Radius of Curvature

ZYGO laser interferometers are powerful and precise instruments for measurement and characterization  of optical components and systems.  One of the most common applications include the measurement of the radius of curvature. The radius of curvature is a fundamental and functional parameter of spherical optical surfaces, which requires quality control during manufacturing.

Interferometers are often the preferred solution for optical manufacturers as they possess key attributes and advantages, including:

  • Non-contact, 3D measurements
  • Precise, high quality data
  • Rapid part setup and measurement
  • Compatible with short- and long-radii surfaces
Radius of Curvature Measurement Test Setups

The radius of curvature of spherical surfaces is commonly determined using a phase measuring interferometer to identify the null positions at the best fit spherical surface (confocal) and center of curvature (cat’s eye) of the test optic. A linear guide provides motion between these positions and one or more displacement sensors are used to record the distance between the cat's eye and confocal positions and, hence, the radius of curvature.

Spherical Optic - Radius of Curvature MeasurementZYGO’s turnkey radius measurement solutions integrate industry-leading interferometers, reference accessories, opto-mechanical sub-systems, and metrology software.  A wide range of configurations are available from manual to automated solutions which typically involve one or more of the following components:

  • Phase-shifting laser Fizeau interferometer configured in a vertical (downward-looking) or horizontal orientation
  • Standard or premium transmission sphere
  • A guide rail positioning system equipped with an encoder or distance measuring interferometer (DMI) for highest precision
  • A manual or motorized five-axis mount to hold and align the surface under test
  • Passive vibration isolation table or workstation

Configuration Options

Verifire VTS Interferometer System - Vertical Test StationZYGO offers several product options for measuring radius of curvature, including horizontal and vertical configurations, with either manual or automated operation.

Verifire™ – Several configuration options are available. Please consult the Laser Interferometer Accessory Guide (PDF) for details. 

Verifire VTS / Workstations – ZYGO stand-alone turnkey interferometer workstations that provide precise radius of curvature measurements in an easy-to-use vertical orientation ideally suited to production environments with integrated passive vibration isolation and small footprint.

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