Efficient fiber coupling of down-conversion photon pairs

We develop and apply an effective analytic theory of a non-collinear, broadband type-I parametric down-conversion to study a coupling efficiency of the generated photon pairs into single mode optical fibers. We derive conditions necessary for highly efficient coupling for single and double type-I crystal producing polarization entangled states of light. We compare the obtained approximate analytic expressions with the exact numerical solutions and discuss the results for a case of BBO crystals.Comment: 15 pages, 4 figure

Point-by-point inscription of 250-nm-period structure in bulk fused silica by tightly-focused femtosecond UV pulses: experiment and numerical modeling

By conducting point-by-point inscription in a continuously moving slab of a pure fused silica at the optimal depth (170 μm depth below the surface), we have fabricated a 250-nm-period nanostructure with 30 nJ, 300 fs, 1 kHz pulses from frequency-tripled Ti:sapphire laser. This is the smallest value for the inscribed period yet reported, and has been achieved with radical improvement in the quality of the inscribed nanostructures in comparison with previous reports. The performed numerical modeling confirms the obtained experimental results

Saturation effects in the sub-Doppler spectroscopy of Cesium vapor confined in an Extremely Thin Cell

Saturation effects affecting absorption and fluorescence spectra of an atomic vapor confined in an Extremely Thin Cell (cell thickness $L < 1 \mu m$) are investigated experimentally and theoretically. The study is performed on the $D_{2}$ line ($\lambda ~= ~852 nm)$ of $Cs$ and concentrates on the two situations $L = \lambda /2$ and $L =\lambda$, the most contrasted ones with respect to the length dependence of the coherent Dicke narrowing. For $L = \lambda /2$, the Dicke-narrowed absorption profile simply broadens and saturates in amplitude when increasing the light intensity, while for $L =\lambda$, sub-Doppler dips of reduced absorption at line-center appear on the broad absorption profile. For a fluorescence detection at $L =\lambda$, saturation induces narrow dips, but only for hyperfine components undergoing a population loss through optical pumping. These experimental results are interpreted with the help of the various existing models, and are compared with numerical calculations based upon a two-level modelling that considers both a closed and an open system.Comment: 11 pages, 12 figure

A 750 mW, continuous-wave, solid-state laser source at 313 nm for cooling and manipulating trapped 9Be+ ions

We present a solid-state laser system that generates 750 mW of continuous-wave single-frequency output at 313 nm. Sum-frequency generation with fiber lasers at 1550 nm and 1051 nm produces up to 2 W at 626 nm. This visible light is then converted to UV by cavity-enhanced second-harmonic generation. The laser output can be tuned over a 495 GHz range, which includes the 9Be+ laser cooling and repumping transitions. This is the first report of a narrow-linewidth laser system with sufficient power to perform fault-tolerant quantum-gate operations with trapped 9Be+ ions by use of stimulated Raman transitions.Comment: 9 pages, 4 figure

Specific local induction of DNA strand breaks by infrared multi-photon absorption

Highly confined DNA damage by femtosecond laser irradiation currently arises as a powerful tool to understand DNA repair in live cells as a function of space and time. However, the specificity with respect to damage type is limited. Here, we present an irradiation procedure based on a widely tunable Er/Yb : fiber femtosecond laser source that favors the formation of DNA strand breaks over that of UV photoproducts by more than one order of magnitude. We explain this selectivity with the different power dependence of the reactions generating strand breaks, mainly involving reactive radical intermediates, and the direct photochemical process leading to UV-photoproducts. Thus, localized multi-photon excitation with a wavelength longer than 1 µm allows for the selective production of DNA strand breaks at sub-micrometer spatial resolution in the absence of photosensitizers

Efficient second harmonic generation by para-nitroaniline embedded in electro-spun polymeric nanofibres

Intense well polarized second harmonic light was generated by poly(methyl methacrylate) nanofibres with embedded para-nitroaniline nanocrystals. Subwavelength diameter fibres were electro-spun using a 1.2 weight ratio of chromophore to polymer. Analysis of the generated second harmonic light indicates that the para-nitroaniline molecules, which nominally crystalize in the centrosymmetric space group, were organized into noncentrosymmetric structures leading to a second order susceptibility dominated by a single tensor element. Under the best deposition conditions, the nanofibrers display an effective nonlinear optical susceptibility approximately two orders of magnitude greater than that of potassium dihydrogen phosphate. Generalizing this approach to a broad range of organic molecules with strong individual molecular second order nonlinear responses, but which nominally form centrosymmetric organic crystals, could open a new pathway for the fabrication of efficient sub-micron sized second harmonic light generators.Hugo Goncalves thanks the Portuguese Foundation for Science and Technology (FCT) for the support under grant PD/BD/111873/2015. The equipment used to characterize the second harmonic response of the electro-spun fibres was acquired within the framework of the Portuguese National Program for Scientific Re-equipment, contract REEQ-25/FIS/2005 with funds from POCI 2010 (FEDER) and FCT. The Raman microscope was acquired through the project nSTeP Nanostructured Systems for Tailored Performance, NORTE-07-0124-FEDER-000039, ON. 2. This work was in part developed in the scope of the projects CICECO-Aveiro Institute of Materials (UID/CTM/50011/2013), financed by national funds through the Fundacao para a Ciencia e a Tecnologia/Ministerio da Educacao e Ciencia (FCT/MEC) and co-financed by FEDER under the PT2020 Partnership Agreement. The authors are grateful to A M P Botas (University of Aveiro) for help in acquiring the hyperspectral microscopy data.info:eu-repo/semantics/acceptedVersio

