K.C. Joshi

Wolf shift and its application in spectroradiometry

Abstract Shifts in spectral lines, due to source correlation and violation of scaling law, have been discussed with reference to spectroradiometric measurements. The large scatter found in the intercomparison of spectroradiometric scales maintained by standards laboratories is attributed to the spectral shifts.

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.

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.

Correlation-induced spectral changes on passing partially coherent light through an annular apecture

An experimental study on spectral changes produced on passing partially coherent light through an annular aperture is made for on-axis and off-axis measurements. The dependence of the observed spectral shift on the ratio of the radius of central obstruction to that of the outer radius of opening of the annular aperture is investigated.

Spectral shift due to source correlation in conventional spectroradiometric measurements

Keeping in view the recent findings of the spectral shift due to source correlation during propagation of light, a study has been undertaken to analyze the errors which may be introduced in spectroradiometric measurements.

Displacement measurements from coherence-induced spectral changes in a Mach-Zehnder interferometer

The spectral changes arising due to interference between two partially correlated beams are investigated experimentally in a Mach-Zehnder interferometer. Two different schemes are used to produce two partially correlated beams. Experimental results obtained from these schemes are compared with the theory. It is shown that the spectral changes in the form of modulations in the superposed spectrum are dependent on the optical path difference of the two beams in the interferometer and can be utilized for determining linear displacements of a few microns.

Spectral shift in a multimode laser due to source correlation

Abstract To observe spectral shift due to source correlation, usually some focussing optics is used and an aperture is placed in the secondary plane for violating the so called scaling law. Such an aperture produces diffraction which complicates the study of spectral shift due to correlation between the source points. Unlike all the earlier experiments, we have started from a coherent source which is made partially coherent by a beam expander and a rotating diffuser. The spectral shift observed in such an experiment and its implications are described.