We report a simple, novel sub-diffraction method, i.e. diffraction interference induced super-focusing in second-harmonic (SH) Talbot effect, to achieve focusing size of less than {lambda}_pump/8 without involving evanescent waves or sub-wavelength a
pertures. By tailoring point spread functions with Fresnel diffraction interference, we observe periodic SH sub-diffracted spots over a hundred of micrometers away from the sample. Our demonstration is the first experimental realization of the proposal by Toraldo Di Francia pioneered 60 years ago for super-resolution imaging.
We demonstrate a novel approach to obtain resonance linewidth below that limited by coherence lifetime. Cross correlation between induced intensity modulation of two lasers coupling the target resonance exhibits a narrow spectrum. 1/30 of the lifetim
e-limited width was achieved in a proof-of-principle experiment where two ground states are the target resonance levels. Attainable linewidth is only limited by laser shot noise in principle. Experimental results agree with an intuitive analytical model and numerical calculations qualitatively. This technique can be easily implemented and should be applicable to many atomic, molecular and solid state spin systems for spectroscopy, metrology and resonance based sensing and imaging.
By modulating transmission function of a weak probe field via a strong control standing wave, an electromagnetically induced grating can be created in the probe channel. Such a nonmaterial grating may lead to self-imaging of ultra-cold atoms or molec
ules in the Fresnel near-field regime. This work may offer a nondestructive and lensless way to image ultra-cold atoms or molecules.
A recent thermal ghost imaging experiment by Wus group constructed positive and negative images using a novel algorithm. This algorithm allows to form the images with use of partial measurements from the reference arm, even which never passes through
the object, conditioned on the object arm. In this paper, we present a simple theory which explains the experimental observation, and provides an in-depth understanding of conventional ghost imaging. In particular, we theoretically show that the visibility of formed images through such an algorithm is not bounded by the standard value 1/3. In fact, it can ideally grow up to unity (with reduced imaging quality). Thus, the algorithm described here not only offers an alternative way to decode spatial correlation of thermal light, but also mimics a bandpass filter to remove the constant background such that the visibility or imaging contrast is improved. We further show that conditioned on one still object present in the test arm, it is possible to construct its image by sampling the available reference data.
We propose to shape biphoton wave packets with an electromagnetically induced grating in a four-level double-$Lambda$ cold atomic system. We show that the induced hybrid grating plays an essential role in directing the new fields into different angul
ar positions, especially to the zeroth-order diffraction. A number of interesting features appear in the shaped two-photon waveforms. For example, broadening or narrowing the spectrum would be possible in the proposed scheme even without the use of a cavity.
