Intensity Of Diffraction Orders Research Articles

Diffraction of vortex Gaussian beams from a two-dimensional Raman-induced grating

In this paper, we study diffraction of a vortex Gaussian probe beam on a two-dimensional (2D) Raman-induced diffraction grating. Both near- and far-field diffraction of a vortex beam is considered. In the near field, quasi-Talbot images occur at specific distances from the grating, which corresponds to the classical Talbot length. Diffraction patterns in the Talbot planes are a periodic 2D array of ring-like vortex beamlets with topological charges (TCs) equal to the illuminating probe beam’s charge. The lateral (off-axis) beamlets consist of several overlapping vortices with the TCs l = 1 and l =−1, and their centers (singular points) are offset relative to each other. It is shown that in the near field the TC is conserved, and the total diffraction field represents a single (global) vortex with an effective TC equal to the charge of the vortex probe beam. In the far field, diffraction patterns are also a 2D array of ring-like local vortices with a period depending on the z coordinate. Their TCs are equal to the charge of the probe field. It is shown that in a far field, the diffracted field’s total TC is also equal to that of the probe field. We demonstrate that by choosing the pump field parameters, one can effectively control the intensity of diffraction orders.

Periodic variations of intensity of diffraction orders in Raman-Nath diffraction

In acousto-optic imaging, the ultrasound-induced optical phase modulation has been widely used in the imaging of biological tissue. However, in Raman-Nath diffraction, the phase of diffracted light has not attracted much attention. Additionally, each order of diffraction has been simply treated as a plane light wave with optical phase shift, and the intensity of diffraction orders hence has been considered to be constant. Then, the phase shift is independent on the diffraction path of light wave in the acousto-optic interaction zone and the corresponding refractive index and the power of the ultrasound wave. Recently, we observe experimentally that the intensity of diffraction orders varies periodically with time. We hence study the periodic variations in depth. It is found that the diffracted light has an ultrasound-induced phase modulation and the periodic variations are due to the phase modulation.

Phase-controlled Optical PT symmetry and asymmetric light diffraction in one- and two-dimensional optical lattices

We propose a novel scheme for asymmetric light diffraction of a weak probe field in a one-dimensional (1D) and two-dimensional (2D) lattice occupied with cold atoms. The atoms are driven into the double-lambda-type configuration by a standing wave, two coupling laser fields and a probe. Our study suggests the proposed scheme is capable of forming an asymmetric diffraction as a result of inducing optical parity-time symmetry in both 1D and 2D lattices. Moreover, it is demonstrated that the asymmetric pattern of diffraction can be dynamically manipulated by means of adjusting the relative phase. Furthermore, it is revealed that in the case of 1D lattice (grating), intensity variation of the coupling fields has a significant impact on the intensity of diffraction orders.

Analytical calculation of diffraction order intensities for a hyperspectrometer

We employ a geometric optics approach to calculate the eikonal of a light field at the output of a diffraction grating in the immediate microrelief vicinity. Analytic relations to calculate the diffraction order intensities as functions of the grating step height, line spacing, wavelength of incident light, and incidence angle are deduced. By way of illustration, intensities of the diffraction orders for a blazed reflection grating with a 555-nm operating wavelength utilized in hyperspectrometers are calculated.

Electromagnetically induced gain-phase grating in a double V-type quantum system.

Finding schemes to promote the efficiency of phase gating nowadays is a main concern. We address this issue by devising a feasible and innovative scheme that enables us to obtain a gain-phase grating. It is shown that a linearly polarized probe field traveling through a double V-type closed-loop atomic system, which is driven by a standing wave and a microwave field, can be efficiently diffracted in higher orders. As a significant result, we find that intensity of the diffracted field is highly amplified in every single order direction compared with the intensity of the input probe field. The responsible mechanism is induced gain accompanied by the large dispersion arising due to the applying microwave field. It is shown that in the presence of a microwave field, among various parameters, the relative phase of the applied fields has the most appreciable effect on enhancing the intensity of diffraction orders. It is also demonstrated that quantum interference between decay channels of the quantum system can be used as a tool to manipulate the intensity of diffraction orders.

Grating mirror for diffraction of electrons

The ability to imprint a phase pattern onto a coherent electron wave would find many applications in electron optics, in analogy to what is already possible with photons in light optics. Spatially dependent phase manipulation is achieved in transmission electron microscopy by passing the beam through a phase plate. However, in transmission mode this technique suffers from crystal imperfections and electron-matter interaction. If instead the electron wave is reflected of a spatially modulated potential, these difficulties can be circumvented. To demonstrate this principle, we consider here a periodic topological mirror structure that results in a sinusoidal plane of reflection for the incident electron. The reflection of the electron then takes place just above the physical mirror surface. Such ``electron grating mirror'' is expected to diffract the incident wave upon reflection by the introduced path length difference. The mirror can then be used as an electron beam splitter and coupler, analogous to semitransparent mirrors used in light optics. This enables for instance a lossless Mach-Zehnder interferometer for electrons. A numerical model that solves the Schr\odinger equation for this system is obtained to enable a quantitative description of the grating mirror. The results show that the obtained diffraction order intensities behave like squared Bessel function of their respective order, and thus for instance the results show how an increase in grating pitch reduces the sensitivity to energy spread in the incident electron beam. Additionally, we show how the use of the WKB approximation enables faster calculations in the case of general patterns.

