M. A. Baig

Measurement of electron density and temperature of a laser-induced zinc plasma

We report spectroscopic studies of the zinc plasma produced in air by the three harmonics of a Q-switched pulsed Nd : YAG laser at 1064, 532 and 355 nm. The electron temperature has been determined from the intensity ratio of the transitions (4s4d 3 D3 → 4s4p 3 P2) at 334.5 nm and (4s5s 3 S1 → 4s4p 3 P2) at 481.0 nm of neutral zinc, whereas the electron number density has been evaluated from the Stark broadening of the (4s4d 3 D3 → 4s4p 3 P2) transition at 334.5 nm. It is observed that both these parameters decrease as the distance from the target surface increases and it increases with an increase in the laser irradiance. The power law is fitted to the experimental data.

A comparative study of single and double pulse of laser induced breakdown spectroscopy of silver

We present a comparative study of the collinear and orthogonal pre-ablation dual pulse configurations of laser induced breakdown spectroscopy (LIBS) of silver using Nd:YAG lasers. The effect of the inter-pulse delay and the ratio of the laser pulse energies on the signal intensity enhancement for both the dual pulse configurations have been investigated. Using the first laser at 532 nm and second laser at 1064 nm delayed by 5 μs, we achieved nearly 2 times signal enhancement in the collinear double-pulsed configuration and nearly 12 times in the pre-ablation orthogonal configuration as compared to SP LIBS. It is ascertained that at the optimized value of the inter-pulse delay between the two lasers, the intensity ratio of the neutral silver lines follows the local thermo dynamical equilibrium (LTE) condition and it is also in excellent agreement with that of the relative transitions probabilities ratio listed in the NIST data base.

Optical emission studies of the mercury plasma generated by the fundamental, second and third harmonics of a Nd : YAG laser

We report the first measurements of the optical emission spectra of mercury plasma produced by the fundamental, second and third harmonics of a Nd : YAG laser, which reveals numerous transitions due to the neutral and singly ionized mercury. The excitation temperature has been determined from the Boltzmann plots, whereas the electron number density is estimated from the Stark broaden profile of the spectral lines. The estimated range of the excitation temperature and the electron number density is (7000–14000) K and (3.6 × 1016 to 2.5 × 1017) cm−3, respectively. The behaviour of the excitation temperature and the electron number density with the laser irradiance has been studied. The spatial distribution of the temperature and the electron number density has also been investigated besides the studies of absorption in the plasma through inverse bremstrahlung and photoionization.

Laser isotope separation of lithium by two-step photoionization

Lithium isotope separation has been achieved employing the two-step photoionization technique along with a narrow band dye laser in conjunction with a time of flight mass spectrometer. The demonstrated method yields a high degree of selectivity by tuning the dye laser at the resonance levels of Li6 and Li7. It is inferred that the concentration of the natural abundance of the Li6 isotope gets enhanced up to over 47% as the exciter dye laser is tuned to the P1∕22 of Li6 even if the linewidth of the exciter laser is not sufficiently narrow to excite the isotopic level. It is also noticed that the much higher energy density of the exciter laser limits the resolution of the fine structure levels of the lithium isotopes that leads to a loss in the enrichment of Li6 due to the power-broadening effect. Measurements of the photoionization cross section of the lithium isotopes from the 2pP1∕2,3∕22, excited states for Li6 and Li7 and the corresponding number densities are reported.

Spatial diagnostics of the laser induced lithium fluoride plasma

We present spatial characteristics of the lithium fluoride plasma generated by the fundamental and second harmonic of a Nd:YAG laser. The plume emission has been recorded spatially using five spectrometers covering the spectral region from 200 nm to 720 nm. The electron density is measured from the Stark broadened line profile of the line at 610.37 nm, whereas the plasma temperature has been determined using the Boltzmann plot method including all the observed spectral lines of lithium. Both the plasma parameters; electron density and plasma temperature decrease with the increase of the distance from the target surface. The thermal conduction towards the target, the radiative cooling of the plasma, and the conversion of thermal energy into kinetic energy are the main mechanisms responsible for the spatially decrease of the plasma parameters.

