Pakistan Research Repository Home

Title of Thesis

Sultan Ahmad
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)
ytterbium, synchrotron radiation, laser radiation, single photon excitation, multi step resonance ionization, photoabsorption spectrum, multichannel quantum defect theory, rydberg atoms, innershell excitation

The spectra of ytterbium have been investigated above and below the first ionization threshold using two different techniques, single photon excitation via synchrotron radiation and multi step resonance ionization spectroscopy. In the synchrotron radiation based experiments, the photoabsorption spectrum in the wavelength region 1200 - 2000 A was recorded in the first order of a 3 meter spectrograph equipped with a 6000 line/mm holographic grating. More than two hundred new levels of YbI are observed, which are interpreted as inner shell transitions 4f446s2 --+ 4f13(2Fs5/2,7/2) nd, ng and doubly excited transitions, 4f446s2 --+ 4f44 5d (2D3/2. 5/2) np, nf and 4f446s2 --+ 4f14 6p(2P1/2 3/2) ns, nd series. All the observed levels lie above the first ionization threshold which are ordered into Rydberg series converging on to six limits. The interchannel interactions between the overlapped series have been parametrized using multichannel quantum defect theory (MQDT).

The laser based stepwise excitation experiments on ytterbium are performed using narrow band width dye lasers pumped by a Nd: YAG laser. The thermionic diode which has a very high gain, high sensitivity and good linearity is used for the ion detection. Four different experiments are employed to investigate the high lying odd and even parity levels. First three experiments are performed to record the principal and inter-combination series. Three colour or three photon spectra are compared with the two color three photon spectra below the first ionization. Moreover, we confirmed the different intermediate levels resulting from the single photon and two photon excitations. It is observed that the relative intensities of levels varies in each experiment, revealing strong influence of perturbers. In the other experiment, we have observed the even parity autoionizing resonances in the range of 70700 - 72000 cm-I using three color four photon excitation technique. More than 40 new levels attributable to the inner shell excitation corresponding to the 4f446s2nl Rydberg series are detected. The spectra are analyzed guided by the spectral line shape, parent ion limit and quantum defect approach.

Download Full Thesis
1833.47 KB
S. No. Chapter Title of the Chapters Page Size (KB)
1 0 Contents
257.6 KB
2 1 Introduction
99.27 KB
  1.1 Rydberg Atoms 2
  1.2 Properties Of Rydberg Atoms 2
  1.3 Quantum Defect Theory 4
  1.4 Isolated Autoionizing Resonance 7
3 2 Experimental Details
161.09 KB
  2.1 Introduction 9
  2.2 The Laser System 9
  2.3 Dye Laser 10
  2.4 The Thermionic Diode Detector 13
  2.5 Data Acquisition System 17
4 3 Experiment Using Synchrotron Radiation
478.7 KB
  3.1 Synchrotron Radiation 18
  3.2 Introduction To The Experiment 19
  3.3 Experimental Details 20
  3.4 Results And Discussion 21
  3.5 Innershell Excitation 23
  3.6 Double Excitations 33
  3.7 Measurement Of Photoionization Cross Section Of The Doubly Excited States 46
5 4 Study Of Principal And Inter-Combination Series Of Ytterbium
376.39 KB
  4.1 Three Color Three Photon Excitation Spectrum Of Ytterbium 49
  4.2 Two Color Three Photon Excitation Spectrum Of Ytterbium 60
  4.3 Mqdt Analysis Of The Odd Parity Rydberg Series Ofyb 67
6 5 Three-Step Laser Excitation Of The Even Parity Autoionizing Resonances In Ytterbium
585.87 KB
  5.1 Introduction 71
  5.2 Experimental Details 73
  5.3 Results And Discussion 75
  5.4 Conclusion 84
  5.5 References 89