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Register a new userLight diffraction from a phase grating at oblique incidence in the intermediate diffraction regime
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We experimentally characterize the positions of the diffraction maxima of a phase grating on a screen, for laser light at oblique incidence (so-called off-plane diffraction or conical diffraction). We discuss the general case of off-plane diffraction geometries and derive basic equations for the positions of the diffraction maxima, in particular for their angular dependence. In contrast to previously reported work [Jetty et al., Am. J. Phys. 80, 972 (2012)], our reasoning is solely based on energy- and momentum conservation. We find good agreement of our theoretical prediction with the experiment. A detailed discussion of the diffraction maxima positions, the number of diffraction orders, and the diffraction efficiencies is provided. We assess the feasibility of an experimental test of the phenomenon for neutron matter waves.
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This work presents a theoretical investigation of an active diffraction grating of the Parity-Time (PT) symmetric architecture. The analytical study of the free-space mode propagation in the grating structure indicates the unique bifurcation property due to the PT-symmetry modulation. It is shown that both the gain/loss contrast and the lattice constant parameters are critical factors to modulate the photonic system in between the PT-symmetry to the symmetry-broken phases. Furthermore, numerical simulations via the Rigorous Coupled-Wave Analysis (RCWA) method discover the existence of a unique Spectral Singularity (SS) phenomenon in this PT grating structure which is corresponding to a non-trivial single-mode and near-zero bandwidth photonic resonant emission. Also, the guiding procedure for fulfilling SS modes is found to be related to the unique formation of the scattering matrix applied in the PT-symmetric diffraction gratings. This theoretical work takes a fresh look into the active PT-symmetric diffraction gratings focusing on the discovery of new free-space emission modes rather than the commonly studied unidirectional properties, which could contribute to the development of novel low-threshold and super-coherent laser devices.
Optical gratings are a key component in many spectroscopy, communications, and imaging systems. While initially static elements, advances in optical materials have enabled dynamically tunable gratings to be designed. One common tuning strategy is relying on mechanical deformation of the grating pitch to modify the diffraction pattern. To date, most mechanically adaptive optical gratings consist of a hybrid system where rigid moieties are patterned on an elastomeric substrate. In the present work, we demonstrate an all-polymer tunable grating that is fabricated using replica molding from the poly(acrylic acid) (PAA)/polyethylene oxide (PEO) polymer stereocomplex. PAA/PEO pristine films exhibit excellent optical transmittance at or above 80% from 500 nm to 1400 nm and stretchability over 800% strain. The experimental studies on the changes of diffraction mode distances with respect to the applied strains agree well with the finite-difference time-domain (FDTD) theoretical modeling.
Ultra-thin optical structures, known as metasurfaces, have shown promising light controlling capability at the nanoscale. In this paper, we study their particular case, a periodic array of high-refractive-index nanoparticles with electric and magnetic resonances. The main result of the work is a numerical demonstration that the lattice effect in the periodic arrangement of nanoparticles changes the resonance position even if the resonances are above the diffraction wavelength (Rayleigh anomaly). We show that the disk resonance changes can be achieved not only by varying periods of the array under normal light incidence but also by changing the incident angle.
In coherent X-ray diffraction microscopy the diffraction pattern generated by a sample illuminated with coherent x-rays is recorded, and a computer algorithm recovers the unmeasured phases to synthesize an image. By avoiding the use of a lens the resolution is limited, in principle, only by the largest scattering angles recorded. However, the imaging task is shifted from the experiment to the computer, and the algorithms ability to recover meaningful images in the presence of noise and limited prior knowledge may produce aberrations in the reconstructed image. We analyze the low order aberrations produced by our phase retrieval algorithms. We present two methods to improve the accuracy and stability of reconstructions.
We report on the observation of emerging beam resonances, well known as Rayleigh-Wood anomalies and threshold resonances in photon and electron diffraction, respectively, in an atom-optical diffraction experiment. Diffraction of He atom beams reflected from a blazed ruled grating at grazing incidence has been investigated. The total reflectivity of the grating as well as the intensities of the diffracted beams reveal anomalies at the Rayleigh angles of incidence, i.e., when another diffracted beam merges parallel to the grating surface. The observed anomalies are discussed in terms of the classical wave-optical model of Rayleigh and Fano.
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