Fresnel Diffraction Effects Research Articles

Hologram simulation for off-axis electron holography

Hologram simulation for electron holography using an electron biprism is described. An electron hologram is superimposed by Fresnel fringes originating from the electron biprism, which affects both the amplitude and the phase of the object wave and the reference wave. In this simulation, we consider the effects of Fresnel diffraction as well as the electron-wave phase shift due to the electromagnetic field produced by the specimen. We also take into account the phase shift due to the inner potential of the specimen, the amplitude modulation due to the absorption of the incident electrons by the specimen, reference-wave distortion caused by the electromagnetic fields, coherency of the electron wave, and quantum noise of the detected electrons. Simulated and experimentally obtained holograms and reconstructed images are compared for the cases of a charged latex spherical particle and a single magnetic-domain spherical particle placed on a carbon film.

2L1400 微小光源・連続X線によるX線顕微鏡像とフレネル回折

2L1400 微小光源・連続X線によるX線顕微鏡像とフレネル回折

Depth Profiling of Optical Absorption in Thin Films via the Mirage Effect and a New Inverse Scattering Theory. Part I: Principles and Methodology

Impulse mirage effect spectroscopy is developed in this work as a nondestructive method for depth profiling the optical properties of samples which are nearly thermally homogeneous with depth. Both a theory and an experimental methodology are presented. An inverse scattering theory of the experimental photothermal deflection signal is derived, based on a previous theory of the impulse mirage effect, which takes into account the effect of Fresnel diffraction on the probe beam. To reconstruct the depth profile of heat source density generated by light absorption in an unknown sample, we have applied our inverse theory to the experimental impulse response, using a regularized minimum square error reconstruction algorithm based on our previously published expectation minimum principle. Because this reconstruction problem is ill posed, it was necessary to identify and compensate for all experimental bias errors significantly affecting the fidelity of the depth profiles. A procedure for obtaining the overall best-fit model of the depth profile given the minimum prior experimental information is presented. These procedures have produced an agreement between the experimental and theoretically predicted mirage effect response to within typical root-mean-square error levels of 0.5% or less.

Wall profile of thick photoresist generated via contact printing

High-aspect-ratio patterns generated by direct contact or proximity printing in LIGA and other similar processes have recently gained great interest in the field of MEMS. One key issue for a successful thick-film lithography Is the control of wall profile. This paper deals with this issue based on an approximation including the effects of Fresnel diffraction and exposure kinetics for various types of photoresist. This approach leads to simple but practical formulas for estimating the wall profile and resolution for the near-field lithography of thick photoresist.

Studies in synchrotron x-ray microradiography: observation ofbiprism-type interference

Synchrotron x-ray microradiographic imaging is a routine and indeed essential prerequisite for the collection of diffraction data from a particular single small crystallite embedded within a mat containing thousands of similarly small-sized individuals when that particular small crystallite has been earmarked for a diffraction study, by reason of its special morphological features or optical properties, for example. The combination of optical microscopic, microradiographic and microdiffraction topographic techniques is proving fruitful in studies of CVD diamond crystallites. The simplest radiographic contrast mechanism applying in the case of negligibly-absorbing objects is refractive deviation of the transmitted beams. However, the optimization of experimental parameters for microradiography brings in factors such as Fresnel diffraction effects and incident-beam uniformity. When faceted objects are radiographed, re-entrants between facets produce the x-ray analogue of the Fresnel biprism. Radiographic experiments are illustrated that plausibly demonstrate biprism interference, on the evidence of the fringe patterns observed.

Electromagnetic Gaussian beam

The governing equations for the paraxial approximation are deduced from Maxwell’s equations. The plane wave, in the paraxial approximation, is found to be transverse electromagnetic. For a field distribution at the input plane having a general azimuthal variation and a radial variation in the form of a Bessel function of an integer order with a Gaussian envelope of a given waist size, the spreading due to the Fresnel diffraction is determined as the paraxial beam is transported in the axial direction. The effects of Fresnel diffraction are illustrated with examples for a beam transporting unit power. Diffraction patterns of azimuthally symmetrical and dipolar modes are presented.

