Low Coherence, Spectrally Modulated, Spherical Wavefront Probe for Nanometer Level Free-Form Metrology

To-date free-form optic manufacture is limited due to inadequate metrology to measure surfaces with free-form and conformal shapes, with large surface slopes and to the required measurement uncertainty. In this proposal we describe a new interferometric non-contact probe capable of measuring free-form optics with nanometer sensitivity. The probe has favorable metrology characteristics and uses a new interferometric modality allowing the advantages of low-coherence interferometry in common path interferometer designs. The combination of high acceptance angles and high sensitivity make possible the use of a simple three-orthogonal-axis metrology frame and fulfills the precision requirements demanded by NASA and industry. The projected data acquisition rates in excess of 10�kHz will provide an attractive manufacturing metrology tool.

Free-form optics, both axially symmetric and non-axially symmetric, enable small and lightweight imaging and projection optical systems. NASA needs small and light, high performance imaging performance. This PROBE's commercial application is to enable those optics to be manufactured. The primary road block to manufacturing high performance free form optics is metrology. 3D interferometers cannot measure free forms due to the reversing curvature. Stylus profilers, 3D contact profilers and coordinate measuring machines have the flexibility to measure the surface, but lack the accuracy, speed or data density to provide adequate process control feedback to manufacture the surfaces. The PROBE being developed in Phase I and implemented in Phase II is a unique approach that combines non-contact interferometric sensitivity with high surface slope acceptance. Thus the accuracy, speed and data density required for free form optics will be met. This combination will enable optical manufacturers to meet NASA's need to acquire nanometer level free-form optics.

The use of free form optics in commercial applications is massive, yet limited by the availability of high performance metrology. Cell phones, tablets, computers and remote mounted cameras all use axially symmetric free forms in the optical designs. The imaging quality of these systems is limited by the lens metrology, limiting the pixel density found in cell phone cameras to ~8 MegaPixels. Improved metrology will mean improved consumer electronics performance and higher manufacturing yields, and potentially lower costs to manufacture. Beyond consumer imaging systems, machine vision, security and defense related imaging and industrial instrumentation all could benefit from free form optics. Non-axially symmetric free forms are needed for projection systems and illumination systems. Again metrology is lacking to produce these optics in the surface accuracy, data density and speed required to be commercially viable. Again, improved metrology means improved performance and higher manufacturing yields, and potentially lower costs to manufacture. The PROBE and Phase II hybrid profiler will meet these commercial market needs for high density data across the whole surface. This technology promises to be the enabling technology to make free-form optics commercially viable.

This is early/mid-stage (TRL 5) — the most realistic path in is NASA SBIR/STTR, which funds small businesses and research institutions to develop technology aligned with NASA's needs (equity-free, phased funding). Check whether a current SBIR/STTR solicitation topic overlaps with this project's technology area, or contact the project directly (above) to ask.

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