Counterintuitive versus regular inversionless gain in a coherently prepared ladder scheme

In this research we study lasing without population inversion from a three-level atom interacting with two laser fields, in the ladder or cascade scheme. We investigate counterintuitive sequencing as well as regular sequencing of the time of laser fields application. In a counterintuitive sequence scheme a short probe pulse is introduced prior to the application of the coupling field, in contrast, to a standard sequence scheme, where both fields are introduced at the same time. The influence of varying the probe pulse width and time delay between the initiation of probe and coupling fields on transient probe gain is investigated. The calculations indicate the potential of producing gain without inversion via counterintuitive sequence scheme.     

Counterintuitive gain without inversion enhancement in pulsed fields sequence

Ultrashort pulse counterintuitive sequencing of three level lambda scheme shows five fold enhancement of the amplification without inversion on the probe transition. Introducing a short pulse weak probe field prior to the strong pump field results in an enhanced dispersion and stronger amplification on the probe field. The presence of an incoherent pump populating the upper level is crucial to the amplification. Parametric study of this effect is briefly presented.     

Counterintuitive Gaussian pulse sequence in three-level ladder scheme

In a recent publication we have studied counterintuitive pulse sequence applied to a three level ladder scheme, utilizing rectangular-shaped pulses. In this research we investigate amplification without population inversion in a three level ladder system interacting with two electromagnetic fields, namely, the probe and coupling fields. We take both probe and drive fields in the form of Gaussian shaped pulses. In a counterintuitive sequence scheme, the short probe pulse is introduced prior to the application of the coupling field, in contrast to a regular sequence scheme, where both fields are introduced at the same time. The influence of varying the probe pulse width and time delay between the initiation times of the probe and coupling fields on transient probe gain is investigated. It is found that the system exhibits a kind of memory about previously applied weak probe pulse. This may allow for detection of the past event by applying a strong drive pulse in the future.     

Faithful representations of groups by automorphisms of topologies

It is proved that every (in general, infinite) group is the full automorphism group of some topology. Supported by RFBR under grant no. 07-01-00101-a.     

Field-driven super/subradiant lasing without inversion in three-level ladder scheme

A model of a superradiant laser comprising of N three-level systems driven by two pumping lasers is considered in semiclassical approximation. Steady-state equations for density matrix elements are solved both analytically and numerically. Various properties of generated light are investigated. It is found that such a laser can exhibit both superradiance, when the intensity scales as N(2), and subradiance when the intensity does not depend on N. The phase of the laser field is locked to the relative phase of the pumping lasers.     

Coherent control of AC Stark allowed transition in Λ system

A three level Λ system is considered and the coherence established on initially forbidden transition is calculated. It is shown that quantum-interference-related phenomena, such as electromagnetically induced transparency, gain without inversion and enhanced refractive index may occur on such transitions, which became dynamically allowed due to AC Stark effect. Gain/dispersion characteristics of such transitions strongly depend upon the relative phase between the driving and probe fields. Unlike allowed transitions, gain/absorption behavior of forbidden transitions exhibit antisymmetric feature on the Rabi sidebands. Absorption/gain spectra possess extremely narrow sub-natural resonances.