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. In this work, we propose and experimentally show that it is possible to probe the trajectory of the boundary by measuring the frequency shifts while changing the initial delay between the incident pulse and the boundary. We demonstrate this effect by reflecting a probe pulse off a short soliton, acting as a moving boundary that decelerates inside a photonic crystal fiber because of intrapulse Raman scattering. We deduce trajectory of the soliton from the measured spectral data for the reflected pulse.

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. The main advantage of our simplified approach is that it provides an analytic expression for the damping distance of beam-width oscillations that shows clearly the role played by various physical parameters.

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. Our results show that the focal spot size depends on the fraction of the beam's diameter over which coherence persists. Focusing ceases to occur, and the beam may even expand at the focal point of a GRIN lens, when this fraction is below 10%.

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. Con A was conjugated using carbodiimide chemistry by coupling -COOH group on the surface of nanoparticles. The paclitaxel-loaded Con A-conjugated nanoparticles were further subjected to the characterization of various parameters, that is, surface morphology, particle size, and polydispersity index. In vitro drug release study of both the formulations (plain & conjugated) was done using a dialysis tube up to 48 h in phosphate buffer (pH 7.4). RESULTS: Studies done in xenograft models evidently propose a dose-dependent cytotoxicity response, that is, shrink in % cell growth with increase in the concentration of the drug. The fluorescence photomicrograph clearly revealed the access of the Con A-conjugated nanoparticles to the tumor. A noteworthy biodistribution difference of the paclitaxel from prepared systems was observed. At the same time, Con A-coupled nanoparticles increased the accumulation of paclitaxel in the tumor cells. CONCLUSIONS: Hence, the Con A-conjugated nanoparticles formulation as compared to uncoupled solid lipid nanoparticles formulation and free drug solution showed nearly two times higher uptake because of the lectin receptors on the surface of tumors. Hence, it was envisaged to design polymeric nanoparticles which would be administered intravenously for better therapeutic efficacy.

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. In this work, frequency shifts of up to 14.3 GHz are achieved by adjusting the voltage of an RF control. With this technique, we can dynamically control light in a cavity within its photon lifetime by tuning the refractive index of the ring resonator electrically.

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.

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. This feature suggests that spatiotemporal waveguides can be realized through cross-phase modulation even when pump pulses have relatively long rise and fall times.

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. Universal testing machine measured fracture resistance. RESULTS: The mean fracture resistance in Group I was 458.6 ± 112.4 N, in Group II was 214.8 ± 104.6 N, in Group III was 428.6 ± 108.2 N, in Group IV was 388.2 ± 126.2 N, and in Group V was 334.8 ± 102.7 N. The difference found to be statistically significant (P < 0.05). Intergroup comparison showed a statistically significant difference (P < 0.05) between Groups I-II, I-V, II-III, and II-IV. CONCLUSION: The authors found that lateral condensation performed with AH Plus sealer and gutta-percha and the Thermafil technique were the highest among all other methods.

Scanning Electron Microscopic and Dye Penetration Evaluation of Hand Instrumentation Techniques on Formation of Smear Layer in Root Canal Preparation: An In vitro 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. Working length was determined, and roots were divided into five equal groups with 35 roots in each group as follows: Group A: K-type files with conventional step-back technique, Group B: Canal Master U instrument with clockwise-counterclockwise rotation, Group C: Flex-R® files with clockwise-counterclockwise rotation, Group D: FlexoFiles® with conventional step-back technique, and Group E: Nickel titanium files with conventional step-back technique. Biomechanical preparation was done according to their respective groups. The teeth in various groups were scanned under scanning electron microscope and scoring was done. All the results were analyzed by SPSS software version 17.0. RESULTS: Scanning electron microscopic results indicated that apparently there seems to be a significant difference in the scoring of the smear layer between each group at all the three levels, but the difference was statistically nonsignificant. Microleakage was present in all the samples. Nonsignificant results were obtained while comparing the microleakage in between different the groups. However, microleakage was highest in Group D. CONCLUSION: The amount of smear layer is maximum at the apical third and lesser in the middle third followed by the coronal third in all the groups. All the samples showed microleakage to a varying extent.

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. In this paper, we present a general method to optimize phase quantization using a PSA made using an SOA, based on gain extinction ratio (GER), which is an experimentally measurable quantity. We present a simple theory to derive the optimal GER required to achieve an M -level quantization. We further experimentally demonstrate two- and four-level phase quantization schemes with an SOA, operated at the optimized GER, with pump power levels as low as 1 mW.

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. Paromomycin sulphate-bearing nanostructured lipid carriers (NLCs) were formulated by a double emulsion solvent evaporation technique, and then chemistry of ring opening trailed by the reaction of fucose's aldehyde groups was analyzed for conjugation. The NLCs and conjugated-NLCs were examined in terms of average size, entrapment efficiency of drugs, polydispersity index, zeta potential, and in vitro drug release. Hemolytic toxicity was measured on whole human blood, and percent hemolysis by drug-loaded fucosylated-NLCs is reduced from 21.09 ± 1.5% to 5.81 ± 0.9 compared to the plain drug. Macrophage uptake of fluorescein isothiocyanate (FITC)-loaded plain NLCs and fucosylated-NLCs showed that mean FITC measured intensity increases in macrophage cell lines. MTT cytotoxicity assay ensured that NLCs could be beneficial as a biocompatible drug carrier for biomedical and pharmaceutical use. BALB/c mice were used for in vivo studies. Qualitative uptake of fucosylated-NLCs was observed by fluorescence microscopy, and the access of fucosylated-NLCs to the liver was revealed. Similar results were obtained by biodistribution studies. Therefore, fucose-conjugated nanoparticulate carriers can be designed to target macrophages with antileishmanial agents against the Leishmania parasite.

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. Numerical simulations were used to establish that our time-lens-based system can accurately measure the shape of infrared pulses between 3 ps and 12 ps. We also use our numerical model to determine how such a system can be modified to measure pulses whose width lies in the range of 1-30 ps, a range of interest for the OMEGA-EP laser at the Laboratory for Laser Energetics.

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. Furthermore, its value varies strongly in the vicinity of the geometrical focus, and its maximum, which need not occur at the focus, can be significantly higher than that of the incident beam.

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. Higher-order solitons can also form, but they propagate stably over shorter distances. We also discuss the impact of third-order dispersion on a GRIN soliton.

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. Our findings open up the possibility to control this fundamental property of random beams in a simple manner.

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. This, in turn, provides control over the beam's directionality, spectrum, and degree of polarization.

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 10-14 s range in optics had to await femtosecond lasers to be detected with difficulty. The spatial shifts have been isolated in many areas but the time delays, though fundamental, generally remain out of reach, particularly with particles. In textbooks usually both quantities are supposed to be simply linked. Here we report, using swivelling detectors, that the spatial and temporal measurements are intimately intermingled, especially in the so-called cyclical regime. Indeed, while the spatial shift does not depend on the type of detection, the measured time delay can be positive, negative or zero, but controllable. We also discuss how such intricate measurements of spatial and temporal effects allow crucial time penalties to be eliminated in guided soliton propagation, and should be used to unambiguously identify the Newton-Wigner time delays for particles.