Jitendra Dhanotia

Automated collimation testing by incorporating the Fourier transform method in Talbot interferometry

In this paper, we report an automated technique for collimation testing by incorporating Fourier fringe analysis of the recorded interferograms in Talbot interferometry. The triangular profile of Talbot interferometric fringes has been recorded using a CCD and computer system. The interferograms corresponding to the in-focus, at-focus, and out-of-focus positions of the collimating lens have been recorded. Direct phase measurement using the Fourier transform method has been used for detection of collimation positions. Good accuracy and precision in measurement have been achieved.

Slope measurement of bent plates using double grating shearing interferometry

A grating-based shearing interferometeric setup for slope measurement of bent plates has been proposed. The specimen under test is illuminated by a collimated beam from the laser. Light reflected from the specimen passes through two identical holographic gratings placed in tandem. The grating frequency has been so chosen that the diffracted orders from each grating are separated out distinctly. Two first-order beams diffracted from each of the gratings superpose in space. In the resulting interferogram, the fringes due to slope information of the object are visualized. Mathematical formulation for experimental determination of slope values has been undertaken. Validation of the experimental results with theoretical predictions in case of cantilever beam provides good correlation. The main advantage of the technique has been the realization of very compact geometry without the need for spatial filtering arrangement commonly associated with the grating-based techniques used to date.

Phase-shifting lateral shearing interferometry using wedge-plate and interferometric grating

A simple and robust method for introducing a phase-shifting test procedure in a wedge-plate shearing interferometer is proposed. The output of the wedge-plate lateral shearing interferometer (LSI) is superposed onto a sinusoidal grating, forming a moiré pattern. The in-plane translation of grating perpendicular to the grating lines is used for introducing a known amount of phase shifts in the interferometer. Direct measurement of phase using a four-step phase-shifting method is undertaken. The applicability of this devised phase-shifting wedge-plate LSI has been successfully tested for setting the collimation position of optical beams. Good accuracy and precision are achieved.

Fingerprint detection and mapping using a phase shifted coherent gradient sensing technique.

In this paper, a full field technique for mapping a latent fingerprint using a coherent gradient sensing (CGS) sensor is proposed. Collimated light from an He-Ne laser illuminates a specimen comprising a fingerprint implanted onto a reflecting surface. Reflected light from the specimen is analyzed using the CGS sensor comprising a pair of gratings. Reflected light carries information regarding the depth and orientation of furrows and ridges in the fingerprint. The topological information of the fingerprint is retrieved using four-step phase shifting interferometry. Well-defined 2D and 3D phase plots have been reconstructed to map the topography of the human fingerprint. The recorded slope data reconstructs the information regarding the separation and depth of the ridges in the latent fingerprint. The proposed technique is noninvasive and full field and does not require any kind of chemical or physical treatment. The sensor is very simple, yields interferometric sensitivity, and has the advantages of easy alignment, compactness, and low cost.

Quality Assessment of Medicinal Leaves Through Biospeckle Technique

In this paper, we report investigations undertaken towards visualization of microbiological objects in medicinal leaves using biospeckle activity approach. Both fresh and infected samples of Ficus Religiosa (peepal leaf) are illuminated by a laser source for generation of biospeckle pattern. Dynamic variation in activity images were grabbed by a Charge Couple Device (CCD) camera and quantized into 8 bit digital image using frame grabber. For image analysis revised version of conventional Fujii’s method i.e. weighted parameterized Fujii method is used. It shows high contrast as compared to the other existing methods when sample is illuminated uniformly. The current study aims to distinguish between fresh and infected leaves for improvement of quality of Ayurvedic medicines.

Fingerprint Detection and Analysis Using Talbot Interferometry

In the present communication, a full field technique for mapping latent fingerprint using Talbot interferometry has been proposed. Collimated light from He–Ne laser illuminates a specimen comprising of a fingerprint implanted onto a reflecting surface. Reflected light carries information regarding the depth and orientation of furrows and ridges in the fingerprint. The topological information of the fingerprint is retrieved using phase shifting interferometric technique. The slope of the phase provides the information regarding variation in ridges of latent fingerprint. The proposed technique does not require any kind of chemical or physical treatment.

Phase contrast imaging of small transparent objects using digital shearography

Phase contrast imaging of small transparent objects having complex shape is difficult to achieve using theoretical modeling. Present communication reports investigations undertaken towards testing applicability of Digital Shearography for phase contrast imaging of small object. The experimental arrangement is simple and primarily uses a pair of gratings. The result of experimental investigation reveals that the technique can be successfully used for mapping the phase of transparent objects.

Measurement of small angle using phase shifted Lau interferometry

An incoherent white-light source illuminates a set of two identical gratings placed in tandem, resulting in the generation of the Fresnel image. This image is projected onto a reflecting object and the reflected images from the object are projected onto the third grating. The resulting moire fringes are recorded using CCD camera. Inclination angle of the object is a function of the interferometric phase. Phase shifting interferometry has been used for the determination of interferometric phase. Hence accurate determination of small tilt angle of object surface could be successfully undertaken. Technique is automated and provides high precision in measurement.

Collimation testing by incorporating Fourier transform method in coherent gradient sensing interferometer

The applicability of Coherent Gradient Sensing (CGS) technique for collimation testing of an optical beam has been proposed. The interferograms corresponding to different positions of the collimating lens have been recorded and analyzed using Fourier transform method for detection of exact collimation position.

Defect Detection in Bent Plates Using Coherent Gradient Sensing

This communication reports investigations undertaken towards testing applicability of Coherent Gradient Sensing for defect detection in bent plates. The CGS based grating shearing interferometer maps the slope pattern of the tested wave front. For the specimen under stress, the surface slope of the defective portions vary in an anomalous manner with respect to un‐defective portions of the specimen. Hence, the defects present in the specimen are visualized prominently. The experimental setup is simple and the detection is undertaken using a pair of identical gratings only. Experimental results conclusively establish the viability of the technique.