Nonlinear plasma spectroscopy of the hydrogen balmer-α line

The plasma line broadening of H_α fine-structure lines is investigated with Doppler-free saturation and polarization spectroscopy in He-H gas and are discharges at plasma densities of 10⁸ cm^?3 <N?1.4×10¹⁴ cm^?3. With a single-mode laser, the shift and broadening of four resolved H_α fs lines are measured in a low pressure discharge forN<10¹¹ cm^?3. With an intense, broadband multi-mode laser the plasma effects of H_α are investigated up toN=1.4×10¹⁴ cm^?3 in a hollow cathode are. Calculations in the classical phase shift and impact approximations can explain the experimental data and peculiarities of the low-density plasma effects and show that the ions are the dominant perturbers. Ion dynamical effects, perturber mass and temperature dependence, are observed and interpreted. Applications of the nonlinear techniques to other H and D lines, other atoms, and for H and D plasma diagnostics are discussed.     

H2， He混合稀释生长微晶硅锗薄膜

采用H₂,He混合气体稀释等离子辅助反应热化学气相沉积法生长微晶硅锗薄膜,并在生长过程中对等离子体进行光发射光谱在线监测.结果表明：混合气体稀释法可以有效提高等离子体中的原子氢数目,降低等离子体中的电子温度;用XRD和光暗电导率表征样品的微结构和光电特性时发现,通过优化混合稀释气体中He和H₂气体的比例,能够减少薄膜中的缺陷态,促进薄膜<220>择优取向生长,有效改善微晶硅锗薄膜结构,提高光电吸收性能. 关键词： 化学气相沉积 微晶硅锗薄膜 光发射光谱 X射线衍射     

Anomalous shifts of hydrogen balmer-α fine structure lines in helium

Resolved H_α fine and hyperfine structure lines are investigated by polarization and double-quantum saturation spectroscopy in a HeH₂ (1%) dc discharge. Anomalous negative density shifts are observed which are correctly predicted by a van der Waals interaction theory. For the pressures below 0.1 Torr a positive shift due to hfs decoupling occurs. Consequences of a comparison with the unresolved H_α line and the alkali D lines are discussed.     

A novel double-pulse laser plasma spectroscopic technique for H analysis in metal samples utilizing transversely excited atmospheric-pressure CO2 laser-induced metastable He atoms

The analysis of hydrogen in a metal sample (zircaloy-4), which is usually difficult to perform using conventional laser-induced breakdown spectroscopy (LIBS) techniques, has been achieved using a double-pulse technique under He gas at atmospheric pressure. In this technique, a transversely excited atmospheric-pressure (TEA) CO₂ laser (1.5 J, 200 ns) was focused onto the metal surface to induce a strong He gas plasma whilst simultaneously focussing a Nd-doped yttrium aluminum garnet (Nd:YAG) laser (120 mJ, 8 ns), synchronized with the TEA CO2 laser, onto the metal to ablate atoms into the resulting He gas plasma. The emission spectrum obtained shows a narrow H linewidth with low background intensity and long lifetime emission, thereby indicating that excitation takes place via metastable He atoms. The H emission from H₂O can be suppressed by a careful pretreatment involving heating the sample in a vacuum chamber.     

L α emission from Ar++H2 collisions in the threshold energy region

In the energy range 2.4 to 33.3 eV_CM, relative cross sections have been measured forL _α emission from impact of Ar⁺ ions in a beam on a H₂ gas target. Absolute cross sections, obtained by normalization to literature data, are 1–10×10^?16cm² for metastable Ar⁺ and 1–20×10^?18cm² for ground state Ar⁺. In the former case, the dominant mechanism is probably dissociative electronic energy transfer, while in the latter case dissociative charge transfer is the most likely process. In addition, at the lowest energiesL _α resulting from a chemiluminescent rearrangement Ar⁺+H₂→ArH⁺+H(2p) has been observed.     

Measurement and MIA analysis of the neutron differential cross section and polarization in the α-D break-up at 33 MeV c.m.

