Optical parametric amplification and oscillation in nonlinear chiral media.

We discuss the nonlinear process of optical parametric amplification inside a chiral crystal. We show that circular birefringence, induced by chirality, leads to two different nonlinear processes with different phase-matching conditions that are associated with the opposite states of circular polarizations. A single nonlinear process occurs only when the states of polarization of the incident pump and signal beams are both circular and orthogonal.

Spatiotemporal Bragg gratings forming inside a nonlinear dispersive medium.

We show that a spatiotemporal Bragg grating can be created inside a nonlinear dispersive medium (such as silica fibers) by launching a periodic train of pump pulses that travel as fundamental solitons. We develop a theoretical model and use it to find the band structure of such gratings. We study the interaction of a probe pulse with the Bragg grating, both within and outside of momentum gaps.

Probing the decelerating trajectory of a Raman soliton using temporal reflection.

Temporal reflection is a process where an optical pulse reflects off a moving boundary with different refractive indices across it. In a dispersive medium, this process creates a reflected pulse with a frequency shift that changes its speed. Such frequency shifts depend on the speed of the moving boundary.

Electrically induced adiabatic frequency conversion in an integrated lithium niobate ring resonator.

Changing the frequency of light outside the laser cavity is essential for an integrated photonics platform, especially when the optical frequency of the on-chip light source is fixed or challenging to be tuned precisely. Previous on-chip frequency conversion demonstrations of multiple GHz have limitations of tuning the shifted frequency continuously. To achieve continuous on-chip optical frequency conversion, we electrically tune a lithium niobate ring resonator to induce adiabatic frequency conversion.

Focusing of partially coherent light by a graded-index lens.

We use coherence theory to study how the focusing of an optical beam by a graded-index (GRIN) lens is affected when the incoming beam is only partially coherent. The Gaussian-Schell model is used to show that the intensity of a partially coherent beam exhibits self-imaging and evolves in a periodic fashion in a GRIN medium with a parabolic index profile. Spatial coherence of the beam affects a single parameter that governs how much the beam is compressed at the focal point.

Spatial beam narrowing in multimode graded-index fiber amplifiers: an analytic approach.

Doped and optically pumped graded-index (GRIN) fibers can be used to amplify an optical beam such that its spatial quality is improved at the output end of the fiber compared with that of the unamplified beam. We develop a simple model of the amplification process in such GRIN fiber amplifiers and show that the resulting equations can be solved analytically with suitable approximations. The solution shows that the width of the amplifying beam oscillates but also becomes narrower because of the radial dependence of the optical gain.

Biodegradable concanavalin A functionalized polycaprolactone nanoparticle: A promising avenue for cancer therapy.

Objective: Receptor-based tumor-selective delivery of therapeutic efficacy and therapeutic index of cytotoxic drugs that exhibit dose-limiting toxicity is observed. Concanavalin A (Con A) was selected as the ligand for the proposed system, which was appended to the polycaprolactone nanoparticles (NPs) carrying the drug to be a very efficient approach for the treatment of cancer.

Methods: Preparation of plain polycaprolactone nanoparticles was carried out employing the emulsion diffusion evaporation technique.

Scanning Electron Microscopic and Dye Penetration Evaluation of Hand Instrumentation Techniques on Formation of Smear Layer in Root Canal Preparation: An Study.

Aims And Objectives: The present study was undertaken for evaluating various hand instrumentation techniques with different instruments in the formation of smear layer.

Materials And Methods: One hundred and seventy-five extracted mandibular molars were collected and were cut at cementoenamel junction. Afterward, the distal roots were separated.

Assessment of Fracture Resistances of Endodontically Treated Teeth Filled with Different Root Canal Filling Systems.

Background: The motive of endodontic therapy is cleaning, shaping, and subsequently obturation. This study assessed different root canal filling systems in terms of fracture resistances of endodontically treated teeth.

Methodology: This study was conducted on eighty single-rooted permanent mandibular incisor teeth which were divided into five groups: Group I was negative control; Group II was positive control; Group III comprised of gutta-percha/AH Plus; Group IV comprised of Thermafil/AH Plus; and Group V Resilon/Epiphany SE.

Impact of the boundary's sharpness on temporal reflection in dispersive media.

We investigate the impact of the finite rise time of a spatiotemporal boundary inside a dispersive medium used for reflection and refraction of optical pulses. We develop a matrix approach in the frequency domain for analyzing such spatiotemporal boundaries and use it to show that the frequency range over which reflection can occur is reduced as the rise time increases. We also show that total internal reflection can occur even for boundaries with long rise times.

Role of frequency dependence of the nonlinearity on a soliton's evolution in photonic crystal fibers.

We reveal the crucial role played by the frequency dependence of the nonlinear parameter on the evolution of femtosecond solitons inside photonic crystal fibers (PCFs). We show that the conventional approach based on the self-steepening effect is not appropriate when such fibers have two zero-dispersion wavelengths, and several higher-order nonlinear terms must be included for realistic modeling of the nonlinear phenomena in PCFs. These terms affect not only the Raman-induced wavelength shift of a soliton but also impact its shedding of dispersive radiation.

Power optimization for phase quantization with SOAs using the gain extinction ratio.

Phase-sensitive amplifiers (PSAs) can work as M - level phase quantizers when waves generated with specific phase values are allowed to mix coherently in a nonlinear medium. The quality of an M - level phase quantizer depends on the relative powers of the mixing waves and requires their optimization. If the mixing waves also experience gain in the nonlinear medium, such as in semiconductor optical amplifiers (SOAs), this optimization becomes non-trivial.

