Stand-alone optical spinning tweezers with tunable rotation frequency

Advances in optical trapping design principles have led to tremendous progress in manipulating nanoparticles (NPs) with diverse functionalities in different environments using bulky systems. However, efficient control and manipulation of NPs in harsh environments require a careful design of contactless optical tweezers. Here, we propose a simple design of a fibered optical probe allowing the trapping of dielectric NP as well as a transfer of the angular momentum of light to the NP inducing its mechanical rotation. A polarization conversion from linearly-polarized incident guided to circularly transmitted beam is provoked geometrically by breaking the cylindrical symmetry of a coaxial nano-aperture that is engraved at the apex of a tapered metal coated optical fiber. Numerical simulations show that this simple geometry tip allows powerful light transmission together with efficient polarization conversion. This guarantees very stable trapping of quasi spherical NPs in a non-contact regime as well as potentially very tunable and reversible rotation frequencies in both directions (up to 45 Hz in water and 5.3 MHz in air for 10 mW injected power in the fiber). This type of fiber probe opens the way to a new generation of miniaturized tools for total manipulation (trapping, sorting, spinning) of NPs.

Pneumatosis cystoides intestinalis revealed after a hand-to-hand aggression: A case report

INTRODUCTION

Pneumatosis cystoides intestinalis (PCI) is a condition defined by the presence of multiple gas-filled cysts within the intestinal wall. We demonstrated a case of PCI presenting as pneumoperitoneum following a hand-to-hand aggression. Consent was obtained from the patient for publication of this paper.

PRESENTATION OF THE CASE

This article describes a case of an 28 year-old man with medical history of gastroduodenal ulcer admitted in the emergency room with an acute abdominal pain secondary to a hand-to-hand aggression. Computed tomography (CT-scan) revealed signs of PCI, the presence of pneumoperitoneum and a small amount of fluid in the Douglas pouch. The patient underwent an urgent laparotomy in front of a high suspicion of a bowel perforation. Per operative findings revealed multiple small cysts of the terminal ileum and there were no bowel perforation.

DISCUSSION

Pneumatosis cystoides intestinalis may be related to a wide spectrum of gastrointestinal conditions. The diagnosis of PCI can be established by endoscopic ultrasound or CT-scan imaging. Management of PCI is conditioned by the clinical and radiological presentation which is essentially related to the primary cause. Conservative approach is allowed in a stable patient with no signs of complications. In the presence of predictive factors of pathologic PCI, namely transmural ischemia and bowel perforation, surgical operation is required.

CONCLUSION

The management of PCI may be challenging particularly in the presence of pneumoperitoneum. Complications must be excluded before considering a conservative therapy. Therefore, PCI should be interpreted with relevance to the entire clinical context.

Implementation of dispersion models in the split-field-finite-difference-time-domain algorithm for the study of metallic periodic structures at oblique incidence

We extend here the finite-difference-time-domain (FDTD) algorithm working in oblique incidence to dispersive media. The split-field method (SFM) is used and adapted for taking into account the metal dispersion. The additional equations to the FDTD algorithm are given. Instead of the 24 field components usually used in the SFM, 38 and 112 field components are needed to implement the cases of Drude and Drude-Lorentz dispersion models, respectively. Some tests are presented to validate our code as long as the angle of incidence is lower than 76 degrees in addition to an application dealing with enhanced transmission and showing original results.

Split-field FDTD method for oblique incidence study of periodic dispersive metallic structures

The study of periodic structures illuminated by a normally incident plane wave is a simple task that can be numerically simulated by the finite-difference time-domain (FDTD) method. On the contrary, for off-normal incidence, a widely modified algorithm must be developed in order to bypass the frequency dependence appearing in the periodic boundary conditions. After recently implementing this FDTD algorithm for pure dielectric materials, we here extend it to the study of metallic structures where dispersion can be described by analytical models. The accuracy of our code is demonstrated through comparisons with already-published results in the case of 1D and 3D structures.

Three-dimensional finite-difference time-domain algorithm for oblique incidence with adaptation of perfectly matched layers and nonuniform meshing: application to the study of a radar dome

The three-dimensional finite-difference time-domain (3D-FDTD) method is developed and implemented in the case of oblique incidence in order to study biperiodic structures that are finished according to the third direction. The perfectly matched layer (PML) is adapted to the developed algorithm. The electromagnetic fields of Maxwell's equations in the main grid and in the PML media are transferred from the E-H domain to the mapped P-Q domain. The modified Maxwell's equations are implemented by the split-field method (SFM). Several tests are made and presented in order to verify and demonstrate the accuracy of our codes. The obtained results are in good agreement with published ones obtained by other methods. The originality of this paper comes, first from the fact that it brings a complete development of the used algorithm, and second, from the study of the spectral response of a radar dome based on annular aperture arrays perforated into a perfect conductor plate.