Differential cross sections at 0° and 20° and polarizations at 20° have been measured for the ²H(α, n) αp reaction at E_α = 100 MeV and the ⁴He(d, n) αp reaction at E_d = 50 MeV. Data have been analyzed by the Modified Impulse Approximation (MIA). Satisfactory agreement was obtained but some discrepancy remained in the analysis of polarization data.     

Spectral behavior and laser activity of 3-(4′-dimethylaminophenyl)-1-(1H-pyrrol-2-yl) prop-2-en-1-one (DMAPrP). A new laser dye

The photophysical properties of DMAPrP have been investigated in different solvents. DMAPrP dye exhibits a large change in dipole-moment upon excitation due to an intramolecular charge transfer interaction. A crystalline solid of DMAPrP give an excimer like emission at 546 nm. The ground and excited state protonation constants of DMAPrP are calculated. DMAPrP acts as good laser dye upon pumping with nitrogen laser in some organic solvents. The laser parameters such as the tuning range, gain coefficient (α), emission cross section (σ_e) and half-life energy (E_1/2) are also calculated. The photoreactivity and net photochemical quantum yield of DMAPrP in chloromethane solvents are also studied.     

Behavioral studies of gain and saturation energy density in a N2 laser with corona preionization

By the use of an oscillator-amplifier (OSC-AMP) TE N₂ laser system, both operating with corona preionizers, the laser parameters (small-signal gain g ₀ and saturation energy density E _s) have been measured at different N₂ gas pressure and for different states of the AMP preionizer. The details of our measurements are presented. In addition, the effect of He buffer gas on the laser parameters has also been investigated; it was found that both laser parameters remain almost constant up to 150 Torr of He gas pressure, indicating that He mainly affects the discharge uniformity. Finally, with the variation of the N₂ laser gain values in the literature, we found that the g ₀-N₂-laser parameter depends strongly on the length of the laser channel. Based on the most recent measurements, a graph showing this dependency is introduced.     

Übertragung von Polarisation bei sensibilisierenden Stößen angeregter Natriumatome

The transfer of magnetic polarization from state 3p ² p _1/2 to state 3p ² p _3/2 sensitizing collisions of sodium atoms with noble gas atoms has been observed. Sodium atoms were excited by absorption ofD ₁σ⁺-quanta. When buffer gas was added to the sodium vapour, unequal amounts ofD ₂σ⁺ andD ₂σ^? quanta could be detected in the fluorescent light. The difference of the amounts turned out to be proportional to the polarization transferred. The measurement of this difference as a function of the buffer gas pressure provided a method of determining the cross-sections of the polarization transfer. Values of the cross-sections are 22, 24, 26, 20, 23 Ų for the buffer gases He, Ne, Ar, Kr, Xe, respectively. A preliminary investigation shows that the sign of the polarization transferred is reversed when the vapour is exposed to a strong magnetic field acting along the incident light beam.     

The differential cross section and polarization quantities in the 4He(d,p)n4He and 2H(α, n)p4He reactions

The differential cross section and the polarization quantities (T₁₁, T₂₀, T₂₁, T₂₂, P_γ') in the deuteron breakup reaction by an α-particle are calculated in the framework of the recently developed three-body model. All values are discussed under the incomplete kinematical condition. All polarization quantities are caused by the difference of the potential between $\text{p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ and $\text{p}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ waves of the N-α interaction. Results of the calculation are compared with the available measurement of (i) the differential cross section and the deuteron vector analysing power in the ⁴He($\text{d}$, p)n⁴He reaction and (ii) the differential cross section and neutron polarization in the ²H(α, $\text{n}$)p⁴He reaction. The agreement with experiment is very satisfactory in each case. Among the tensor analysing powers of the deuteron the absolute value of T₂₀ is very large. Observables at the FSI peak corresponding to ⁵He_g.s. are discussed systematically in the energy region of 5.4–20 MeV of the incident deuteron in the ⁴He(d, p)n⁴He reaction. Although the differential cross section is not sensitive to the energy of the three-body resonance, the polarization quantities T₁₁, T₂₀, P_γ' are quite sensitive to it.     

