Absorption of light through isolated and coupled resonances in horizontal InP nanowire arrays

We have studied the interaction of light with two types of closely related nanostructures: a single horizontal InP nanowire and an infinite periodic array of such nanowires. The study has been done theoretically by calculating the absorption cross section of the nanowires via a semi analytical method, the Mie theory, and two numerical methods, the scattering matrix method (SMM) and the finite element method (FEM) to perform electromagnetic modeling. The absorption spectra obtained by the Mie theory show strong polarization dependency. Also, we have noticed that the peaks in the spectra red shift by increasing the radius of the nanowires. To study this redshift, we assumed that the nanowires can be seen as optical waveguides that can capture the light in certain eigenmodes much like a whispering gallery mode. Due to this, a semi analytical eigenfunction method has been employed to investigate the eigenmodes in the nanowire. The results show that the eigenmodes are the origin of the Mie resonances and redshift by increasing the radius of the nanowire. By moving to study the optical response of the periodic array consisting of infinitely many nanowires, an additional set of optical resonances is introduced to the absorption in the nanowires. These resonances are due to Bragg grating condition for constructive interference of scattered light between neighboring nanowires, and these resonances depend on the period of the structure. These new resonances are called lattice resonance throughout this thesis. We show that for specific combination of the period of the array and the radius of the constituent nanowires, the lattice resonances couple with the single nanowire resonances. This coupling can boost the absorption in the array by a factor of 18 compared to that in single nanowires. Through such resonant absorption, the nanowires can absorb 200 times stronger than the same amount of InP material in bulk form.Objects with dimensions in the order of nanometer (1 millionth fraction of 1mm), have special characteristics that enable them with the potential to be applied in a variety of technologies, including solar cells and LEDs. Light behaves differently when it interacts with special materials with such small dimensions. In the current work, we try to explain this interaction between light and these objects called nano-structures, specifically an infinitely long single indium phosphide (InP) nanowire and an infinite periodic array of such nanowires. Essentially, a nanowire is a one dimensional nano-structure with the length from a few tens of nanometers to several micrometers and the radius around 50-100 nanometers (1000 times thinner than a human hair). InP is a semiconductor with electrical conductivity between that of insulators (e.g. glass) and metals (e.g. copper). Furthermore, semiconductors can absorb the energy of the light and convert it to electricity in opto-electronics devices such as photovoltaic cells and photo-detectors. This study has been done theoretically via semi analytical methods for simple systems like a single nanowire and via numerical methods for more complicated systems like the array of nanowires. The calculations show that the absorption mechanism of light in the single nanowire depends on the radius of the nanowire. Due to the small size of the nanowire, part of the light is captured inside the nanowire where it is absorbed and part of it leaks out from the nanowire. Then, in the periodic array, this leaked light can interact with the neighboring nanowires and change the absorption pattern. Therefore, the absorption in the periodic array not only depends on the radius of the nanowires but also on the period of the structure, that is, on the distance between the nanowires. We show that for specific combinations of the period of the array and the radius of the constituent nanowires, the leaked light from a single nanowire interferes constructively inside the neighboring nanowires. This constructive interference can boost the absorption up to 18 times in contrast to that in a single nanowire. Through such resonant absorption, the nanowires can absorb 200 times stronger than the same amount of InP material in bulk form. The direct consequence of this is achieving higher efficiency of photo-devices exploiting the interaction of light and semiconductor nanowires. A higher efficiency facilitates lower utility of the material and a potentially lower cost

Investigating the pathogenicity of Alternaria alternata on Lonicera japonica

This study was carried out to investigate the pathogenicity of Alternaria alternata and the effect of its metabolites on L. japonica from 2015- 2016 in Birjand plain area in eastern Iran. A. alternata isolates were inoculated on L. japonica detached leaves in laboratory conditions, on plants by spore suspension in the greenhouse and on young branches by fungal mycelia. The effect of A. alternata metabolites was examined by injection of extracted metabolites from a 10-day culture of the fungus in a Czapek broth media into the leaves of the plant. Inoculated detached leaves, after 3 to 7 days of inoculation, exhibited different ranges of chlorosis and necrosis, with or without a yellow halo around some of this spot. Leaves of inoculated plants in the greenhouse showed chlorosis, necrosis and leaf spots with (Mo8) or without (H44) a yellow halo. Inoculated stems demonstrated rotting and death in the inoculation site and wilting of stems. Metabolites of some isolates particularly isolate with a yellow halo (Mo8) in inoculated detached leaves, caused necrotic leaf tissues five days after injection. The results showed that A. alternata could be a cause of leaf spot, chlorosis, and necrosis, and the metabolites of some isolates can cause the death of leaf cells of L. japonica. This is the first report of the A. alternata pathogenicity on this plant in the eastern part of Iran