ФОРМИРОВАНИЕ ПАРАЗИТОФАУНЫ ОВЕЦ В УСЛОВИЯХ СОДЕРЖАНИЯ НА ОГРАНИЧЕННЫХ ПАСТБИЩНЫХ ТЕРРИТОРИЯХ ПРЕДГОРНОЙ ЗОНЫ АРМЕНИИ

21 parasite species have been found in structure of variety of parasite species from hybrid sheep (mouflon × domestic sheep hybrids) contained within limited grazing territories of foothill zones of Armenia. These included 9 species of nematodes, 4 of cestodes, 3 of trematodes, 3 of ixodid ticks and larvae of nasopharyngeal gadfly Oestrus ovis and sheep ked Melophagus ovinus. An analysis of paths of circulation of larvae of some biohelminthes, particularly Dicrocoelidae and Protostrongylidae, realized through invertebrate intermediate hosts (land snails) have shown that mean infection of the latter varied from 2,5 to 8,0 %.У гибридных с муфлоном овец, содержащихся в условиях ограниченных пастбищных территорий предгорной зоны Армении, выявлен 21 вид паразитов, из которых большая часть гельминты (16 видов). Нематоды представлены 9 видами, цестоды – 4 и трематоды – 3 видами. Установлено паразитирование также 3 видов иксодовых клещей и 2 видов насекомых. Исследования путей циркуляции личиночных стадий дикроцелий и протостронгилид, осуществляемых при участии беспозвоночных животных, в частности, наземных моллюсков показали их естественную зараженность от 2,5 до 8,0%

РЕКОМЕНДАЦИИ ПО БОРЬБЕ С ПРОТОСТРОНГИЛИДОЗАМИ ОВЕЦ И КОЗ В УСЛОВИЯХ АРМЕНИИ

Protostrongyloses are widely-spread in small cattle all over the world and may cause a significant economic damage manifested in decrease in livestock productivity as well as death of animals.Based on our studies, the infestation of sheep and goats with protostrongylides was detected in all landscape zones of the republic of Armenia and in animals of all ages. As a rule, the protostrongylide invasion rate of goats is higher than of sheep.  Within the republic, the average invasion extensity in goats of different age groups ranges between 20,4 and 44,1%, and in sheep – between  16,5 and 37,0%.In some stationary invasion foci, more than a half of livestock suffers through protostrongyloses. The highest protostrongylide invasion was found in animals older than 3 years of age, and the lowest – in animals of the first year of life, it means that the invasion increases with the age.The invasion of animals in mountains is higher in comparison with animals from plain areas. The peak of invasion falls on autumn and winter seasons.Taking into account a high level of protostrongylide invasion in small cattle in the republic of Armenia, and the unavailability of guidelines on this infectious disease, we have developed (based on the long term investigation of more than 3000 head of animals) methodical recommendations for the struggle against protostrongyloses.The implementation of these measurements proved their high efficacy and contributed to the significant reduction in morbidity of small cattle due to protostrongyloses.Протостронгилидозы широко распространены среди мелкого рогатого скота во всем мире и являются причиной существенного экономического ущерба, складываемого как от значительного уменьшения продуктивности животных, так и от их гибели.Согласно нашим исследованиям, зараженность овец и коз протостронгилидами установлена во всех природно-ландшафтных поясах республики и у животных всех возрастов. Как правило, зараженность коз протостронгилидами большая, чем у овец. В среднем по республике, экстенсивность инвазированности коз различных возрастных групп колеблется в пределах 20,4-44,1%, а овец от 16,5 до 37,0%. В некоторых стационарных очагах этих инвазий более половины поголовья животных переболевает протостронгилидозами. Наибольшая зараженность протостронгилидами установлена у животных старше трехлетнего возраста, а наименьшая у животных текущего   года рождения, т.е. с возрастом животных инвазированность повышается. Зараженность животных горных поясов, по сравнению с животными низменных поясов, более высокая. Пик зараженности животных приходится на осенне-зимний период.Учитывая высокую инвазированность мелкого рогатого скота в Республике Армения протостронгилидами и отсутствие нормативных рекомендаций против вызываемых ими заболеваний, нами на основании многолетних исследований, проведенных на более чем 3 тыс. голов животных, было разработано методическое наставление по борьбе с протостронгилидозами. Испытания этих мероприятий свидетельствовали о высокой их эффективности и способствовали значительному сокращению заболеваемости мелкого рогатого скота протостронгилидозами