Gain narrowing in few-atom systems

Using a density matrix approach, we study the simplest systems that display both gain and feedback: clusters of 2 to 5 atoms, one of which is pumped. The other atoms supply feedback through multiple scattering of light. We show that, if the atoms are in each other's near-field, the system exhibits large gain narrowing and spectral mode redistribution. The observed phenomena are more pronounced if the feedback is enhanced. Our system is to our knowledge the simplest exactly solvable microscopic system which shows the approach to laser oscillation

Scattering Lasers

In this thesis, we present a study of the fundamental building blocks of laser systems. In this respect, we face the question of presenting a workable definition of a laser. It is rewarding to formulate such a definition since this clarifies semantic issues right from the beginning and allows us to focus on the physics of the systems we present. In this thesis, we adopt the following definition: A single-mode laser is a system which combines gain and feedback, such that one field mode (the laser mode) is characterized by a gain-induced increase of its spectral weight at the cost of all other system modes. The amplitudes of all system modes decay in time to an external bath and are replenished by the gain source. Our definition of a single-mode laser is, although debatable, a workable definition in terms of experimentally observable quantities; its usage allows us to disregard laser-related semantic issues and concentrate on the physics of the systems at hand

Light scattering from three-level systems: The T-matrix of a point-dipole with gain

We present an extension of the T-matrix approach to scattering of light by a three-level system, using a description based on a Master equation. More particularly, we apply our formalism to calculate the T-matrix of a pumped three-level atom, providing an exact and analytical expression describing the influence of a pump on the light scattering properties of an atomic three-level system