Optical spectroscopic studies of titanium plasma produced by an Nd : YAG laser

We present optical emission characteristics of the titanium plasma produced by the fundamental (1064 nm) and second (532 nm) harmonics of a Q-switched Nd: YAG laser using laser induced breakdown spectroscopy (LIBS). The experimentally observed line profiles of neutral titanium (Ti I) have been used to extract the electron temperature (T _e ) using the Boltzmann plot method. The electron number density (N _e ) is calculated using the Stark broadening profile of 368.73 nm spectral line. Beside we have studied the spatial variation of electron temperature and number density as a function of laser energy for titanium plasma by placing the target material in air (at atmospheric pressure). We have determined the electron temperature and the electron number density along the axial position of the plasma plume.     

Optical emission studies of sulphur plasma using laser induced breakdown spectroscopy

We present the optical emission studies of sulphur (S) plasma generated by the first (1064 nm) and second (532 nm) wavelengths of a Q-switched Nd:YAG laser. The target material was placed in front of laser beam in air at atmospheric pressure. The experimentally observed line profiles of neutral sulphur have been used to extract the electron temperature (T _e ) using the Boltzmann plot method, whereas the electron number density (N _e ) has been determined from the Stark broadening. The electron temperature is calculated by varying, distance from, the target surface along the line of propagation of plasma plume and also by varying the laser irradiance. Beside we have studied the variation of number density as a function of laser irradiance as well as its variation with distance from the target surface. It is observed that electron temperature and electron number density increases as laser irradiance is increased.     

Diagnostics of Tin Plasma Produced by Visible and IR Nanosecond Laser Ablation

We present the optical emission spectroscopic studies of the Tin (Sn) plasma, produced by the fundamental (1064 nm) and second (532 nm) harmonics of a Q switched Nd: YAG pulsed laser having pulse duration of 5 ns and 10 Hz repetition rate which is capable of delivering 400 mJ at 1064 nm, and 200 mJ at 532 nm using Laser Induced Breakdown Spectroscopy (LIBS). The laser beam was focused on target material by placing it in air at atmospheric pressure. The experimentally observed line profiles of four neutral tin (Sn I) lines at 231.72, 248.34, 257.15 and 266.12 nm were used to extract the electron temperature (T_e) using the Boltzmann plot method and determined its value 6360 and 5970 K respectively for fundamental and second harmonics of the laser. Whereas, the electron number density (N_e) has been determined from the Stark broadening profile of neutral tin (Sn I) line at 286.33 nm and determined its value 5.85 x 10¹⁶ and 6.80 x 10¹⁶cm^–3 for fundamental and second harmonics of the laser respectively. Both plasma parameters (T_e and N_e) have also been calculated by varying distance from the target surface along the line of propagation of plasma plume and also by varying the laser irradiance. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical emission spectroscopic studies on laser ablated TiO2 plasma

Optical emission spectroscopic investigations of the plasma produced during Nd:YAG laser ablation of sintered TiO₂ targets, in oxygen and argon gas environments are reported. The spatial variations of electron temperature (T_e) and electron number density (N_e) are studied. The effect of oxygen/argon pressure on electron temperature (T_e) and electron number density (N_e) is presented. The kinematics of the emitted particles and expansion of plume edge are discussed. Spatio-temporal variations of various species in TiO₂ plasma were recorded and corresponding velocities were calculated. The effect of oxygen pressure on intensity of neutral/ion species and their corresponding velocities is also reported.     

Optical Emission Diagnostics of an U-Shaped Argon Stabilized d.c. Arc

The radial distribution of parameters has been measured by using the optical emission spectroscopy of an U-shaped argon stabilized low current arc at atmospheric pressure. All the measurements reported here were performed from a side-on observation direction by applying the Abel inversion routine. Radial distributions of apparent temperatures (T_exc., T_e, T_i, T_g) and of electron number density (n_e) for the plasma were measured, with and without presence of KCl (spectrochemical buffer). The measured data of n_e are compared to the theoretically calculated values of the equilibrium plasma composition. On the basis of the measured data, the validity of LTE concept is considered. It was found that deviation from LTE increases to the plasma periphery.     

