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Abstract: In a recent experiment we have shown that the constraints in the yester-experiments to verify the Fresnel and Arago interference laws can be overcome by using the temporal coherence property in a Mach–Zehnder interferometer. In this note we are giving a theoretical treatment to those experimental. This analysis is based on the matrix representation of the electric field and the polarizers. [Copyright &y& Elsevier]

Abstract: In this study a novel method for determining surface flatness based on spectral interferometry is reported. In the traditional method a laser is used to produce intensity interference fringes and by measuring the shift in the position of a fringe when a test plate is put on a reference plate, the surface flatness of the test plate is determined. In the present study we have used a broad-band source for determining the flatness of a test plate. By studying the changes in the spectrum of the source on interference that are produced when a test plate is put on a reference plate, the surface flatness is determined. It has been found that the surface flatness determined by spectral studies comes out to be of the same order as that with a quasi-monochromatic laser light. This method might provide an edge over the present method by reducing the time taken in the study and also provide a cost-effective solution. [Copyright &y& Elsevier]

The crystal structures of the R2Pd2Pb (R=Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, and Lu) compounds were determined using X-ray powder diffraction. The investigated compounds crystallize with Mo2FeB2 structure type (space group P4/mbm, Pearson code tP10). The importance of stabilization by polar intermetallic R–Pd bonding is underscored by a bonding analysis derived from electronic band structure calculations. [Copyright &y& Elsevier]

Anomalous behavior of the spectra at phase singularity produced by various zone plates near the focus of a converging partially coherent polychromatic wave is studied using a simple experimental technique. It is found that the spectrum of the wave on the zone plate consisting of a single spectral profile shows almost vanishing intensity at all frequencies with a tendency of splitting into two peaks at the on-axis point and shows redshift and blueshift around the phase singularity. [Copyright &y& Elsevier]

An improved technique is described for determining the optical source-intensity-profile. The spectral degree of coherence produced by a quasi-homogeneous source masked with an amplitude grating, on the plane of a double slit of fixed baseline length, over the accessible frequencies in the visible range of the electromagnetic spectrum, is determined by measuring the single slit spectra and the superposed spectrum by applying the spectral interference law. The masking of the source by the amplitude grating enables to map the degree of coherence obtained experimentally over zero spatial frequency. The Fourier-inversion of the spectral degree of coherence over the mapped spatial frequencies is used to determine the source intensity-profile. This technique may have some practical applications namely automated inspection. [Copyright &y& Elsevier]

In this study, it is shown that the light emerging from two pinholes, after it has passed through two identical diffusers having same correlation properties but moving in opposite directions with same linear speed, has the properties of cross-spectrally pure light. It is also shown that the visibility of the interference fringes formed in the observation plane is directly related to the characteristics of the diffuser, i.e. the average roughness of the diffuser surface. Therefore, by measuring the visibility of the interference fringes over a few pinhole separations, the average roughness of the diffuser surface can easily be determined. [Copyright &y& Elsevier]

Presents the experimental observation of the phenomenon of spectral switching for class of partially coherent light. Difference of the on-axis spectrum of the light in the far-field from the spectrum of light in the aperture; Dependence of the radius on the value of the parameter; Generation of spectral lines.

Abstract: The intensity variation of bright and dark fringes in Young''s double slit experiment shows that a light beam propagating through the focus of a lens experiences a phase shift (called the Gouy phase shift [Gouy CR. Acad Sci Paris 1890;110:1251]) with respect to its plane wave counterpart. The additional phase change of π introduced on focusing the light beam and then further propagating it in one arm of the interferometer changes a bright fringe into a dark fringe and vice-versa. We have, thus, made direct visualization of the Gouy phase shift by a simple experiment. [Copyright &y& Elsevier]

Abstract: We perform two-photon coincidence subwavelength interference experiments from double slit using independent photons obtained from a pseudo-thermal light source produced by (i) slowly rotating ground glass (RGG) with turbid solution of a different density and (ii) RGG. The turbid solution is water solution containing 3μm diameter polystyrene microspheres. It is found that the visibility of the obtained interference pattern decreases in first experiment with increasing the density of the turbid solution from N =1010 spheresm−3 to N =1014 spheresm−3. However, the results are reported here for the density of N =1014 spheresm−3. The visibility obtained with RGG with turbid solution having N =1014 spheresm−3is 23% which increases to 27% with RGG but the resolution decreases. The effect of coherence width of source in two-photon interference pattern is also studied with pseudo-thermal light obtained by RGG. It was observed that on increasing the coherence width the visibility of interference fringes increased and quality of the fringe reduced and when the coherence width was more then slit separation, in coincidence measurements, no interference pattern appeared. The results are used to explore the classical subwavelength interference nature with thermal light. [ABSTRACT FROM AUTHOR]

