Search

We numerically investigated lateral Goos-Hänchen shifts a two-dimensional Airy beam experiences when it is reflected at the interface between air and an epsilon-near-zero metamaterial. Angular spectrum theory is employed to decompose Airy beam into plane waves, followed by beam vectorization to overcome the paraxial propagation assumption. The reflected light field can then be obtained by integrating plane waves weighted by Fresnel reflection coefficients. Results show that Airy beam experiences nonzero GH shift at normal incidence due to asymmetric angular spectrum. Influences of beam parameters and permittivity are further investigated. Our study provides foundation for deep understandings of Airy beam in epsilon-near zero metamaterials. [ABSTRACT FROM AUTHOR]

In the lithography process, overlay describes the position errors of placing one mask layer pattern over an existing pattern on the wafer, and overlay metrology is one of the key challenges in semiconductor manufacturing. With the increase of process complexity especially for multiple patterning technologies in advanced nodes, the demand for accuracy, precision and process robustness in overlay metrology continues to tighten. In this paper, we have proposed and demonstrated a novel overlay metrology method with high process robustness. A straightforward theory called interference of diffraction light is developed for explanations why this method works for single layer overlay metrology. The overlay signals with continuous wavelengths and angles are simultaneously acquired in the pupil plane. Therefore, compared with the current monochrome measurement technology, this work can gather and utilize as much overlay information as possible for measurements. Experiments illustrate that this technique can achieve better measurement repeatability, faster measurement speed and better process robustness than current monochrome method, and thus this method has great potential to meet the higher node requirements for measurement accuracy. What’ more, our work provides a novel idea for scatterometry technology in the field of micro-nano measurement. [ABSTRACT FROM AUTHOR]

This research aims to make a comparison between the analytical and numerical methods of simulation of the Gaussian beam propagation in free space. This comparison brings evaluation of the accuracy and applicability limitations of the angular spectrum diffraction algorithm. In this approach, planar harmonic waves are assumed as basic components of a propagating wave, so the algorithm combines the angular spectrum technique and the 2D fast Fourier transformation procedures. It means a quite different approach than the well-established Huygens–Fresnel–Rayleigh–Sommerfeld one, based on spherical waves. The Gaussian beam is a rare case of the exact analytical 3D solution of a specific wave diffraction problem, in paraxial scalar approximation. Gaussian beam form has been chosen here as an evaluation reference. It allows to avoid comparisons between two numerical procedures, both of which may suffer from imperfections. In this comparison, the respective 2D cross-sections of calculated 3D complex valued wave fields distributions are presented. Also values of specific Gaussian beam parameters like full phase and Gouy phase shift and wave-front curvature radius are presented. The comparison between that form and the results of the angular spectrum algorithm brings information about the performance quality of that algorithm. [ABSTRACT FROM AUTHOR]

This research aims to make a comparison between the analytical and numerical methods of simulation of the Gaussian beam propagation in free space. This comparison brings evaluation of the accuracy and applicability limitations of the angular spectrum diffraction algorithm. In this approach, planar harmonic waves are assumed as basic components of a propagating wave, so the algorithm combines the angular spectrum technique and the 2D fast Fourier transformation procedures. It means a quite different approach than the well-established Huygens–Sommerfeld one, based on spherical waves. The Gaussian beam is a rare case of the exact analytical 3D solution of a specific wave diffraction problem, in paraxial scalar approximation. Gaussian beam form has been chosen here as an evaluation reference. It allows to avoid comparisons between two numerical procedures, both of which may suffer from imperfections. In this comparison, the respective 2D cross-sections of calculated 3D complex valued wave fields distributions are presented. Also values of specific Gaussian beam parameters like full phase and Gouy phase shift and wave-front curvature radius are presented. The comparison between that form and the results of the angular spectrum algorithm brings information about the performance quality of that algorithm. [ABSTRACT FROM AUTHOR]

The coupled wave equations for second harmonic generation of flat-topped beam propagating in birefringent uniaxial anisotropic medium are presented. Based on them, specific physical models of single and twin BBO crystals have been established and numerically computations have been carried out. The influences of beam waist, medium structure on second harmonic generation are analyzed. The calculation results indicate that a wider beam waist can make a better phase matching, therefore the second harmonic beam will maintain the flat-topped property better but with a lower intensity and twin crystals can eliminate beam walk-off in some way. [ABSTRACT FROM AUTHOR]

Abstract: Coupled wave equations that consider two-dimensional distribution and phases of gratings are derived by using weak grating and slow varying approximation. The result of angular selectivity on rand binary data page shows that each minimum is nonzero and each maximum that is not the middle maximum is a little bit smaller than that on plane wave volume hologram. Angular multiplexing is also modeled using the same method, and the middle page is read out in two different angular spacings. The relationship about PSNR versus angular spacing at different multiplexing pages is analyzed to reflect crosstalk between pages. All simulative results show this method is effective for volume holograms simulation. [Copyright &y& Elsevier]

