. Assuming the oscillation frequency to be determined by the strength of the magnetic field B generated in the plasma, we obtained an estimate of B that is in reasonable agreement with other measurements and estimates of this quantity. Our theoretical analysis allowed explanation of the emission spectra observed when flat fluoroplastic targets were heated by intense picosecond laser pulses.     

Scaling of x-ray emission and ion velocity in laser produced Cu plasmas

The x-ray emission from slab targets of copper irradiated by Nd:glass laser (1.054 μm, 5 and 15 ns) at intensities between 10¹² and 10¹¹W/cm² has been studied. The x-ray emissions were monitored with the help of high quantum efficiency x-ray silicon photo diodes and vacuum photo diodes, all covered with aluminium filters of different thickness. The x-ray intensity vs the laser intensity has a scaling factor of (1.2–1.92). The relative x-ray conversion efficiency follows an empirical relationship which is in close agreement with the one reported by Babonneau et al. The ion velocities were monitored using Langmuir probes placed at different angles and radial distances from the target position. The variation of the ion velocity with the laser intensity follows a scaling of the form Φ ^β where β ∼0.22 which is in good agreement with the reported scaling factor values. The results on the x-ray emission from Cu plasma are reported.     

Spectrum of X-ray emission from nsec CO2-laser produced (CH2)n and A1 plasmas

Studies of the X-ray emission from nsec CO₂ laser produced plasmas indicate a stronger deviation of the electron distribution from equilibrium for a (CH₂)_n plasma than for an A1 plasma. The lowest spectral temperature measured is ～ 300 eV at the maximum flux of 5 × 10¹²W·cm^-2.     

Electron dynamics and prompt ablation of aluminum surface excited by intense femtosecond laser pulse

Thin aluminum film homogeneously heated by intense IR femtosecond laser pulses exhibits on the excitation timescale consequent fluence-dependent rise and drop of the IR-pump self-reflectivity, followed by its final saturation at higher fluences F > 0.3 J/cm². This prompt optical dynamics correlates with the initial monotonic increase in the accompanying laser-induced electron emission, which is succeeded by its non-linear (three-photon) increase for F > 0.3 J/cm². The underlying electronic dynamics is related to the initial saturation of IR resonant interband transitions in this material, followed by its strong instantaneous electronic heating via intraband transitions during the pump pulse resulting in thermionic emission. Above the threshold fluence of 0.3 J/cm², the surface electronic heating is balanced during the pump pulse by simultaneous cooling via intense plasma removal (prompt ablation). The relationship between the deposited volume energy density in the film and its prompt electronic temperature derived from the self-reflection measurements using a Drude model, demonstrates a kind of electron “liquid–vapor” phase transition, driven by strong cubic optical non-linearity of the photo-excited aluminum.     

On the search for density isomers in interaction of relativistic12C nuclei with lead

A Pb target was bombarded with¹²C nuclei of an energy of 15 and 43 GeV. The target was periodically transported to the inside of the neutron multiplicity detector which allowed measuring time distributions for events of multiple emission of delayed neutrons. Abnormal neutron emitters have not been found. Upper limits of probabilities of their production were estimated for the half-life range 10–10⁵ s and for different mean multiplicities of neutrons¯n. The values obtained are within the interval from 1.4·10^?9 (for¯n=12)to 4·10^?6(for¯n=2).     

Influence of ultrashort laser pulse duration on the X-ray emission spectrum of plasma produced in cluster target

Line emission spectrum of a laser plasma produced in an argon cluster jet target was measured on the n ¹ P1?1¹ S ₀ (n=5–9) transitions of the helium-like Ar XVII ion for a pulse duration varying from 45 fs to 1.1 ps and a constant fluence of ～10⁵ J/cm². The independent modeling of the relative intensities of the transitions from the n=5,..., 10 levels, as well as of the 2¹ P ₁? 1² S ₀ and 2³ P ₁?1² S ₀ lines and dielectronic satellites indicates that the electron temperature is anomalously low and that the electron density in emitting plasma increases with shortening the laser pulse. The excitation from the ground state by a small fraction of hot electrons is expected to be the main channel of populating the Ar XVII levels.     