Plasma Diagnostic Study of Alumina

In this paper, we present the spectroscopic studies of the plasma generated at the surface of alumina (Al₂O₃) by the fundamental (1064 nm) and second harmonic (532 nm) of a Q-switched Nd:YAG laser. The spectrum reveals numerous transitions of neutral aluminum along with molecular bands of the <i>B</i>²Σ- <i>X</i>²Σ system of AlO. We have studied the spatial behavior of the plasma temperature <i>Te</i> and electron number density <i>Ne</i> determined using the Boltzmann plot method and Stark broadening of line, respectively. Moreover, we have studied the variation of the plasma parameters as a function of the laser energy.

(\hbox{Al}_{2} \hbox{O}_{3})

We present a systematic study on the optimization of the following: 1) interpulse delay; 2) the pulse energies ratio; and 3) the combination of laser wavelengths to achieve the signal enhancement in double-pulse laser-induced breakdown spectroscopy (LIBS) on magnesium target using two Nd:YAG lasers in collinear configuration. More than 350 times signal intensity enhancement is achieved in the neutral magnesium lines on an appropriate combination of laser wavelengths with the optimized values of the interpulse delay and the laser pulse energies ratio.

Generated by the Fundamental and Second Harmonics of a Nd:YAG Laser

We present the first measurements of the photoionization cross-section of the 3p 2 P1/2, 3/2 excited states for both the lithium isotopes Li 6 and Li 7 in the region close to the Li + 1s 21 S threshold (from 0 to 3 eV) using the two-step photoionization and the saturation technique. Narrow linewidth dye lasers have been used in combination with a locally developed atomic beam-TOF mass spectrometer to measure the photoion signals as a function of energy density of the ionizing laser. It is observed that the cross-section is maximum near the ionization threshold and decreases monotonically as the excess photon energy of the ionizing laser is increased. The deduced number densities of the isotopes are Li 6 (1.2 × 10 8 atoms cm −3 ) and Li 7 (1.2 × 10 9 atoms cm −3 ), which are found to be close to their natural abundance ratio within the experimental error. Our experimental results of the measurement of the cross-section are also in good agreement with earlier theoretical work. (Some figures in this article are in colour only in the electronic version)

On the Optimization for Enhanced Dual-Pulse Laser-Induced Breakdown Spectroscopy

We present photoionization cross section measurements from the 6s6p 1 P1 and 3 P1 excited states of barium at and above the first ionization threshold. The experiments have been performed using a thermionic diode ion detector in a space charge limited mode in conjunction with a Nd:YAG laser system and the saturation technique to determine the photoionization cross sections. The absolute values of the photoionization cross section from the 6s6p 1 P1 and 3 P1 excited states at the first ionization threshold have been determined as 90 ± 14 Mb and 102 ± 15 Mb, respectively. The measured values of the photoionization cross section from the 6s6p 1 P1 excited state are compared with available experimental and theoretical work, while the absolute photoionization cross sections from the 6s6p 3 P1 excited state are reported for the first time. (Some figures in this article are in colour only in the electronic version)

Simultaneous measurements of photoionization cross-sections of lithium isotopes from 3p 2P1/2, 3/2

The photoionization cross section from the 3s3p 1P1 excited state has been measured in the energy region from the first ionization threshold up to 1.4 eV excess energy using a two-step photoionization and saturated ionization technique in conjunction with an atomic beam source and a time-of-flight mass spectrometer that enables the separation of the three stable isotopes of magnesium on the time axis. The absolute value of the photoionization cross sections from the 3s3p 1P1 excited state near the 3s ionization threshold has been measured as 90 ± 16 Mb (at 354.5 nm ionizing wavelength) for the dominating isotope (24Mg) whereas the value at the peak of the 3p2 1S0 auto-ionizing resonance has been determined as 785 ± 141 Mb. The present experimentally measured photoionization cross sections are compared with the existing experimental and theoretical work, showing excellent agreement.