Enhancement of image resolution beyond the diffraction limit by double dark resonances

Abstract

We show how quantum coherence effects can be used to improve the resolution and the contrast of diffraction-limited images imprinted onto a probe field. The narrow and sharp spectral features generated by double-dark resonances (DDR) are exploited to control absorption, dispersion and diffraction properties of the medium. The spatial modulated control field can produce inhomogeneous susceptibility of the medium that encodes the spatial feature of the control image to probe field in the presence of DDR. The transmission of cloned image can be enhanced by use of incoherent pump field. We find that the feature size of cloned image is four times smaller than the initial characteristic size of the control image even though the control image is completely distorted after propagation through 3 cm long Rb vapour cell. We further discuss how spatial optical switching is possible by using of induced transparency and absorption of the medium.

Generation of optical  -antisymmetry in a coherent N-type atomic medium

“…With the advent of electromagnetically induced transparency (EIT) [1] of a weak coherent field probing the coherence evolved in a laser-driven multilevel atom, it has been possible to introduce spatially dependent coherence effects like electromagnetically induced focusing and waveguiding [2][3][4], coherent control of optical image transfer via EIT [5][6][7], electromagnetically induced grating (EIG) [8][9][10], atom localization in EIT-related systems [11][12][13][14][15] and so on. In such phenomena, spatially modulated coherence plays a vital role, which is to be controlled by varying the system parameters.…”

Microwave field controlled electromagnetically induced focusing

“…However, in these experiments, the focused spot size is more than 100 µm, which is not much of practical use where a small beam size is required. 7,[18][19][20] In addition to this limited beam size, a strong absorption causes another restriction for further applications of such systems. To propose a better system, in this paper, we predict how a microwave field driving the hyperfine levels of the Λ-system can lead to strong focusing of the probe beam and how a spatial resolution below 100 µm can be achieved considering practical circumstances.…”