A Formulation of Paromomycin Sulphate as a Promising Fucose-Conjugated Nanostructured Lipid Carrier for Antileishmanial Drug Delivery.

Environmental and individual risk factors make leishmaniasis an important public health problem. Presently, there are several medicines existing for the cure of leishmaniasis, but a major problem associated with them is their adverse effects. The affinity to the fucose receptor increases the phagocytosis of ligand-bound carriers and simultaneously targets the delivery of the antileishmanial agent.

Distributed feedback lasing based on a negative-index metamaterial waveguide.

This Letter lays the foundation of a new type of distributed feedback (DFB) laser whose optical feedback is due to the evanescent coupling between an active positive-index material (PIM) waveguide and a lossy negative-index metamaterial (NIM) waveguide. Active PIM-NIM coupled-mode equations are presented and solved to characterize the dispersion relation, resonant optical gain, and lasing. The photonic bandgap of this grating-less DFB laser does not depend on a Bragg wavenumber, but depends on the difference between the wavenumbers of the PIM and NIM waveguides; controlling this wavenumber difference allows for single-mode lasing and, ultimately, single-mode broadband lasing.

A time-to-frequency converter for measuring the shape of short optical pulses.

A time-to-frequency converter was constructed using an electro-optic phase modulator as a time lens, allowing the pulse shape in time to be transferred to the frequency domain. We used such a device to record the temporal shape of infrared pulses at a wavelength of 1053 nm (width about 7 ps) and compared these measurements to those made by using both a streak camera and an autocorrelator. This side-by-side comparison illustrates the benefits and limitations of each of the measurement methods.

Fraunhofer diffraction and the state of polarization of partially coherent electromagnetic beams.

We generalize the concept of Fraunhofer diffraction to partially coherent electromagnetic beams and show how the state of polarization is affected by a circular aperture. It is illustrated that the far-zone properties of a random beam can be tuned by varying the aperture radius. We find that even an incident beam that is completely unpolarized can sometimes produce a field that is highly polarized.

Degree of polarization in the focal region of a lens.

We examine the 3D distribution of the degree of polarization (DOP) in the focal region of a thin paraxial lens. Analytic expressions for the case of a focused Gaussian-Schell model beam are derived. These show that the DOP satisfies certain spatial symmetry relations.

Graded-index solitons in multimode fibers.

We investigate stability of optical solitons in graded-index (GRIN) fibers by solving an effective nonlinear Schrödinger equation that includes spatial self-imaging effects through a length-dependent nonlinear parameter. We show that this equation can be reduced to the standard NLS equation for optical pulses whose dispersion length is much longer than the self-imaging period of the GRIN fiber. Numerical simulations are used to reveal that fundamental GRIN solitons as short as 100 fs can form and remain stable over distances exceeding 1 km.

Controlling the degree of polarization of partially coherent electromagnetic beams with lenses.

We show theoretically that the degree of polarization of a partially coherent electromagnetic beam changes dramatically as the beam is being focused. A low numerical aperture lens can considerably enhance the degree of polarization at its geometrical focus. When two identical lenses are employed in a 4f configuration, the degree of polarization of a beam can be tailored by using amplitude masks in the Fourier plane located in the middle of the two lenses.

Fourier processing with partially coherent fields.

We describe how Fourier signal processing techniques can be generalized to partially coherent fields. Using standard coherence theory, we first show that focusing of a partially coherent beam by a lens modifies its coherence properties. We then consider a 4f imaging system composed of two lenses and discuss how spatial filtering in the Fourier plane allows one to tune the coherence properties of the beam.

Dynamics and detection of the Newton-Wigner time delays at interfaces using a swivelling method.

Evanescent waves are ubiquitous at interfaces with optical, seismic or acoustic waves, and also with electron, neutron or atom beams. Newton was the first to suspect that both small time delays and spatial shifts exist during total internal reflection. However, these effects are so tiny that the spatial shifts were only observed in 1947 in optics, whereas the time delay values predicted by the Wigner model in the 10 s range in optics had to await femtosecond lasers to be detected with difficulty.

Dynamics of soliton cascades in fiber amplifiers.

We study numerically the formation of cascading solitons when femtosecond optical pulses are launched into a fiber amplifier with less energy than required to form a soliton of equal duration. As the pulse is amplified, cascaded fundamental solitons are created at different distances, without soliton fission, as each fundamental soliton moves outside the gain bandwidth through the Raman-induced spectral shifts. As a result, each input pulse creates multiple, temporally separated, ultrashort pulses of different wavelengths at the amplifier output.

Theoretical analysis of hot electron injection from metallic nanotubes into a semiconductor interface.

Metallic nanostructures under optical illumination can generate a non-equilibrium high-energy electron gas (also known as hot electrons) capable of being injected into neighbouring media over a potential barrier at particle boundaries. The nature of this process is highly nanoparticle shape and size dependent. Here, we have derived an analytical expression for the frequency dependent rate of injection of these energetic electrons from a metallic nanotube into a semiconductor layer in contact with its inner boundary.

Design of all-optical, hot-electron current-direction-switching device based on geometrical asymmetry.

We propose a nano-scale current-direction-switching device(CDSD) that operates based on the novel phenomenon of geometrical asymmetry between two hot-electron generating plasmonic nanostructures. The proposed device is easy to fabricate and economical to develop compared to most other existing designs. It also has the ability to function without external wiring in nano or molecular circuitry since it is powered and controlled optically.