Dynamics of collective radiation of molecules

V. A. Morozov

Abstract A system of equations is obtained for describing the dynamics of the secondary photoreaction of two-level molecules emitting spontaneous fluorescence at initial excitation of one of them. The system is derived using the Schrödinger equation for the compound system of a reagent molecule, a reaction product molecule, and a quantized radiation field. Unlike those commonly used in similar modeling, optical Bloch equations describing the dynamics of a non-selective (collective) population of the ground states of two molecules (i.e., the total number of molecules of a pair in their ground states), the system of equations (and its generalization allowing for the longitudinal and transverse relaxation of excited states of molecules) allows estimates of the relative number of reagent molecules and the product in their ground states, the use of which provides a complete idea of the effectiveness of the reaction.

Игорь Сергеевич Осадько

Hans Frauenfelder

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.

Fritz Haake

Benjamin Fain

The intensity of radiation, stimulated by laser pulses of arbitrary shape, is derived up to fourth-order terms. It is shown that there is a linear fourth-order mechanism of emission that depends on linear susceptibilities of molecules. This linear mechanism reveals collective, super-radiant features. The intensity of laser-driven spontaneous emission (LDSE) is proportional to for samples smaller than , where is a wavelength of emitted radiation, and N is the number of molecules. For extended volumes , the intensity of LDSE is proportional to . Equations of motion describing collective radiation damping are derived.