Temporal Evolution of Coherent Optical Pumping

J. Brossel

Eugeny Korsunsky, Wolfgang Maichen, Laurentius Windholz

This work is concerned with the temporal evolution of the coherent population trapping (CPT) process in the case of additional optical pumping to states not contributing to the CPT superposition states. Special attention is paid to the influence of weak external magnetic fields that can change the laser-atom interaction considerably. The theoretical analysis is completed by experimental observations on a sodium atomic beam, which show good agreement with our theory. The results obtained are of importance for a realistic picture of CPT schemes in practical applications.

Rao Li, Daipeng Sui, Xiaochao Wang +1 more

Broadband low-coherence light has been applied in many fields such as optical imaging, atmospheric optical communication and laser inertial confinement fusion(ICF). It’s meaningful to investigate the temporal shaping technology of broadband low-coherence light. We propose and experimentally demonstrate a scheme of achieving all-optical arbitrary temporal shaping of broadband low-coherence light based on saturable absorption effect. Compared to traditional temporal shaping schemes such as electro-optic modulation(EOM) shaping or acousto-optic modulation(AOM) shaping, the modulation on the shaped pulse profile is much smaller, reduced from 14% (by acousto-optic modulator) to 3%(close to the ASE noise). Furthermore, we explore the evolution of shaped pulse contrast (intensity ratio between front edge and end edge) with the pump energy and contrast changing. The contrast of shaped pulse can be adjusted from 1:1.32 to 1:1.02 when pump contrast is 1:2, and from 1:2.25 to 1:1.90 when pump contrast is 1:3. And the maximum contrast of shaped pulse can reach 1:17 within the measurement accuracy. By changing the energy and contrast of pump, the contrast of the shaped pulse can be controlled flexibly. It’s useful to achieve all-optical arbitrary temporal shaping and pre-compensation during pulse amplification.

Claude N. Cohen-Tannoudji

Claude N. Cohen-Tannoudji

Arif Warsi Laskar, Niharika Singh, Arunabh Mukherjee +1 more

In a thermal ensemble of atoms driven by coherent fields, how does evolution of quantum superposition compete with classical dynamics of optical pumping and atomic diffusion? Is it optical pumping that first prepares a thermal ensemble, with coherent superposition developing subsequently or is it the other way round: coherently superposed atoms driven to steady state via optical pumping? Using a stroboscopic probing technique, here we experimentally explore these questions. A 100 ns pulse is used to probe an experimentally simulated, closed three-level, Λ-like configuration in rubidium atoms, driven by strong coherent ( control ) and incoherent fields. Temporal evolution of probe transmission shows an initial overshoot with turn-on of control , resulting in a scenario akin to lasing without inversion. The corresponding rise time is dictated by coherent dynamics, with a distinct experimental signature of half-cycle Rabi flop in a thermal ensemble of atoms. Our results indicate that, in fact, optical pumping drives the atoms to a steady state in a significantly longer time-scale that sustains superposed dark states . Eventual control turn-off leads to a sudden fall in transmission with an ubiquitous signature for identifying closed and open systems. Numerical simulations and toy-model predictions confirm our claims. These studies reveal new insights into a rich and complex dynamics associated with atoms in thermal ensemble, which are otherwise absent in state-prepared, cold atomic ensembles.