Use of chopped laser light in electronic speckle pattern interferometry

The mode shapes of a tennis racket and the effects of vibration dampers on those mode shapes

The vibrational behavior of a tennis racket was studied using a speckle-pattern interferometry system. Specifically, the first 12 mode shapes of a racket are shown and discussed. In addition, the speckle-pattern interferometry system was used to compare the effects of four commercially available vibration damping systems. It was found that these vibration dampers produce a variety of effects on the vibrational behavior of the racket, though these effects may not be noticeable during play.

Electronic shear interferometry: application of a (double-) pulsed laser

The use of a double-pulsed laser in interferometric metrology relaxes the stability requirements for the experimental setup. The use of such a laser also makes it possible for one to study high-speed dynamic processes. We justify the use of a double-pulsed laser in electronic shear interferometry. We show how image subtraction can be applied to produce high-quality fringe patterns without a special aperture design. The fringe visibility is studied theoretically and is compared with the fringe visibility obtained when the closely related television-holography technique is used. The new double-pulse subtraction technique offers the possibility of compensation for laser intensity fluctuations that can affect the fringe visibility significantly in pulsed electronic shear interferometry.

Effect and use of exposure control in vibration analysis using TV holography

A time-averaged recording of a sinusoidally vibrating object reconstructs a fringe function, which is determined by the ratio between the exposure time and the vibration period. For short exposures, compared with the vibration period, the fringe function is highly dependent on the number of vibration cycles recorded and on the starting point of the exposure in the vibration cycle. When several fringe functions that are recorded at different parts of the vibration cycle are added, the resulting averaged fringe function is similar to the normal J(o)(2) function, even at short exposures. The frequency ranges at which numerical analysis can be used in these two cases are defined, and the result of short exposures permitting digital fringe analysis, even under extremely unstable situations, is demonstrated. Extending the standard video exposure time permits recording vibrations at low frequencies as the normal J(o)(2) function and improves the light economy.

Double-pulse characteristics of a single-oscillator Nd:YAG laser affecting its performance in TV holography

The relevance of several double-pulse laser parameters for the fringe quality in TV holography is emphasized theoretically. It is demonstrated that single-oscillator Nd:YAG lasers can show significantly reduced characteristics in double-pulse operation, limiting the performance of these lasers in double-pulse TV holography.

Optically phase-locked electronic speckle pattern interferometer

The design, theory, operation, and characteristics of an optically phase-locked electronic speckle pattern interferometer (OPL-ESPI) are described. The OPL-ESPI system couples an optical phase-locked loop with an ESPI system to generate real-time equal Doppler speckle contours of moving objects from unstable sensor platforms. In addition, the optical phase-locked loop provides the basis for a new ESPI video signal processing technique which incorporates local oscillator phase shifting coupled with video sequential frame subtraction.

Electronic speckle pattern interferometric measurements of the basilar membrane in the inner ear

A setup incorporating electronic speckle pattern interferometry, reference beam phase modulation, chopped laser light, and a simple microscope has been used to observe vibrations of the basilar membrane in human temporal bones. A postmortem effect ensures that no special treatment of the semitransparent membrane is required. Amplitudes (down to 20 A) and phases of the membrane motion are analyzed both in real time and video recordings. Observations include phase variations across the membrane and motions of Mossbauer sources (pieces of cobalt) on the membranes.

Electronic speckle pattern interferometric system based on a speckle reference beam

A new electronic speckle pattern interferometric (ESPI) technique is introduced. The technique is based on a reference beam combined with a large aperture optical system. The basic principles are described and compared with conventional ESPI setups. The new interferometer is easy to adjust, it is invulnerable to dust and scratches on the optical components, and is very compact. It is well-suited for practical engineering applications. Light sensitivity and fringe quality are comparable with the conventional ESPI features. Superior fringe pattern can be obtained by use of a new speckle reduction technique to be described.