Kanchan Saxena

Intensity Distribution Across a Source from Spectral Measurements

Abstract The degree of spectral coherence (μ12(ω)) over the plane of a double slit is determined from the measurement of spectral changes in Youngs interference experiment using the spectral interference law. The experimental and theoretically calculated values of μ12(ω)) for the experimental parameters agree well within experimental error, thus supporting the theoretical prediction of D. F. V. James and E. Wolf (1991, Phys. Lett. A, 157 6). The degree of spectral coherence determined is used for estimating the intensity distribution across a source. This new approach, being a simple spectral measurement technique, might find its application in astronomy, particularly for the study of intensity distribution across stars.

Spectral changes due to source correlation in Young's interference experiment

Abstract In this communication we show that spectral changes are produced on superposing partially coherent light emerging from two pinholes in Youngs interference experiment. These changes have been studied for on-axis and off-axis points of observation.

Angular Separation of a Pair of Sources by Spectral Interferometric Technique

Abstract We discuss a new experimental technique to verify the theoretical predictions made by James et al. that the measurement of the spatial coherence properties of a field by spectroscopic means (i.e. spatial coherence spectroscopy) could be applied to determine the separation of a pair of sources.

Novel alignment technique for surface stabilized ferroelectric liquid crystal

An alignment method for obtaining excellent surface stabilized ferroelectric liquid‐crystal devices is described. Alignment is obtained by obliquely depositing the SiO in two steps. The first deposition involves vacuum coating at 60° angle and the second at 85° (orthogonally to the first) with the substrate normal. The method induces a high (∼20°–25°) pretilt surface which depends on the thickness of the second layer. The glass substrates are matched with antiparallel direction of evaporation of second coating. This ensures a selective pretilt of molecules and the uniformly tilted smectic layer structure. The advantages of this new method are the ease of large‐scale production, defect‐free large uniform monodomains, good contrast, bistability, and microsecond switching speed response.

Spatial coherence properties of electroluminescence from Alq3-based organic light emitting diodes

We report the measurement of spatial coherence properties of light emitted by organic electroluminescent devices based on tris-(8-hydroxyquinoline) aluminum. Coherence measurements were performed using Young’s double slit experiment. Fourier-transform technique was used for the measurement of visibility of the interference fringes from which the modulus of the degree of spatial coherence was determined. Experimental results were compared with the theoretical values and it is shown that the coherence properties of the light emitted by a simple organic light emitting device match with those of practical Lambertian sources.

Field correlations from spectral measurements in Young's interference experiment

Abstract Spectral changes produced on superposing partially coherent light emerging from two pinholes in Youngs interference experiment have been studied and attributed to the source correlation effect. For the first time, the degree of spectral coherence has been determined from spectral measurements rather than by the usual fringe visibility measurement method. The degree of spectral coherence thus determined shows that it varies with the distance of the pinholes from the illuminating source.

Experimental studies of field correlations using spectral interferometric technique

Abstract By making use of the findings that the spectral analysis of light in the region of superposition in Youngs interference experiment provides information about the spectral correlation properties of the radiated fields, experimental studies are conducted on the determination of the degree of spectral coherence by spectral measurements over a broad range of frequencies in the far zone of a broadband, planar, secondary, quasi-homogenous (PSQh) source and the results are reported.

Removal of Zig-Zag Defects in Surface-Stabilized Ferroelectric Liquid Crystal Cells

We have succeeded in eliminating the zig-zag type of defects of surface-stabilized ferroelectric liquid crystal cells by applying an alternating electric field of suitable frequency to polyamide-coated rubbed glass plates. This has been achieved in those cases of sample thickness in which the oscillatory movement in the hairpin texture associated with the zig-zag defects occurs on the application of the ac field. The sample shows uniform contrast, remains defects free even after the removal of the field, and exhibits the characteristics of fast-switching bistable SSFLC displays.

Direct pulse technique for spontaneous polarization dynamics and molecular reorientation processes in ferroelectric liquid crystals

A method has been devised for studying the spontaneous polarization, dynamics of polarization reversal, and the molecular reorientation processes that occur in the bulk and surfaces of ferroelectric liquid crystals. These studies have been carried out by analyzing the current response to triangular‐ and square‐wave forms. The current response to a triangular wave yields the spontaneous polarization by conveniently subtracting the background contribution due to the conductive and capacitive currents. Molecular reorientation processes which take place within the bulk and the boundary surface layer can be studied by the appearance of polarization current peaks on the triangular‐wave response. The dynamics of polarization reversal between bistable states and of the polarization change between the zero‐field relaxed state and either of the saturation remanent polarization states have been studied by applying ‘‘symmetric’’ and ‘‘asymmetric’’ square waves. The technique can also be successfully applied to solid ...

Miniaturized total‐reflection ferroelectric liquid‐crystal electro‐optic switch

A total internal reflection (TIR) ferroelectric liquid‐crystal optical switch has been described using a larger value of birefringence and higher extraordinary refractive index (ne) of FLC than the refractive index (ng) of glass. The off‐axis orientations of voltage selected optic axes directions provide a convenient matching of transmission and reflection characteristics. This enables one to decrease the critical angle for TIR. The electro‐optic switch can be miniaturized and a large switch array (1×4; 4×4) architecture is feasible.