Influence of the generated power, measurement bandwidth, and noise level on intensity statistics of a quasi-CW Raman fiber laser

In the present paper we numerically study instrumental impact on statistical properties of quasi-CW Raman fiber laser using a simple model of multimode laser radiation. Effects, that have the most influence, are limited electrical bandwidth of measurement equipment and noise. To check this influence, we developed a simple model of the multimode quasi- CW generation with exponential statistics (i.e. uncorrelated modes). We found that the area near zero intensity in probability density function (PDF) is strongly affected by both factors, for example both lead to formation of a negative wing of intensity distribution. But far wing slope of PDF is not affected by noise and, for moderate mismatch between optical and electrical bandwidth, is only slightly affected by bandwidth limitation. The generation spectrum often becomes broader at higher power in experiments, so the spectral/electrical bandwidth mismatch factor increases over the power that can lead to artificial dependence of the PDF slope over the power. It was also found that both effects influence the ACF background level: noise impact decreases it, while limited bandwidth leads to its increase

Phenomenology of GeV-scale Heavy Neutral Leptons

We review and revise phenomenology of the GeV-scale heavy neutral leptons (HNLs). We extend the previous analyses by including more channels of HNLs production and decay and provide with more refined treatment, including QCD corrections for the HNLs of masses $\mathcal{O}(1)$ GeV. We summarize the relevance of individual production and decay channels for different masses, resolving a few discrepancies in the literature. Our final results are directly suitable for sensitivity studies of particle physics experiments (ranging from proton beam-dump to the LHC) aiming at searches for heavy neutral leptons.Comment: journal versio

Extreme value statistics in Raman fiber lasers

We present the numerical study of the statistical properties of the partially coherent quasi-CW high-Q cavity Raman fiber laser. The statistical properties are different for the radiation generated at the spectrum center or spectral wings. It is found that rare extreme events are generated at the far spectral wings at one pass only. The mechanism of the extreme events generation is a turbulent-like four-wave mixing of numerous longitudinal generation modes. The similar mechanism of extreme waves appearance during the laser generation could be important in other types of fiber lasers

Revealing spectral cross-correlations in radiation of multiwavelength fiber laser with randomly distributed feedback

In present paper correlations between different parts of spectrum of a fiber laser with randomly distributed feedback (RDFL) were experimentally measured directly. Implemented statistical analysis demonstrate weak cross-correlations between different lines in generation spectrum. These correlations were vizualized by plotting 2-D probability density functions. Linear correlation coefficient (Pearson coefficient) was calculated for each pair of spectrum lines

Restrictions on the lifetime of sterile neutrinos from primordial nucleosynthesis

We analyze the influence of decaying sterile neutrinos with the masses in the range 1-140 MeV on the primordial Helium-4 abundance, explicitly solving the Boltzmann equations for all particle species, taking into account neutrino flavour oscillations, and paying special attention to systematic uncertainties. We show that the Helium abundance depends only on the sterile neutrino lifetime and not on the way the active-sterile mixing is distributed between flavours, and derive an upper bound on the lifetime. We also demonstrate that the recent results of Izotov & Thuan [arXiv:1001.4440], who find 2sigma higher than predicted by the standard primordial nucleosynthesis value of Helium-4 abundance, are consistent with the presence in the plasma of sterile neutrinos with the lifetime 0.01-2 seconds. The decay of these particles perturbs the spectra of (decoupled) neutrinos and heats photons, changing the ratio of neutrino to photon energy density, that can be interpreted as extra neutrino species at the recombination epoch.Comment: 17 pp. + Appendices. Analysis of deuterium bounds and more accurate account of CMB bounds on Helium-4 is added. Final version to appear in JCA

SCINTILLATION SPECTROMETER SBL-1 FOR THE X-RAY DENSITOMETER OF RADIOACTIVE TECHNOLOGICAL SOLUTIONS

Results of property study of the developed high-acting scintillation spectrometer to be used in x-ray densitometer of radioactive solutions with 241Am "transmitting" radiant are presented. Fast crystals YAlO3:Ce (Æ25x0.4 and Æ25x1.0 mm) are used as scintillators. Strong energy resolution dependence of the spectrometer with thin scintillators at crystal illumination (from 16.3 to 20.3 % for a g-line 59.5 keV) is revealed. The spectrometer input count-rate is over 5·105 1/s, and spectrum accumulation speed is not lower than 2·105 1/s. Due to the conversion gain program stabilization the relative shift and the peak broadening Eγ = 59.5 keV do not exceed 0.25 % and 7.5 %, accordingly.Keywords: YAlO3:Ce, x-ray scintillation spectrometer, thin crystal, 241Am, radioactive solutions, program stabilization, high count-rate, energy resolution.DOI: http://dx.doi.org/10.15826/analitika.2013.17.1.003 M.P. Belousov1, M.A. Gorbunov2, S.V. Dudin1, O.V. Ignatyev1,S.G. Morozov2, A.A. Pulin2 1Ural Federal University named after the first President of Russia B.N. Yeltsin, Ekaterinburg, Russian Federation2 ATOM Electronics Ltd, Ekaterinburg, Russian Federation Results of property study of the developed high-acting scintillation spectrometer to be used in x-ray densitometer of radioactive solutions with 241Am "transmitting" radiant are presented. Fast crystals YAlO3:Ce (Æ25x0.4 and Æ25x1.0 mm) are used as scintillators. Strong energy resolution dependence of the spectrometer with thin scintillators at crystal illumination (from 16.3 to 20.3 % for a g-line 59.5 keV) is revealed. The spectrometer input count-rate is over 5·105 1/s, and spectrum accumulation speed is not lower than 2·105 1/s. Due to the conversion gain program stabilization the relative shift and the peak broadening Eγ = 59.5 keV do not exceed 0.25 % and 7.5 %, accordingly.Keywords: YAlO3:Ce, x-ray scintillation spectrometer, thin crystal, 241Am, radioactive solutions, program stabilization, high count-rate, energy resolution.DOI: http://dx.doi.org/10.15826/analitika.2013.17.1.00

