4D Technology (United States)

We present a method for measuring surface roughness of 2μm RMS and below in a single camera frame acquisition. The interferometer employs two camera sensors with pixelated phase-masked detector arrays. Each camera uses a different wavelength of light to facilitate a two-wavelength dynamic interferometric measurement. The large effective wavelength derived from the two wavelengths enables phase unwrapping over surface roughness steps that visible light typically cannot handle. This allows for the instantaneous measurement of traditionally challenging surfaces, such as machined, ground, or sandblasted metal, using a single camera frame acquisition.

Precision-machined parts in aviation, automotive, and manufacturing industries have tightly controlled tolerances for the dozens of small geometries spread throughout a single part. These parts can also have stringent specifications for any defects along the surface. The sheer number of measurements needed on each part paired with the volume of parts demands the ability to take not only one measurement quickly, but dozens in a rapid process. Coupling a polarized structured light technique with robotic automation allows for accurate measurements at volume. This paper will discuss automated optical measurements of stationary parts, parts moving on a production line, and rotationally symmetric parts on a rotary stage. The paper will also look at ongoing projects combining the automated polarized structured light method with bright field techniques to accomplish automatic defect identification and inspection.

For three decades, my work in optics has encompassed a wide variety of research projects and commercial products that all relied on the fringes produced from optical interference to measure different physical parameters. This paper describes some of the most unique experiments and novel commercial products including: measurement of air velocity in wind tunnels, residual stress in metals, space telescope performance in vacuum chambers and surface shape of turbine blades with a hand-held instrument. Some of these ideas achieved commercial success; all were collaborations with other scientists, including the late Chandra Vikram.

In the last decade, imaging polarimeters based on micropolarizer arrays have been developed for use in terrestrial remote sensing and metrology applications. Micropolarizer-based sensors are dramatically smaller and more mechanically robust than other polarimeters with similar spectral response and snapshot capability. To determine the suitability of these new polarimeters for astronomical applications, we developed the RIT Polarization Imaging Camera to investigate the performance of these devices, with a special attention to the low signal-to-noise regime. We characterized the device performance in the lab, by determining the relative throughput, efficiency, and orientation of every pixel, as a function of wavelength. Using the resulting pixel response model, we developed demodulation procedures for aperture photometry and imaging polarimetry observing modes. We found that, using the current calibration, RITPIC is capable of detecting polarization signals as small as ∼0.3%. The relative ease of data collection, calibration, and analysis provided by these sensors suggest than they may become an important tool for a number of astronomical targets.

Cost, weight, performance, and lifetime requirements for precision components used throughout the aerospace and defense industries are driving innovative mechanical designs, manufacturing processes and use of new materials. In turn, these advanced components typically require tighter dimensional and surface tolerances to function as designed. Scratch testers, microscope-based systems, and other traditional metrology systems are inadequate for roughness, small-scale geometry, and defect determination on many of these parts. This talk will examine the advantages and disadvantages of some of the new technologies developed to provide more robust, versatile, and sensitive measurements of precision components for advanced manufacturing environments.

This paper describes recent advances in developing an automatic background leveling algorithm for a new, novel interference microscope system and presents images and data of live biological samples. The specially designed optical system enables instantaneous 4-dimensional video measurements of dynamic motions within and among live cells without the need for contrast agents. "Label-free" measurements of biological objects in reflection using harmless light levels are possible without the need for scanning and vibration isolation. This instrument utilizes a pixelated phase mask enabling simultaneous measurement of multiple interference patterns taking advantage of the polarization properties of light enabling phase image movies in real time at video rates to track dynamic motions and volumetric changes. Optical thickness data are derived from phase images. This data is processed with an automatic background leveling routine which separates the objects from the background by thresholding the calculated gradient magnitude of the optical thickness data. Low-order Zernike surfaces are fit to the unmasked background pixels and the resulting background shape is removed. This method effectively eliminates background shape for datasets containing both large and small objects. By applying this method to many sequential frames, it results in all the frames having the same mean background value across all frames which is essential for quantitatively montoring time-dependent processes.

A compact, vibration insensitive interferometer design that is well suited for measuring optics while mounted in-situ on polishing equipment is presented. The system employs a single frame phase sensor that permits acquisition in tens of microseconds to mitigate the effects of vibration or relative motion with the test part. The theory of operation is presented along with experimental test results, which characterize repeatability and precision under static and high-vibration conditions.

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The development of the pixelated polarization camera is enabling dynamic interferometry, a new metrology technique that is insensitive to vibration and suits use in an industrial environment.