A highly efficient method for splitting the probe beam produced by a scanning low-coherence distance-measuring
interferometer (SLCDI) is presented. The SLCDI is used to measure thicknesses of materials with thicknesses in the
range of 12 microns-50 mm, with a repeatability of 0.1 microns. The measurements are made optically with a beam with
a wavelength of 1.3 microns. The SLCDI is also capable of simultaneous measurement of a stack of multiple films.
Splitting of the beam from the SLCDI probe to create a multi-point probe allows for multiple, simultaneous
measurements to be made at a surface. An advantage of this capability is that it provides the ability of to measure the
surface normal at each of the surfaces that are under test. The operation of the SLCDI will be described along with how
the operation impacts the requirements for the multi-point probe system. The requirements are discussed from the
standpoint of the coherence length of the SLCDI source and the operational usage of the probe. The splitting is achieved
through the use of polarization components. The function and performance of the resulting probe is also discussed.
Conformal windows reduce drag, but introduce optical aberrations. Corrector optics minimize such optical
aberrations, but they feature complex surfaces that cannot presently be measured interferometrically. To address
this problem, ASE Optics has developed a non-contact "Quad-Probe" that measure the position and orientation
of surfaces. By scanning the probe over the surface of the optic, a 3D model of the interior and exterior surfaces
can be built. Furthermore, the Quad-Probe can be used inside a polishing machine, and feedback from the
Quad-Probe can be used to guide the scanner in measuring an unknown part.
Despite increasing demand for freeform optical elements, at present there are no commercial systems to measure
such components. In previously published research we demonstrated that a scanning low-coherence dual-wavelength
interferometer can accurately measure the transmitted wavefront of hemispheric dome optics by
mapping the optical thickness of the dome as a function of probe probe position. To address the issue of more
generalized freeform surfaces, we have developed a new probe for the interferometer. This probe incorporates
a reference surface and simultaneously projects four beams. This allows the instrument to measure both the
position and orientation of the surface with respect to the probe as the probe is scanned over the object. Both the
interior and exterior surfaces can be measured simultaneously. Furthermore, by overlapping the measurement
regions, the redundant data can be used to minimize some forms of measurement error.
We present experimental results for a low-coherence, dual-wavelength metrology system capable of measuring
simultaneously both optical thickness and surface ﬁgure. The system measures optical thicknesses as thin as
12 microns to as wide as 12 mm with an accuracy of 0.1 microns. The current system scans at a resolution of
50 microns, which is limited by the spot-size of the measurement beam. We validate that SLCDI yields results
in agreement with traditional interferometry and demonstrate its ability to measure aspheric “saddle” mirrors
and complex three-dimensional surfaces.
Modern missile domes are up to 7 inches in diameter, subtending an angular aperture of 180 degrees. Quantifying
the transmitted wavefront of these domes is critical for quality control, but such optics are diffcult or impossible
to measure using conventional interferometric techniques. To address this issue, we have developed a non-contact
measurement process that uses a technology similar to optical coherence tomography (OCT) to map the optical
thickness of the dome over its full aperture. The technique has been termed Scanning Low Coherence Dual
Interferometry (SLCDI), and has the unique ability to measure the optical thickness of component layers within
multilayer domes to an accuracy of 0.1 micron. In this paper we demonstrate the capability of SLCDI by
measuring the optical thickness of a seven inch diameter BK7 dome at a sampling resolution of 0.2 mm. SLCDI
yields results comparable to those from a Zygo interferometer, and the two methods agree to within 0.2 micron.
From this we conclude that SLCDI is an effective tool for measuring the optical quality of hemispheric domes.
WS1058: Critical Skills for Compelling Research Proposals
A successful research proposal requires hundreds of hours of effort, and the stakes are high. Just beginning the process is intimidating. This interactive workshop teaches students to overcome their apprehensions by starting with small steps, building a strong proposal from the inside out.
SC1170: The Very Least You Need To Know About Optics
This course is tailored to the thousands of professionals working in the optics industry who are not engineers. The curriculum develops a foundational understanding of the core principles of optics by relying on visual examples rather than mathematics. Upon completion of the course, students will be able to follow the thread of most technical optical presentations, and they will be well-positioned to study more specialized topics related to specific industries. The class size is limited to 20 participants. <strong>Early registration is recommended.</strong>