Distinguishing coherent atomic processes using wave mixing

We are able to clearly distinguish the processes responsible for enhanced low-intensity atomic Kerr nonlinearity, namely coherent population trapping and coherent population oscillations in experiments performed on the Rb D1 line, where one or the other process dominates under appropriate conditions. The potential of this new approach based on wave mixing for probing coherent atomic media is discussed. It allows the new spectral components to be detected with sub-kHz resolution, which is well below the laser linewidth limit. Spatial selectivity and enhanced sensitivity make this method useful for testing dilute cold atomic samples.Comment: 9 pages, 5 figure

Development of Filters with Minimal Hydraulic Resistance for Underground Water Intakes

The development of modern structures of water wells filtering equipment with enhanced performance characteristics is a vital task. The purpose of this work was to create filters for taking water from underground sources that have high performance, long service life, quickly and economically replace or repair in case of performance loss. The selection of the filter device must be made taking into account all the geological features of the aquifers, the performance characteristics of the filter devices and the size of the future structure. Filter equipment designs for water intake wells have been developed in this study. These filters have low hydraulic resistance, high performance and are easy to repair. This article presents the dependency of flow inside the receiving part of the well, the dependence of filter resistance at various forms of the cross section of the filter wire and the selected optimal section. The paper proposes a method for selecting the optimal cross-section of the filter wire used in the manufacture of a water well filter. The proposed structures of easy-to-remove well filters with increased productivity allow replacing the sealed well filter with a new one easily, reducing capital and operating costs, and increasing the inter-repair periods of their operation. Based on the presented method, examples are given for selecting the parameters of the filter wire cross-section. The above calculations showed that the use of the hydraulic resistance criterion at the design stage of underground water intakes can significantly reduce the cost of well construction. Studies have found that the minimum hydraulic resistance to ensure maximum filter performance is achieved when using filter wire teardrop and elliptical shapes

Directional infrared emission resulting from cascade population inversion and four-wave mixing in Rb vapours

Directional infrared emission at 1367 and 5230 nm is generated in Rb vapours that are step-wise excited by low-power resonant light. The mid-infrared radiation originating from amplified spontaneous emission on the 5D-6P transition consists of forward- and backward-directed components with distinctive spectral and spatial properties. Diffraction limited near-infrared light at 1367 nm generated in the co-propagating direction only is a product of parametric wave mixing around the 5P-5D-6P-6S-5P transition loop. This highly non-degenerate mixing process involves one externally applied and two internally generated optical fields. Similarities between wave mixing generated blue and near-IR light are demonstrated.Comment: 4 pages, 5 figure

Steep anomalous dispersion in coherently prepared Rb vapor

Steep dispersion of opposite signs in driven degenerate two-level atomic transitions have been predicted and observed on the D2 line of 87Rb in an optically thin vapor cell. The intensity dependence of the anomalous dispersion has been studied. The maximum observed value of anomalous dispersion [dn/dnu ~= -6x10^{-11}Hz^{-1}] corresponds to anegative group velocity V_g ~= -c/23000.Comment: 4 pages, 4 figure

Absorption resonance and large negative delay in Rb vapor with buffer gas

We observe a narrow, isolated, two-photon absorption resonance in Rb for large one-photon detuning in the presence of a buffer gas. In the absence of buffer gas, a standard Lambda configuration of two laser frequencies gives rise to electromagnetically induced transparency (EIT) for all values of one-photon detuning throughout the inhomogeneously (Doppler) broadened line. However, when a buffer gas is added and the one-photon detuning is comparable to or greater than the Doppler width, an absorption resonance appears instead of the usual EIT resonance. We also observe large negative group delay (~ -300 us for a Gaussian pulse propagating through the media with respect to a reference pulse not affected by the media), corresponding to a superluminal group velocity v_g= -c/(3.6x10^6)=-84 m/s.Comment: 4 pages, 5 figure

Comparison of collimated blue-light generation in Rb-85 atoms via the D-1 and D-2 lines

We experimentally and theoretically studied the characteristics of the collimated blue light (CBL) produced in Rb-85 vapor by two resonant laser fields exciting atoms into the 5D(3/2) state, using either the 5P(1/2) or the 5P(3/2) intermediate state. We compared the CBL output at different values of frequency detunings, powers, and polarizations of the pump lasers in these two cases and confirmed the observed trends using a simple theoretical model. We found that in general the CBL yield was higher for the the D-1 excitation scheme compared to the D-2 excitation scheme under similar conditions. We also demonstrated the importance of the repump laser, preventing the accumulation of atomic population in the uncoupled hyperfine ground state, which resulted in nearly an order of magnitude increase in CBL power output. One interesting finding was the existence of the optimal power ratios between the two pump lasers, leading to the maximum blue- light power, observed both in the experiment and in the calculations. (C) 2018 Optical Society of Americ