Description: We propose an innovative, low coherence probe for rapid measurement of free-form optical surfaces based on a novel method of spectrally controlled interferometry. The key innovations are the use of a new interferometric modality and a novel non-contact optical probe that together measure high surface slope acceptance angles to nanometer sensitivity. When the probe is integrated with a precision motion, x, y, & z metrology frame (Phase II) (see Figure-1), it will meet NASA's need to measure free-form optical surfaces from 0.5 cm to 6 cm diameter ranging from F/2 to F/20, including slopes up to 20 degrees (with potential for 60 degrees), with an uncertainty targeted at 2 nm RMS. The probe operation does not require tilting to measure slopes. This results in this simplified cartesian metrology frame, also critical to achieve 2 nanometer measurement uncertainty. These features: nanometer resolution and 20 degree slope acceptance angle, have up to this time not been found in a single probe or sensor, non-contact or contact. This proposal integrates the spectrally controlled source and breadboard probe developed under a previous SBIR to develop a practical detection method reading the technology for a successful SBIR Phase II project.

Benefits: Free-form optics, both axially and non-axially symmetric, enable small and lightweight imaging and projection optical systems required by NASA.Future NASA missions with alternative low-cost science and small-sized payloads are constrained by the traditional spherical form optics. These could benefit greatly by the free-form optics as they provide non-spherical optics with better aerodynamic characteristics for spacecraft with lightweight components to meet the mission requirements- quoted from the NASA SBIR 2016 Phase I Solicitation. This application aims to enable those optics to be manufactured to the required tolerances to enable free-form optics to be used as envisioned. As of today there are no metrology tools available to meet the 2 nm RMS measurement uncertainty required to meet these mission requirements. Thus the primary road block to manufacturing high performance free form optics is metrology. 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 achieved. 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. 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. New telescope designs at MIT Lincoln Laboratory promise wider fields of view with higher lateral resolution. Again metrology is lacking to produce these optics in the surface accuracy, data density and speed required to be commercially viable. Improved metrology means improved performance and higher manufacturing yields, and potentially lower costs to manufacture. The PROBE and Phase II profiler will meet these commercial market needs for high density data across the whole surface. This technology promises to make free-form optics commercially viable.