Thomson Scattering Applied to a Noisy Radiative Plasma

Thomson scattering with a 1.5 ms long pulse mode 20 J ruby laser has been applied to a radiative argon plasma with electron densities n_e from 2.5 10¹⁹ m^?3 to 1.5 10²⁰ m^?3 and an electron temperature T_e of about 3 eV. Photon counting techniques have been used. The accuracy of n_e and T_e to be reached is about 5% after 10 shots. The signal to noise ratio S/N has been optimized by the use of optical filters and a special purpose grating. The effects of these elements on S/N have been calculated. The entrance angle, transmission and quantum efficiency have also been optimized. A comparison between 5 possible laser systems, including a normal mode and a Q-switched mode ruby laser, has been carried out.     

Spatiotemporal spectroscopic diagnostics of a pulse-periodic strontium vapor laser

Results of spectroscopic investigations into plasma of a pulse-periodic strontium vapor laser operating in the superradiance mode on the infrared transition at λ = 6.45 μm are presented. The method of determining the electron temperature and concentration as well as the gas temperature – T _e , n _e , and T _g – based on measuring the absolute intensities of some SrI and SrII and buffer gas (helium or neon) spectral lines is used. Time dependences of the line intensities during a current pulse (τ = 150 ns) and near afterglow (up to 3 μs) are obtained under conditions of non-equilibrium plasma ionization and recombination. The optical system collects radiation from the entire length of the plasma column by means of separating radial volume zones, includingthe central zone and the zone closer to the walls, with the monochromator slit. The results obtained allow us not only to calculate T _e , n _e , and T _g values, but also to trace the spatiotemporal plasma evolution.     

Investigation of the Plasma of a Magnetron Discharge during Titanium Deposition

In the present work the deposition of titanium layers using a planar-magnetron sputtering system is performed. To optimize the sputtering process and to improve the layer quality the plasma has been monitored in front of the target and near the substrate. The plasma was studied by means of Langmuir-probe diagnostics and optical emission spectroscopy (OES). The internal plasma parameters (n_e, k_B T_e) and the relative power dependence of the neutral densities (n_Ti) at the target as well as at the substrate have been determined as functions of discharge power and pressure. It was found that the plasma densities increase with power and pressure and reach a maximum at a certain gas pressure (0.8 Pa) connected with a maximum of the energy influx and a maximum of the mass density of the deposited films.     

Langmuir probe and optical emission spectroscopy studies for RF magnetron sputtering during TiON thin film deposition

Low-pressure plasma of gas mixture of Ar, O₂ and N₂ generated by RF magnetron sputtering was characterized by Langmuir probe and optical emission spectroscopy (OES). The electron temperature (T_e), ion density (n_i) and electron energy distribution function (EEDF) in Ar-O₂-N₂ plasma atmosphere were calculated from I-V characteristic of Langmuir probe. Boltzmann plot method was applied for calculating the vibrational temperature (T_vib) of the second positive system of N₂ (N₂SPS) in Ar-O₂-N₂ plasma. The T_e, n_i, EEDF and T_vib in Ar-O₂-N₂ plasma were studied as a function of O₂ percentages. It was found, the T_vib increased from 0.47 eV to 0.55 eV as the oxygen percentage in Ar-N₂-O₂ plasma increased from 10% to 40%. Further, the T_e increased from 1.6 eV to 3 eV as the O₂ concentration increased from 10% to 40%.     

Electron temperature (T e) measurements by Thomson scattering system

Thomson scattering technique based on high power laser has already proved its superoirity in measuring the electron temperature (T _e and density (n _e) in fusion plasma devices like tokamaks. The method is a direct and unambiguous one, widely used for the localised and simultaneous measurements of the above parameters. In Thomson scattering experiment, the light scattered by the plasma electrons is used for the measurements. The plasma electron temperature is measured from the Doppler shifted scattered spectrum and density from the total scattered intensity. A single point Thomson scattering system involving a Q-switched ruby laser and PMTs as the detector is deployed in ADITYA tokamak to give the plasma electron parameters. The system is capable of providing the parameters T _e from 30 eV to 1 keV and n _e from 5 × 10¹²cm⁻³−5 × 10¹³cm⁻³. The system is also able to give the parameter profile from the plasma center (Z=0 cm) to a vertical position of Z=+22 cm to Z=−14 cm, with a spatial resolution of 1 cm on shot to shot basis. This paper discusses the initial measurements of the plasma temperature from ADITYA.     

