Extraction of difference of two images using periodic carrier modulation

The optical method of extraction of difference between transparencies using periodic carrier modulation was first proposed and successfully demonstrated by Pennington. His method was based on the modulation of each of the image transparencies by the same grating with the difference that one modulating carrier was shifted by half-period with respect to the other. In order to ensure extraction of difference signal from unwanted sum signal, the modulating carrier frequency must be too low. This poses a serious problem because shifting a high frequency grating exactly by a half-period is not an easy task. In order to surmount this difficulty Belvaux and Lowenthal proposed that instead of using a grating, the images transparencies can be modulated by fringes obtained in a Wollaston prism. It is well-known that these fringes can be shifted by a half-period by rotating an analyzer at the output side by 90°. The optical methods of subtraction of images suffer from the disadvantage that the photographic record has to be developed and fixed by wet processes. The processed record is then Fourier transformed and suitably filtered to extract the difference signal. In the present paper we have carried out extraction of difference of two images using the principle of periodic carrier modulation by carrying out spatial frequency filtering of the total irradiance distribution numerically. Some of the results of subtraction are presented.     

Voltage and temperature dependence of current noise in double-barrier normal-superconducting structures

We study theoretically the current-noise energy (voltage bias and temperature) dependence for a N-N'-S structure, where N and S stand for bulk normal metal and superconductor, respectively, and N' for a short diffusive normal metal. Using quasiclassical theory of current fluctuations we determine the noise for arbitrary distributions of channel transparencies on both junctions. The differential Fano factor turns out to depend on both junction transparencies and the ratio of the two conductances. We discuss analytically the coherent and incoherent regimes and the case when one of the two conductances dominates the other one. Measurement of differential conductance and noise can be used to probe the channel distribution of the interfaces. We discuss recent experiments in the light of our results.     

Subtraction via processing simultaneously recorded holographic images

The Fourier transform of two transparencies positioned centrally symmetric one with respect to the other, is recorded in the presence of a symmetric π/2 phase shifted reference beam. Illumination of the recorded hologram generates the subtracted image of the two inputs.     

Image subtraction by polarization-shifted periodic carrier

A coherent image subtractor is described that makes use of a periodic carrier that is effectively shifted by one-half period by simple sheet polarizing material. As the system has two input stations, the two transparencies to be subtracted are simultaneously visible to facilitate alignment.     

Transparencies of dielectric layers formed from size-controlled Bi-based glass powders obtained by spray pyrolysis

Submicron-size Bi-based glass powders were directly prepared by high-temperature spray pyrolysis. The mean sizes of the Bi-based glass powders were changed from 0.48 to 0.91 μm by changing the concentrations of spray solution. The dielectric layers formed from the Bi-based glass powders with fine size had higher transparencies than those of the dielectric layers formed from the Bi-based glass powders with large size. The transparencies of the dielectric layers formed from the glass powders obtained by spray pyrolysis from spray solution of 0.05 M decreased from 94 to 67% when the firing temperatures of the dielectric layers were changed from 580 to 500 °C. At the same firing temperatures, the transparencies of the dielectric layers formed from the glass powders obtained by spray pyrolysis from spray solution of 0.5 M decreased from 83 to 28%. The dielectric layers formed from the glass powders with fine size had dense and homogeneous structures even at low firing temperatures. PACS 42.70.Ce; 85.60.Pg; 71.55.Jv     

Characteristics of photopolymer holographic matched filters in a van der Lugt correlator

Parameters of van der Lugt holographic matched filters for phase and amplitude transparencies, including random phase masks, are studied. Conditions for recording such filters in a phase self-developing photopolymer are determined. A significant difference in the recording conditions for the holographic filters for amplitude transparencies and phase masks is demonstrated. The holographic filters for phase masks with a signal-to-noise ratio of 20–40 dB and η from 6 to 70% that are recorded in the photopolymerizable composition seem to be promising for optical pattern recognition.     

