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Contact photolithography for photoresist layers thicker than 1 micron is widely used in creating microreliefs in production technologies of microelectromechanical systems, micropackaging, optical printed circuit boards and other microdevices. Microrelief walls slope in photoresist inflicts significant influence on the microdevice output parameters. Based on analysis of the contact photolithography features, it is proposed a mathematical model based on the Fresnel diffraction of image generation in the thick photoresist layers. The model and statistical processing of results obtained on its basis adequately describe relationship between the photolithography output parameters, i.e. the microrelief sidewalls slope, and the photoresist absorption coefficient and thickness. [ABSTRACT FROM AUTHOR]

Laser-induced periodic surface structures are created on Si (100) and Si (111) wafers by 500 fs laser pulses at 248 nm. The periodic structure is concentric and highly regular. The spatial period is consistently varying between 1.1 µm and 3.3 µm in the radial direction. It is shown that the fluence of the irradiation at the same pulse number determines the size of the area where the periodic structure is created and for the same fluence the pulse number determines the regularity of the created grooves by melting processes. The origin of this structure is identified as the inhomogeneity of the laser beam profile caused by Fresnel diffraction close to the focal plane. Further improvement of the formation of periodic structure with femtosecond laser pulses is suggested. [ABSTRACT FROM AUTHOR]

Soft X-ray microscopy is well recognized as a powerful tool of high-resolution imaging for hydrated biological specimens. Projection type of it has characteristics of easy zooming function, simple optical layout and so on. However the image is blurred by the diffraction of X-rays, leading the spatial resolution to be worse. In this study, the blurred images have been corrected by an iteration procedure, i.e., Fresnel and inverse Fresnel transformations repeated. This method was confirmed by earlier studies to be effective. Nevertheless it was not enough to some images showing too low contrast, especially at high magnification. In the present study, we tried a contrast enhancement method to make the diffraction fringes clearer prior to the iteration procedure. The method was effective to improve the images which were not successful by iteration procedure only. [ABSTRACT FROM AUTHOR]

A hard x-ray imaging microscopy and microtomography system is now being developed at the beamline 37XU of SPring-8. In the latest improvement, a spatial resolution of about 50 nm is achieved in two-dimensional imaging at 6 keV x-ray energy using a Fresnel zone plate objective with an outermost zone width of 35 nm. In the tomographic measurement, a spatial resolution of about 100 nm is achieved at 8 keV using an x-ray guide tube condenser optic and a Fresnel zone plate objective with an outermost zone width of 50 nm. [ABSTRACT FROM AUTHOR]

An incoherent white-light source illuminates a set of two identical gratings placed in tandem, resulting in the generation of the Fresnel image. This image is projected onto a reflecting object and the reflected images from the object are projected onto the third grating. The resulting moiré fringes are recorded using CCD camera. Inclination angle of the object is a function of the interferometric phase. Phase shifting interferometry has been used for the determination of interferometric phase. Hence accurate determination of small tilt angle of object surface could be successfully undertaken. Technique is automated and provides high precision in measurement. [ABSTRACT FROM AUTHOR]

The beam smoothing in the focal plane of high power lasers is of particular importance to laser-plasma interaction studies in order to minimize plasma parametric and hydrodynamic instabilities on the target. Here we investigate the focal spot structure in different geometrical configurations where standard paraxial hypotheses are no longer verified. We present numerical studies in the cases of single flat top square beam, LMJ quadruplet and complete ring of quads with large azimuth angle. Different calculations are made with Fresnel diffraction propagation model in the paraxial approximation and full vector Maxwell's equations. The first model is based on Fourier transform from near to far field method. The second model uses first spherical wave decomposition in plane waves with Fourier transform and propagates them to the focal spot. These two different approaches are compared with Miró [1] modeling results using paraxial or Feit and Fleck options. The methods presented here are generic for focal spot calculations. They can be used for other complex geometric configurations and various smoothing techniques. The results will be used as boundary conditions in plasma interaction computations. [ABSTRACT FROM AUTHOR]

We report a technique which provides the details of three dimensional phase profile of a transparent microscopic sample. The depth resolution achievable is of the order of nanometers. The physical dimensions of the sample are obtained from the numerically reconstructed phase of the object wave. The method involves digital holographic recording of interferograms produced by superposition of the object wave and the coherent reference wave. We sequentially record four different holograms by altering the phase differences between the object wave and the reference wave. To introduce different phase differences between the two interfering beams, we have made use of polarization phase shifting. Therefore, the configuration used is simple and provides accuracy as the phase is introduced by simply rotating a linear polarizer. Experimental results for a microhole etched on glass are presented. [ABSTRACT FROM PUBLISHER]

Two-photon "ghost" imaging, based on the second-order intensity correlation, was first realized with entangled light, but has now been demonstrated with true thermal light. Following our work on lensless and high-order ghost imaging with thermal light, we have recently shown that both entangled and thermal light may be used to produce twophoton correlation Talbot effects. In the Talbot effect, first observed in 1836, a periodic object illuminated with coherent light can give rise to repeated self-images at specific positions within the Fresnel diffraction field without any lens. Using an incoherent thermal light source, we have experimentally observed second and higher order Talbot self-images, including fractional and phase-reversal images, at multiples of the Talbot length in a lensless setup containing two optical paths. We have also recently observed another surprising imaging phenomenon which does not depend on the secondorder correlation function, and can produce both negative and positive images of a nonlocal object. It is expected that these types of imaging will find novel applications in both the microscopic and macroscopic regimes. [ABSTRACT FROM AUTHOR]

This paper discusses the evaluation of diffracted signals from cracks in 2D based on a new Huygen-Fresnel Diffraction Model (H-FDM). The model employs the frequency-domain far-field displacement expressions derived by Miller & Pursey [1] in 2D for a line source located on the free surface of a semi-infinite elastic medium. At each frequency in the bandwidth of a pulsed excitation, the complex diffracted field is obtained by summing over the unblocked virtual sources located in the section containing a vertical crack. The time-domain diffracted signal is obtained using standard FFT procedures. The effect of beam refraction from a wedge-based finite transducer has been modeled by treating the finite transducer as an array of line sources. The model has been used for predicting diffracted signals in time-of-flight from the crack like defect. The model allows the evaluation of back wall signal amplitude and lateral wave amplitude as well. Experiments have been carried out on 10 mm thick aluminum sample with surface breaking crack of lengths 2 mm and 4 mm using shear probe shoe. The simulated A-Scan results for the aluminum sample with 2 mm and 4 mm surface breaking lengths compare very well in relative amplitudes and time of arrivals with experiments. The H-FDM model offers a tool to evaluate diffraction and related phenomena quantitatively with modest computational resources. [ABSTRACT FROM AUTHOR]

We present an investigation about Fresnel diffraction of Bessel beams, propagating as nondiverging within a distance Ln, with or without phase singularities, by rectilinear and fork-shaped gratings. The common general transmission function of these gratings is defined and specialized for three different cases: binary amplitude gratings, amplitude holograms and their phase versions. Solving the Fresnel diffraction integral in cylindrical coordinates, we obtain analytical expressions for the diffracted wave amplitude for all types of proposed gratings, and make conclusions about the existence of phase singularities and corresponding topological charges in the created by the gratings beams of different diffraction orders. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]