Jornal de Lasers, Óptica e Fotônica

We study exciton-like electromagnetic excitations in non-ideal microcavity lattice with the use of the virtual crystal approximation. The effect of point defects (vacancies) on the excitation spectrum is being numerically modeled for a quasi-two-dimensional non-ideal binary microcavity supercrystal. The adopted approach permits to obtain the dispersion dependence of collective excitation frequencies and the energy gap width on defect concentrations in a microcavity lattice. Based on the representations of the ideal photonic structures, the non-ideal polaritonic crystal, which is a set of spatially ordered cavities containing atomic clusters, is considered too. The analytical expressions for polaritonic frequencies, effective mass and group velocities, as a function of corresponding quantum dots and vacancies concentrations is obtained.

Optical coherence tomography (OCT) elastography (OCTE) has the potential to be an important diagnostic tool for pathologies including coronary artery disease, osteoarthritis, malignancies, and even dental caries. Many groups have performed OCTE, including our own, using a wide range of approaches. However, we will demonstrate current OCTE approaches are not scalable to real-time, in vivo imaging. As will be discussed, among the most important reasons is current designs focus on the system and not the target. Specifically, tissue dynamic responses are not accounted, with examples being the tissue strain response time, preload variability, and conditioning variability. Tissue dynamic responses, and to a lesser degree static tissue properties, prevent accurate video rate modulus assessments for current embodiments. Accounting for them is the focus of this paper. A top-down approach will be presented to overcome these challenges to real time in vivo tissue characterization. Discussed first is an example clinical scenario where OTCE would be of substantial relevance, the prevention of acute myocardial infarction or heart attacks. Then the principles behind OCTE are examined. Next, constrains on in vivo application of current OCTE are evaluated, focusing on dynamic tissue responses. An example is the tissue strain response, where it takes about 20 msec after a stress is applied to reach plateau. This response delay is not an issue at slow acquisition rates, as most current OCTE approaches are preformed, but it is for video rate OCTE. Since at video rate each frame is only 30 msec, for essentially all current approaches this means the strain for a given stress is changing constantly during the B-scan. Therefore the modulus can’t be accurately assessed. This serious issue is an even greater problem for pulsed techniques as it means the strain/modulus for a given stress (at a location) is unpredictably changing over a B-scan. The paper concludes by introducing a novel video rate approach to overcome these challenges.

In this paper we propose an accelerated plane wave expansion method (PWEM) for calculation of slab photonic crystal (slab PC) modes. In this method instead of creating artificial periodicity in the direction of slab normal and solving the problem as a full 3D one, which is done in standard PWEM, we consider constant coefficients in 2D PWEM as functions of slab normal component. Then we eliminate electric and magnetic fields in Maxwell’s equations in favor of electric and magnetic vector potentials to obtain equations that contain Laplace operator. Using the Green’s function for Laplace operator we then change the problem from differential to integral form. Replacing the integral operators with their matrix representations and doing some matrix algebra we finally obtain a matrix which slab PC modes can be extracted from its eigenvalues. Advantages of this method over the common approach are its less computational complexity, faster creation of the eigenvalue problem, and faster convergence of eigenvalues as the matrix dimensions increase.

This paper aims at to providing a self-consistent outline of new analytical prospects that deal with the laser dynamics issue, from which results that go beyond the well-known linear stability analysis are extracted. The method of investigation is rooted in weak and strong- harmonic Fourier-expansions applied to the laser equations when these operate under unstable conditions. Both routines are shown to apply equally well to the simple Lorenz-Haken model as well as to the much complex integro-differential Maxwell-Bloch equations

This paper focuses on the design and development of measurement technique and processing of signal for the detection of various explosive simulants like RDX(cyclo-trimethylene-tri-nitramine), TNT(Trinitro toluene), Sarin, TATP(Tri acetone triperoxide), their simulants like nitrobenzene, DNT(Dinitro toluene), DMMP(DiMethyl Methyl Phosphonate), acetone, propanol, etc. (in different states of matter) adsorbed on a metallic surface from a standoff distance ranging from few meters up to a distance of 25 meters in the wavelength range of 7-9 μm. The focus also lies on the measurement methodologies and the instrumentation employed in these systems. A dedicated single screen, single user, user friendly Graphical User Interface(GUI) for controlling the entire system, acquisition and processing of the incoming signal and demonstration of results has been developed with the help of Laboratory Virtual Instrument Engineering Workbench (LABVIEW). The dual phase sensitive detection technique has been employed. The “Data Acquisition for Explosive Detection System” (DAEDS) also carries out precise operation sequencing, parameter control, parameter measurement and storage of data. The incoming signal profile has been normalized with respect to the reference laser profile to obtain the resultant graph. Various experiments have been conducted and the resultant graphs have been plotted with intensity on the y-axis and wave-number on the x-axis as shown in the results section of this paper. Furthermore, online determination of the explosive or the simulant has been carried out. An engineering proto-type system has been developed which indicates the detected explosive/ simulant using the developed software.