Electrostatic Probe Measurements in the Glow Discharge Plasma of a D. C. Magnetron Sputtering System

The characteristics of the plasma surrounding the substrates in a planar magnetron sputtering system with a graphite target have been investigated by electrostatic probe measurements. The behaviour of the ion density n_i and the electron temperature T_e, determining the ion flux that can be extracted by the substrate, with the variation of the basic system parameters, has been studied.     

Spectroscopic studies of sodium nitrate plasma produced by nanosecond laser ablation

We present the optical emission characteristics of the sodium plasma produced at the surface of sodium nitrate (NaNO₃) also known as Chile saltpeter. We used a Q-switched Nd:YAG (Quantel Brilliant) pulsed laser having a pulse duration of 5?ns and 10?Hz repetition rate which is capable of delivering 400?mJ at 1064?nm and 200?mJ at 532?nm. The target material was placed in front of laser beam in air (atmospheric pressure). The experimentally observed line profiles of neutral sodium have been used to extract the electron temperature using the Boltzmann plot method, whereas the electron number density has been determined from the Stark broadening. The electron temperature is calculated by varying the distance from the target surface along the line of propagation of the plasma plume and also by varying the laser irradiance. Besides, we have studied the variation of number density as a function of laser irradiance as well as its variation with the distance from the target surface. It is observed that electron temperature and electron number density increase as the laser irradiance is increased.     

Kinetische Diagnose des Helium-Niederdruckfunkens

In a short spark discharge (energy release time < 0,5 μs) at pressures between 10 and 100 Torr a pure helium plasma was created and investigated by spectroscopic techniques. The following time dependent plasma parameters could be determined (0,5 ≦ t ≦ 5 μs): pressure p from hydrodynamic considerations, electron density n_e from the line profiles and gas temperature T_g from the Boltzmann population of the higher levels, i ≧. The population densities of the levels 3 and 4 deviated from the Boltzmann-T_g-straight line and thus indicated a strong disturbance of thermal equilibrium. For the determination of the electron temperature T_e an ionization rate equation was formulated, which took into consideration electron impact ionization, three body recombination and radiation recombination. The deviation from thermal equilibrium of the spark plasma was nearly constant in the investigated pressure-time region: the ratio T_g/T_e gave ≈ 0,06; the ration n_e/n_o was about 7 orders of magnitude below the corresponding Saha ratio.     

VUV emission model of REB-heated plasma

VUV emission model of a hygrogen plasma with oxygen impurity (T _e=tens of eV,n _e 10¹⁴–10¹⁶ cm^–3,ⁿimp=1–3 % n_e) is constructed in order to judge different possibilities of plasma diagnostics (especiallyT _e measurements) in the REBEX experiments. Two sets of calculations based on the nonstationary corona model are performed: time dependent continuous and line spectra in the range 5 eV—5 keV in the constantT _e approximation (discussion ofT _e measurements by the filter-method) and time dependent intensities of selected spectral lines (2s-2p type) of ionsO ²⁺–O⁵⁺ at variableT _e (including plasma heating by REB and radiative cooling). A possibility of plasma energy content determination from radiation losses is shown.We would like to acknowledge many helpful discussions with dr. P. unka; we thank also dr. J. Ullschmied for comparing our results with diamagnetic measurements.     

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).     

Laser-based optical emission studies of barium plasma

We present the optical emission characteristics of the barium plasma produced at the surface of barium hydroxide Ba(OH)₂, also known as baryta, generated by the first harmonic (1,064 nm) of a Q-switched Nd:YAG laser. The laser beam was focused on target material by placing it in air at atmospheric pressure. The experimentally observed line profiles of neutral barium have been used to extract the electron temperature using the Boltzmann plot method, whereas the electron number density has been determined from the Stark broadening. The electron temperature is calculated by varying distance from the target surface along the line of propagation of plasma plume and also by varying the laser energy. Besides, we have studied the variation of number density as a function of laser energy as well as its variation with distance from the target surface. It is observed that electron temperature and electron number density increase as laser energy increases.     