Resonance transition 795-nm rubidium laser using He buffer gas

We report a demonstration of a 795-nm rubidium optical resonance transition laser using a buffer gas consisting of pure ³He. This follows our recent demonstration of a hydrocarbon-free 795-nm rubidium resonance laser which used naturally-occurring He as the buffer gas. Using He gas that is isotopically enriched with ³He yields enhanced mixing of the Rb fine-structure levels. This enables efficient lasing at reduced He buffer gas pressure, improved thermal management in high average power Rb lasers and enhanced power scaling potential of such systems.     

Near resonance charge transfer from a laser excited donor state

A laser induced charge transfer from Na(3p) to hydrogen-ions at different kinetic energies has been studied. An enhancement factor of about 90% in the production rate of Lyman-α radiation has been demonstrated to occur only with H⁺ and Na(3p) atoms reaction; no enhancement was observed with either H ₂ ⁺ or H ₃ ⁺ ions. Absolute cross-section for the production of Lyman-α radiation during the collision of H⁺, H ₂ ⁺ and H ₃ ⁺ ions and Na(3p) and Na(3s) atoms have been measured in the energy range 1–600eV. The charge exchange reactions involving hydrogen-ions and Na(3p) atoms created by two different methods have also been compared.     

Hydrogen and Deuterium Analysis Using Laser‐Induced Plasma Spectroscopy

Abstract

Hydrogen emission in laser plasma has been studied by focusing a TEA CO₂ laser and Nd‐YAG lasers on various types of samples, such as glass, quartz, and zircaloy pipes doped with hydrogen. It was found that H_α emission with a narrow spectral width occurs with high efficiency when the laser plasma is produced in low‐pressure host gas. In contrast, the conventional well‐known laser‐induced breakdown spectroscopy (LIBS), which operates at atmospheric air pressure, cannot be applied for the analysis of hydrogen as impurity. The specific characteristic of hydrogen emission in low‐pressure plasma is interpreted on the basis of our shock wave model, taking account of the fact that the hydrogen mass is extremely light compared to that of the host target. Another experimental study on gas analysis was conducted using an Nd‐YAG laser and helium host gas at atmospheric pressure on a sample of mixed water (H₂O) and heavy water (D₂O) in vapor form. It was shown that completely resolved hydrogen (H_α) and deuterium (D_α) emission lines that are separated by only 0.179 nm could be obtained at a properly delayed detection time when the charged particles responsible for the strong Stark broadening effect in the plasma have mostly disappeared. It is argued that a helium metastable excited state plays the important role in the hydrogen excitation process.     

Plasma shift and broadening of single hydrogen Balmer-α fine-structure lines

With high-resolution laser spectroscopy plasma effects of four single hydrogen Balmer-α fine structure transitions have been investigated in a HeH dc discharge. For charged-particle densities of 10⁸ to 10¹¹ cm^?3 the signs and magnitudes of shift and broadening can be explained with linear and quadratic Stark effect by treating both electrons and ions in impact approximation and by taking inelastic fine-structure transfer collisions into account. Contributions to the understanding of plasma effects and the application of the method for low-density plasma diagnostics are discussed.     

Pressure broadening and collisional shift of the Rb D2 absorption line by CH4, C2H6, C3H8, n-C4H10, and He

The pressure broadening and shift rates of the rubidium D2 absorption line 5²S_1/2→5²P_3/2 (780.24 nm) with CH₄, C₂H₆, C₃H₈, n-C₄H₁₀, and He were measured for pressures ≤80 Torr using high-resolution laser spectroscopy. The broadening rates γ_B for CH₄, C₂H₆, C₃H₈, n-C₄H₁₀, and He are 28.0, 28.1, 30.5, 31.3, and 20.3 (MHz/Torr), respectively. The corresponding shift rates γ_S are −8.4, −8.8, −9.7, −10.0, and 0.39 (MHz/Torr), respectively. The measured rates of Rb for the hydrocarbon buffer gas series of this study are also compared to the theoretically calculated rates of a purely attractive van der Waals difference potential. Good agreement is found to exist between measured and theoretical rates.     

