Young's Interference Fringes Research Articles

Speckle Cross-Correlation Method in Measuring Fine Surface Displacements

Industrial applications need regular testing for the lifetime, movement, strength, and performance of manufacturing machines during production process. Since speckle photography is a simple economic technique, it is used in investigating object response under mechanical and thermal effects depending on the movement of the speckle patterns with respect to the deformation strength and direction. In the present work, the cross-correlation technique is used to analyze the speckle patterns by iterative method to define both values and directions of rigid body translation and expansion. In order to check the accuracy of the cross-correlation technique, the results are compared with the displacement values given by analyzing the Young's interference fringes resulted from the Fourier transformation of the speckle patterns. This noncontact technique is found to be accurate and informative depending on the stability and sensitivity of the optical system. This method of measurement is an effective tool in studying the hard cases of objects and machines under various effects.

Coherent and incoherent spectral broadening in a photonic crystal fiber

The coherence of the spectral broadening process is the key requisite for the application of supercontinua in frequency combs. We investigate the coherence of two subsequent supercontinuum pulses created in a photonic crystal fiber pumped by a femtosecond laser. We measure Young interference fringes from a Michelson-type interferometer at different wavelengths of the output spectrum and analyze their dependence on pump intensity and polarization. The visibility of these fringes is a direct measure of the coherence of the spectral broadening processes.

The van Cittert-Zernike Theorem

The beam of light emanating from a quasi-monochromatic point source (or a sufficiently distant extended source) is said to be spatially coherent: the reason is that, at any two points on a given cross-section of the beam, the oscillating electromagnetic fields maintain their relative phase at all times. If an opaque screen with two pinholes is placed at such a cross-section, Young's interference fringes will form, and the observed fringe contrast will be 100% (at and around the center of the fringe pattern). This is the sense in which the fields at two points are said to be spatially coherent relative to each other. If the relative phase of the fields at the two points varies randomly with time, the pair of point sources will fail to produce Young's fringes and, therefore, the fields are considered to be incoherent. In practice there is a continuum of possibilities between the aforementioned extremes, and the resulting fringe contrast may fall anywhere between zero and 100%. The fields at the two points are then said to be partially coherent with respect to one another, and the properly defined fringe contrast in Young's experiment is used as the measure of their degree of coherence. Optical systems involving partially coherent illumination are explored in several other chapters of this book; see, for example, “Coherent and incoherent imaging” (Chapter 5), “Michelson's stellar interferometer” (Chapter 35), “Zernike's method of phase contrast” (Chapter 38), and “polarization microscopy” (Chapter 39).

Young's interference fringes in electron microscopy revisited

Young's interference fringes (YIF) have long been known as a helpful tool in image processing of electron micrographs by laser optics or computer. In this paper, the usefulness of the YIF method is given a critical look.

A new method for extractingspeckle fringes of a holo-specklegram

The interrogation of a holo-specklegram from point to point results in two side lobes as well as the formation of central Young's fringes. It is proved theoretically and experimentally that these fringes in the side lobes are, in essence, the Young's interference fringes of the first-order diffractions of the pair of identical speckles in the holo-specklegram. A practical quantitative formula is presented to calculate the in-plane displacement.

Measurement of the phase contrast transfer function and the cross-correlation peak using young interference fringes

Cross-correlation of micrographs taken under identical optical conditions allows measurement of (a) the optical transfer function free from electron and photographic noise and (b) object change, especially that due to radiation damage. Light optical methods based on superposition diffractograms are discussed. A subtraction procedure is described for measuring the optical transfer function, and a two-step diffraction process is presented for measuring object change. As an example, experiments with radiation damage in carbon foil are described. Here increased stability regarding radiation-induced change was found with increasing dose, making possible measurement of deviations from the “zero dose image”.

On Measurement of Three Dimensional Deformation Using Moire Method and Light Slicing Method

Methods of photographing orthographic projections of a grating and a contour on a curved surface were proposed. In photographing a contour, a sheet of light is projected on an object intermittently and the object is moved so that its surface may be swept by the sheet, while a camera is focused at the sheet. The contour obtained in this way corresponds to what would be observed from direction of movement of the object. In photographing a grating, a sheet of light is projected continuously. These methods can be applied to any object regardless of its size, whereas in the usual methods using the tele-centric system, spread of region to be photographed is restricted by the aperture of the field lens. Some related methods of measuring shape using Young's interference fringes were modified in similar way. Further, a procedure of measurement of strain in the three dimensional deformation of sheet bulging was shown.