Laser-induced plasma electron number density:Stark broadening method versus the Saha-Boltzmann equation

We report spectroscopic studies on plasma electron number density of laser-induced plasma produced by ns-Nd：YAG laser light pulses on an aluminum sample in air at atmospheric pressure. The effect of different laser energy and the effect of different laser wavelengths were compared. The experimentally observed line profiles of neutral aluminum have been used to extract the excitation temperature using the Boltzmann plot method, whereas the electron number density has been determined from the Stark broadened as well as using the Saha-Boltzmann equation （SBE）. Each approach was also carried out by using the AI emission line and Mg emission lines. It was observed that the,SBE method generated a little higher electron number density value than the Stark broadening, method, but within the experimental uncertainty range. Comparisons of Ne determined by the two methods show the presence of a linear relation which is independent of laser energy or laser wavelength. These results show the applicability of the SBE method for Are determination, especially when the system does not have any pure emission lines whose electron impact factor is known, Also use of Mg lines gives superior results than Al lines.

Spectral Characteristics of Laser-Induced Graphite Plasma in Ambient Air

An experimental setup of laser-induced graphite plasma was built and the spectral characteristics and properties of graphite plasma were studied. From the temporal behavior of graphite plasma, the duration of CN partials （B2 ∑＋ →-X2 ∑＋） emission was two times longer than that of atomic carbon, and all intensities reached the maximum during the early stage from 0.2 μs to 0.8 μs. The electron temperature decreased from 11807 K to 8755 K, the vibration temperature decreased from 8973 K to 6472 K, and the rotational temperature decreased from 7288 K to 4491 K with the delay time, respectively. The effect of the laser energy was also studied, and it was found that the thresholds and spectral characteristics of CN molecular and C atomic spectroscopy presented great differences. At lower laser energies, the electron excited temperature, the electron density, the vibrational temperature and rotational temperature of CN partials increased rapidly. At higher laser energies, the increasing of electron excited temperature and electron density slow down, and the vibrational temperature and rotational temperature even trend to saturation due to plasma shielding and dissociation of CN molecules. The relationship among the three kinds of temperatures was Telec〉Tvib〉Trot at the same time. The electron density of the graphite plasma was in the order of 1017 cm-3 and 1018 cm-3.

Time-resolved evaluation of uranium plasma in different atmospheres by laser-induced breakdown spectroscopy

This work reports spectroscopic studies of uranium containing plasma generated in air and argon environments. The 532 nm Q-switched Nd：YAG laser generates the optical breakdown plasma, which was recorded by a spectrometer and an intensified charge coupled device having a resolution of 25 pm. Neutral and ionized uranium lines in the wavelength range of 385.8-391.9 nm indicate significant width and shift variations during the first few microseconds. Electron temperature and density of the plasma are determined using the Boltzmann plot and the Saha-Boltzmann equation at various time delay. The study reveals the power law decay pattern of electron temperature and density, which changes to exponential decay pattern if large gate- width is used to acquire the signal, due to an averaging effect.

Spectral Characterization of Laser Induced Plasma from Titanium Dioxide

Optical emission from TiO2 plasma, generated by a nanosecond laser is spectroscopically analysed. The main chemical species are identified and the spatio-temporal distribution of the plasma parameters such as electron temperature and density are characterized based on the study of spectral distribution of the line intensities and their broadening characteristics. The parameters of laser induced plasma vary quickly owing to its expansion at low background pressure and the possible deviations from local thermodynamic equilibrium conditions are tested to show its validity.

Keyhole formation and its characteristics in laser welding mode transition

Keyhole is the most important characteristic for laser deep penetration welding, and its formation indicates the beginning of laser deep penetration welding mode. The keyhole developing process was analyzed and the keyhole formation time was calculated according to welding speed and the length of weld bead formed in the keyhole formation process. The results showed that the keyhole forms in 40 -70 ms at different rate of change of laser power. In laser deep penetration welding process, the variation of light intensity radiated by laser induced plasma can identify the keyhole formation, but it can not be used to estimate the keyhole formation time because of delay effect.

Laser-induced liquid tin discharge plasma and its EUV spectra

Laser-induced discharge plasmas(LDPs) have the potential to be inspection and metrology sources in extreme ultraviolet(EUV) lithography. An LDP EUV source was developed to avoid tin electrode erosion in which a tin pool was used as a cathode. A CO2 pulse laser was focused on the liquid tin target surface, and then a breakdown occurred in a very short time. The voltage-current characteristics of the discharge oscillated, lasting for several microseconds, and an RLC fitting model was used to obtain the inductance and resistance. An intensified chargecoupled device(ICCD) camera was used to investigate the dynamics of LDP, which can explain the formation of a discharge channel. The EUV spectra of laser-induced liquid tin discharge plasma were detected by a grazing incident ultraviolet spectrometer, compared with a laser-produced tin droplet plasma EUV spectrum. To explain the EUV spectrum difference of laser-induced liquid tin discharge plasma and laser-produced tin droplet plasma,the collision radiation(CR) model combined with COWAN code was used to fit the experimental EUV spectrum, which can estimate the electron temperature and density of the plasma.

Characteristics of laser induced discharge tin plasma and its extreme ultraviolet radiation

In this paper,a CO_(2) laser induced discharge plasma extreme ultraviolet(EUV)source experimental device was established.The optical emission spectroscopy was used to diagnose the characteristics of the plasma,and the evolution of electron temperature and electron density with time was obtained.The influence of discharge voltage on plasma parameters was analyzed and discussed.The EUV radiation characteristics of the plasma were investigated by self-made grazing incidence EUV spectrometer.The EUV radiation intensity and conversion efficiency were discussed.