Application of moiré technique to the measurement of modulation transfer functions (MTF) of printing systems

It is shown theoretically and verified experimentally that by writing a low spatial frequency Ronchi grating by a computer and printing two copies of it on two transparencies by a printer, the modulation transfer function (MTF) of the printed image can be evaluated by measuring the transmittance of the superimposed gratings in a moiré fringe spacing. Application of the technique is quite simple and the results are reasonably reproducible. The technique does not require a high sensitive intensity detector and a very narrow slit for transmission scanning. Also, the presented technique can be applied to other imaging systems.     

Real time addition or subtraction of two images by vector wave interferometry

The present article reports a new optical method for real time addition or subtraction of two photographic images. Two transparencies which are placed in the two arms of a Mach-Zehnder interferometer with two orthogonal polarizers are subsequently added or subtracted by rotating an analyser inserted in the output beam. A linear combination of the amplitudes of the two images can also be observed for different orientations of the transmission axis of the analyser. Some experimental results are presented.     

Electromagnetically induced transparency and saturable absorption in all-fiber devices based on C2H2-filled hollow-core photonic crystal fiber

Electromagnetically induced and saturable absorption transparencies are observed in several lines of the ν₁ + ν₃ acetylene absorption band using two novel all-fiber devices based on a hermetically sealed hollow-core-PCF filled with acetylene at sub-millibar pressure. The method for sealing the hollow-core-PCF at vacuum pressure is described and the devices’ flexibility is demonstrated by the generation of electromagnetically induced transparency at cryogenic temperature.     

A transparent metamaterial to manipulate electromagnetic wave polarizations

We design an anisotropic ultrathin metamaterial to allow perfect transmissions of electromagnetic (EM) waves for two incident polarizations within a common frequency interval. The transparencies are governed by different mechanisms, resulting in significant differences in transmission phase changes for two polarizations. The system can thus manipulate EM wave polarizations efficiently in transmission geometry, including polarization conversion and rotation. Microwave experiments performed on realistic samples are in excellent agreement with numerical simulations.     

Transparent luminescent layers via ionic liquid-based approach to LaPO<Subscript>4</Subscript>:RE (RE = Ce,Tb, Eu) dispersions

Transparent layers containing the highly luminescent nanophosphors LaPO₄:Ce,Tb and LaPO₄:Eu are realized by ink-jet printing on standard transparencies and black paper. The luminescent material is non-agglomerated, 15 nm in size, and applied as a dispersion in ethanol for printing. The structured layers exhibit intense green (LaPO₄:Ce,Tb) or red (LaPO₄:Eu) emission. While printing on overhead transparencies, an optical transmission of about 90% is realized. This value, in fact, is limited due to the performance of the underlying polymer material. A microwave-assisted synthesis in ionic liquids as a novel concept of synthesis is prerequisite to gain the nanoscale phosphor materials. PACS 61.46.+w; 78.67.Bf; 81.07.-b     

Quantum interference in a probe spectrum of an atom embedded in a photonic crystal

Quantum interference in the probe absorption spectrum of a four-level atom embedded in a double-band photonic crystal has been investigated. The double V-type transitions from the two upper levels to the two lower levels interact with the free vacuum modes and the PBG modes synchronously. We study the additional transparency and the elimination of the probe absorption line in this paper. The new features of two transparencies resulting from the singularity of the state density of PBG modes are also predicted.     

Colour image enhancement by white light spatial filtering

Colour enhancement of transparencies with degraded colours is obtained by attenuation of the zero order component of the white light spatial spectrum. The filtering is performed in two ways, directly and sequentially, and the efficiency of the enhancement is estimated through the measurement of the colour difference for several pairs of colours of the object. The method is described in detail and some colour results are presented.     

EXOSAT observation of ?Geminga?

