Dr. Thomas C. Hale Profile

Dr. Thomas C. Hale

Technical Staff Member

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Publications (4)

Proceedings Article | 15 March 1998 Paper

Ultrasonic vibration modal analysis of ICF targets using a photorefractive optical lock-in

Thomas Hale, Thomas Asaki, Kenneth Telschow, Jim Hoffer

Proceedings Volume 3399, (1998) https://doi.org/10.1117/12.302541

KEYWORDS: Modulation, Crystals, Modal analysis, Ultrasonics, Laser crystals, Four wave mixing, Signal to noise ratio, Phase measurement, Signal processing, Photodetectors

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A photorefractive optical lock-in is discussed in relation to ultrasonic vibration modal analysis of inertial confinement fusion (ICF) targets. In this preliminary report, the method is used to analyze specimens with similar response characteristics to ICF targets with emphasis on both the displacement and frequency resolution of the technique. The experimental method, based on photorefractive frequency domain processing, utilizes a synchronous detection approach to measure phase variations in light scattered from optically rough, continuously vibrating surfaces with very high, linear sensitivity. In this photorefractive four-wave mixing technique, a small, point image of the object surface is made to interfere with a uniform, frequency modulated reference beam inside a Bismith Silicon Oxide crystal. Optical interference and the photorefractive effect of electronic charge redistribution leads to the formation of a refractive index grating in the medium that responds to the modulated beams at a frequency equal to the difference between the signal and reference frequencies. By retro-reflecting the reference beam back into the crystal, a diffracted beam, counter-propagating with respect to the original transmitted beam, is generated. Using a beamsplitter, the counter-propagating beam can be picked-off and deflected toward a photodetector. The intensity of this diffracted beam is shown to be a function of the first-order ordinary Bissel function, and therefore linearly dependent on the vibration displacement induced phase modulation depth (delta) , for small (delta) ((delta) < 4 (pi) (xi) /(lambda) < < 1) where (xi) is the vibration displacement and (lambda) is the source wavelength; analytical description and experimental verification of this linear response are given. The technique is applied to determine the modal characteristics of a rigidly clamped disc from 10 kHz to 100 kHz, a frequency range similar to that used to characterize ICF targets. The results demonstrate the unique capabilities of the photorefractive optical lock-in to detect and to measure vibration signals with very narrow bandwidth and high displacement sensitivity. This level of displacement sensitivity is particularly important in detecting changes in vibrational mode shapes and frequencies that might be associated with asymmetries in ICF targets.

Proceedings Article | 25 October 1996 Paper

Vibration modal analysis using all-optical photorefractive processing

Thomas Hale, Kenneth Telschow

Proceedings Volume 2849, (1996) https://doi.org/10.1117/12.255496

KEYWORDS: Signal processing, Modal analysis, Modulation, Phase measurement, Four wave mixing, Transient nonlinear optics, Signal detection, Bessel functions, Photodetectors, Crystals

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Proceedings Article | 3 December 1993 Paper

Nondestructive testing of adhesively bonded structures using synchronized pressure stressing

Thomas Chatters, Bruno Pouet, Sridhar Krishnaswamy

Proceedings Volume 2001, (1993) https://doi.org/10.1117/12.163847

KEYWORDS: Speckle, Nondestructive evaluation, Speckle pattern, Phase modulation, Phase shift keying, Fringe analysis, Video, Modulation, Image processing, Inspection

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Proceedings Article | 28 May 1993 Paper

ESPI with synchronized pressure stressing

Thomas Hale, Bruno Pouet, Sridhar Krishnaswamy

Proceedings Volume 1821, (1993) https://doi.org/10.1117/12.145561

KEYWORDS: Camera shutters, Composites, Image processing, Aluminum, CCD cameras, Video, Nondestructive evaluation, Image acquisition, Speckle pattern, Speckle

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