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Journal de Physique IV (Proceedings)

COOPERATIVE - RADIATION DYNAMICS IN l30Te2 AND 125Te2

J. MEZZIANE, Etienne Boursey, Ari S. Topouzkhanian

Published Dec 1, 1991• 0 citations
Publisher

Abstract

We present new results on Te2 superfluorescence induced by short YAG-pumped dye laser pulses analyzed at high resolution by comparison with C.W. laser induced fluorescence observed by Fourier transform spectroscopy. A complete identification of the transitions involved based on intensity measurements and supported by calculated Franck-Condon factors has been achieved. The cooperative emission in Te2 has been studied by time resolved spectroscopy as a function of density. As the density or temperature of the sample is increased, the emission evolves continuously from characteristic spontaneous emission to superfluorescence. The dependence of the superradiant pulse parameters (relaxation time and half-width) with respect to density will be presented and compared to predictions of current theories.

DOI
10.1051/jp4:19917140

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High-resolution analysis results are presented for Te/sub 2/ superfluorescence induced by short pulses from a YAG-pumped dye laser pulses, and a comparison is made with CW-laser-induced fluorescence observed by Fourier transform spectroscopy. A complete identification of the transitions involved, based on intensity measurements and supported by calculated Franck-Condon factors, has been achieved. The cooperative emission in Te/sub 2/ has been studied by time resolved spectroscopy as a function of density. With increasing density or temperature of the sample, the emission changes continuously from characteristic spontaneous emission to superfluorescence. The evolution of the time characteristics of the signal with the number of partners are presented and compared with the predictions of current theories.>
The cooperative emission process in KCL;O2{\mathrm{O}}_{2}O2​${\mathrm{}}^{\mathrm{\ensuremath{-}}}$ has been studied as a function of the dephasing rate of the transition dipole. As the temperature of the sample is increased from 10 to 30 K, the emission evolves continuously from that characteristic of superfluorescence to that of amplified spontaneous emission. These results are in qualitative agreement with the predictions of current theories, but quantitative agreement is obtained only when current theories are modified so that the noise source that initiates the emission process is allowed to act continuously during the superfluorescent buildup.
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We have studied the nature of the emission from a laser-excited KCI : O 2 − crystal and have observed that the emission evolves continuously from superfluorescence (SF) to amplified spontaneous emission (ASE) as the temperature of the crystal and hence the dephasing rate of the optical transition are increased. The sample is excited by a 30-ps pulse from a frequency-quadrupled Nd:YAG laser, and the 629.1-nm emission is detected using a streak camera system. At a temperature of 10 K the emission is characterized as SF with an average delay time of 200 ps and an average pulse width of 60 ps. As the temperature is increased to ~20 K, the output pulse broadens and the time delay increases to its maximum value of ~2 ns. As the temperature is increased still further, the time delay is observed to decrease, and at a temperature of 30 K the emission is characterized as ASE with a very small delay time and with an exponentially decaying time evolution. We modeled our experiment using the Maxwell-Bloch formalism and find good agreement for our measured output pulse shapes and for the dependence of delay time and pulse width on the dephasing rate.
The dependence of the emission of a concentrated (∼10 19 cm −3 solution of Rhodamine C on the power density Φ of exciting laser radiation was studied. The emission intensity for the power density of exciting radiation above ∼10 25 cm −2 s −1 was found to have a nearly quadratic dependence on the power density Φ, and this emission was interpreted as the cooperative spontaneous emission of a Dicke type. For Φ≲10 25 cm −2 s −1 , the emission intensity increased with increasing Φ according to the exponential law. This emission was interpreted as the amplified spontaneous emission. The spectra of cooperative emission depended on the pump radiation power only weakly. The absence of lasing in dye solutions at high concentrations, which is a well-known phenomenon, was shown to be caused by the development of the cooperative spontaneous emission and not by the concentration quenching, and the former process is more rapid than the latter.