Abstract: Power of an electromagnetic field in a plane is derived exactly as a function of the angular spectrum of only electric field components at another plane based on Maxwell equations and Poynting vector. Then, this quantity is acquired as a function of the electric field components. In this calculation, a function appears that is general and does not depend on the electromagnetic field function. [Copyright &y& Elsevier]

In the recent works on Mathieu beams, the angular spectrums commonly used are even and odd angular Mathieu functions with an angular variation vary between 0 to 2 π. In this work, we propose to introduce a new index m characterizing the rotation repetitions (m- times) of the structure of the original angular spectrum of Mathieu beams on the total circle in the frequency space. With this index, the angular spectrum of Mathieu beams rotation can be controlled to change the beam symmetry. We study the effect of these repetitions of the angular spectrum on the even and odd Mathieu modes features when they propagate through a paraxial optical system. We show that rotated repetitions of the angular spectrum does not affect the nondiffracting property of the beams. To illustrate the rotation repetitions of the angular spectrum, the Fourier transform of the beam is calculated in the focal plane of a thin lens. From the obtained results, we can conclude that the rotation repetitions of the angular spectrum can be used to produce others Mathieu beams shapes and can enrich the applications of these kinds of beams. [ABSTRACT FROM AUTHOR]

Cladding pumping is a common method to amplify signal channels in space-division multiplexing (SDM) systems. A high-power laser pump is directly launched to multi-core doped fiber (MCDF), and depending on the arrangement of cores in the MCDF, a small fraction of power goes to each core and amplifies the signal. Therefore, we have designed two diffractive optical elements, vortex lens (VL) and beam fanner (BF), to properly form the transverse pump distribution and increase pump power efficiency. Phase-only approximation and angular spectrum (AS) based methods are used to design the elements. We have found that using VL and BF allowed a significant increase in the pump power efficiency compared to direct cladding pumping. [ABSTRACT FROM AUTHOR]

• Studying the superposition of shifted Laguerre–Gaussian beams and their intensity distribution and analytical formulate for the angular spectrum of the superposed beams and obtaining the relation of their orbital angular momentum. • Generating finely focused spots to increase the efficiency of the optical tweezers by tuning the real transverse shift, topological charge, and radial index parameters of using superposed shifted Laguerre–Gaussian beams. • Designing gear-like beams by tune the number of the superposition of constituent beams for using in micro-particle manipulation and control of micro-machines gears. In this research, the superposition of shifted Laguerre–Gaussian (LG) beams and their intensity distribution are studied in cylindrical coordinates. By complex transverse shifting of conventional LG beams, the symmetry of intensity structure is lost and deformed to the crescent. Increasing the amount of beam pure imaginary shift causes the beam is focused on a smaller crescent. The obtained results from applying changes on the real transverse shift, topological charge, and radial index parameters of superposed LG beams depict the possibility of these beams to apply in optical trapping. As the radial index increases, in addition to the radial variation of the intensity distribution, the position and shape of the crescents are changed. Besides, analytical formulate for the angular spectrum of the superposed beams is derived and the relation of their orbital angular momentum (OAM) obtained. It is observed, by increasing the OAM, the radius of intensity distribution is increased. By the combination of these difference adjustable parameters, the localized intensity distribution has been prepared, which could be used for the production of controllable optical traps. The obtained experimental results confirm the simulation results. [ABSTRACT FROM AUTHOR]

Elastic light scattering has been proven to be an effective tool to characterize particles in a non-contact manner for the advantage of sub-wavelength resolution and ability of retrieving optical properties. But measurements based on plane wave scattering usually yield to weak scattering light, which poses strict requirements on the sensitivity of detection system. Gaussian light sheet that converges in one dimension can greatly enhance the intensity of scattering light, but it leads to the position dependence of light scattering. In this paper, characteristics of light scattering of a sphere in a Gaussian light sheet are numerically studied. Influences of sphere radius, refractive index, waist radius and sphere positions are systematically investigated via parametric study. Results show that the structure and optical information of the sphere are encoded into the scattering light. When the sphere radius is much less than the waist radius of light sheet, the angular distribution of scattering light of Gaussian light sheet is similar to that of plane wave scattering. The similarity decreases with increase of sphere radius and deviation from the optical axis. The proposed numerical method has the advantage of high efficiency and precision, providing the theoretical basis for inverse modeling. [ABSTRACT FROM AUTHOR]

Abstract: Self-imaging objects are not restricted to periodic ones. Montgomery derived the necessary and sufficient conditions in order that a plane object, illuminated by a plane monochromatic wave of normal incidence, images itself. On the basis of the reduced wave equation, he showed that the conditions for this case demand that the spatial frequencies of the self-imaging object should lie on discrete rings. In this paper, the above result has been obtained by using angular spectrum concept. [Copyright &y& Elsevier]