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CNAA / Theses / 2005 / May /

Two-quanta emissions at the interaction of nonlinear media with electromagnetic fields


Author: Viorel Ciornea
Degree:doctor of physics and mathematics
Speciality: 01.04.02 - Theoretical and mathematical physics
Year:2005
Scientific adviser: Nicolae Enache
doctor habilitat, professor, Institute of Applied Physics of the
Scientific consultant: Andrei Andrieş
doctor habilitat, professor, Institute of Applied Physics of the
Institution:
Scientific council:

Status

The thesis was presented on the 30 May, 2005
Approved by NCAA on the 22 September, 2005

Abstract

Adobe PDF document – 2.32 Mb / in romanian

Keywords

quantum optics, nonlinear optics, theoretical physics

Summary

The doctorate research deals with different aspects of generation of pairs of entangled photons at the interaction of nonlinear media with cavity electromagnetic fields.

It was analyzed the two-quanta emission generated at the interaction of cavity coherent electromagnetic field with nonlinear crystals, without center of inversion, described by the secondand third-order nonlinearities. The research shows that the third order nonlinearity conduct the generation process of the entangled photon pairs. The Master equation was solved via two different ways: the Fokker-Planck equation method and the method of antinormal order of operators. To develop the first method we decomposed the density matrix using the non-diagonal generalized P representation of coherent states of belonging to SU(1,1) algebra. The solution of Fokker-Planck equation was obtained only after the change of its symmetry. For the second method we had to extend the techniques of solving the Master equations for symmetry SU(2) to SU(1,1) symmetry. Comparing the obtained results it was founded that the solutions, in generally, do not converge, and therefore we have to develop continuously the methods of solving the Master equations. Taking into account the obtained results it was possible to study the statistics of generated two-photons, as well as the domain where the two-quanta generation highly increase.

It was investigated the one- and two-quanta emission generated at the interaction of electromagnetic field with a stream of atoms prepared in a coherent state. Considering that the stream is fast, it was investigated the quantum statistics of the emitted single- and two-photon light. To solve the Master equation it was proposed the lemma of representation of free operators through the source operators. In this case the exact solutions for the kinetic equations were obtained, and the time dependence of sub-harmonic field operators was studied.

The trapping conditions for a pair of dipole-forbidden atoms, crossing a quantized cavity mode, were established. Taking into account the properties of cavity electromagnetic field, the different aspects of its statistics were obtained. In particular, the photon statistics may take a sub- or a supper-Poisson characteristics.

The methods of studying the processes of generation of one and two-quanta in resonators were used in description of laser type generation of phonons in non-crystalline materials. Thus, it was demonstrated that the possibility of increasing of the absorption coefficient in the process of excitation of chalcogenide glasses with short laser pulses of low intensity is stimulated by the laser type generation of localized phonons in the relaxation process of non-equilibrium excitations.