The dimension of the core and the tail of the plasma produced by laser ablating SiC targets

Optical emission of the plasma generated on SiC samples by pulsed laser beam from an Nd:YAG laser was used to investigate the spatial evolution of the electron temperature (Te) and density (Ne) of the plasma. The range and the profile of the plasma were characterized by the electron temperature Te and the electron density Ne, as functions of the distance from the SiC surface. It was found that the characterized spatial distribution closely coincided with the spatial images of the plasma recorded by a digital camera. The results obtained from the two different experimental measurements are consistent with other data from the literature, obtained either by models or experiments. The present result may give the insight to the complex physical phenomena in the thin film preparations using the pulsed laser deposition (PLD).     

Axial distribution of plasma fluctuations,plasma parameters,deposition rate and grain size during copper deposition

Floating potential fluctuations, plasma parameters and deposition rate have been investigated as a function of axial distance during deposition of copper in direct current (DC) magnetron sputtering system. Fluctuations were analyzed using phase space, power spectra and amplitude bifurcation plots. It has been observed that the fluctuations are modified from chaotic to ordered state with increase in the axial distance from cathode. Plasma parameters such as electron density (n_e), electron temperature (T_e) and deposition rate (D_r) were measured and correlated with plasma fluctuations. It was found that more the deposition rate, greater the grain size, higher the electron density, higher the electron temperature and more chaotic the oscillations near the cathode. This observation could be helpful to the thin film technology industry to optimize the required film.     

Electron cooling in three‐dimensional Dirac fermion systems at low temperature: Effect of screening

Hot electron cooling rate P, due to acoustic phonons, is investigated in three‐dimensional Dirac fermion systems at low temperature taking account of the screening of electron–acoustic phonon interaction. P is studied as a function of electron temperature T_e and electron concentration n_e. Screening is found to suppress P very significantly for about T_e < 0.5 K and its effect reduces considerably for about T_e > 1 K in Cd₃As₂. In Bloch–Grüneisen (BG) regime, for screened (unscreened) case the T_e dependence is P ～ T_e⁹(T_e⁵) and the n_e dependence gives P ～ n_e^–5/3 (n_e^–1/3). The T_e dependence is characteristic of 3D phonons and n_e dependence is characteristics of 3D Dirac fermions. The plot of P /T_e⁴ vs. T_e shows a maximum at temperature T_em which shifts to higher values for larger n_e. Interestingly, the maximum is nearly same for different n_e and T_em/n_e^1/3 being nearly constant. More importantly, we propose, the n_e dependent measurements of P would provide a clearer signature to identify 3D Dirac semimetal phase. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

CO2-laser gas discharges in narrow gaps

We have studied RF discharges as excitation mechanisms for distributed feedback (DFB) CO₂ lasers. For CO₂ laser plasmas the reduced electric fieldE/N has to be in a well-defined range. The reduced electric fieldsE/N of gas discharges in the narrow gaps with widths of the order of 100 m required for DFB are considerably above this range. In order to study the feasibility of these RF-excited discharges for DFB CO₂ lasers we have measured the electron temperatureT _e in their plasmas. From helium-line-intensity ratios we have deduced a lower limit of the electron temperatureT _e of 4eV. The observed high intensities of bands of singly ionized nitrogen indicate an even higher electron temperature, but an efficient pumping of the upper laser level is not possible with an electron temperature above 2.5 eV.We have estimated the electron densityn _e and the current densityj _e from ratios of the intesities of forbidden and allowed helium lines. The high current densityj _e is in the range of abnormal glow discharges.In the gas discharges between narrow gaps the electron oscillation amplitudex _e is large than the electrode separationd. In order to replace the resulting high electron losses a high electron temperatureT _e is necessary to sustain the gas discharge. Because of this high electron temperatureT _e an efficient pumping of the upper laser level is not possible.