Control of the spontaneous emission rate of complex molecules by focused laser radiation

V. P. Klochkov, E. B. Verkhovskiĭ

V. P. Klochkov, E. B. Verkhovskiĭ

Emission spectra of concentrated (~10 18 –10 19 cm –3 ) ethanol solutions of Rhodamine C excited by high-power (~10 25 –10 26 cm –2 s –1 ) laser radiation were measured. The emission spectrum consists of two narrow bands (with half-widths of ~200–300 cm –1 ). The long-wavelength band was interpreted as cooperative spontaneous emission, and the short-wavelength band was assigned to the amplified spontaneous emission. The ratio of their intensities depends on the dye concentration and the pump power density. The ratio of band intensities is assumed to be determined by the dephasing rate of excited molecules responsible for cooperative spontaneous emission.

C. H. Raymond Ooi, Karl-Peter Marzlin, Jürgen Audretsch

M. Pototschnig

V. P. Klochkov, E. B. Verkhovskiĭ

The threshold pump power density for lasing in dye solutions is found to depend on the photon energy of pumping radiation. An increase in the pumping photon energy can significantly lower the threshold pump power of dye lasers. For an ethanol solution of rhodamine 6G with a concentration of 4×10 18 cm −3 , the threshold power density for pumping radiation with a wavelength of 532 nm is 20-fold higher than for pumping radiation with a wavelength of 347 nm. This phenomenon is associated with the competition of collective spontaneous emission, which can lead to the efficient deactivation of excited molecules in femtosecond times, and the dephasing of excited molecules due to the intramolecular nonradiative processes of absorbed-energy conversion. An increase in the dephasing rate with the increasing energy of exciting photons lowers the efficiency of collective spontaneous emission and increases the concentration of dephased excited molecules responsible for lasing.

Inna Rebane, Rein Koch

Abstract The influence of the anisotropy of the host crystal on the spontaneous emission rate of the single‐impurity molecule and thus also on the radiative line width has taken into account. The anisotropy reveals itself in the dependence of the spontaneous emission rate on the orientation of the radiative transition dipole moment in the crystal. In this paper calculations of the relative spontaneous emission rate (the spontaneous emission rate divided by the spontaneous emission rate in the case when the transition dipole moment is parallel to the optical axis) of the quadrupole transition in a uniaxial host crystal are presented in the form which is convenient for experimenters. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)