Search

We investigate free-space diffraction of light that emanates from obliquely cleaved end faces of single-mode fibers. Emphasis is placed on precise prediction of the wave-front sphericity of fiber-generating waves in the nonparaxial Fresnel propagation region spanning an entire hemispherical observation surface. Rayleigh-Sommerfeld scalar diffraction theory is used to produce an analytic closed-form solution with a nonparaxial approximation. The result allows the wave front's sphericity and the amplitude distribution of fiber-generating waves to be evaluated precisely with less computation than for existing numerical or infinite-series solutions.

The activation of p38 mitogen-activated protein kinase (MAPK) has been implicated in the pathological changes accompanying inflammatory and apoptotic processes of various cell types including neurons. In a kainic acid (KA)-induced mouse seizure model, p38 MAPK is induced in reactive astrocytes in the CA3 region of the hippocampus where severe neuronal loss occurs. Here we report the delayed and protracted activation of p38 MAPK in the CA3 region of the hippocampus of mice treated with KA. In this model, the inhibition of p38 MAPK isoforms by SB203580, a specific inhibitor, attenuated neuronal loss in the CA3 and CA1 regions of the hippocampus, which was accompanied by the suppression of the p38 MAPK activation as well as astrogliosis. Thus, the delayed and sustained induction of p38 MAPK plays a crucial role in the neuronal damage of KA-induced brain seizures.

We measure the spatial distribution of the mechanical stress induced inside translucent glass/epoxy composites by means of polarizationsensitive optical coherence tomography. The Stokes parameters determined from two orthogonal polarization components of the backscattered light allow the internal stress to be identified in terms of its magnitude and principal direction based on a birefringence light scattering model of glass/epoxy composites. Measurement examples show the particular case of stress concentration near a through hole and the internal structural damages caused by excessive tensile loading.

We present a new interferometer system devised for surface-profile metrology with multiple two-point-diffraction sources that are made from a pair of single-mode optical fibers. The diffraction interferometer system performs an absolute profile measurement by projecting multiple fringe patterns on the object surface and then fitting the measured phase data into a global model of multilateration. Test measurement results demonstrate that the proposed profiling method is suited for rough surfaces with excessive surface irregularities, which are difficult to measure with conventional two-arm interferometers.

We propose a new configuration for a high-resolution heterodyne interferometer that employs a two-longitudinal-mode He-Ne laser with an intermode beat frequency of 600-1000 MHz. The high beat frequency is downconverted to 5 MHz such that the phase change of the interferometer output is precisely measured with a displacement resolution of 0.1 nm. A thermal control scheme is adopted to stabilize the cavity length of the He-Ne plasma tube such that a frequency stability of 2 parts in 10(9) is obtained by suppression of frequency drifts caused by t he phenomena of frequency pulling and polarization anisotropy. This two-longitudinal-mode He-Ne laser yields a high output power of 2.0 mW, which permits multiple measurements of as many as 10 machine axes simultaneously.

We present a point-diffraction interferometer that has been specially devised to perform absolute distance measurements in three dimensions. It is composed of two main parts: One is a target that moves in three dimensions, and the other is a stationary two-dimensional array of photodetectors. The target is made of point-diffraction sources that emit two spherical wave fronts, whose interference is monitored by the photodetectors. Application of a phase-shifting technique allows the phase values of the photodetectors to be precisely measured, which are then fitted to a geometric model of multilateration so as to determine the xyz location of the target by minimization of least-squares errors. Experimental results show that the proposed diffraction interferometer is capable of measuring the xyz coordinates of the target with a volumetric uncertainty of less than 1.0 microm over a working volume of a 100-mm side.