Abstract: We report an experimental study of lensless ghost imaging by measuring reflected photons from an object using pseudo-thermal light radiation. A laser beam is passed through a multiple scattering medium to produce pseudo-thermal random light. Ghost image of the object is reconstructed by measuring the second-order correlation in intensity fluctuation. The study is conducted to explore the sensitivity of the imaging technique for the source parameters, i.e. coherence width and transverse size of the source. It is found that the higher the coherence width of the source higher is the visibility but the quality (resolution) becomes poor. However for higher transverse size of the source improves image quality. In addition it is verified that the observed pattern is an actual image of object. The object is chosen in the form of two very thin reflecting lines, i.e. a form of a double slit. The factors contributing to measurement uncertainty are discussed in detail. It is found that the reconstructed image gives the width of the object lines within an uncertainty of ±15%. [Copyright &y& Elsevier]

Cylindrical vector beams with azimuthal and radial polarization distributions are studied for singularities. It is shown experimentally that these beams have screw dislocation as well as edge dislocation at the same time. The relation between phase and polarization of light beam is the key to understand this fact. We envisage that this has potential application in phase synthesis using polarization engineering. Further, the polarization singularities in these inhomogeneously polarized beams are examined by measuring Stokes parameters across the cross-section of these beams. [ABSTRACT FROM AUTHOR]

Abstract: We present a theoretical study of the optical transmission from a thin metallic double slit. The second-order correlation function as a function of the displacement of the detectors for different values of slit separation is studied. It is shown that surface plasmons excited at one slit and propagating to the other slit modulate the coincidence counts with the variation of slit separation. Sub-wavelength interference effect has also been observed for the field assisted by surface plasmons. It is also shown that the second order interference-diffraction pattern changes with slit separation and at some particular value of slit separation it changes into the Hanbury Brown and Twiss (HBT) effect. [Copyright &y& Elsevier]

Abstract: A method of measurement of diffusion length L in p type c-Si wafers based on the lateral collection of minority carriers is reported. In this method, wafer requires a p–p+ junction on entire back surface and an n+–p interface on a part of the front surface leaving the rest part as bare for illumination. A photo-current I sc is generated when a rectangular area of a part of the bare front surface in the vicinity of the n+–p interface is illuminated with a laser beam. The magnitude of I sc varies with the normal distance d between the electron collecting n+–p interface and the nearest edge of the illuminated region. The slope Φ of the normalized I sc vs. d curve is used to determine a parameter sinh−1 θ, which has a linear relation with d. The reciprocal of the slope of sinh−1 θ vs. d curve in the linear region gives the diffusion length L. The value of L is less susceptible to error due to the effect of S f of bare silicon surface if the linear region of sinh−1 θ vs. d curve lies in the region of smaller d values. The present method has an advantage over the other methods in that it does not depend on the intensity of the illumination and absorption coefficient of Si. Additionally, method has no limitation in terms of wafer thickness to diffusion length ratio and is applicable to all practical L values. [Copyright &y& Elsevier]

Abstract: An n+–p–p+ structure was formed by depositing a thin Al layer on one side and a semitransparent Pd layer on other side of a p–Si wafer, and the diffusion length L was determined from the slope of short circuit current density Jsc vs. illumination intensity Pin characteristics by illuminating the p+ side with a laser light of wavelength λ =789nm, following the photocurrent generation method. The slope was found to decrease after the specimen was exposed to air for a few hours before the measurement. The present investigation revealed that the degradation of slope was owing to increase in surface recombination velocity S significantly, e.g. to 2800cm/s for air exposure of 8h, above its initial value 10cm/s. This resulted from adsorption of moisture on Pd surface which decreases work function of Pd and lowers the accumulation potential barrier. The adsorbed water molecules could be removed from Pd surface by vacuum pumping and then S again became small and the slope regained its original value. The true value of L, smaller or larger than the wafer thickness, can be determined using single monochromatic illumination if S is known or has a negligibly small value, as in our case where the specimen was stored in vacuum. In our specimen we determined L =56μm when S was negligibly small. However, using the experimental slopes of Jsc –Pin curves at two monochromatic illuminations obtained by Sharma et al. we determined both S and L and found their values 1390cm/s and 94μm, respectively. [Copyright &y& Elsevier]