Investigation of the plasma of a 308-nm XeCl excimer light emitter based on an inert-gas-CCl4 mixture

Results are presented from optical measurements of the plasma of a transverse volume discharge in He(Ar)/Xe/CCl₄(HCl) mixtures (at pressures of P=10–100 kPa) that are used in excimer lamps emitting the XeCl 308-nm band. Emission spectra in different stages of the formation and degradation of the active medium, as well as temporal and resource characteristics of the emitter, are studied. The main products of decomposition of CCl₄ molecules that are detected by the plasma emission are C* atoms and C ₂ ^* and CN* radicals. The operating resource of the XeCl emitter is found to be (3–5)×10⁴ pulses and depends strongly on the pressure and composition of the active medium. The duration of the emission pulse at a wavelength of λ=308 nm is 200–300 ns.     

Hot microplasma in the channel of a solid target induced by a sequence of femtosecond laser pulses

The dynamics of the hard X-ray yield is studied as a function of the laser-shot number, and the maximum temperature of the hot electron plasma component in the channel formed by a sequence of tightly focused near-IR femtosecond laser pulses (τ = 110 fs, λ = 1.24 μm, and I = 10¹⁵–10¹⁶ W/cm²) in air at various pressures (P = 0.01–760.00 Torr) is analyzed. The dependence of the depth of the channel in which the hard X rays are generated with the highest efficiency on the air pressure and the laser focusing is obtained. The electron concentration in air plasma in the laser beam waist is estimated using the spectral shift of the second harmonic radiation that is back reflected from the target channel.     

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.     

Emission characteristics and parameters of tin and CuSbSe2 laser plumes

The emission characteristics and parameters of laser plumes of tin and CuSbSe₂ compound are studied at distances of 1 and 7 mm from the target. The recombination times of singly and doubly charged tin ions are, respectively, 116 and 27 ns at a distance of 1 mm from the target and 148 and 64 ns at a distance of 7 mm. In the case of the CuSbSe₂ compound, the recombination times of antimony and copper ions are determined to be, respectively, 60 and 75 ns at a distance of 1 mm and 707 and 976 ns at a distance of 7 mm. The time-averaged temperatures and concentrations of electrons of the tin laser plasma are determined at a distance of 7 mm from the target (T _e = 0.42 eV and n _e = 2.9 × 10¹⁵ cm^?3), and the same parameters for the laser plasma based on the CuSbSe₂ compound are determined at distances of 1 and 7 mm from the target (T _e = 0.62 eV, n _e = 1.4 × 10¹⁶ cm^?3 and T _e = 0.86 eV, n _e = 8.4 × 10¹⁵ cm^?3).     

Variations in the parameters of the erosion lead plasma with distance from the laser target

The main parameters of the erosion lead plasma (the atomic density, the densities of electrons and single-and double-charged ions, the pressure, the mean free path, and the degree of ionization) at distances 1 and 7 mm from the laser target are investigated using emission spectroscopy. The plasma was produced by using a repetitive neodymium laser with a peak intensity of (3–5) × 10⁸ W/cm², wavelength of 1.06 μm, pulse duration of 20 ns, and repetition rate of 12 Hz. Original Russian Text ? A.K. Shuaibov, M.P. Chuchman, 2006, published in Zhurnal Tekhnicheskoĭ Fiziki, 2006, Vol. 76, No. 11, pp. 61–65.     

Generation of THz Radiation from Laser Beam Filamentation in a Magnetized Plasma

The terahertz (THz) frequency radiation production as a result of nonlinear interaction of high intense laser beam with low density ripple in a magnetized plasma has been studied. If the appropriate phase matching conditions are satisfied and the frequency of the ripple is appropriate then this difference frequency can be brought in the THz range. Self focusing (filamentation) of a circularly polarized beam propagating along the direction of static magnetic field in plasma is first investigated within extended‐paraxial ray approximation. The beam gets focused when the initial power of the laser beam is greater than its critical power. Resulting localized beam couples with the pre‐existing density ripple to produce a nonlinear current driving the THz radiation. By changing the strength of the magnetic field, one can enhance or suppress the THz emission. The expressions for the laser beam width parameter, the electric field vector of the THz wave have been obtained. For typical laser beam and plasma parameters with the incident laser intensity ≈ 10¹⁴ W/cm², laser beam radius (r₀) = 50 μm, laser frequency (ω₀) = 1.8848 × 10¹⁴rad/s, electron plasma (low density rippled) wave frequency (ω₀) = 1.2848 × 10¹⁴ rad/s, plasma density (n₀) = 5.025 × 10¹⁷cm^–3, normalized ripple density amplitude (μ)=0.1, the produced THz emission can be at the level of Giga watt (GW) in power (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Parameters of the cathode spot upon field emission

