Young's double slit interference pattern from a twisted beam

The interference pattern of a Laguerre Gaussian beam in a double slit experiment is reported. Whereas a typical laser beam phase front is planar, a Laguerre Gaussian beam exhibits a wave front that is twisting along the direction of propagation. This leads to a distorted interference pattern. The topological charge also called the order of the twisted beam can be then readily and simply determined. More precisely, the naked eye resolution of the distortion shift of the interference pattern directly informs about the number of twists made as well as on the sign of the twist. These results are in very good agreement with theoretical calculations that offer a general description of the double slit interference with twisted beams.Comment: 11 pages, 4 figure

Rotation of millimeter-size objects using ordinary light

International audienceThe ability to optically rotate bodies offers new degrees of control of micro-objects with applications in various domains including micro-electromechanical-systems (MEMS), biomanipulations or optofluidics. Here we demonstrate the optically induced rotation of simple asymmetric two-dimensional objects using plane waves originating either from ordinary laser sources or from black body radiation. The objects are floating on an air/water interface. We observe a steady state rotation depending on the light intensity and on the asymmetry of the object. We interpret this rotation in terms of light diffraction by the edges of the object. Such systems could be easily implemented in optofluidic devices to induce liquid flow without the need for special light sources

Soap lms as 1D waveguides

International audienceLaser light is injected in a free standing hori-zontal draining soap lm through the glass frame sustain-ing the lm. Two propagation regimes are clearly identi-ed depending on the lm thickness. At the beginning of the drainage, the soap lm behaves as a multimode-one dimensional optoouidic waveguide. In particular, we ob-serve that the injected light creates a bottleneck in the lm and part of the injected light is refracted leading to whiskers. At the end of the drainage where the lm thick-ness is below µm, there is a strong selection among the various possible optical modes in the lm, and part of the light is deeected. This leads to a self selection of the mode propagation inside the lm

Determination of the topological charge of a twisted beam with a Fresnel bi-prism

International audienceThe self-interference pattern of a Laguerre Gaussian beam using a Fresnel bi-prism is shown to be very different from what could be expected from a usual laser beam. Actually it resembles the interference pattern that could be obtained using a double slit experiment. The interferences are shifted and the topological charge and its sign can be readily determined considering the shift order of the pattern only. However, since there is no diffraction nor absorption loses unlike in a double slit interference, such a set up could be used even for low power twisted beams or beams with high topological charge. Even fractional topological charges could be determined with an absolute precision of 0.05

Profile of the liquid film wetting a channel

International audienceWe have developed a simple optical technique to investigate the characteristics of liquid films wetting solid surfaces. To validate this technique, we have studied the wetting film that separates a train of lamellas moving through a channel. Total reflection of the laser beam on the wetting film/air interface is used to extract the profile and the thickness of the wetting film. For quasistatic movement of lamellas, we show that the thickness is well described by a capillary number power law

Mechanism of angular momentum transfer from microwaves to a copper ring

International audienceIn the exchange of orbital angular momentum between an electromagnetic wave and a copper ring we examine the origin of the Angular Momentum. We then investigate the transfer mechanism between the microwave and the object, and compare it with other mechanisms. We evidence a transfer mechanism based on the reflection of the electromagnetic field on the copper ring. In particular, at a microscopic scale, we show that the electromagnetic field induces alternative electric currents in the ring, with a small drift. Although little, the resistivity of copper leads to a force that rotates the ring. The estimation of the torque, which is of the order of 10 −8 Nm, is in good agreement with the experimental measurements. We also show that the transfer of electromagnetic orbital angular momentum to objects could be a way to measure the orbital angular momentum carried by electromagnetic fields, and we discuss possible applications. PACS. 41.20.Jb Electromagnetic wave propagation; radiowave propagation – 45.20.da Forces and torques – 84.40.Ba Antennas: theory, components and accessories – 42.50.Tx Optical angular momentum and its quantum aspect

Favorable and unfavorable conditions for the development of the self determination of students in the process of cognitive activity

У статті представлено результати емпіричного дослідження самодетермінації учнів в процесі пізнавальної діяльності. Описуються діагностичні методики. Факторний аналіз засвідчує, що існують сприятливі і несприятливі умови розвитку самодетермінації. Доводиться позитивний вплив особистісної самодетермінації на розвиток пізнавальної діяльності.Results of empirical research of the self-determination of students in the process of cognitive activity are presented in article. A description of diagnostic techniques is given also. Using factor analysis favorable and unfavorable conditions for the development of the self-determination were identified. It is also proved that the self-determination is a powerful catalyst for the development of cognitive activity. Blockade of the self-determination, respectively, inhibits the formation of cognitive activity

Are there limits to growth in data traffic?:on time use, data generation and speed

This discussion paper considers the nature of growth in data traffic across the Internet, as a basis for asking whether and how such growth might slow down or otherwise be limited. Over the last decade, data growth has been dramatic, and forecasts predict a similar ongoing pattern. Since this is associated with increasing electricity consumption, such a trend is significant to global efforts to reduce carbon emis- sions. In this paper, we selectively explore aspects of data growth that are linked to everyday practices and the way they draw upon and generate Internet data. We suggest that such growth does have some conceivable limits. However, the nature of ‘Internet use’ is changing and forms of growth are emerging that are more disconnected from human ac- tivity and time-use. This suggests that although there may well be limits, in principle, to some forms of growth, total data traffic seems likely to continue growing. This calls for careful attention to the nature of the trends involved, as a basis for intentionally building limits into this system be- fore levels of Internet electricity demand becomes directly and more explicitly problematic

Als huiselijk geweld en georganiseerde misdaad samenkomen...:De weerbare professional op het grensvlak tussen strafrecht en hulpverlening

There is casuistry, where on the one hand it is the turn of the professionals from the investigation, enforcement and prosecution and on the other hand the turn of the social workers from the social domain. This is the case, for example, when domestic violence occurs in circles that are also involved in organized crime. In theory it is possible that the professionals involved work together, but it is also not impossible that they will get into each other’s waters because they have a different vision of the problem to be tackled and, of course, also have to fulfill other roles and tasks based on their positions. A professional must be able to handle complex situations of this kind