Field Diffraction Pattern Research Articles

Soret effect in periodic forced rayleigh scattering

In Forced Rayleigh Scattering of mixtures or suspensions the temperature gratings generate, by Soret effect, concentration gratings that may be very important since they produce both a phase and an amplitude grating superimposed on the principal one. We give an explicit expression for the diffracted signal as a function of the driving parameters and of the material properties. Fundamental differential equation describing the temperature and concentration profiles are introduced and solved for a sinusoidal modulation of the pump beams and hence the far field diffraction pattern is computed by means of the Fraunhofer integral.

Calculation of probe beam diffraction at laser induced thermal lens

An expression is obtained for a far field diffraction pattern of a gaussian probe team passing through a laser heated sample. Fractional change of probe beam intensity is discussed for various experimental conditions. The analysis presented includes off-axis signal variation.

Crystalline to Amorphous Transformation of Fe3B By 1 MeV Electron Irradiation

ABSTRACTSpecimens of amorphous Fe75B25 produced by rapid quenching from the melt were annealed to complete crystallization and subjected to 1 MeV electron irradiation in a transmission electron microscope at room temperature and at 130 K. The irradiation was interrupted at various intervals in order to obtain bright field images and diffraction patterns. The Fe3B crystals did not become amorphous at room temperature, even after damage levels of several dpa, whereas at 130 K the crystalline to amorphous transformation was observed to be complete at damage levels below 1 dpa. The results are combined with those of ion irradiation work on Fe3B; qualitative agreement is found between Fe3B and previous work on the Zr3Al alloy concerning their response to displacement damage by electron and ion irradiation.

Near field diffraction pattern of ion acoustic waves

Grid-excited linear ion-acoustic waves are found to exhibit amplitude modulations which resemble nonlinear particle trapping or the beating of two modes. The modulation is shown to be the antenna pattern of the exciting grid. Double-plasma waves display the same behavior although the modulations are weaker. A model that explains this difference in terms of the excitation mechanisms is suggested.

Cube corner retroreflector test and analysis

Cube corner retroreflectors with nominal dihedral angles of 90 degrees 0' 1.5'' were fabricated, tested, and analyzed to determine the return energy in the annular ring of the far field diffraction pattern required by the Laser Geodynamic Satellite. Performance was assessed for variations in the dihedral angles, optical surfaces, and thermal environment. Despite relatively high independent axial and radial sensitivities, the changes caused by the anticipated thermal environment were found to be negligible; however, there were substantial variations between the analytical predictions and measured performance.

Far Field Diffraction Patterns of Circular Gratings

The fine structure of the annular images of circular gratings is analyzed in terms of diffraction patterns of axicon pairs. Each image arises substantially from only one converging and one diverging axicon of equal deflection angle. Single main lobe, symmetric double main lobe, and various intermediate asymmetric double lobe structures are obtained depending on the phase relationship and strengths of the two axicon beams, which in turn depend on the design of the circular grating. Approximate expressions are derived for the intensity distribution and energy content of the symmetric single and double lobe images.

Holographic particle sizing techniques

Holography provides a method of storing the information (size and relative position) of a dynamic three-dimensional distribution of particles so that a stationary image can be produced for detailed study. The depth of field is considerably better than normal image formation. The major technique involves forming an in-line Fraunhofer hologram; this hologram is the interference pattern formed between the far field diffraction pattern of the particles and an in-line background. Off-axis holography can also be used. The basic principles of these methods are described, and practical limitations and advantages discussed. Application of the methods to fog, mist, sprays, rocket engine studies, two phase flow, bubble chamber photography, electron beam holography, etc. are reviewed.

Near field diffraction pattern behind a sinusoidal phase grating

The near field diffraction pattern of a plane wave passing through a sinusoidal phase grating is studied theoretically, and the results are verified experimentally. The conclusions are of interest for redundant coherent imaging.

Far-Field Diffraction Pattern for Corner Reflectors with Complex Reflection Coefficients*

The far field diffraction pattern of a geometrically perfect corner reflector is examined analytically for normally incident monochromatic light. The states of polarization and the complex amplitudes of the emerging light are expressed through transformation matrices in terms of those of the original incident light for each sextant of the face in a single coordinate system. The analytic expression of the total diffraction pattern is obtained for a circular face. This expression consists of three component functions in addition to the basic Airy function. The coefficient of each function is expressed in terms of complex coefficients of reflectance of the reflecting surface. Some numerical results for different reflecting surfaces, including total internal reflection, are presented. The iso-intensity contours of the diffraction pattern evaluated from the analytical expressions for an uncoated solid corner reflector are also presented along with the photographs of the pattern.

Far Field Diffraction Patterns of Single and Multiple Circularly Symmetric Apertures

Some equations are derived for computing the form of the far-field diffraction pattern of an area element of a circle whose dimensions are large compared with the wavelength of the incident radiation and over which the amplitude and phase are constant. These equations are derived in such a way that it becomes possible not only to compute the form of the far-field diffraction pattern of individual apertures of circular symmetry, but also for combinations of such apertures over which the amplitudes and phases are constant but differ from aperture to aperture. With the aid of an I. B. M. 7090 computer, these equations have been used to compute the forms of the far-field diffraction patterns of three circularly symmetric apertures over which the amplitudes and phases are constant, and three dimensional models have been constructed to describe the radiant flux distribution. A start has also been made on the more complicated problem of multiple apertures by computing the form of the far-field diffraction pattern of two adjacent semicircular apertures over which the amplitudes and phases are constant in the two apertures, but the amplitudes in the two apertures have been assumed to be equal and the phases different. Some corresponding photographed far-field diffraction patterns are also included for comparison purposes and to illustrate the wide variety possible.