NMF™ Metrology
Precision Metrology for Aspherical and Freeform Optics
NMF systems are built to meet the demands of modern optical manufacturing—where complex surfaces and nanometer-level tolerances are the norm. Leveraging non-contact confocal sensing and a unique cylindrical-coordinate architecture, NMF enables fast, stable, and highly accurate metrology of aspheres, freeforms, and more.
Measuring with NMF (Nanometer-precision Measurement of Freeform Optics: NANOMEFOS)
In optical manufacturing, you can only produce what you can accurately measure. As aspherical and freeform surfaces become more advanced, high-precision metrology is the key to unlocking their full performance. NMF systems, built on TNO’s proven NANOMEFOS technology, were developed specifically to meet this need. By combining versatility, large measurement capability, non-contact probing, speed, and nanometer-level accuracy, NMF delivers a powerful solution for 3D form measurement of complex optics.
A Universal Cylindrical-Coordinate Measurement Platform
At the core of the NMF design is a cylindrical-coordinate measurement architecture—often described as a “giant CD player.” This unique setup enables true versatility. Whether the optic is flat, spherical, aspherical, freeform, convex, or concave, the system can measure it with exceptional precision.
The optic is mounted on a high-stability air-bearing spindle that rotates continuously, typically at one revolution per second. A non-contact confocal probe is mounted on a dedicated Ψ-axis, keeping it perpendicular to the surface—or the best-fit rotationally symmetric surface for freeforms. The probe moves via precision R- and Z-stages, allowing it to reach any point within the measurement volume.
High-Performance Non-Contact Confocal Probe
The NMF optical probe is based on the confocal principle and features a high-NA objective combined with a patented dual-stage servo design. Traditional high-resolution optical probes have a very shallow depth of focus, often only a few micrometers. Moving heavy mechanical stages rapidly enough to maintain focus would introduce unwanted dynamics and reduce measurement quality.
NMF overcomes this challenge through its dual-stage probe mechanism. The main R and Z stages remain stationary while only the lightweight objective—about 50 g—actively tracks the surface. This dramatically improves system dynamics and extends the effective range of the probe from micrometers to several millimeters. The result is fast, accurate measurement even on optics with departures of ±2.5 mm and local slope variations up to ±20° from the best-fit asphere.
Stabilized Metrology System for Nanometer Accuracy
To guarantee traceable and repeatable results, NMF incorporates a dedicated metrology system based on a stabilized HeNe interferometer and a Silicon Carbide reference frame. The probe’s position is measured interferometrically relative to this ultra-stable frame, forming a patented short metrology loop. Meanwhile, capacitive sensors track spindle error motion directly against the frame.
Through this combination of rigid design, thermal stability, and active error compensation, NMF systems achieve repeatability below 1 nm RMS and deliver the accuracy required for today’s most challenging optical surfaces.
NMF Metrology Systems
The NMF series is built for modern optics manufacturing, where precision, speed, and universality are essential. Developed from TNO’s proven NANOMEFOS technology, NMF systems provide accurate, non-contact 3D form measurement for flat, spherical, aspherical, and freeform optics.
With a stable cylindrical-coordinate platform and dual-stage confocal probe, each system in the NMF family delivers nanometer-level accuracy with rapid measurement cycles—ideal for high-end applications in aerospace, semiconductor, defense, and advanced imaging.
Learn More About NMF Metrology
Explore how NMF metrology systems can expand your capabilities and streamline your production.
Request a consultation today to find the right fit for your measurement needs.