This work is devoted to studying the parameters of the cathode spot of a vacuum arc. According to calculations under conditions of autoelectronic emission, the temperature of the cathode spot is T _n = (1–2.5) × 10³ K, the electric-field strength is E = (1–6) × 10⁷ V cm^?1, and the current density in the spot is j _n = (0.15–3) × 10⁷ A cm^?2. The values of the cathode-spot parameters for cathodes of different materials are obtained and the type of electron emission is determined.     

A miniature tunable TEA CO<Subscript>2</Subscript> laser using isotope <Superscript>13</Superscript>C<Superscript>16</Superscript>O<Subscript>2</Subscript> and <Superscript>12</Superscript>C<Superscript>16</Superscript>O<Subscript>2</Subscript>

A miniature tunable TEA CO₂ laser using isotope ¹³C¹⁶O₂ as the active medium is developed to extend the spectral range of CO₂ lasers for further application. The optimization of the energy parameters of the tunable TEA ¹³C¹⁶O₂ laser and the same laser using ¹²C¹⁶O₂ are studied. When a gas mixture (¹³C¹⁶O₂: N₂: He = 1: 1: 3) at a total pressure of 6.4 × 10⁴ Pa is used, the TEA ¹³C¹⁶O₂ laser of a 45-cm³ active volume obtains 51 emission lines in the [00⁰1–10⁰0] and [00⁰1–02⁰0] bands. The maximum pulse energy of the TEA ¹³C¹⁶O₂ laser is about 357 mJ. The same laser using the conventional gas mixture (¹²C¹⁶O₂: N₂: He = 1: 1: 3) at a pressure of 6.66 × 10⁴ Pa is measured to obtain 69 laser emission lines and the maximum pulse energy of laser radiation is about 409 mJ.     

Neutrals' temperature in laser-generated plasma at LNS

A Nd–YAG laser operating at 532 nm with a maximum intensity of 10¹⁰ W/cm² was used to ablate aluminium and tantalum targets placed in vacuum.

A mass quadrupole spectrometer (MQS) at high sensitivity, operating in the range of 1–300 amu, with a resolution better than 1 amu, was used to analyse the atomic emission produced by the laser ablation. The neutrals' emission produced by laser-generated plasma at INFN-LNS was investigated in terms of temperature, ablation yield, angular distribution and velocity.

The neutrals' detection through the MQS permitted to measure the mass energy distribution. Results demonstrate that the maximum temperatures of the neutral species are of the order of 100 eV. The angular emission of neutrals is peaked along the normal to the target surface, as it was observed for the ions; the ablation yield increases suddenly at low laser intensity and decreases at high laser intensity, owing to the higher ionization processes; the flow velocity follows the adiabatic expansion of the plasma in vacuum and it is of the order of 10⁴ m/s.

Measurements will be presented and discussed, according to the available models.     

The ground state of molecular hydrogen

The v = 0?0 quadrupole spectrum of H₂ has been recorded using a 0.005-cm^?1 resolution Fourier transform spectrometer. The rotational lines S(1) through S(5) are observable in the spectra, in the region 587 to 1447 cm^?1. The spectral position for S(0) was also obtained from its v = 1-0 ground-state combination difference. The high accuracy of the H₂ measurements has permitted a determination of four rotational constants. These are (in cm^?1) B₀ = 59.33455(6); D₀ = 0.045682(4); H₀ = 4.854(12) × 10^?5; L₀ = ?5.41(12) × 10^?8. The hydrogen line positions will facilitate studies of structure and dynamics in astrophysical objects exhibiting infrared H₂ spectra. The absolute accuracy of frequency calibration over wide spectral ranges was verified using 10-μm CO₂ and 3.39-μm CH₄ laser frequencies. Standard frequencies for 5-μm CO were found to be high by 12 MHz (3.9 × 10^?4 cm^?1).