Abstract: The anomalous spectral behavior of polychromatic light in a modified Mach–Zehnder (MMZ) Interferometer is studied. In our numerical analysis, we found that, by varying the path difference between the interfering beams in the MMZ interferometer, one may find drastic spectral changes in the vicinity of dark rings of the interference field. In addition we extend the study to explore possibilities for information encoding and transmission in free-space using temporal coherence-induced spectral switching. By using unique features of the MMZ interferometer we propose two interesting prototype of optical devices for single channel and 1×2 channel (one input port and two output port) information transmission through spectral anomalies of interference pattern. The prototypes are based on contrived ideas and may find applications in developing spectral switching based optical devices. [Copyright &y& Elsevier]

Abstract: An experimental study is carried out to investigate a special kind of three-dimensional intensity distribution of a partially coherent optical beam known as optical bottle beam produced by using an annular aperture and lens combination (Lens Aperture System). In this paper, we are demonstrating the experimental results of our observations. The investigation also includes the effects of coherence modulation and central obstruction of the annular aperture (used in Lens Aperture System) on the resultant partially coherent optical bottle beam. The method discussed in this paper is simple and cost effective. [Copyright &y& Elsevier]

Abstract: Indinavir sulphate is a potent and specific protease inhibitor of human immunodeficiency virus (HIV). It is used for the treatment of acquired immune deficiency syndrome (AIDS). At elevated temperature the drug which otherwise remains crystalline undergoes a phase transition to an amorphous phase to form degradation products. In the present study, thermal stability of indinavir sulphate is evaluated using diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. Infrared spectra of the drug before and after the exposure to thermal radiation at different temperatures were acquired in the diffuse reflectance mode using a Fourier transform infrared (FTIR) spectrophotometer. The differential scanning calorimetry (DSC) and the X-ray diffraction (XRD) studies were used as complimentary techniques to adequately implement and assist the interpretation of the infrared spectroscopy results. The DRIFT spectra reveal that the drug remains stable up to 100°C, degrades slightly at 125°C and undergoes complete degradation at about 150°C to produce degradation products. The degradation products can easily be characterized using the infrared spectra. [Copyright &y& Elsevier]

Abstract: It has been shown both theoretically and experimentally that drastic spectral changes take place around phase singularity and the shift in the spectral lines gives rise to the phenomenon called spectral switching. The shift of spectral lines towards the blue end or towards the red end of the spectrum might perhaps be used in free space communication applications. In more recent investigations, the possibility of information encoding with spectral anomalies have been discussed for two different optical systems. In this paper, we present schemes of information encoding and information hiding in the Airy pattern formed by diffraction of spatially coherent light after passing through a circular aperture. We propose a communication system that might be used to realize a new communication technique. [Copyright &y& Elsevier]

Abstract: Extensive experimental study is carried out to investigate spectral behavior of spatially polychromatic coherent light diffracted by an annular aperture. It is found that the spectrum at the observation plane exhibits anomalous behavior after passing through the annular aperture. Experimental observations show that at a particular diffraction angle, the diffracted spectrum splits into two halves, while at other diffraction angles the spectrum either shifts towards lower wavelengths (blue-shift) or shifts towards higher wavelengths (red-shift). These spectral changes take place in the vicinity of the dark ring of the Airy pattern. Moreover, the behavior of the spectrum in the Fraunhofer region around a small circular loop centered at a critical direction is also studied and it is found that these spectral changes are qualitatively different from the spectral changes of the spectrum of the focused waves on a circle centered at the singular point. It is discussed in detail that such spectral anomalies of spatially coherent light may be exploited for information encoding and information hiding for free-space communications. The possibility to entangle bits in the spectral anomalies is also proposed. Such technique might be very useful to improve the throughput of information transmission in free space. [Copyright &y& Elsevier]

Abstract: An investigative infrared spectroscopic study is undertaken of nano polyaniline (PANI) samples differing in size and morphology in order to explore the sensitivity of spectral behavior on these factors. IR spectroscopy is used for studying the changes in the interaction between polymeric molecules as parts of nanodimensional structures. A time dependent interfacial oxidative polymerization of aniline monomer is conducted in order to obtain the desired nano PANI samples in doped form. The morphological changes in samples so obtained are characterized using scanning electron microscopy (SEM). The SEM images of samples obtained using the time dependent interfacial polymerization show preferential formation of 1D nano/micro structures with dimensions varying with reaction time intervals, which is also confirmed by transmission electron microscopy (TEM). X-ray diffraction study is undertaken to assess the crystalline nature of the samples. The IR spectra and the X-ray diffraction pattern of samples reflect these morphological variations. A comparative study of bulk polyaniline sample obtained using standard procedures is also undertaken. Significant variations in the conductivity of different polyaniline samples are also observed. The 10min sample shows significantly enhanced conductivity as compared to the 20min and 24h. PANI samples having well defined nanofibers. [Copyright &y& Elsevier]