Raheel Ali

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.

Spectroscopic characterization of laser ablation brass plasma

We present optical emission studies of the laser ablation brass plasma generated by the fundamental, second, and third harmonics of a neodymium doped yttrium aluminum garnet laser. The spectra predominantly reveal the spectral lines of the neutral and singly ionized copper and zinc. The excitation temperatures are determined by the Boltzmann plot method, whereas the electron number densities have been extracted from the Stark broadened line profiles. The spatial variations in the spectral line intensities and the plasma parameters at 1000, 500, and 100 mbar air pressures have been evaluated. Besides, the effect of the ambient gases (He, Ne, and Ar), the laser irradiance, and the laser wavelengths on the plasma parameters have been investigated.

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.

On the Rydberg transitions and elemental compositions in the laser produced Al (6063) plasma

! 3p 2 P1=2,3=2 (n ¼ 3 – 8), ns 2 S1=2 ! 3p 2 P1=2,3=2 (n ¼ 4–6), and the dominant spectral lines of the other constituent elements. We have extracted the relative abundance of the impurities using the relative intensity ratio method. Besides, we have calculated the electron temperature (� 7580 K) from the Boltzmann plot method and the electron number densities (� 1.4 � 10 17 =cm 3 ) from the Stark widths of the aluminum spectral lines. The plasma parameters determined in the present work are in agreement with that reported in the literature. The molecular vibrational transitions of the AlO free radical associated with the B 2 P !X 2 P band system have also been identified. V C 2011 American Institute of Physics. [doi:10.1063/1.3625552]

Two-colour three-photon excitation of the 6snf 1,3F3 and 6snp 1P1, 3P1,2 Rydberg levels of Yb I

We report a reinvestigation of the 6snf 1,3F3 (9 < or = n < or = 30), 6snp 1P1 (12 < or = n < or = 56), 6snp 3P1 (12 < or = n < or = 21) and 6snp 3P2 (12 < or = n < or = 19) Rydberg states of ytterbium atom using a two-colour three-photon resonant excitation technique through the 4f146s5d 1D2 intermediate level. The spectra were observed using two dye lasers simultaneously pumped by a common Nd:YAG laser in conjunction with a thermionic diode ion detector. Some new levels have been identified in the vicinity of the 6snf (9 < or = n < or = 16) Rydberg levels. Three new perturbers 4f135d 26s3D3 at 48 584.1 cm-1, 4f135d26s 1F3 at 49 122.4 cm-1 and 4f135d26s 3G3 at 49 661.6 cm-1 have been located in addition to observation of the 6s9d 1D2 and 6p2 1D2 even parity levels due to sequential excitation from the 6s6p 1P1 level. The interchannel interactions among the J = 2 and J = 3 channels have been analysed using multichannel quantum defect theory.

Near-threshold photoionization spectra of strontium

Abstract We report a comparison between the excitation of an even parity isolated autoionization resonance (4d2+5p2) 1 D 2 of strontium from the ground state by two-photon non-resonant excitation and two-step resonant excitation processes. It is observed that although the line shape q-parameter is different for the two processes, the width of the resonance is independent of the excitation mechanism.

On the first ionization potential of lithium

New experimental data on the highly excited Rydberg states of lithium have been acquired, using a two-step laser excitation technique in combination with a thermionic diode ion detector. The atoms are prepared in the 3s 2S1/2 intermediate level by two-photon excitation from the ground state, whereas the np 2P1/2,3/2 levels have been approached via single photon absorption. The new observations include much extended np 2P1/2,3/2 Rydberg series (15 ? n ? 60). The Rydberg relation fit to the new data yields the quantum defect for the np 2P1/2,3/2 series as 0.051(4) and the binding energy of the 3s 2S1/2 level as 16?281.19(2) cm?1. Adding the energy of the 3s 2S1/2 level and its binding energy reveals the first ionization potential of lithium as 43?487.26(3) cm?1.

THREE-COLOUR FOUR-PHOTON RESONANT EXCITATION OF THE EVEN-PARITY AUTOIONIZING RESONANCES IN YB I

We report new data on the even-parity autoionizing resonances due to the 4f inner-shell excitation in ytterbium using a three-colour four-photon resonant excitation technique. The spectra were observed using three dye lasers simultaneously pumped by a common Nd:YAG laser in conjunction with a thermionic diode ion detector. More than 50 new levels corresponding to the 4f136s2n Rydberg series have been detected. The data were analysed in the light of the spectral lineshapes, parent ion configurations and quantum defect approach.

DIAGNOSTICS OF COPPER PLASMA PRODUCED BY THE FUNDAMENTAL, SECOND AND THIRD HARMONICS OF A Nd:YAG LASER

We report measurements of the copper plasma parameters generated by the fundamental, second and third harmonics of a Nd:YAG laser. The 3d94s5s2D3/2→3d94 s4p2F5/2 at 464.25 nm, 4p 2P3/2→3d94s2D5/2 at 510.55 nm, 4d 2 D3/2→4p2P1/2 at 515.32 nm 4d 2 D5/2→4p2P3/2 at 521.82 nm and 4p 2 P3/2→3d94s2D3/2 at 570.02 nm transitions have been used to estimate the electron temperature through the Boltzmann plot method. The number density has been estimated from the Stark broadened profiles of the spectral lines. The spatial behaviour of the electron temperature and number density has been examined at different ambient air pressures and with laser irradiance. The temperature and number density are found to be in the range from 14700 to 13600 K and 2.1×1016 to 1.78×1016cm-3 for the 1064 nm laser, from 14200 to 12800 K and 2.2×1016 to 1.8×1016cm-3 for the 532 nm laser and from 14100 to 12500 K and 2.4×1016 to 1.9×1016cm-3 for the 355 nm laser.

Measurements of photoionization cross sections from the 5s5p 1P1 and 5s6s 1S0 excited states of strontium

We present new measurements of the photoionization cross section from the 5s5p 1 P1 state employing two-step excitation and from the 5s6s 1 S0 state using two-photon excitation and then a second laser for subsequent ionization in each case. The two dye lasers, pumped by a common Nd:YAG laser, have been used in conjunction with a thermionic diode ion detector in one set of experiments and an atomic beam apparatus in the second experiment. The photoionization cross sections have been measured at six different wavelengths between 355 nm and 410 nm. The absolute value of the cross section at the peak of the (4d 2 +5p 2 ) 1 D2 autoionizing resonance is determined as 5450 (18%) Mb. The photoionization cross section from the 5s6s 1 S0 state is estimated as 0.41 (16%) Mb.