Энергетический обмен при встречном двухволновом взаимодействии в кристалле Bi-=SUB=-12-=/SUB=-GeO-=SUB=-20-=/SUB=- среза (001)

The regularities of energy transfer between two linearly polarized light waves as their contra-directional mixing on a volume reflection holographic grating formed in a photorefractive Bi12GeO20 crystal of the (001)-cut are analyzed. The values of the crystal thickness and the azimuths of the linear polarization of the light waves, at which the amplification of the object wave is achieved, are determined. The change in the direction of energy transfer to the opposite, depending on the thickness of the crystal, has been experimentally demonstrated.

Novel Generalized Three-Step Phase-Shifting Interferometry with a Slight-Tilt Reference

A convenient and powerful method is proposed and presented to find the unknown phase shifts in three-step generalized phase-shifting interferometry. A slight-tilt reference of 0.1 degrees is employed. As a result, the developed theory shows that the unknown phase shifts can be simply extracted by subtraction operations. Also, from the theory developed, the tilt angle of the tilt reference can also be calculated, which is important as it allows us to extract the object wave precisely. Numerical simulations and optical experiments were performed to demonstrate the validity and efficiency of the proposed method. The proposed slight-tilt reference allows the full and efficient use of the space-bandwidth product of the limited resolution of digital recording devices as compared to the situation in standard off-axis holography where typically several degrees for off-axis angle is employed.

Wide-band Beam-scanning by Surface Wave Confinement on Leaky Wave Holograms

A two-dimensional (2-D) metasurface design for backward leaky wave suppression in microwave regime is proposed based on the theory of holography. The so-called Rabbit’s ears phenomenon describes that the backward mode in the reference wave plays the destructive role and makes the holography principle to behave properly mainly in an only narrow frequency interval. Here, we explore the utilization of the surface wave reflectors to suppress the backward mode to achieve wide-band holograms. Therefore, the reference wave form is manipulated by the choice of various reflector shapes and some providing forward mode dominant reference wave are analyzed and simulated. The less backward mode participates in the reference wave; the wider operation frequency range is obtained. With the canceled Rabbit’s ears phenomenon, variations in the reference wave frequency cause elevation angle scan. The results provide general insights into relation of the Rabbit’s ears phenomenon and the object wave accuracy in frequencies except the design frequency. The idea is also applied to multiple object wave holograms. The concept is verified using both electromagnetic full-wave simulations and experimental measurements.

Transient four-wave mixing in a transparent two-component medium

We analyze changes in the spatial structure of an object wave under four-wave mixing in a transparent two-component medium in schemes with opposing and concurrent pump waves. It is shown that in the spatial spectrum of the object wave there is a dip, whose position is determined by the propagation direction of the second pump wave. Angular rotation and frequency shift of the pump waves lead to a decrease in the conversion efficiency of high spatial frequencies. The bandwidth of the spatial frequencies cut out by the four-wave radiation converter decreases monotonically over time, whereas the bandwidth of the most efficiently converted spatial frequencies increases.

Reconstruction Method for Phase-Shifting Electron Holography Fitted with Fresnel Diffraction Affected Fringes

Phase shifting electron holography is a transmission electron microscope technique that a number of holograms with different initial phases are acquired by changing the angle of the incident electron beam, and the intensity variation at a certain point on the holograms is fitted by sinusoidal curve to retrieve the object wave passing through a specimen. In reality, however, Fresnel fringes caused by the electrostatic biprism modulates the electron wave, limits the fitting accuracy and results in phase errors in phase reconstruction. In this study, we suggest a modified phase reconstruction method for phase shifting electron holography. The intensity variations at a certain point on each hologram are fitted not by sinusoidal curve, but by Fresnel diffraction affected curve to retrieve the object wave. This would provide better fitting accuracy, and has a potential to improve the precision of phase shifting electron holography. Simulations demonstrated the improvements of this method comparing with conventional phase shifting holography method.

Preprocessing for Interference Fringe of Spherical Object Wave

A simple preprocessing method for interference fringe of holograms generated between spherical object wave fronts and plane wave reference is suggested. The formulae to calculate the diameters of the interference concentric circle and then to get the radius of spherical wave are deduced strictly and the flowchart for the algorithm is given clearly. By using the proposed method the characteristics of a spherical object wave can be achieved directly with only one recording frame and then a simulated one can be gained by numerical simulation. The corresponding experiments show that this technique is simple, effective and convenient for use.