Pakistan Research Repository Home

Title of Thesis

Institute/University/Department Details
Department of Physics/ Quaid-i-Azam University, Islamabad
Number of Pages
Keywords (Extracted from title, table of contents and abstract of thesis)
multi-photon excitation, strontium, multistep excitation, ionization probability, thermionic diode detectors, strontium vapor

Multi-photon and multi-step excitation schemes have been used to investigate the spectra of strontium in the discrete and autoionization regions using two different experimental arrangements, a thermionic diode ion detector and an atomic beam apparatus, in conjunction with a Nd: YAG pumped dye laser system. In the first experiment we have recorded the laser assisted collisionally induced sequential excitation and ionization spectrum of strontium using the two-photon excitation scheme. This experiment covers both direct two-photon excitation from the ground state and the sequential excitation from the 5s5p IPI level. The intensity variations among the 5snd 1D2 and 3D2 are discussed in the light of its interactions with the 4d6s 1D2 and 3D2 interlopers. To supplement the experiment their interactions are parameterized using two channels MQDT-model, which seem to be appropriate to describe the 5snd 1, 3D2 series perturbations. In the second experiment an even parity isolated autoionizing resonance (4d2 + 4p2) 1D2 has been studied via direct two-photon excitation from the ground state and via the 5s5p 1P1 intermediate level. It is observed that although the width of the autoionizing resonance remains constant and is independent of the excitation mechanism but its line shape q-parameter does depend on the excitation path. In the third, experiment three-photon excitation four-photon ionization spectra of strontium have been recorded in the laser energy region from 14970 - 15350 cm-1. The 5snp 1P1 and 5snf,1F3 Rydberg series have been identified along with an additional dominating signal, lying adjacent to the three-photon ionization threshold, arising from two-photon resonant three-photon ionization through the 5s6s 1S0 level. In the fourth experiment while using two-color three-photon excitation scheme a number of odd parity autoionizing Rydberg series possessing J=l, 2 and 3 have been recorded attached to the 4d 2D3/2,5/2 ionic levels excited via 4d2 3p0 and 4d2 3P2 intermediate levels. It is observed that the Rydberg levels attached to the 4d 2D3/2 limit are observable from the 4d2 3p0 intermediate whereas only the levels built on the 4d 2D5/2 ionization limit are observable when excited from the 4d2 3P2 intermediate level. The level assignments and the line shapes simulations of the autoionizing resonances have been made using the multichannel quantum defect theory.

Download Full Thesis
916.4 KB
S. No. Chapter Title of the Chapters Page Size (KB)
1 0 Contents
79.31 KB
2 1 Introduction
117.45 KB
  1.1 Multiphoton excitation 1
  1.2 Multistep excitation 2
  1.3 Ionization probability 3
  1.4 Rydberg states 6
  1.5 Thermionic diode detectors 7
  1.6 Atomic beam apparatus 9
3 2 Molecular Dissociatve Sequential Excitation And Ionization Of Strontium Vapor
247.95 KB
  2.1 Historical background 12
  2.2 Experimental setup 13
  2.3 Results and Discussion 14
4 3 Near Threshold Photoionization Spectrum Of Strontium
99.85 KB
  3.1 Historical background 31
  3.2 Experimental setup 32
  3.3 Results and Discussion 32
5 4 Three-Photon Excitation Of Strontium Rydberg Levels
105.17 KB
  4.1 Historical background 39
  4.2 Experimental setup 40
  4.3 Results and Discussion 41
6 5 Two-Color Three-Photon Resonant Excitation Spectrum Of Strontium In The Autoionization Region
315.65 KB
  5.1 Historical background 47
  5.2 Experimental setup 49
  5.3 Results and Discussion 50
7 6 Conclusion 69
58.52 KB
  6.1 References 71