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Tilted Wave Interferometer Integrates Hexapod 6-axis Motion

The Mahr Tilted Wave Interferometer (MarOpto TWI 60) is a highly flexible interferometer for the quick and high precision measurement of aspheres.

An asphere or aspheric lens is an optic whose surfaces are defined by a polynomial equation. Aspheres are rotationally symmetrical around the optical axis, but their radius of curvature changes with the distance from the center. Aspheric lenses provide higher performance compared to conventional lenses, allowing a reduction in size, mass, and number of elements used – important features for miniaturization. Manufacturers of medical instruments, telescopes, and cameras use aspheres to improve their products. As the saying goes, “Where there is light, there must be shadow” and in the case of aspheres, the production and metrology of such lenses requires more complex and innovative technologies compared to traditional lenses.

The novel non-contact metrology system uses ‘Tilted Wave Front Interferometry (TWI)’ which makes use of the multi-axis flexibility and accuracy of hexapod parallel kinematics 6-axis motion systems to position a calibration sphere. The new measurement method, implemented by Mahr combines speed and flexibility into one process. The MarOpto TWI 60 machine can measure surface shapes with high lateral resolution directly on the production line with a measuring uncertainty of less than 50 nanometers. The metrology system acquires several subapertures that are active at different times and combines the individual interference patterns to form a single pattern.

During the data acquisition time of approximately 30 seconds, the entire surface of the asphere is measured at a high lateral resolution and with low measurement uncertainty. Most importantly, neither a CGH (Computer Generated Hologram) nor stitching is required.
Measured Surface Deviations
  • Flexible interferometric measurements of aspherical lenses without CGH
  • Measurements without the need for stitching
  • Short data acquisition time of approximately 30 seconds
  • Beam diameter 100 mm
  • Permitted aspherical deviation compared to a best-fit sphere approximately 1.5 mm

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