Shaukat Mahmood

Diagnostics of cadmium plasma produced by laser ablation

Optical measurements of the cadmium plasma produced by the fundamental, second, and third harmonics of a Nd:YAG laser are reported. The excitation temperature and ionic temperature have been determined from the Boltzmann plot and Saha equation, whereas the number density is estimated from the Stark broadened profile of the spectral lines. The variations in the excitation temperature and number density with the ambient air pressure as well as with the laser irradiance have been studied. Besides, the spatial distributions of the temperature and number density have been investigated.

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.

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.

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.

Laser induced isotopic studies using time of flight mass spectrometer

The present work is devoted to the spectroscopic studies of the lithium isotopes using a locally designed and fabricated atomic beam - Time of Flight mass spectrometer system. Different intermediate states 2p 2P1/2, 3/2, 3s 2S, 3p 2p, 3d 2D, 4s 2S, 4p 2p and 4d 2D of lithium have been exploited for the isotope separation. The proposed method enabled the isotope separation even if the isotopes have not been selectively excited. Fine structure in the 2p excited state for both the isotopes Li6 and Li7 has been resolved for the first time using this new technique. 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. We have investigated the yield of Li6 exploiting the above mentioned excited states. An efficient pathway for the quantitative enrichment of the Li6 isotope by tuning the exciter laser at the 3p 2p1/2,3/2 state of Li6 have also been proposed in which a concentration up to 60 % is demonstrated from a natural isotopic abundant lithium sample. In addition, we proposed an alternate technique for the simultaneous measurement of photo ionization cross section of the excited states of the isotopes and their corresponding number densities. We report extensive new measurements of the photo ionization cross section of the above mentioned excited states. By varying the frequency of the ionizer laser, different regions of the continuum have been investigated and a decreasing behavior of the photo ionization cross section by increasing the energy of the ionizer laser is reported experimentally for the first time. The photoionization cross section from the 2p 2pl/2,3/2, 3p 2p, 4p 2p, 3d 2D and 4d 2D excited states of the lithium isotopes is maximum near the ionization threshold and a smooth decrease in the cross section is observed for the excess energy above threshold. However, for the 3s 2S and 4s 2S excited states, the cross section of the photoionization is lower at threshold and then increases to a maximum value and then decreases. It is also observed that the decrease in the cross section of the 3d 2D and 4d 2D excited states is more hydrogenic than that of the 2p 2P1/2,3/2, 3p 2p, and 4p 2p excited states and for the 3s 2S and 4s 2S excited states, it is purely non- hydrogenic