Modeling of precipitated Xe atoms in aluminum and the fresnel effect in hrtem imaging

High-resolution transmission electron microscope (HRTEM) images with a 〈111〉 orientation of nanosized tetradecahedral Xe precipitates in an Al matrix have been observed and compared with simulated images. The HRTEM image simulation was carried out by changing the defocus value of the objective lens and the size of the objective aperture. The real size of the precipitated Xe crystal is not obvious from the HRTEM images because of the effect of Fresnel diffraction (Fresnel fringes) at the boundaries between the Xe atoms and the Al matrix, except when the defocus conditions are at or within 50 nm of the Scherzer defocus value. This means that the minimum size of the Xe crystal image does not necessarily show the real size. This phenomenon is independent of the size of the objective aperture. When two Xe bubbles with same size and orientation both lie along the beam direction in the Al matrix, the image intensity of the two Xe crystals is enhanced and the contrast becomes higher than the image intensity of one Xe crystal alone in the Al matrix.

Effects of Fresnel diffraction on confocal imaging with an annular lens

yOptoelectronic Imaging Group, Department of Applied Physics, Victoria Universityof Technology, PO Box 14428, MCMC, VIC 8001, AustraliazDepartment of Physical Optics, University of Sydney, NSW 2006, AustraliaSubmitted 9 January 1997, accepted 26 June 1997Abstract. The effect of the Fresnel diffraction on the imaging properties of confocalmicroscopy with one circular aperture and one annular aperture is investigated. Theresults show that the Fresnel diffraction patterns alter the axial imaging properties moreseriously than the transverse imaging properties. The axial response of such a confocalmicroscope is sharpened, but severely distorted.Keywords: Fresnel diffraction, annular pupil, confocal microscopy1. IntroductionAnnular aperture is a widely used spatial filter in confocalmicroscopy. It gives some improvement in transverseresolution, but a degradation in axial resolution appears ina confocal system with an annular structure [1,2]. Recentresearch suggests that the use of annular apertures as spatialfilters can suppress the scattered photons [3]. For example,a reflection-mode confocal system with an annular aperturein the illumination path is reported to show a significantenhancement in signal-to-noise ratio for imaging through ahighly scattering medium [4].In practice, an annular aperture cannot be placed exactlyat the back focal plane of an objective. In this case,Fresnel diffraction by the annular aperture exists. Fresneldiffraction of a finite-sized aperture can produce bright anddark fringes because of the interference of the waveletscontributed from points over the aperture [5,6]. Theintensity modulation caused by the interference fringes canalter the imaging properties of confocal microscopy, sincethe effective pupil function of the objective illuminatedby the Fresnel patterns changes accordingly, resulting inthe alteration of the intensity in the focal region [7–10].Therefore, it is important to investigate the effect of Fresneldiffraction on the imaging performance of a confocalsystem with an annular aperture.This paper is organized as follows. Section 2 presentsthe Fresnel diffraction of an annular aperture. The effectof Fresnel diffraction patterns of an annular aperture on theimaging properties of confocal microscopy is discussed insection 3.2. Fresnel diffraction of an annular apertureIf an aperture is placed in the back focal plane of anobjective then focusing is described by Debye theory. TheFresnel number is infinity in this situation. However, ifthe aperture is placed away from the back focal plane by adistance

A Fresnel bi-prism device for atomic matter waves

The principle of a simple bi-prism for coherent atomic translational waves is studied. The scheme of the experiment consists of a diffracting slit, in front of which the evanescent wave running along a tapered optical fibre provides a converging gradient of optical potential for two-level atoms. The combined effects of Fresnel diffraction and bi-prism interferences are described in different experimental configurations. The influence of gravitation is outlined. Orders of magnitude and feasibility are discussed in the case of thermal neon atoms, for which experiments are under consideration.

