Aspheres and other complex optical surface shapes have become common to many optical systems as they offer wider design flexibility, lighter weight, smaller volume, and optimized optical performance.  CGHs are a natural extension of Fizeau interferometry, the industry standard for optics metrology, and offer significant benefits for metrology of aspheres.  But challenges remain for CGHs in production applications.

How Does Computer-Generated Hologram Work?

Modern optical designs utilize an increasingly wide range of optical surface shapes such as aspheres and freeforms which have been enabled by significant improvements in manufacturing and polishing capabilities. However, measuring aspheric surfaces is not always straightforward. That’s where a CGH comes in.

CGHs are known as a “null element” and work by diffracting light of the interferometer test beam in a specifically designed way to match the aspheric part under test.  When light is reflected back to the interferometer, the measurement behaves just like a “normal” interferometer measurement of a sphere or plano surface.

Aspheric and Freeform Optics Measurement Setup Using CGH

How CGH turns a spherical wavefront into an aspheric wavefront

Using CGHs for asphere and freeform optics metrology have numerous benefits over conventional aspheric methods including significantly faster surface measurement, high precision, high resolution and low total production cost.  However, the alignment of such test setups can be sensitive and can be difficult to implement for production volumes.

Looking Ahead

ZYGO is redefining the use of CGHs  with innovative and unique integration and alignment methods that make the measurement of complex surfaces easy and ideally suited for production-level volumes. It expands our metrology capabilities by enabling our customers to quickly and precisely qualify challenging surface shapes.

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