Structural and optical properties of silicon nanoparticles prepared by pulsed laser ablation in hydrogen background gas

We studied the structural and optical properties of silicon (Si) nanoparticles (np-Si) prepared by pulsed laser ablation (PLA) in hydrogen (H₂) background gas. The mean diameter of the np-Si was estimated to be approximately 5 nm. The infrared absorption corresponding to Si-H_n (n=1,2,3) bonds was observed at around 2100 cm^-1, and a Raman scattering peak corresponding to crystalline Si was observed at around 520 cm^-1. These results indicate that nanoparticles are not an alloy of Si and hydrogen but Si nanocrystal covered by hydrogen or hydrogenated silicon. This means that surface passivated Si nanoparticles can be prepared by PLA in H₂ gas. The band-gap energy of np-Si prepared in H₂ gas (1.9 eV) was larger than that of np-Si prepared in He gas (1.6 eV) even though they are almost the same diameter. After decreasing the hydrogen content in np-Si by thermal annealing, the band-gap energy decreased, and reached the same energy level as np-Si prepared in He gas. Thus, the optical properties of np-Si were affected by the hydrogenation of the surface of np-Si. PACS 81.15.Fg; 61.46.+W; 78.67.Bf     

Short delay time UV preionized TEA CO2 laser operating with binary CO2/H2 and CO2/He gas mixtures

In order to obtain short tail-free output laser pulses from a TEA CO₂ laser, parametric study of the laser operation with CO₂/H₂ and CO₂/He binary gas mixtures containing high CO₂ concentrations was carried out. A small scale UV preionized short delay time TEA CO₂ laser was employed. In terms of the maximum extractable output pulse energy and power, the more conventional CO₂/He gas mixture was found to be inferior in comparison with the CO₂/H₂ mixture proposed here.     

Nondynamical calculation of polarization observables in d+d reactions at low energies

The parametrization of polarization observables in terms of (l, s, J) matrix elements is given for²H(d, p)³H and²H(d, n)³He reactions at low energies. It is shown that transverse polarizations of outgoing nucleons are to be measured in order to obtain a complete set of cross-section, analysing powers, spin-correlation and polarization transfer experiments.     

Polarization of atomic hydrogen lines upon collision with an electron beam

A technique is described for the analytical calculation of the degree of linear polarization of atomic hydrogen lines formed by several radiative transitions with different polarizations upon excitation by an electron impact. The degree of linear polarization of the line L of the hydrogen atom is calculated as an example. The analytical equations used are derived by the Born method. The results of the analytical calculation are compared with experiment and with other calculations. The effective excitation cross sections and the degree of linear polarization of the H_α and H_β lines of the hydrogen atom are calculated analytically for the case of electron-beam excitation. The results of the analytical calculation of the effective excitation cross section of the H_α line are compared with the available experimental and calculated data.     

Performance studies of a pulsed HF laser with a sliding discharge plasma cathode

The plasma electrode design concept is applied for the first time to an HF laser. The discharge along the surface of a dielectric (sliding discharge) is used as a plasma cathode for the main laser discharge. The laser operates at atmospheric pressure with a gas mixture of He/SF₆/C₃H₈. Details are presented on the efficiency of energy transfer, the dependence of laser performance on circuit parameters, gas mixture, relative energy loading and time delay between the plasma electrode and main discharges. The F atom production rate is estimated from the linear dependence of the output energy on the electric charge passed through the discharge. Output energies of 600 mJ were obtained at 1.6% efficiency from a small active discharge of 108 cm₃ volume and 38 cm length, while the maximum specific input and output energies were 370 J/1 and 5.7 J/1, respectively. These values compare favourably with those reported in the literature for non-chain-reaction-type gas mixtures at 1 atm pressure and demonstrate that the plasma electrode design is a powerful scheme for developing gas-discharge lasers.