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Browsing Department of Physics by Subject "Atomic Coherence"

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    Atomic Coherence Based Electromagnetic Wave Interferometry
    (2023) Shylla, Dangka
    This thesis reports on the theoretical and experimental studies of closed loop multi-level systems, where electromagnetically induced transparency (EIT) is dependent on the phase difference between the electromagnetic fields forming the loop. We first theoretically investigate a scheme to develop an atomic-based microwave (MW) interferometry in Rb, based on a six-level loopy ladder system involving the Rydberg states in which two excitation pathways interfere constructively or destructively depending on the phase between the MW electric fields closing the loop. Then we compared the field strength sensitivity to previous demonstrations on MW electrometry employing Rydberg atomic states, this is two orders of magnitude more sensitive to field strength. Because previously investigated atomic systems are only sensitive to field strength but not to phase, this scheme offers a great opportunity to characterize the MW completely, including the propagation direction and wavefront. Currently, we do not have the experimental facility for Rydberg excitation so we cannot conduct the experiment of the above theoretically proposed work. However, we could demonstrate the phase-dependent EIT in the different configurations of a closed loop double-lambda system at 780 nm and 420 nm transitions in 87Rb at room temperature. For the MW field measurements, the sensitivity can be improved by employing the cold atoms because cold atoms reduce the Doppler mismatch between the 780 nm probe and 480 nm control fields and also minimizes the collisions and transit time dephasing effect. Taking this into consideration, we have also set up the cold atom experiments and so far, we have characterized the 85Rb atoms in the MOT using the 5S1/2(F = 3) → 5P3/2(F = 4) broad cyclic IR transition at 780 nm where we trap around 1.5×108 number of atoms at a typical temperature of 500 μK. In laser cooling and trapping experiments, the temperature of the cold atoms is sensitive to the lock point of the laser fields. The laser locking can have an offset from the line center of the transition which depends upon the linewidth of the transition. In order to determine the laser lock o set on a particular atomic transition, we also present an experimental study on the effect of detuning on a velocity-induced population oscillation (VIPO) dip which is used to precisely determine the lock point with an uncertainty of around 100 kHz.
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    Novel aspects of electromagnetic radiation in isotropic and anisotropic media
    (2022) Daloi, Nilamoni
    The kernel of the thesis is rooted in the interaction of lasers with atomic or molecular vapor. A quantitative explanation of the physics behind laser-atom interaction is given in terms of something known as "atomic coherence" in the literature. The value of atomic coherence depends on parameters such as the laser frequency, intensity, and temperature of the atomic vapor. The optical properties of the atomic vapor, such as refractive index, absorption, isotropy, anisotropy, and the group velocity of a pulse inside the medium, can be manipulated by controlling the atomic coherence. Based on the premise of "atomic coherence," four research problems are formulated in this thesis. The first problem proposes a pulse amplification method in atomic vapor, that preserves the initial pulse shape after amplification. The second problem is a similar study of pulse amplification in a vapor of polar molecules possessing permanent dipole moments (PDMs). The presence of PDMs leads to interesting phenomena that are forbidden in the atomic counterpart and can be utilized for pulse amplification purposes. The remaining two problems deal with the propagation of special laser beams called "vector beams" (VBs) through an atomic vapor medium. Vector beams have a nonuniform polarization distribution on their transverse plane, having applications in quantum computing, microscopy, laser cutting, etc. In this thesis, two schemes are proposed, that exploit atomic coherence to control the polarization rotation of VBs and realize waveguiding of VBs through the atomic vapor medium, respectively. In summary, this thesis aims to conglomerate a few applications of "atomic coherence" manipulation in different fields of optics.