We report on reflection spectra of ceasium atoms in close vicinity of a nanostructured metallic meta-surface. We show that the hyperfine sub-Doppler spectrum of the 6 2 S 1/2 − 6 2 P 3/2 resonance transition at 852 nm is strongly affected by the coupling to the plasmonic resonance of the nanostructure. Fine tuning of dispersion and positions of the atomic lines in the near-field of plasmonic metamaterials could have 1 arXiv:1603.08287v1 [cond-mat.mes-hall]

Multimode fibers (MMFs) have the potential to carry complex images for endoscopy and related applications, but decoding the complex speckle patterns produced by mode-mixing and modal dispersion in MMFs is a serious challenge. Several groups have recently shown that convolutional neural networks (CNNs) can be trained to perform high-fidelity MMF image reconstruction. We find that a considerably simpler neural network architecture, the single hidden layer dense neural network, performs at least as well as previously-used CNNs in terms of image reconstruction fidelity, and is superior in terms of training time and computing resources required. The trained networks can accurately reconstruct MMF images collected over a week after the cessation of the training set, with the dense network performing as well as the CNN over the entire period.

The 6S 1/2 − 5D 5/2 electric quadrupole transition is investigated in Cesium vapor at room temperature via nonlinear Doppler-free 6P-6S-5D three-level spectroscopy. Frequency-resolved studies of individual E2 hyperfine lines allow one to analyze optical pumping dynamics, polarization selection rules and line intensities. It opens the way to studies of transfer of light orbital angular momentum to atoms, and the influence of metamaterials on E2 line spectra. © 2018 Optical Society of America OCIS codes: (020.2930) Hyperfine structure; (300.6420) Spectroscopy, nonlinear; (300.6210) Spectroscopy, atomic; (140.0140) Lasers and laser optics http://dx.doi.org/10.1364/OL.41.002005With the appearance of laser sources, nonlinear Doppler-free Laser Spectroscopy (DFLS) has undergone a very fast development. It has been utilized for atomic and molecular spectral analyses, collisional studies in the vapor phase and investigation of fundamental processes [1,2]. Up to now, in atomic physics, DFLS has been mainly performed by using laser sources resonant for electric-dipole (E1) transitions. Dipoleforbidden transitions, particularly electric quadrupole (E2) transitions, are important in new avenues of atomic physics for fundamental studies like parity violation [3] or devising of ultrahigh-accuracy optical clocks [4][5][6]. Spectroscopic studies of E2 transitions in vapors are generally hindered by Dopplerbroadening, and in most cases averaged over the internal structure of the E2 transition (e.g. hyperfine multiplets) [7,8]. A noteworthy exception is the early work by Weber and Sansonetti [9] who performed resonantly enhanced stepwise excitation to high lying states of Cesium, using the 5D 3/2 level as the intermediates state. In this way, they have been able to get Doppler-free spectra and resolve the hyperfine lines of the 6S 1/2 − 5D 3/2 E2 transition. Recent studies include Dopplerfree 5p-6p transitions in Rubidium [10] and magnetic-fieldmixing of forbidden hyperfine transitions of Cs D2 line [11]. Another well-explored approach to study the internal structure of highly-excited D levels of alkalis and measure their energy makes use of Doppler-free two-photon spectroscopy [12,13]. In this letter we analyze Doppler-free hyperfine spectral lines of the Cs 6S 1/2 − 5D 5/2 E2 transition, as observed via threelevel Raman-type nonlinear spectroscopy [14][15][16] on the 6P-6S-5D coupled system. We investigate polarization properties and optical pumping processes responsible for the E2 spectral line intensities, demonstrating the important role played by transit time relaxation. This work should pave the way to investigate such specific properties as transfer of non-zero e.m. orbital angular momentum to atomic systems [17,18], vapor-surface physics [7,8] and atomic gas combined with nanostructured interface [19][20][21].To investigate Doppler-free spectroscopic characteristics on an E2 transition, we address the 6S 1/2 → 6D 5/2 transition of Cesium at λ = 685 nm (Fig. 1). This E2 line has a transition rate of γ 5D−6S = 2π · 3.5...

Microscopes and various forms of interferometers have been used for decades in optical metrology of objects that are typically larger than the wavelength of light λ. Metrology of sub-wavelength objects, however, was deemed impossible due to the diffraction limit. We report the measurement of the physical size of sub-wavelength objects with deeply sub-wavelength accuracy by analyzing the diffraction pattern of coherent light scattered by the objects with deep learning enabled analysis. With a 633 nm laser, we show that the width of sub-wavelength slits in an opaque screen can be measured with an accuracy of ∼ λ/130 for a single-shot measurement or ∼ λ/260 (i.e., 2.4 nm) when combining measurements of diffraction patterns at different distances from the object, thus challenging the accuracy of scanning electron microscopy and ion beam lithography. In numerical experiments, we show that the technique could reach an accuracy beyond λ/1000. It is suitable for high-rate non-contact measurements of nanometric sizes of randomly positioned objects in smart manufacturing applications with integrated metrology and processing tools.

We tailor the atom-surface Casimir-Polder interaction of cesium atoms using near-infrared surface plasmons of a metamaterial.