C. S. Vikram

Speckle photography of lateral sinusoidal vibrations: error due to varying halo intensity.

The effect of varying halo intensity in speckle photography of lateral sinusoidal vibration using Youngs fringes is discussed. An interesting new result is found that, for nonunity contrast or visibility, the relative fringe shift (or the error) for minima is always minimum for the lower-order fringes. Also the error in the fringe maxima position is lowest generally at intermediate fringe orders. However, as the visibility reduces the trend becomes similar to that for the case of minima. For maxima and minima both, the error is less for larger amplitude vibrations and higher visibility.

Simple approach to process speckle-photography data.

A simple approach to incorporate the effect of the variation in diffraction halo intensity on Youngs fringes in speckle photography is described. Detailed solutions for the shifts in maxima and minima positions are presented for the case of double exposure.

Gaussian beam effects in far-field in-line holography

Far-field in-line holography has been studied in detail when one or both of the beams used for recording and reconstruction are Gaussian. The contrast of the high frequency interference fringes and hence their recordability have been investigated with a specific example of the object having circular cross section. For reconstruction the effects of uniform as well as Gaussian beams are studied and compared.

Fraunhofer Holography In Cylindrical Tunnels: Neutralizing Window Curvature Effects

For in-line Fraunhofer holography in cylindrical tunnels, two methods are proposed to neutralize the window curvature effects. One is to modify the usually flat outer surfaces of the window into curved surfaces parallel to the original cylindrical direction; the desired outer curvature is determined in this paper. The second method proposes two separate parallel cylindrical lenses (one on each side) for zero net power. The desired lens parameters are determined in terms of the known physical quantities.

In-line Fraunhofer holography at a few far fields

The process of in-line Fraunhofer holography of particles is studied by an analysis of the four terms in the reconstructed field. Specific results are discussed for objects with circular cross section. The image shape and contrast are described in detail. The study is particularly useful when the recording is performed at a few far fields. It has been found that the recording at a higher far field is better due to a higher image-to-background irradiance ratio at the edges of the reconstructed image.

Volume magnification in particle field holography

An image-object volume relationship in holography for applications in quantitative particle fields is determined in terms of known physical parameters. The general relationships are described for collimated, point reference, or reconstruction sources. Some relevant methods for correlating the transverse magnification at different longitudinal distances are also described.

Simple Spectrum Analysis In Laser Doppler Studies Of Sinusoidal Vibrations

In laser Doppler vibrometry of sinusoidal vibration, direct analysis of the photodetector output or the heterodyne signal using a spectrum analyzer is emphasized. A technique utilizing the spectra at the carrier frequency and the first sideband is proposed for unambiguous analysis of the vibration amplitude. Experimental results demonstrate the validity of the proposed technique.

Measurement of subspeckle-size changes by laser-speckle photography

A simple method for the measurement of subspeckle-size lateral changes by double-exposure laser-speckle photography is described and practically demonstrated. It requires a known lateral movement of the subject (or the camera) orthogonal to that of the unknown movement. The orientation of Young’s fringes gives the unknown deformation. The method is time ordered and reasonably sensitive. The lower measurement range can easily be reduced to 1 order of magnitude of the usual limit.

Direct observation of laser speckles for real-time analysis of lateral motions

A method for real-time observation of speckle movement for the analysis of lateral motions is suggested. The method involves significant magnification using lenses and a TV-camera monitor system. This approach has the advantages of conventional speckle photography without the need for any chemical processing.

Single Relay Lens Magnification Effects In Off-Axis Particle Field Holography

Transverse and volume magnification effects are described for the case of a single lens used to relay the object space in off-axis holography of micro-objects. Using a single calibration of the transverse magnification at a mean longitudinal image distance, we derive relationships for transverse and volume magnifications for a given control volume. The validity of simple limiting solutions in relevant physical conditions is also discussed. Using the knowledge of the transverse magnification at two longitudinal locations, we determine a simple solution for the magnification calculation at any third location. The exact solutions for the transverse and volume magnifications are then obtained in a simpler manner.