On-machine and in-process surface metrology for precision manufacturing

A software configurable optical test system (SCOTS) based on the geometry of the fringe reflection or phase measuring deflectometry method was developed for rapidly, robustly, and accurately measuring large, highly aspherical shapes such as solar collectors and primary mirrors for astronomical telescopes. In addition to using phase shifting methods for data collection and reduction, we explore the test from the point view of performing traditional optical testing methods, such as Hartmann or Hartmann-Shack tests, in a reverse way. Using this concept, the slope data calculation and unwrapping in the test can also be done with centroiding and line-scanning methods. These concepts expand the test to work in more general situations where fringe illumination is not practical. Experimental results show that the test can be implemented without complex calibration for many applications by taking the geometric advantage of working near the center curvature of the test part. The results also show that the test has a large dynamic range, can achieve measurement accuracy comparable with interferometric methods, and can provide a good complement to interferometric tests in certain circumstances. A variation of this method is also useful for measuring refractive optics and optical systems. As such, SCOTS provides optical manufacturers with a new tool for performing quantitative full field system evaluation.

Software configurable optical test system: a computerized reverse Hartmann test

Review of phase measuring deflectometry

Deflectometric methods that are capable of providing full-field topography data for specular freeform surfaces have been
around for more than a decade. They have proven successful in various fields of application, such as the measurement of
progressive power eyeglasses, painted car body panels, or windshields. However, up to now deflectometry has not been
considered as a viable competitor to interferometry, especially for the qualification of optical components. The reason is
that, despite the unparalleled local sensitivity provided by deflectometric methods, the global height accuracy attainable
with this measurement technique used to be limited to several microns over a field of 100 mm. Moreover, spurious
reflections at the rear surface of transparent objects could easily mess up the measured signal completely. Due to new
calibration and evaluation procedures, this situation has changed lately. We will give a comparative assessment of the
strengths and – now partly revised – weaknesses of both measurement principles from the current perspective. By
presenting recent developments and measurement examples from different applications, we will show that deflectometry
is now heading to become a serious competitor to interferometry.

Deflectometry challenges interferometry: the competition gets tougher!

In a previous paper, the University of Arizona (UA) has developed a measurement technique called: Software Configurable Optical Test System (SCOTS) based on the principle of reflection deflectometry. In this paper, we present results of this very efficient optical metrology method applied to the metrology of X-ray mirrors. We used this technique to measure surface slope errors with precision and accuracy better than 100 nrad (rms) and ~200 nrad (rms), respectively, with a lateral resolution of few mm or less. We present results of the calibration of the metrology systems, discuss their accuracy and address the precision in measuring a spherical mirror.

Non-null full field X-ray mirror metrology using SCOTS: a reflection deflectometry approach

A contactless fingerprint sensor provides deformation-free, high-quality fingerprint images and offers users a cleaner and
more comfortable measurement environment Here we propose and design an innovative prototype optical, contactless,
compact, fingerprint sensor that quickly produces high-quality, high-contrast interoperable fingerprint images A proofof-
concept contactless, aliveness-testing (CAT) fingerprint sensor, which is connected to a PC via a firewire cable, was
constructed and is currently operating in our laboratory The CAT sensor affords a more user-friendly interface
compared to existing contactless fingerprint sensors and also provides robust aliveness testing and spoof detection In
this paper, we present the imaging system design concepts, finger aliveness detection techniques, and the user-friendly
interface approach Various fingerprint matching results using the CAT sensor device are also presented and discussed

A novel contactless aliveness-testing (CAT) fingerprint sensor

Illumination is critical to achieve high-contrast, contactless fingerprint images. In this paper, we report results of
fingerprint imaging experiments performed under different illumination conditions. We studied how polarization states,
illumination wavelength, detection wavelength, and illumination direction influence the contrast of fingerprint images.
Our research findings provide a selection rule for optimum illumination and a basis for us to construct an illuminator that
generates uniform illumination and high-contrast contactless fingerprint images.

Illumination scheme for high-contrast, contactless fingerprint images

Software Configurable Optical Test System (SCOTS), a computerized “reverse Hartmann test,” can rapidly quantitatively measure complex 3-D specular surfaces, for instance solar collectors, faceted automotive headlight or free-form surfaces without complex calibrations.

A low-cost, flexible, high dynamic range test for free-form illumination optics

We propose two parameters CS and AS for fast estimating sensitivities to constant coma and linear astigmatism in a
misaligned lens system. We show that these figures correlate well with actual tolerancing of some lens systems.

Lirong Wang

Papers

Software configurable optical test system: a computerized reverse Hartmann test

A novel contactless aliveness-testing (CAT) fingerprint sensor

Illumination scheme for high-contrast, contactless fingerprint images

A low-cost, flexible, high dynamic range test for free-form illumination optics

Merit figures for fast estimating tolerance sensitivity in lens systems