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Title of Thesis

Mansoora Majeed
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)
pump phase fluctuations, correlated spontaneous emission laser, phase fluctuations, noise-free amplification, phase squeezing, two-photon laser

The fundamental source of noise in laser and optical amplifier is spontaneous emission. However, it is possible to reduce this noise by preparing the gain medium (atoms) in coherent superposition of states. There are essentially two schemes for generating atomic coherence in optical amplifiers.

First scheme involves the preparation of atoms in a coherent superposition of states before injecting them inside the cavity. In the other scheme atoms (initially pumped incoherently) are continuously driven by an external pump field inside the cavity. Almost all the studies concerning the quenching of spontaneous emission noise in optical amplifiers, based on the notion of atomic coherent superposition, ignore the finite bandwidth of the field that is responsible for generating coherence. In this dissertation, we have examined the effect of the finite bandwidth associated with the phase fluctuations of the driving field on a number of noise quenching schemes.

It is known that coherent preparation of atoms can, under certain conditions, lead to noise-free amplification and almost 50 percent phase squeezing in a two-photon correlated emission laser. We study the effect of phase fluctuations in the injected atoms on the phase noise of the field in these systems. We discuss the conditions under which squeezing is preserved in the two-photon linear amplifiers. We also show that, even for very large phase fluctuations in the injected atoms, almost 50 percent phase squeezing can be achieved. The corresponding gain is however significantly reduced.

We also study a system of phase-sensitive amplifier where atoms are prepared in a coherent superposition of states by a strong classical field. We study the role of pump phase fluctuations associated with the finite linewidth on the quantum statistical properties of the radiation field. A study of output field characteristics reveals that the presence of a weak pump field gives rise to equal variances in both the field quadratures which are independent of linewidth. On the other hand, the presence of strong pump field alters the output field characteristics with the generation of squeezing which is later on destroyed due to the presence of phase fluctuations.

Download Full Thesis
780.34 KB
S. No. Chapter Title of the Chapters Page Size (KB)
1 0 Contents 0
72.47 KB
2 1 Introduction 1
127.04 KB
  1.1 Quantum-Mechanical Description Of Amplifiers
  1.2 Atomic Coherence And Its Significance
  1.3 Two-Photon Correlated Spontaneous Emission Laser
  1.4 Phase Diffusion Model And The Laser Linewidth
  1.5 Outline Of Thesis
3 2 Quantum Theory Of Linear Amplifier And Correlated Spontaneous Emission Laser
243.61 KB
  2.1 Introduction
  2.2 Linear Amplification Process: General Description
  2.3 Phase-Sensitive Amplification In A Three-Level Atomic System
  2.4 Theory Of Two-Photon Correlated Spontaneous Emission Laser
4 3 Role Of Phase Fluctuations In Noise-Free Amplification And Phase Squeezing In A Two-Photon Laser
153.32 KB
  3.1 Introduction
  3.2 Natural linewidth Of laser
  3.3 Noise-Free Amplification
  3.4 Effect Of Phase Fluctuations On Correlated Emission Laser
5 4 Role Of Pump Phase Fluctuations In A Two Photon Phase-Sensitive Amplifier
255.76 KB
  4.1 Introduction
  4.2 Formulation Of Problem
  4.3 Master Equations For The Evaluation Of Density Matrices
  4.4 Influence Of Pump Phase Fluctuations On Amplitude Variance
  4.5 Results And Discussions
6 5 Reference
58.52 KB