Lyle G. Shirley

BISPECTRAL ANALYSIS OF THE WAVELENGTH DEPENDENCE OF SPECKLE : REMOTE SENSING OF OBJECT SHAPE

A bispectrum-based technique is presented for analyzing the wavelength dependence of the laser speckle intensity from diffuse three-dimensional objects. This new technique yields extremely high-resolution measurements of the scattering object’s range-resolved laser radar cross section. These measurements are useful in remote sensing of an object’s size, shape, and surface-scattering properties. The technique is illustrated on laboratory measurements obtained with a tunable Ti:sapphire ring laser.

High-precision surface profiling with broadband accordion fringe interferometry

Accordion fringe interferometry (AFI) is an active-triangulation, surface-profiling technique based on projecting interference fringes onto the surface of an object from a source at one location and viewing with a camera at another location. Interference fringes have the advantage of infinite depth of field, which allows large or complex objects to be illuminated without the need for source focus. Conventional AFI produces the interference fringes by using a laser to form two mutually coherent source points. Coherent illumination, however, produces speckle in the image that limits range resolution. A technique that significantly improves the range resolution of AFI is described and demonstrated experimentally. This technique uses broadband illumination to eliminate speckle effects, while maintaining the advantages of interference-fringe projection.

Comparison of surface contour measurements based on speckle pattern sampling and coordinate measuring machines

A noncontact 3D imaging technique based on tunable lasers is investigated to assess its performance compared to commercially available methods. In this technique, an object is flood illuminated by an external cavity tunable diode laser. As the laser frequency is scanned, the time-varying speckle-intensity pattern provides information about the depth of the scattering object. The patterns are recorded with a CCD camera, and the objects height profile is then extracted from the 3D fast Fourier transform. This paper presents the first quantitative comparison of results using this technique with those from a well-known standard instrument--the coordinate measuring machine. The object used for the comparison is a pressed sheet-metal part with dimensions of approximately 1-- by 100 by 20 mm. We found the standard deviation (sigma) of the difference between the two profiles to be less than 0.2 (Delta) z, where (Delta) z is the raw range resolution of the speckle-pattern-sampling technique.