Эффективный алгоритм определения уровня полезных сигналов при расшифровке магнитных и вихретоковых дефектограмм

To ensure traffic safety of railway transport, non-destructive testing of rails is regularly carried out by using various approaches and methods, including magnetic and eddy current flaw detection methods. An automatic analysis of large data sets (defectgrams) that come from the corresponding equipment is still an actual problem. The analysis means a process of determining the presence of defective sections along with identifying structural elements of railway tracks on defectograms. At the same time, under the conditions of significant volumes of incoming information, fast and efficient algorithms of data analysis are of most interest. This article is an addition to the previous article devoted to the problem of automatic determination of a threshold level of amplitudes of useful signals (from defects and structural elements of a railway track) during the analysis of defectograms (records) of magnetic and eddy current flaw detectors, which contains an algorithm for finding the threshold level of a rail noise and its theoretical justification with examples of its operation on several fragments of real magnetic and eddy current defectograms. The article presents a simple and effective implementation of the algorithm, which is successfully used in practice for the automatic analysis of magnetic and eddy current defectograms. Для обеспечения безопасности движения на железнодорожном транспорте регулярно проводится неразрушающий контроль рельсов с применением различных подходов и методов, включая методы магнитной и вихретоковой дефектоскопии. Актуальной задачей по-прежнему остается автоматический анализ больших массивов данных (дефектограмм), которые поступают от соответствующего оборудования. Под анализом понимается процесс определения по дефектограммам наличия дефектных участков наряду с выявлением конструктивных элементов рельсового пути. При этом в условиях значительных объемов поступающей на обработку информации наибольший интерес представляют быстрые и эффективные алгоритмы анализа данных. Данная статья является дополнением к предыдущей статье авторов, посвященной задаче автоматического определения порогового уровня амплитуд полезных сигналов при расшифровке дефектограмм магнитных и вихретоковых дефектоскопов, в которой был предложен алгоритм нахождения порогового уровня шума рельсов с его теоретическим обоснованием, а также рассматривались примеры работы алгоритма на фрагментах реальных магнитных и вихретоковых дефектограмм. В настоящей статье приводится простая и эффективная реализация этого алгоритма, которая с успехом применяется на практике при автоматическом анализе магнитных и вихретоковых дефектограмм

Об определении уровня полезных сигналов при расшифровке магнитных и вихретоковых дефектограмм

To ensure traffic safety of railway transport, non-destructive testing of rails is regularly carried out by using various approaches and methods, including magnetic and eddy current flaw detection methods. The paper is devoted to the problem of automatic determination of a threshold level of amplitudes of useful signals (from defects and structural elements of a railway track) during the analysis of defectograms (records) of magnetic and eddy current flaw detectors. A signal is considered useful (and is subject to further analysis) if a deviation of its value from an average of all signals is at least twice the threshold noise level of rails. The probability of obtaining a signal from a section without structural elements (a rail noise signal) is characterized by the normal distribution law. Thus, the rule of three sigma can be used to calculate the threshold noise level. And a signal is useful if its amplitude deviation from a sample mean exceeds twice the threshold noise level. The paper proposes an algorithm for finding the threshold level of a rail noise and gives its theoretical justification, and it also examines examples of its operation on several fragments of real magnetic and eddy current defectograms. Для обеспечения безопасности движения на железнодорожном транспорте регулярно проводится неразрушающий контроль рельсов с применением различных подходов и методов, включая методы магнитной и вихретоковой дефектоскопии. Статья посвящена задаче автоматического определения порогового уровня амплитуд полезных сигналов (от дефектов и конструктивных элементов рельсового пути) при расшифровке дефектограмм магнитных и вихретоковых дефектоскопов. Сигнал считается полезным (и подлежит дальнейшему анализу), если отклонение его значения от среднего значения всех сигналов как минимум в два раза превосходит пороговый уровень шума рельсов. Вероятность появления сигнала с некоторой амплитудой в бездефектных рельсах на участке без конструктивных элементов, т. е. являющегося рельсовым шумом, характеризуется законом нормального распределения. Таким образом, для вычисления порогового уровня шума может быть задействовано правило трех сигм. А удвоение порога шума дает уровень, превышение которого по амплитудному отклонению от выборочного среднего означает, что сигнал является полезным. В статье предлагается алгоритм нахождения порогового уровня шума рельсов и дается его теоретическое обоснование, а также рассматриваются примеры его работы на нескольких фрагментах реальных магнитных и вихретоковых дефектограмм.