Summary 1E 0630+178, the X-ray source associated with the gamma-ray source Geminga (2CG195+04), has been observed by the EXOSAT satellite. The X-ray images, recorded by the CMA instruments at the foci of the two low-energy telescopes equipped with different filters, show clearly the source. The flux value, computed from the count rate after correction for dead time and window transparencies, agrees, within the errors, with the one recorded by the IPC instrument on board the Einstein Observatory. Paper presented at the 2° Convegno Nazionale di Fisica Cosmica, held at L'Aquila, 29 May–2 June 1984.     

Chaotic dot-superconductor analog of the Hanbury Brown-Twiss effect

As an electrical analog of the optical Hanbury Brown-Twiss effect, we study current cross correlations in a chaotic quantum dot-superconductor junction. One superconducting and two normal reservoirs are connected via point contacts to a chaotic quantum dot. For a wide range of contact widths and transparencies, we find large positive current correlations. The positive correlations are generally enhanced by normal backscattering in the contacts. Moreover, for normal backscattering in the contacts, the positive correlations survive when suppressing the proximity effect in the dot with a weak magnetic field.     

An improved three-dimensional display system

Ultrasonic scans are taken in the usual way in a number of planes a regular distance apart, say 1 cm. These are transferred through the optics of the device onto a single film or plate in the form of small transparencies. Through the same optics, now working backwards, using stroboscopic illumination, the transparencies are projected onto a set of ground perspex screens mounted along a helix on the circumference of a rotating drum. Each component image is thus formed in the right position relative to the others. Images of different depths can be formed in different colours improving discrimination. Brightness of the images of different depths is variable independently of the others, further improving discrimination. The angle of viewing is extremely wide. None of these advantages can be achieved by holography.     

Spontaneous emission spectrum of a four-level atom in a double-band photonic crystal

The spontaneous emission spectrum from a four-level atom in a double-band photonic crystal has been investigated.We use the model which assumes three atomic transitions. One of the transitions interacts with the free vacuum modes,and the other two transitions couple to the modes of the isotropic photonic band gap (PBG), the anisotropic PBG and another free vacuum. The effects of the fine structure of the lower levels on the spontaneous emission spectrum of an atom are investigated in detail in the three cases. New features of four (two) transparencies with two (one) spontaneous emission peaks, resulting from the fine structure of the lower levels of an atom, are predicted in the case of isotropic PBG modes.     

Co-tunneling of the charge through a 2-D electron island

A double barrier Single Electron Transistor is realized in two dimensions by confining the 2-D electron gas of a GaAs/GaAlAs heterojunction to a small island by means of Schottky gates. Two gates provide adjustable tunnel barriers and a central gate controls the electron number in the island. The island has small single-particle energy level spacing and forms a metallic island. Periodic conductance oscillations characteristic of Coulomb blockade are observed when the central gate voltage is varied. The ability to vary the tunnel conductance allows us to study the basic physics of the Coulomb blockade: our results show that the quantum charge fluctuation mechanism which limits the tunneling blockade at low temperature is of second order in tunnel barrier transparencies in agreement with the charge Macroscopic Quantum Tunneling (q-MQT) or co-tunneling model.     

Coherent control of narrow structures in absorption,transparency and dispersion by interference induced among the Rabi-split resonances

The evolution of nonlinear behaviour of electromagnetically induced absorption and transparency subject to coherent perturbation, is presented in a triply driven five-level atomic system. It has been shown that the coherence effects like absolute line narrowing, single or multiple transparencies, sharply varying dispersion and two opposite types of quantum switching can be efficiently controlled by interference induced among the Rabi-split resonances at various situations. As far as measurement induced subwavelength atom localization is concerned, this model can be very much useful in controlling single peak atom localization in subwavelength and sub-half-wavelength domain by three different ways.     

Redundancy modulation for coherent imaging systems

In order to image continuous-tone transparencies with coherent light, special types of diffuse speckle-free illumination are required to achieve high image quality. Several types of speckle-free modulation have been investigated which appear to provide high redundancy for such systems.