Higher-order Diffraction Peaks Research Articles

Parity-time symmetry and asymmetric diffraction of light in four-level triple quantum wells

In this paper, we investigate two-dimensional parity-time (PT) symmetry and electromagnetically induced grating (EIG) in four-level asymmetric triple quantum wells (QWs). Here, PT-symmetry and EIG are realized by appropriately varying the detuning value of the probe, and the modulation amplitudes of a coupling field and standing wave (SW) pump. By virtue of its PT symmetry, the EIG asymmetrically diffracts the probe beam. The angular switching of the diffracted beam can be achieved either by varying the probe or the coupling and SW pump fields. The intensity distribution of the diffracted beam over higher-order diffraction peaks depends on the interaction length in the QW. For small interaction lengths, most of the energy is distributed close to the central diffraction peak. With an increase in the interaction length, energy is gradually transferred to higher order diffraction peaks.

Optical spectra of periodically patterned dielectric surface simulated by finite-different time-domain method

A dielectric film imprinted with a hexagonal periodical pattern of nanosphere holes can be fabricated by a two-step process of depositing a dielectric thin film on a hexagonally patterned array of nanospheres fabricated by convective deposition, and then removing the nanosphere particles. In this work, the optical transmission through a dielectric slab with hexagonal pattern of half-sphere holes was simulated by finite-different time-domain (FDTD) methods. In the simulation, a short gaussian pulse of electromagnetic waves was generated and propagated through the dielectric patterned slab and the near-field diffraction from the structure was collected as a function of time. Using a Fourier transformation, the optical spectra of the structure were evaluated. The far-field diffraction was also investigated by evaluating the analytical Green’s function at given points. Several parameters of the optical response including full width at half maximum and relative intensities of high order diffraction peaks were examined for various structure sizes. The structures examined were composed of a periodic hexagonal pattern of half nanosphere holes (radius of 290 nm). In addition, the effect on the optical response of 10% elliptical shape deformation of the half-sphere holes was studied. Our calculations enable us to identify parameter schemes where the third order diffraction exceeds second order diffraction efficiency from gratings.

Emergence and magnetic-field variation of chiral-soliton lattice and skyrmion lattice in the strained helimagnet Cu2OSeO3

We demonstrate emergence of both the chiral soliton lattice and skyrmion lattice and investigate their magnetic-field variation in the strained ${\mathrm{Cu}}_{2}{\mathrm{OSeO}}_{3}$ thin plate by means of small-angle resonant soft x-ray scattering. The tensile strain stabilizes a helical spin structure with the modulation vector along the strain direction. Consequently, when increasing the field perpendicular to the modulation vector, it undergoes large shrinkage and higher-order diffraction peaks are also observed, which is in accord with a typical feature of the chiral soliton lattice. The skyrmion lattice also appears in the presence of tensile strain but is elongated along the strain direction in reciprocal space. The magnetic-field dependence of the modulation vector along the strain direction agrees with the theoretical model quantitatively, while that along other directions does not. The agreement, however, becomes worse at lower temperatures, which may be attributed to the large potential barrier for skyrmion annihilation.

X-ray Diffraction from X-ray Waveguide Arrays for Generation of Coherent X-ray

The generation of coherent x-ray beams by using a multi-slit diffraction phenomenon is presented. The mode-confinement conditions in the x-ray waveguide (XWG) needed to obtain single-mode beams are determined. The XWGs are stacked to form an XWG array. The core of the XWG array is used as a slit in an opaque screen, similar to those used for visible light. Diffraction patterns that interfered constructively in the XWG array are investigated based on multi-slit diffraction theory. The irradiance distributions are studied at on observation screen. The FWHM of diffracted x-ray spectra were between $1.67{\times}10^{-4}$ to $3.30{\times}10^{-5}$ radians which lead to a spot-size of a few tens of micrometers on the screen at distance of 1 m. The intensities decrease with increase in the period of the XWG array, i.e. a thicker cladding, due to growth of the higher-order diffraction peaks.

Influence of irregular gaps between primary mirror segments on telescope image quality

We study the effect of gaps between the segments on image quality of the extremely large ground-based telescope. We show that if the width of the gap changes arbitrarily from one intersegment boundary to another, the regular diffraction pattern is distorted and speckles appear. Two mechanisms producing irregularity in the gaps' distribution are considered: a random shift of the segment's center and an error in the segment's shape. The analytical approach allows an estimation of ensemble averaged characteristics of the point-spread function, such as a halo and high-order diffraction peaks. We deliver simple formulas for the quantitative estimation of the position and the intensity of the halo as well as the intensity of the diffraction peaks.

Analytical study of diffraction effects in extremely large segmented telescopes.

We present an analysis of the diffraction effects from a segmented aperture with a very large number of segments-prototype of the next generation of extremely large telescopes. This analysis is based on the point-spread-function analytical calculation for Keck-type hexagonal segmentation geometry. We concentrate on the effects that lead to the appearance of speckles and/or a regular pattern of diffraction peaks. These effects are related to random piston and tip-tilt errors on each segment, gaps between segments, and segment edge distortion. We deliver formulas and the typical numerical values for the Strehl ratio, the relative intensity of higher-order diffraction peaks, and the averaged intensity of speckles associated with each particular case of segmentation error.