Successive diffraction model based on Fourier optics as a tool for the studies of light interaction with arbitrary ultrasonic field

In this paper we presented theoretical predictions of light diffraction by complex acoustic fields such as: two adjacent and superposed ultrasonic beams or ultrasound of cylindrical symmetry. The numerical calculations of light intensity of diffraction orders were performed by means of two methods: Nth Order Approximation (NOA) and Successive Diffraction Model (SDM) based on Fourier optics. The latter technique involves dividing the ultrasonic field into several adjacent sections provided that in each section the interaction of light and ultrasound is considered to fulfill Raman-Nath approximation. Propagation of light inside and behind the region with ultrasonic wave was described within the formalism of Fourier optics so that only both transfer and transmission functions had to be appropriately defined. It was revealed that SDM method based on Fourier optics might be applied in the studies of acousto-optic interaction in the cases of complex ultrasonic fields.

Design and investigation of colour separation diffraction gratings

The performance of colour separation diffraction gratings is studied using the rigorous electromagnetic theory. The diffraction order intensities as a function of the period-to-wavelength ratio are calculated. The applicability limit of the scalar diffraction theory for designing such gratings is evaluated. The colour separation gratings are designed within the framework of the rigorous electromagnetic theory using a gradient method. The optimality of the scalar-theory-based solutions is estimated.

Interaction between surface plasmon and magnetic material

The present paper concerns the interaction between a surface plasmon and a magnetic material with a transverse Kerr effect configuration type. The surface plasmon is optically generated at the surface of a gold layer. The associated evanescent wave interacts with a cobalt diffraction grating patterned on gold. The magneto-optical interaction is observed in reflection and transmission modes by measuring the intensity of diffraction orders and the enhancement of the magneto-optical effect due to the surface plasmon is discussed.

Surface-profile dependence of photon-plasmon-polariton coupling at a corrugated silver surface

The influence of the surface-profile Fourier decomposition on photon–surface-plasmon-polariton (SPP) coupling at a corrugated silver surface, as probed by changes in diffraction-order intensities, line shapes, and peak positions, is explored. The effect of higher spatial harmonics on diffraction orders is considered for coupling to the SPP in the vicinity of a grating-induced minigap as well as away from the minigap region. Numerical results are obtained with the reduced Rayleigh equations, which are accurate in the range of corrugation strengths that optimize photon–SPP coupling for silver. Under first-order-coupling conditions away from the minigap region the presence of a particular spatial harmonic in the surface profile enhances a specific diffraction order in an easily predictable way. The selectivity, sensitivity, and associated line-shape changes for enhancement are examined as a function of harmonic amplitude for several higher harmonics. In connection with recent experiments [ J. Opt. Soc. Am. B8, 1348 ( 1991)] we investigate the influence of the second and the third spatial harmonics on the propagating orders in the vicinity of the (+ 1, −2) minigap region of an 870-nm grating at 633 nm. The interaction between first- and second-order couplings to the opposite branches of the SPP dispersion relation is tuned by variation of the corrugation depth. It is found that changes in the profile Fourier decomposition with corrugation depth, which arise in the holographic fabrication of diffraction gratings, can explain the observed momentum gap in the −1 diffraction order in this case.

Diffraction of Wide and Narrow Light Beams by Distorted Finite-Amplitude Progressive Ultrasonic Waves in Water

Results of an investigation of diffraction of light passing through a distorted finite amplitude ultrasonic wave are given. A method is developed and used to determine the second harmonic component of the distorted wave at various distances from the transducer while maintaining a constant local fundamental component. It is shown that the observed discrete diffraction order intensities (wide light beam) and the observed continuous light distribution (narrow light beam) are in good agreement with theoretically predicted values. Measurements were made at 3.0 Mc in water with approximately 23 atm local fundamental pressure amplitude.

Theoretical Investigation on the Diffraction of Light by Superposed Ultrasonic Waves

An analytical treatment for the calculation of intensities of diffraction orders in a general case of superposed sound waves of frequencies in the ratio 1 :n and having any phase difference Δ is given proceeding from Raman and Nath's simplified theory for normal incidence. Because of the integral harmonic relationship between the frequencies of the sound waves superposed, a particular order may contain a number of combination lines in addition to the orders due to the individual sound waves. As such, Fues theory, which gives a single expression for the intensity of a combination line, cannot be applied to this case. Expressions are obtained for the intensities of the diffraction orders in the two specific cases of even and odd values of n. In the case diffraction by two sound waves of frequencies in the ratio 1:2k+1 expressions for the intensities of the orders suggest symmetry in diffraction for all values of Δ. But, when the superposed frequencies are in the ratio 1:2k, the expressions suggest asymmetry in diffraction for all values of λΔ, except π/2. When Δ = π/2, the diffraction is, however, symmetric. Using the expressions, the intensities of the diffraction orders obtained by two sound waves of frequencies in the ratio 1:3 superposed in three different phases 0, π/2, and π are calculated for the values of v1 = 1 and v3 = 1, 2, and 3.