We propose a two-wavelength interferometric system based on a single optical element, i.e., a shear plate. The observation of beat formation phenomenon and the measurement of phase at synthetic wavelength are demonstrated for the first time using two wavelengths simultaneously in a lateral shearing interferometer. Shearing interferograms are recorded both at individual wavelength and at synthetic wavelength. The phase map at synthetic wavelength is obtained by means of subtracting the phase maps at individual wavelength as well as directly from the synthetic interferogram, and the results are found in good agreement. The validity of the principle is applied for collimation testing and reconstructing the phase map of transparent objects. The main advantages of the present system over the previous systems based on two-wavelength interferometry are high stability, nearly common path interferometry, single optical element (shear plate) requirement, compactness, and low cost.
In this paper we present phase shifting Talbot interferometry for the measurement of surface topography of the gas turbine blades. Interferograms of the different steps are recorded and displayed on the computer monitor using digital techniques. Presence of the harmonic components in the phase map due to the Ronchi gratings are removed by using Fourier filtering. The variation of the surface height at the different points of the objects is obtained by generating the phase map. The results obtained by phase shifting Talbot interferometric techniques are in good agreements with that of the measured by the manually controlled co- ordinate measuring machine. The critical analysis of results alongwith error analysis is presented.
We propose a distance measuring system based on lateral shearing interferometer (LSI) with extended range of measurement and improved resolution. The sensor is based on a wedge-shaped plate LSI and due to the presence of tilt, a finite number of fringes parallel to the direction of shear appear and hence significant spatial carrier frequency is generated at the focus position. On varying the distance of the object surface from the focus position, the orientation, fractional and integer order, and the width of the interference fringes change. It is shown that the orientation of the fringes is the most sensitive parameter, by means of which one can detect small changes in distance. The Fourier transform method for fringe analysis is used, and from the position of the maxima of the first-order Fourier spectrum the orientation of the fringes and hence the distance is measured. Experimental results of distance measurement by changing the focal length of the lens are presented. A large range of measurement without any fringe ambiguity problem can be achieved using the system.
A distance measuring system and surface profiler with extended range based on collimation testing technique using lateral shearing interferometry is proposed. The sensor works on the principles of focus sensing and interferometry and the depth gating is achieved by collimation testing. A wedge-shaped shearing plate was used for the interferometer and when the object surface is exactly at the focus of the collimating lens the interference fringes are perfectly parallel to a reference line with a finite spatial frequency. If the object surface is out of focus of the collimating lens the fringe pattern is oriented with a change in the spatial frequency. The orientation of the interference fringes and their spatial-frequency increases as we move the object farther from the focused position. Fourier transform method for fringe analysis is used and from the maximum of the Fourier spectrum the distance and three-dimensional surface profile of the objects is measured. Since the surface profile is reconstructed from the maxima of the first-order Fourier spectrum, a large range of measurement without any fringe ambiguity problem can be achieved using the system. The system works both for smooth as well as diffuse objects and is compact, robust and inexpensive. A high-depth of resolution of the order of 10 micrometer achieved with a range measurement 10mm.