Where is the energy of slow light stored?

We analyze the energy storage process of light propagating with slow group velocity in a sample where electromagnetically induced transparency (EIT) is created by a strong coupling field. We compare the formation of slow light in EIT and in self-induced transparency (SIT). For SIT, soliton-like propagation of light with essentially reduced group velocity takes place because of the temporary storage of an appreciable part of the pulse energy in the atoms. For EIT, no energy of the probe is stored in the atoms. This energy is transformed to the coupling field and leaves the sample with phase velocity c without absorption. Slow light is formed by a low frequency coherence induced at the input by the probe and coupling fields in a two-quantum excitation process. This coherence propagates as a “spin wave” with small group velocity, and at a large distance from the input, the coherence rules the process of the energy transformation from the coupling field to the probe, reproducing exactly the temporal profile of the probe at the input.     

Controlling absorption of gamma radiation via nuclear level anticrossing

A significant reduction of absorption for single gamma photons has been experimentally observed by studying M?ssbauer spectra of 57Fe in a FeCO3 crystal. The experimental results have been explained in terms of a quantum interference effect involving nuclear level anticrossing due to the presence of a combined magnetic dipole and electric quadrupole interaction.     

Modulation resonance in a laser

The response of the active atoms of an operating laser to the modulation of their energy intervals by an external field is theoretically investigated. On the condition that the active atoms are strongly saturated by off-resonant laser radiation, the resonant peculiarities take place in response to the modulating field.     

Lasing without inversion due to cooling subsystem

The new possibility of inversionless lasing is discussed. We have considered the resonant interaction of a two-level system (TLS) with photons and the adiabatic interaction with an ensemble of Bose particles. It is found out that a TLS with equally populated energy levels amplifies the coherent light with Stokes-shifted frequency. This becomes possible as photon emission is accompanied by Bose particles excitation. The energy flow from the TLS to the photon subsystem is realized due to the Bose subsystem being at finite temperature and playing the cooler role. The advantage of this new lasing principle is discussed. It is shown that lasing conditions strongly differ from conventional ones. This revised version was published online in August 2006 with corrections to the Cover Date.     

Slowing down of gamma photons

Hyperfine Interactions - By a transformation to a rotating reference system, a nuclear level mixing scheme is equivalent to a scheme with pure quadrupole splitting and a strong RF-drive between...     

Level mixing induced transparency

We discuss level mixing induced transparency (LMIT), which is experimentally found in a thick absorber of FeCO₃ containing the ⁵⁷Fe Mössbauer nuclei. LMIT is observed if two hyperfine levels of the excited state nucleus cross. Absorption of gamma radiation drops by about 25% with respect to the sum of two overlapping absorption lines. The absorption deficit is explained by the mixing of the crossing levels with a symmetry breaking interaction. The level mixing induces a polarization change of the scattered radiation. In such a way, the radiation develops in “normal modes,” which are less absorbed in a thick absorber. We show that, in spite of the absorption drop, the area of the absorption line does not change. This confirms the general knowledge that interference phenomena (destructive or constructive) do not change the lifetime of an excited state particle (atom, nucleus, etc).     

Group velocity in a nuclear EIT-like Λ scheme and comparison with optical EIT

The group velocity of gamma radiation scattered in the forward direction by a nuclear lambda scheme experiencing level mixing induced transparency, which shows some similarity to optical EIT, has been investigated. The equations for the nuclear coherences governing the group velocity have been solved. The group velocity decreases with the density of the resonant nuclei and with a decrease in the intensity of the mixing interaction. A comparison between the group velocity of the gamma radiation and the probe radiation in “classical” optical EIT conditions has been made.     

New applications of the Mössbauer effect

Results from a Mössbauer experiment to observe acoustic oscillations induced by pulsed laser excitation in MgO:⁵⁷Fe²⁺ crystal are presented. Time-domain spectra are satsifacorily described by the theory of the frequency modulation of Mössbauer radiation transmitted through a vibrating resonance medium. It is proposed that the D _4Ω/D _2Ω ratio of the fourth and second Fourier harmonics of the modulated radiation be used to measure the amplitude of nuclear oscillations.