Background Fringes Research Articles

Imagining density distribution of molecular orbitals in IR+XUV co-rotating circular laser fields by frequency-domain theory

Abstract We have investigated the angle-resolved ATI spectrum of oriented molecules in the IR+XUV co-rotating circular laser fields. According to the different roles of IR and XUV laser in the ionization process, we purposefully adjust the photon energy of XUV and the intensity of IR laser to make the ionization spectrum of the molecule distributed in a suitable momentum region. Moreover, under the same laser conditions, the background fringes in the ionization spectrum of the molecule can be removed by using the ionization spectrum of the atom with the same ionization energy as the molecule, so that the molecular orbital density distribution in the suitable momentum region can be obtained. That is, for any unknown molecule, as long as the ionization energy of the molecule can be measured, the density distribution of the molecular orbital can be imaged in a definite momentum region by adjusting the laser field conditions, which may shed light on the experimental detection of molecular orbitals.

Phase Extraction from Single Interferogram Including Closed-Fringe Using Deep Learning

In an optical measurement system using an interferometer, a phase extracting technique from interferogram is the key issue. When the object is varying in time, the Fourier-transform method is commonly used since this method can extract a phase image from a single interferogram. However, there is a limitation, that an interferogram including closed-fringes cannot be applied. The closed-fringes appear when intervals of the background fringes are long. In some experimental setups, which need to change the alignments of optical components such as a 3-D optical tomographic system, the interval of the fringes cannot be controlled. To extract the phase from the interferogram including the closed-fringes we propose the use of deep learning. A large amount of the pairs of the interferograms and phase-shift images are prepared, and the trained network, the input for which is an interferogram and the output a corresponding phase-shift image, is obtained using supervised learning. From comparisons of the extracted phase, we can demonstrate that the accuracy of the trained network is superior to that of the Fourier-transform method. Furthermore, the trained network can be applicable to the interferogram including the closed-fringes, which is impossible with the Fourier transform method.

Weighted reconstruction of three-dimensional refractive index in interferometric tomography.

Interferometric tomography can reconstruct 3D refractive-index distributions through phase-shift measurements for different beam angles. To reconstruct a complex refractive-index distribution, many projections along different directions are required. For the purpose of increasing the number of the projections, we earlier proposed a beam-angle-controllable interferometer with mechanical stages; however, the quality of reconstructed distribution by conventional algorithms was poor because the background fringes cannot be precisely controlled. To improve the quality, we propose a weighted reconstruction algorithm that can consider projection errors. We demonstrate the validity of the weighted reconstruction through simulations and a reconstruction from experimental data for three candle flames.

重复脉冲激光造成扫描型CCD背景条纹的规律

In order to obtain the generating law of background fringes in the video of a scanning CCD camera induced by repetitive pulse lasers,a mathematic model describing fringes induced by repetitive square pulse lasers is established.In this model,the relation of camera parameters including stage number of time delay integrations,integration time of one stage as well as laser pulse width and laser repetitive period can be used to estimate whether the fringes appear or not and to calculate what is the dimensions of fringes,in which the precision of calculation is 1 pixel.An experiment is performed by using repetitive picosecond pulse lasers and a fluorescent lamp to irradiate the scanning CCD camera respectively,and the results validate the correction of estimation and calculation based on the model.Finally,combing the intensity relation of background light and scattered laser with the model,the visibility expression of fringes is given,which is also validated in the experiment.

Theoretical Role of Square Wavelet Analysis in Stereopsis and Binocular Rivalry: A Mathematical Model and Computer Simulation

To determine stereopsis, a mathematical model and computer simulation specify that square wavelet coefficients be independently estimated for the images in each eye. Then, by comparing these independently determined coefficients, the model theorizes that the visual system both identifies those parts of the two images which lie across corresponding points and identifies those parts of the two images which lie across noncorresponding or disparate points. Given the latter occurrence, the retinal disparity is evaluated as being either stereopsis or binocular rivalry. If stereopsis is indicated, the wavelet coefficients provide a reference plane by which the depth of a disparate area is located either nearer than or more distant than the reference plane. In the model also it is proposed that the determination of depth with respect to the reference plane provides a signal for vergence of the eyes. If binocular rivalry is indicated, the model's computer simulation identifies the locus of the background fringes associated with binocular rivalry. In sum, it seems theoretically tenable that stereopsis or binocular rivalry occurs as a consequence of the comparison of one eye's wavelet coefficients with those of the other eye.

Time smear effects in spatial frequency multiplexed holography

Spurious background fringes have been observed in time-resolved holograms recorded with a pulsed laser source and a rapidly deflected reference beam. These fringes were determined to be a time smear effect due to the small change in the angle of incidence of the reference beam during the exposure time. By analyzing the phenomenon theoretically, equations were derived that could be used to describe the observed fringe formation. A numerical solution was obtained for a realistic laser pulse time profile and an analytical solution was obtained using a simple mathematical model of the pulse profile. These solutions allow an a priori determination of bounds of the exposure parameters that would reduce the time smear effects to acceptable levels.

Optical biasing on quasi-interferometry with coded correlation filtering

A new method for optical biasing is developed to improve the performance of quasi-interferometry with coded correlation filtering. First, by defocusing a mask, a quadratic phase factor is added to the object under test; this yields background fringes. Second, a linear phase factor is introduced by off-axis shifting of masks. The formulas describing these two effects are derived for various possible configurations. The condition of invariance is discussed. Simplified systems are also studied to obtain continuous changing of sensitivity independent of quadratic phase biasing. Some experiments and applications are illustrated.

Application of three-beam holographic interferometry to the study of a thermal turbulent wake

A Q-switch ruby laser supplying two pulses, has been used to carry out high speed holographic interferometry for the study of a thermal turbulent wake considered as a phase object. The duration of time separating the two pulses can be varied from 5 to 250 mu s. Using a hologram recorded in a parallel beam of light, one can obtain either lines of equal phase at a given instant of time or lines of equal phase shift between two close instants of time. The temperature fall and spread of the wake as a function of distance from the thermal source can be deduced from measurements made on interferograms with background fringes. In diffuse light, time differential interferograms have shown the existence of a threshold of detection for the smallest turbulences and give an aspect of the evolution of the wake in time.

Production and location of background fringes

The production and location of background fringes was analysed for spherical and plane waves for two methods of practical application in holographic interferometry. The result of the analysis was used to predict the fringe separation for a practical system and gave good agreement.

Fracional–Fringe Holographic Plasma Interferometry

Holographic interferometry can be applied to plasmas whose density results in shifts of less than one fringe by superposing the small shifts on an arbitrarily shaped and positioned background fringe pattern. The sensitivity of holographic interferometry is thereby increased to that of conventional interferometry, while the inherent advantages of holography are retained. The background fringes also simplify detection of the spurious phase changes that can arise in holography from motions of the apparatus.