Kevin G. Harding

Projection moire interferometer for vibration analysis.

A projection moire interferometer is presented which was developed to study rotating vibrating objects such as turbine blade assemblies. Three methods of moire interferometry were used in this study: pulsed; time-average; and real time. Real-time moire interferometry used in conjunction with image derotation and strobe techniques is shown to be a viable method of studying traveling wave modes on a rotating disk.

3D laser measurements on scattering and translucent surfaces

Laser based scanning methods have proven to be a valuable tool for a variety of 3D measurement applications. However, just as touch probes do not measure soft or flexible parts well, laser based methods have encountered problems with surfaces which are very rough or translucent. Either type of surface tends to spread the laser light out over an extended region, creating an uncertainty blob which can lead to false measurements. This paper discusses the types of errors associated with these light scattering surfaces, and efforts to minimize these effects through tight control of the viewing optics. Specific data is presented from tests performed with a laser based measurement probe on a variety of surfaces from smooth metal to translucent plastics.

Phase grating use in moire interferometry

When using coherent light in projected fringe moire interferometry, a phase grating will often produce a higher contrast pattern with greater light efficiency than will an amplitude grating. This paper describes the nature and mechanics of this phenomenon and presents experimental examples using this technique.

Design and Construction of Three Infrared Ellipsometers for Thin-Film Research

The University of Dayton Research Institute (UDRI) has de-signed and built three infrared ellipsometers in support of the Air Force high energy laser program. One of these instruments is a conventional null-type ellipsometer for operation in the 3.39 to 4.00 um wavelength range. Ellipsometric parameters are determined with a precision of 0.01 ° at any angle of incidence from 20 ° to 85 °. Repeatability and absolute accuracy also approach 0.01 °, which yields optical constants accurate to 0.1 percent in some cases. All components are mounted on removable carriers for easy interchange, although operation is normally in the PCSA (polarizer, compensator, sample, analyzer) configuration. The system software has special provisions for the second instrument, which is also a null-type ellipsometer dedicated to monitoring vacuum deposited coatings in real time at 3.39 Am. The software can model nonideal components in the optical path using Jones or Mueller matrices and provide completely corrected data with a single zone measurement after the instrument is characterized. The third instrument is a rotating polarizer, automated ellipsometer tunable from 1 to 12µm. A dedicated computer operates the instrument and reduces data.

Analysis Of Rotating Structures Using Image Denotation With Multiple-Pulsed Lasers And Moire Techniques

During the past decade the optical measurement technique of image derotated hologram interferometry has evolved to a point where it has become an extremely useful laboratory tool for studying the resonant structural response of rotating bodies such as turbomachinery bladed disks. The results obtained using derotated hologram interferometry to study a simple bladed disk are presented. Both stationary and traveling disk modes of vibration were recorded. Also presented is an extension of the technique to quantitatively measure traveling mode shapes using a triple-pulsed laser. Combining moire analysis with image derotation is also discussed, and some preliminary experimental results are given.

Real-time response of a rotating disk using image-derotated holographic interferometry

A recently developed technique that shows great promise for studying the structural response of rotating objects is that of image-derotated holographic interferometry. The technique consists of optically subtracting the rotational motion of a disk by passing the image of the rotating disk through a prism that is rotating at half the disks angular velocity. Heretofore, a pulsed ruby laser had to be used to record the rotating objects out-of-plane modes of vibration. This study reports on the extension of the technique to the real-time analysis of rotating objects by replacing the pulsed ruby laser with an acousto-optically modulated argon laser. Using the strobed argon laser in conjunction with the optical derotator, the rotating disks normal displacement can be observed as it is being excited in real-time. This technique offers the distinct advantage of being able to observe the rotating disks structural response over a wide range of pulse frequencies at any point in the disks cycle of revolution.

Sine wave artifact as a means of calibrating structured light systems

Structured light systems made to provide dense data over full image fields present a unique challenge to the task of calibration. Localized artifacts made for CMM or hard gages are often a poor fit for testing actual 3D performance. This paper considers the use of a sine wave artifact to provide a mapping of a calibration matched to full-field capabilities. The sine wave offers the advantages of a continuous function across the full field, with a well defined and easy to analyze shape. Changes in scale in all dimensions, as well as localized variations can be mapped in clear detail using this method.

Design Approach To A High-Precision Reflectometer For Component Study Evaluation

High-power lasers require beam directing optics with high damage thresholds. To achieve this, coatings with very high reflectivity and low absorption are being developed by many investigators. This paper describes a reflectometer for measuring these high reflectances to a very high precision. Parameters investigated for this design are source stability, detector limitations, data collection schemes, and the basic optical configuration. The most promising optical configurations investigated include a single-bounce system and a goniometric type double-bounce system. Data collection was best accomplished using a noise-eliminating sample and hold system in conjunction with a gain compensated, AC coupled amplifier referenced to a duplicate system sampling the source output. Conventional lock-in and differential amplifiers were not found acceptable for the high precision sought.

Front Matter: Volume 9110

This PDF file contains the front matter associated with SPIE Proceedings Volume 9110, including the Title Page, Copyright information, Table of Contents, Invited Panel Discussion, and Conference Committee listing.

Video-camera-based optical bore gauge

We will present a new optical bore gage design based on, forming a ring of light on the inner surface of a bored hole and then superimposing arc sections of that ring onto one magnified video camera image which is fed to a computer for analysis. This unique 3D machine vision system provides a high-precision measurement of diameter and other geometric properties of the bore. THe presentation will outline the optics, describe the processing, and review calibration issues.