Olga Kocharovskaya

Amplification and lasing without inversion

Abstract We review all the schemes providing amplification without inversion and identify two different mechanisms of inversionless amplification. In both mechanisms we find some kind of effective inversion which is hidden in the way coherent superposition states in active atoms are prepared.

Slow, Ultraslow, Stored, and Frozen Light

The article illustrates recent experiments in which light is slowed, frozen, reversed, and stored in hot atomic vapors via electromagnetically induced transparency.

Narrowing of electromagnetically induced transparency resonance in a Doppler-broadened medium

We derive an analytic expression for the linewidth of EIT resonance in a Doppler broadened system. It is shown here that for relatively low intensity of the driving field the EIT linewidth is proportional to the square root of intensity and is independent of the Doppler width, similar to the laser induced line narrowing effect by Feld and Javan. In the limit of high intensity we recover the usual power broadening case where EIT linewidth is proportional to the intensity and inversely proportional to the Doppler width.

Coherent control of the waveforms of recoilless γ-ray photons

The concepts and ideas of coherent, nonlinear and quantum optics have been extended to photon energies in the range of 10–100 kiloelectronvolts, corresponding to soft γ-ray radiation (the term used when the radiation is produced in nuclear transitions) or, equivalently, hard X-ray radiation (the term used when the radiation is produced by electron motion). The recent experimental achievements in this energy range include the demonstration of parametric down-conversion in the Langevin regime, electromagnetically induced transparency in a cavity, the collective Lamb shift, vacuum-assisted generation of atomic coherences and single-photon revival in nuclear absorbing multilayer structures. Also, realization of single-photon coherent storage and stimulated Raman adiabatic passage were recently proposed in this regime. More related work is discussed in a recent review. However, the number of tools for the coherent manipulation of interactions between γ-ray photons and nuclear ensembles remains limited. Here we suggest and implement an efficient method to control the waveforms of γ-ray photons coherently. In particular, we demonstrate the conversion of individual recoilless γ-ray photons into a coherent, ultrashort pulse train and into a double pulse. Our method is based on the resonant interaction of γ-ray photons with an ensemble of nuclei with a resonant transition frequency that is periodically modulated in time. The frequency modulation, which is achieved by a uniform vibration of the resonant absorber, owing to the Doppler effect, renders resonant absorption and dispersion both time dependent, allowing us to shape the waveforms of the incident γ-ray photons. We expect that this technique will lead to advances in the emerging fields of coherent and quantum γ-ray photon optics, providing a basis for the realization of γ-ray-photon/nuclear-ensemble interfaces and quantum interference effects at nuclear γ-ray transitions.

Lasing without inversion: The double Λ scheme

Abstract We determine the conditions under which a four-level medium in a resonant cavity can start lasing when there is no population inversion between the lasing levels. The mechanism which is used is the creation of low-frequency coherence by a pair of external pump fields. it is shown that lasing with frequency upconversion requires population inversion at (low-frequency) nonlasing transitions.

Decaying-dressed-state analysis of a coherently driven three-level Λ system

We introduce decaying-dressed states for a three-level Λ system driven at one atomic transition and probed at the adjacent one. These states allow for a simple interpretation and classification of various coherent effects in such a system.

Inversionless amplification of ultrashort pulses and coherent population trapping in a three-level medium

Coherent bleaching of an absorbing three-level medium and inversionless amplification of an ultrashort pulse are predicted. Both effects are related to the well-known phenomenon of coherent population trapping.

Laser control of Mossbauer spectra as a way to gamma-ray lasing

We give a comparative analysis of basic schemes of optical control of Mossbauer spectra providing an elimination of resonant absorption by a gamma-ray nuclear transition and suggest a novel scheme of frequency non-selective optical pumping which turns out to be the most promising for a realization of induced gain in the gamma-ray range.

Basic models of lasing without inversion: general form of amplification condition and problem of self-consistency

We derive an amplification condition which generalizes the traditional population inversion requirement for the basic schemes of inversionless amplification. We develop a self-consistent quantum approach for the description of such schemes and demonstrate the limitations of the traditional phenomenological approach.

Frequency up-conversion in a three-level medium without inversion

Abstract We study a three-level medium in a Λ configuration. The two low-lying levels interact with a strong resonant field and we investigate the amplification conditions for fields resonant between the upper and any of the lower levels. We identify a mechanism by which such amplification is possible.