Persistent Link:
http://hdl.handle.net/10150/188115
Title:
DIGITAL SPECKLE-PATTERN INTERFEROMETRY (OPTICAL TESTING).
Author:
CREATH, KATHERINE.
Issue Date:
1985
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
A digital speckle-pattern interferometer was built utilizing a 100 x 100 element Reticon diode array interfaced to an HP-9836C desk-top computer. A single-mode optical fiber mounted in the center of the system's aperture stop creates a spherical-wave reference beam. Secondary interference fringes are calculated inside the computer by subtracting speckle patterns before and after a deformation, and squaring this difference. This technique has been shown superior to that of taking the absolute value of the difference. The traditional vibrational observation technique of low-pass filtering a single speckle pattern and squaring the result is emulated in software. It is compared to four other vibration observation techniques. A new technique records the self-interference terms in a reference frame, and subtracts these from the time-averaged vibration data. It provides very good fringe contrast for moderately unstable objects, as well as interferometers which have not been optimized to minimize self-interference terms. The best vibration fringe contrast is obtained by subtracting two time-averaged speckle patterns of a single object resonance. One exposure has a relative π phase-shift between object and reference beams to cancel self-interference terms. This last technique is not real-time; whereas, the new technique is. Double-exposure speckle interferograms are averaged using a technique which utilizes a stepping motor to change the object illumination angle. Results of averaging deformation measurements and double-exposure vibration techniques show a large increase in fringe contrast with an accompanying reduction in speckle noise. Quantitative measurements of object deformations is demonstrated by applying phase-shifting interferometry techniques. A deformation's phase is found by subtracting modulo 2π phases measured for each object state. Phase discontinuities are removed with the aid of noise reduction algorithms. Limitations are low intensity modulation as the phase is shifted, and speckle decorrelation during object deformation. It is shown that 10 waves of object deformation are measurable to λ/10 across the detector array. The double-exposure phase-measurement technique works well and is applicable to many different metrological measurements. To show the versatility of this technique, an optically smooth surface is contoured using two illumination wavelengths.
Type:
text; Dissertation-Reproduction (electronic)
Keywords:
Interferometry.; Speckle.
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Optical Sciences; Graduate College
Degree Grantor:
University of Arizona
Advisor:
Wyant, Jim

Full metadata record

DC FieldValue Language
dc.language.isoenen_US
dc.titleDIGITAL SPECKLE-PATTERN INTERFEROMETRY (OPTICAL TESTING).en_US
dc.creatorCREATH, KATHERINE.en_US
dc.contributor.authorCREATH, KATHERINE.en_US
dc.date.issued1985en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractA digital speckle-pattern interferometer was built utilizing a 100 x 100 element Reticon diode array interfaced to an HP-9836C desk-top computer. A single-mode optical fiber mounted in the center of the system's aperture stop creates a spherical-wave reference beam. Secondary interference fringes are calculated inside the computer by subtracting speckle patterns before and after a deformation, and squaring this difference. This technique has been shown superior to that of taking the absolute value of the difference. The traditional vibrational observation technique of low-pass filtering a single speckle pattern and squaring the result is emulated in software. It is compared to four other vibration observation techniques. A new technique records the self-interference terms in a reference frame, and subtracts these from the time-averaged vibration data. It provides very good fringe contrast for moderately unstable objects, as well as interferometers which have not been optimized to minimize self-interference terms. The best vibration fringe contrast is obtained by subtracting two time-averaged speckle patterns of a single object resonance. One exposure has a relative π phase-shift between object and reference beams to cancel self-interference terms. This last technique is not real-time; whereas, the new technique is. Double-exposure speckle interferograms are averaged using a technique which utilizes a stepping motor to change the object illumination angle. Results of averaging deformation measurements and double-exposure vibration techniques show a large increase in fringe contrast with an accompanying reduction in speckle noise. Quantitative measurements of object deformations is demonstrated by applying phase-shifting interferometry techniques. A deformation's phase is found by subtracting modulo 2π phases measured for each object state. Phase discontinuities are removed with the aid of noise reduction algorithms. Limitations are low intensity modulation as the phase is shifted, and speckle decorrelation during object deformation. It is shown that 10 waves of object deformation are measurable to λ/10 across the detector array. The double-exposure phase-measurement technique works well and is applicable to many different metrological measurements. To show the versatility of this technique, an optically smooth surface is contoured using two illumination wavelengths.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.subjectInterferometry.en_US
dc.subjectSpeckle.en_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineOptical Sciencesen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorWyant, Jimen_US
dc.contributor.committeememberBarrett, Harryen_US
dc.contributor.committeememberShannon, Boben_US
dc.identifier.proquest8603336en_US
dc.identifier.oclc696817641en_US
All Items in UA Campus Repository are protected by copyright, with all rights reserved, unless otherwise indicated.