Possible ambiguity in defining the ionospheric origin of quasiperiodic scintillations

Abstract It is found that quasiperiodic scintillation events (QPS) originating in the ionosphere have a close counterpart in non-ionospheric QP scintillations (QPR and QPA). The presence of QPA, resulting from an interference of radio signals from two satellites, has been known for some time but rarely referred to in publications. The addition of a new type of regular scintillations (QPR) which have an extended ringing structure, modulation envelope and central maximum, makes it necessary to evaluate the quasiperiodic scintillation data carefully. Unlike QPA, the new type of quasiperiodic scintillations can be generated by an interference effect between a ground transmitter and the Doppler-shifted radio transmission from a satellite. A close resemblance between quasiperiodic events recorded from VHF television transmission, reported to be caused by a Fresnel diffraction effect, and QPR events may indicate their common origin. A careful analysis of the different types of the regular fading, presented here, may help workers in this field to distinguish between the trivial and real types of the specific regular scintillation activity.

Detection of short pulses by Fresnel preprocessing

Short pulses create unique Fresnel diffraction effects, as they propagate through an acousto-optic signal-processing system, that produce an interference pattern. By following the detection of the interferometric pattern with spectral analysis, we extract information about pulse width, pulse separation, and relative time of arrival. Laboratory models of the Fresnel-transform processing system and an optical spectrum analyzer were built and tested to verify the basic concepts. Pulses as short as the theoretical limit of 20 ns for this system and separated by as little as 60 ns or as much as 17 µs were detected and measured. Short pulses were also detected in the presence of cw signals by use of a frequency-variant matched-filtering operation.

X-Ray Phase-Shifting Mask for 0.1-µm Pattern Replication under a Large Proximity Gap Condition

The effects of Fresnel diffraction on the patterning characteristics in synchrotron radiation lithography are greatly influenced by X-ray phase shift in the absorber, especially when a low-contrast X-ray mask is used. We show that the resolution in sub-quarter-micron region can be markedly improved without reducing the proximity gap by utilizing the phase-shifting effects in the absorber. By controlling the absorber thickness within a suitable range (1.5≤mask contrast≤4.0, -30°≥phase shift φ≥-120°), fine patterns as small as 0.1 µm can be replicated with a large exposure latitude at a large proximity gap of 30 µm. Based on these results, we propose a novel X-ray phase-shifting mask with shallowly etched patterns (L in width) at the absorber edge as a phase shifter. This mask can be fabricated by a simple self-alignment process and also offers the possibility of 0.1-µm pattern replication at the 30-µm proximity gap by using 0.02≤L≤0.1 µm.

Compact sources of suprathermal microwave emission detected in quiescent active regions during lunar occultations

Solar quiescent active regions are known to exhibit radio emission from discrete structures. The knowledge of their dimensions and brightness temperatures is essential for understanding the physics of quiescent confined plasma regions. Solar eclipses of 10 August 1980 and 28 January 1990, observed with high sensitivity (0.01 s.f.u.) and high time resolution (30 ms) at 22 GHz, allowed the unprecedented opportunity to identify Fresnel diffraction effects during lunar occultations of active regions. The present results indicate the presence of quiescent discrete sources smaller than one arcsecond in one dimension that can be associated to the compact sources of suprathermal microwave emission. Assuming symmetrical sources, their brightness temperatures were larger than 2x107 K and 8x107 K, for the 1980 and 1990 observations, respectively. From energetic point of view the results give new information about confinement of plasmas in active regions.

Effects of Fresnel Diffraction on Resolution and Linewidth Control in Synchrotron Radiation Lithography

To investigate the influence of Fresnel diffraction on resolution and linewidth control in synchrotron radiation (SR) lithography, a detailed analysis is performed that takes X-ray phase shift in the absorber into account. The phase shift for 0.65-µm-thick Ta absorber is estimated to be -180°. It becomes clear that the phase shift plays a important role in limiting pattern resolution and linewidth control, especially for replicating fine (<0.3 µm) patterns. The conditions for replicating 0.2-µm lines-and-spaces resist patterns under practical conditions-i.e., with a mask contrast of 7 and a proximity gap of around 30 µm-are described. Designing a Ta absorber that is slightly narrower (<0.05 µm) than 0.2 µm is a great advantage for replicating 0.2-µm patterns because the dose-margin for replicating the patterns faithfully is improved.

