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Solitary waves induce waveguide that can split light beams (Vol. 43 No. 3)
Formation of the multiple dark photovoltaic solitons from even initial conditions in steady state regime.
Simulations are performed to help understand the occurrence of multiple solitary optical waves that are used to reconfigure optical beams. Researchers have designed the first theoretical model that describes the occurrence of multiple solitary optical waves, referred to as dark photovoltaic spatial solitons. Because the shape of dark solitons remains unaffected by the crystal in which they travel, they induce waveguides, which can be used, for example, to reconfigure optical beams by splitting them.
Dark solitons are generated in so-called photorefractive crystals - crystals that respond to an incoming light beam by decreasing their refractive index as optical intensity increases, causing the incoming beam to defocus. This effect is called nonlinear self-defocusing. Dark solitons occur when the diffraction of an incoming beam by the notch, located at the crystal's entrance, is compensated by the crystal's self-defocusing effect. As a result, dark solitons can induce waveguides for light beams, allowing them to travel unchanged through photorefractive crystals.
The authors develop the first numerical simulation to model the formation and evolution of one-dimensional multiple dark solitons inside a photorefractive crystal, relying on an approximation technique called the beam propagation method. By expanding the width of the dark notch located at the entrance of the crystal, which, unlike in previous studies, was not given any special function, they showed it was possible to create multiple dark solitons.
These solitons appeared in either odd or even numbers, depending on the initial beam phase or amplitude. The authors also confirmed previous findings that showed that when multiple solitons are generated, the separation between them becomes smaller. Further, the solitons become progressively wider and less visible, the farther away they are from the main dark notch entry location.
Steady-state multiple dark photovoltaic spatial solitons
Y. Zhang, K. Lu, J. Guo, K. Li and B. Liu, Eur. Phys. J. D, 66, 65 (2012)
[Abstract]
Swirls study to optimise contacts between fluids (Vol. 43 No. 3)
A representation of the two currents occurring between the concentric cylinders.
A fluid dynamics model of the interface between two swirling fluids gives clues to how to optimise homogeneous feeding of cells in suspension from a liquid nutriments supply in a bioreactor. Studying mixing between two incompatible fluids shows that it is possible to control the undercurrents of one circulating fluid to optimise its exposure to the other. This is the work presented in this article.
The authors compare quantitative experimental observations of a viscous fluid, similar to honey, with numerical simulations. They focus on a fluid, partially filling the space between two concentric cylinders with the inner one rotating, a system previously used to study roll coating and papermaking processes.
They observe the presence of several flow eddies, stemming from fluid flowing past the inner cylinder, causing it to swirl, and the appearance of reverse currents including one orbiting around the rotating cylinder and a second underneath. They make the second eddy disappear by increasing the fluid filling or its velocity.
Instead of using a highly viscous oil combined with air as a top fluid, this model could be applied to a suspension of bioreactor cells typically used to produce biotech medicines, combined with a light oil-containing nutriments as a top fluid. Ultimately, it could help identify the right parameters and adequate mixing time scales to ensure that nutriments feed all the cells homogeneously with no segregation.
Free surface flow between two horizontal concentric cylinders
J. Peixinho, M. Mirbod and J.F. Morris, Eur. Phys. J. E 35, 19 (2012)
[Abstract]
Enterococcus faecalis biofilm in an air plasma jet
Effective inactivation of enterococcus faecalis biofilms. After only 5 min of the plasma treatment, all the bacteria are killed, not only on the surface but also in the 17th layer of the 25.2 µm-thick biofilm.
Enterococcus faecalis is a gram-positive bacterium, which often infects root canals during endodontic dental treatments and is among the most antibiotic- and heat-resistant pathogens, which strongly resist calcium hydroxide treatment. Inactivation of these pathogens is particularly challenging because they form thick self-organized biofilms. Effective inactivation of a record thick 25.2 µm-thick biofilm by using a handheld, 12 V DC battery-operated plasma jet device is reported. The plasma jet, called the Plasma Flashlight operates in open air at atmospheric pressure and does not require any external gas supply or wall power. This makes the Plasma Flashlight suitable for various point-of-care applications, such as in ambulance emergency outcalls, natural disaster rescue and military combat operations, treatments in remote locations, etc. It produces a plasma plume with the temperature of 20-28°C, which is very close to room temperature. The device is extremely energy efficient and only 60 mW DC power is required to sustain the discharge. The figure shows the results of inactivation of the Enterococcus faecalis bacteria in each of the 17 layers within a 25.2 µm-thick biofilm. These results advance our ability to effectively inactivate biofilms formed by notoriously drug- and treatment-resistant pathogens. The reported mobile, handheld plasma jet device may also be used for surface treatment and functionalization in nanotechnology, device fabrication, and several other applications where surface temperature sensitivity is an issue.
Inactivation of a 25.5 µm Enterococcus faecalis biofilm by a room-temperature, battery-operated, handheld air plasma jet
X. Pei, X. Lu, J. Liu, D. Liu, Y. Yang, K. Ostrikov, Paul K. Chu and Y. Pan, J. Phys. D: Appl. Phys., 45, 165205 (2012)
[Abstract]
High carrier injection for all-silicon laser
Presently, laser diodes are mainly used to convert electronic signals into optical signals in fast communication systems. They are manufactured with a wide variety of semiconductors different from silicon and the incorporation of these lasers in silicon layers leads to distortion of the signals, degradation of sensitivity, and limits the reliability. Silicon, with more than 95% of the international market share, dominates other semiconductors. A silicon laser source would provide the ideal improvement for future high-speed electronics. The structure of silicon limits its light-emitting efficiency and, despite the very fast development of silicon based electronics, optical applications of silicon devices have not been conducted thoroughly.
The question “which silicon device will be useful for transforming electronic signals into optical signals?” is still relevant today. This paper presents an advance in optoelectronic silicon devices since it introduces and formulates a process for the creation of an optical active layer inside silicon devices. A degradation of the structure is induced by hot carriers injection. The process has been controlled by the analysis of the junction characteristic. The authors suggest that the created defects disturb the lattice periodicity by creating energy states in the band gap of the silicon. The model is based on a population inversion associated with a defect layer for carrier confinement and an electrical stimulation of light is demonstrated. The emitted light is localized is an area close the emitter-base junction. The authors measure the amplification of emitted light, and they showed that defect layer appears as an optical cavity. This groundwork introduces practical ways for improving the optical properties of silicon devices for optoelectronic applications.
High carrier injection for all-silicon laser
H. Toufik, W. Tazibt, N. Toufik, M. El Tahchi, F. Pélanchon and P. Mialhe, Eur. Phys. J. AP 58, 10103 (2012)
[Abstract]
