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Journal de Physique Lettres

Observation of two visible Dicke-superradiant transitions in atomic europium (*)

Catherine Bréchignac, Ph. Cahuzac

Published Jan 1, 1979• 8 citations
Publisher

Abstract

We report the first experimental evidence of visible superradiance for the europium lines at λ = 557.7 nm and λ = 545.3 nm. The superradiant character of these lines is checked by studying the variation of pulse heights, widths and delays versus atomic density. We show that the peculiar population inversion mechanism is essentially due to the existence of a strong superradiant infrared emission at λ = 1 759.6 nm.

DOI
10.1051/jphyslet:01979004006012300

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We report the first experimental evidence of visible superradiance for the europium lines at λ = 557.7 nm and λ = 545.3 nm. The superradiant character of these lines is checked by studying the variation of pulse heights, widths and delays versus atomic density. We show that the peculiar population inversion mechanism is essentially due to the existence of a strong superradiant infrared emission at λ = 1 759.6 nm.
We report the observation of near-infrared Dicke superradiant pulses. The active medium (atomic Na vapor) is optically pumped in the 5S125{S}_{\frac{1}{2}}5S21​​ state and superradiates on transitions cascading down from this level at 3.41, 2.21, and 9.10 \ensuremath{\mu}m. The superradiant character of the emission is checked by studying variations of pulse heights and delays versus initial population inversion density.
ABSTRACT We have applied the concept of superradiance introduced by Dicke in 1954 to astrophysics by extending the corresponding analysis to the magnetic dipole interaction characterizing the atomic hydrogen 21 cm line. Although it is unlikely that superradiance could take place in thermally relaxed regions and that the lack of observational evidence of masers for this transition reduces the probability of detecting superradiance, in situations where the conditions necessary for superradiance are met (close atomic spacing, high velocity coherence, population inversion, and long dephasing timescales compared to those related to coherent behavior), our results suggest that relatively low levels of population inversion over short astronomical length-scales (e.g., as compared to those required for maser amplification) can lead to the cooperative behavior required for superradiance in the interstellar medium. Given the results of our analysis, we expect the observational properties of 21 cm superradiance to be characterized by the emission of high-intensity, spatially compact, burst-like features potentially taking place over short periods ranging from minutes to days.
We report the first observation of a microscopically resolved interaction between two trapped atoms. This is also the first observation of two-ion superradiance and subradiance, the most elementary example of Dicke's theory. Its signature is the variation of the spontaneous emission decay rate of a laser-cooled two-ion crystal, +1.5+1.5%+1.5 and $\ensuremath{-}1.2%$, as the ion-ion distance is changed from 1380 to 1540 nm, in agreement with a no-free-parameter theory. The experiment uses an ion microtrap (80 \ensuremath{\mu}m radius) with planar electrodes and a new few-atom technique for measuring lifetimes.
We report the experimental observation of a superradiant emission emanating from an elongated dense ensemble of laser cooled two-level atoms, with a radial extent smaller than the transition wavelength. In the presence of a strong driving laser, we observe that the system is superradiant along its symmmetry axis. This occurs even though the driving laser is orthogonal to the superradiance direction. This superradiance modifies the spontaneous emission, and, resultantly, the Rabi oscillations. We also investigate Dicke superradiance in the emission of an almost fully inverted system as a function of the atom number. The experimental results are in qualitative agreement with ab-initio, beyond-mean-field calculations.
A superradiant and amplified spontaneous transition pulse is obtained from an iodine photodissociation laser amplifier which uses i-C3F7I as an active molecule and is pumped with a flashlamp (full width at half maximum=3 μs). We have observed a sharp leading pulse of superradiance whose rise time is less than 50 ns, and the amplified spontaneous emission follows the superradiance during the pumping flash. By measuring the population inversion density in the active medium of the amplifier, we have obtained the threshold condition for the superradiance to take place. Also, the buildup time and peak intensity of the pulse are measured as a function of the flashlamp input energy. By placing a reflecting mirror at a varying distance (from 173 to 673 cm) behind the amplifier, we have found a periodic intensity fluctuation in the superradiance; the period (Δt) depends linearly on the distance (d), i.e., Δt=2d/c, where c is the light velocity.