Band-Passing Nonlinearity in Reset Elements

This paper addresses nonlinearity in reset elements and their effects. Reset elements are known for having less phase lag compared to their linear counterparts; however, they are nonlinear elements and produce higher-order harmonics. This paper investigates the higher-order harmonics for reset elements with one resetting state and proposes an architecture and a method of design which allows for band-passing the nonlinearity and its effects, namely, higher-order harmonics and phase advantage. The nonlinearity of reset elements is not entirely useful for all frequencies, e.g., they are useful for reducing phase lag at cross-over frequency region; however, higher-order harmonics can compromise tracking and disturbance rejection performance at lower frequencies. Using proposed "phase shaping" method, one can selectively suppress nonlinearity of a single-state reset element in a desired range of frequencies and allow the nonlinearity to provide its phase benefit in a different desired range of frequencies. This can be especially useful for the reset elements in the framework of "Constant in gain, Lead in phase" (CgLp) filter, which is a newly introduced nonlinear filter, bound to circumvent the well-known linear control limitation -- the waterbed effect

Tuning of Constant in gain Lead in phase (CgLp) Reset Controller using higher-order sinusoidal input describing function (HOSIDF)

Due to development of technology, linear controllers cannot satisfy requirements of high-tech industry. One solution is using nonlinear controllers such as reset elements to overcome this big barrier. In literature, the Constant in gain Lead in phase (CgLp) compensator is a novel reset element developed to overcome the inherent linear controller limitations. However, a tuning guideline for these controllers has not been proposed so far. In this paper, a recently developed method named higher-order sinusoidal input describing function (HOSIDF), which gives deeper insight into the frequency behaviour of non-linear controllers compared to sinusoidal input describing function (DF), is used to obtain a straight-forward tuning method for CgLp compensators. In this respect, comparative analyses on tracking performance of these compensators are carried out. Based on these analyses, tuning guidelines for CgLp compensators are developed and validated on a high-tech precision positioning stage. The results show the effectiveness of the developed tuning method

Single-shot coherent control of molecular rotation by fs/ns rotational coherent anti-Stokes Raman spectroscopy

We present a novel method, to our knowledge, to control the shape of the spectra using 2-beam hybrid femtosecond (fs)/nanosecond (ns) coherent anti-Stokes Raman scattering (RCARS). The method is demonstrated experimentally and theoretically by utilizing a species-selective excitation approach via a field-free molecular alignment as an illustrative example. Two non-resonant fs laser pulses with proper delay selectively create and then annihilate N2 resonances in a binary mixture with O2 molecules. The RCARS signal is simultaneously resolved in spectral and temporal domains within a single-shot acquisition. The method requires very low pulse energies for excitation, hence minimizing multiphoton ionization probability, allowing for coherent control at various temperatures and pressures, with spectroscopic applications in non-stationary and unpredictable reacting flows

Tuning of CgLp based reset controllers: Application in precision positioning systems

This paper presents the tuning of a reset-based element called "Constant in gain and Lead in phase" (CgLp) in order to achieve desired precision performance in tracking and steady state. CgLp has been recently introduced to overcome the inherent linear control limitation - the waterbed effect. The analysis of reset controllers including ones based on CgLp is mainly carried out in the frequency domain using describing function with the assumption that the relatively large magnitude of the first harmonic provides a good approximation. While this is true for several cases, the existence of higher-order harmonics in the output of these elements complicates their analysis and tuning in the control design process for high precision motion applications, where they cannot be neglected. While some numerical observation-based approaches have been considered in literature for the tuning of CgLp elements, a systematic approach based on the analysis of higher-order harmonics is found to be lacking. This paper analyzes the CgLp behaviour from the perspective of first as well as higher-order harmonics and presents simple relations between the tuning parameters and the gain-phase behaviour of all the harmonics, which can be used for better tuning of these elements. The presented relations are used for tuning a controller for a high-precision positioning stage and results used for validation