LASER ASSISTED 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.\ud \ud 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- hydrogeni