Effects of Photo- and Auger Electron Scattering on Resolution and Linewidth Control in SR Lithography

The effects of photo- and Auger electron scattering on resolution and linewidth control in X-ray lithography are quantitatively evaluated employing resist patterns replicated using a novel contact replication method. In this method, the effects of penumbral shadow and Fresnel diffraction can be neglected because exposure, development and SEM observation are carried out keeping the absorber pattern on the resist. The depth of the undercut of the resist pattern from the absorber pattern edge, which means the range of electron scattering in the lateral direction, increases from zero to the Bethe range as a function of exposure dose, and reaches 0.16 µm in SR lithography with spectra ranging from 0.2 to 1.4 nm. It is shown that the maximum range of photo- and Auger electron scattering does not determine the resolution directly, but rather affects the linewidth control.

Analysis of Developed Pattern Profiles in X-Ray Lithography with Monochromatic X-Rays

Developed pattern profiles in X-ray lithography, including various line edge degradation effects such as the spatial spreading of photo and Auger electrons, the penumbra and the Fresnel diffraction effects with monochromatic X-ray beams of Mo Lα and Al Kα, are simulated. The developed pattern profiles are degraded by the penumbra effect to a larger extent than by the diffraction effect when patterns with a size of a quarter micron are fabricated. However, Fresnel diffraction has an appreciable degradation effect when patterns with a size of 100 nm are fabricated. The results show that a contrast of 1:1/9, which is defined as the ratio of the X-ray intensities through the opaque region of the mask to that through the clear region, is high enough to make line-and-space patterns of 200 nm period with the Al Kα X-ray source.

Fresnel diffraction effects in misfocused vision

If a narrow line stimulus on an opposite contrast background is observed with appropriately misfocused vision, the stimulus appears as a number of alternating bright and dark fringes. A numerical calculation of this effect was performed. As a result it was found that the banding phenomenon is a Fresnel diffraction effect depending on the details of both the narrow line stimulus and the eye pupil.

Effect of Fresnel Diffraction on Measurement of Degree of Coherence of Electron Beam with Electron Biprism

Effect of Fresnel Diffraction on Measurement of Degree of Coherence of Electron Beam with Electron Biprism

Effects of multiple scattering and Fresnel diffraction on random volume scattering

A wave incident on a volume of random fluctuations of medium parameters will be scattered in all directions. Two kinds of effects on random volume scattering are considered: 1) multiple scattering effect, and 2) Fresnel diffraction effect. The cumulative forward scattering is known to be responsible for the scintillation phenomenon. When strong, such cumulative or multiple scattering can drive the signal statistics into the saturated regime in which the complex amplitudes behave as a complex Gaussian process. These cumulative scattering effects on signals of a bistatic radar are investigated. Additionally, to allow for the possibility that the size of the irregularity is comparable or larger than the first Fresnel zone, Fresnel diffraction instead of Fraunhofer diffraction is considered. A generalized formula for calculating average scattered power, taking both multiple scattering and Fresnel diffraction into account, is derived. It shows that the Fresnel diffraction pattern appearing around the forward direction tends to be smeared out by multiple scattering. Also, both multiple scattering and Fresnel diffraction effects weaken and broaden the forward-scattered beam, and reduce the backscattered power when compared with the single scattering and Fraunhofer diffraction cases respectively. Under certain conditions, the enhancement effect of the backward scattered power is confirmed.

Non-modified propagation of optical mutual intensity in the Fresnel diffraction region

The propagation problem of mutual intensity from a source plane to an object plane is discussed. The propagated mutual intensity remains unmodified in any object plane in the paraxial approximation region of Fresnel diffraction if the mutual intensity in the source plane is space-invariant and propagated to a region of interest around the propagation axis in which the Fresnel diffraction effect by the edge of an aperture in the source plane is almost negligible.