Resonant nonstationary amplification of polychromatic laser pulses and conical emission in an optically dense ensemble of neon metastable atoms

Experimental and numerical investigation of single-beam and pump-probe interaction with a resonantly absorbing dense extended medium under strong and weak field-matter coupling is presented. Significant probe beam amplification and conical emission were observed. Under relatively weak pumping and high medium density, when the condition of strong coupling between field and resonant matter is fulfilled, the probe amplification spectrum has a form of spectral doublet. Stronger pumping leads to the appearance of a single peak of the probe beam amplification at the transition frequency. The greater probe intensity results in an asymmetrical transmission spectrum with amplification at the blue wing of the absorption line and attenuation at the red one. Under high medium density, a broad band of amplification appears. Theoretical model is based on the solution of the Maxwell-Bloch equations for a two-level system. Different types of probe transmission spectra obtained are attributed to complex dynamics of a coherent medium response to broadband polychromatic radiation of a multimode dye laser.Comment: 9 pages, 13 figures, corrected, Fig.8 was changed, to be published in Phys. Rev.

TRANSVERSE ON-RESONANCE RESHAPING IN COHERENT PROBE AND PUMP SOLITONS ASYMPTOTIC EVOLUTION IN A THREE-LEVEL SYSTEM

L'étude d'un transfert d'énergie en résonance entre une pompe et une sonde durant leur propagation dans un milieu à trois nivaux est rapportée. La longueur d'onde de la pompe est plus courte que celle de la sonde. Nous considérons une évolution asymptotique où l'effet de la nonlinearité du milieu est compensé par celui de la diffraction. Le formulisme semi-classique est adopté. Dans le but d'optimiser l'extraction bi-chromatique de l'énergie les vitesses de groupe sont égales pour garantir le recouvrement des deux impulsions. Le phénomène de la diffraction, donc des effets transverses, est essentiel pour l'évolution des deux solitons. Le soliton associé à la sonde apparaît tout d'abord suivi de celui associé à la pompe. Un diagramme de phase démontre le caractère à valeur multiple nonlinéaire de l'interaction.The coherent frequency conversion between on-resonance pump and probe beams is examined in the physical situation where the medium nonlinearity balances the linear diffraction for each transition. Without diffraction neither soliton can occur. The paraxial-Maxwell Bloch formalism is adopted. To achieve optimally the energy transfer the pulse velocities must be equal to maintain maximum overlap throughout the propagation. The sequential evolution of probe soliton then pump soliton is reported in conjunction with pump depletion diffraction rigorously accounted for. Phase diagram of the pump and probe areas exhibit multi-value features