TEMPORAL CLOAKING THROUGH KERR NONLINEARITY AND DOPPLER BROADENING

Abstract

The newborn phenomenon of temporal cloaking is investigated under the e®ects of Doppler broadening and Kerr nonlinearity in di®erent atomic me- dia. The optical properties of these media are manipulated in such a manner that a time gap is created in the propagating probe light where events or information can be transmitted undetected. To create the cloaking time gap, the enhanced subluminal and superluminal behaviors of the probe ¯eld are focused. The opened temporal gap is closed by an inverse process that involves reverse modi¯cation of the optical properties of the medium. Ini- tially, we consider a ¯ve-level M-type atomic con¯guration of rubidium. The concept of Doppler broadening is introduced along with the superposition of the double resonant ¯elds in the system. Phase shift variations are caused in the medium which result into a signi¯cant delay and advancement of the probe pulse. The delay and advancement times lead to the generation of a time hole for concealing information in the temporal domain. A microsecond time gap is attained without signi¯cant distortion in the pulse shape. The time gap is further increased to several orders of microseconds with increase in the Doppler width. Next, we investigate propagation of the light pulse in a four-level Doppler broadened sodium atomic system. The possibility of creating a temporal gap is discussed on the basis of spectral hole burning in the system. The probe pulse is observed to delay in the hole burning region while it advances in the nearest neighboring region. A cloaking time gap of the order of microseconds is achieved in the slow and fast light regime. The time gap is modi¯ed with the inverse Doppler e®ect. The time gap can also be tuned and modi¯ed with the strengths of the coupling ¯elds, if the Doppler width is kept constant in the system. Finally, we extend our studies to the three-level rubidium atomic system. The pulse delay and advancement vi times are observed at speci¯c system parameters in the presence of self-Kerr ¯eld e®ect. The delay and advance times are enhanced with increase in the intensity of self-Kerr ¯eld. A cloaking time gap of the order of nanosecond is created in the observed fast and slow light. Increase of the time gap is observed with increase in the intensity of self-Kerr nonlinearity. The time gap is enhanced to several orders of nanosecond, su±cient to hide any prac- tical event. The time gaps are closed by reverse manipulation of the optical properties. Our results may contribute to strengthening the idea of hiding events in successive temporal gaps for achieving enhanced security of the communication systems.