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Plasma CVM (Chemical Vaporization Machining)

Plasma CVM, or chemical vaporization machining, is a method of non-contact fabrication using plasma generated at normal atmospheric pressure. This ultra-precise fabrication technique is based on a totally new concept.
Unlike conventional manufacturing methods including grinding and polishing, plasma CVM is an ultra-precise method for optical components that is capable of achieving high shape accuracy without causing damage to their surfaces.


A lens is shaped using an electrode; plasma generated at the tip of the electrode is scanned over the lens surface.




In plasma CVM, an electrode is placed in a gas mixture of sulfur hexafluoride (SF6) and helium, at a pressure of about one atmosphere. Plasma is generated near the electrode tip by applying rf power.
To fabricate a lens, for example, the electrode (with plasma around the tip) is brought close to the surface of the lens blank.
The plasma causes the SF6 to disassociate, and the resulting fluorine radicals chemically react with the surface atoms of the lens blank. The reactive products evaporate, leading to the removal of the surface. In this process, by scanning plasma so as to remove shape errors on the surface as shown in the photo, the lens with high accuracy can be achieved.

The plasma CVM method has a shape accuracy of 0.1 μm or better (PV), and a surface roughness of 0.5 nm or better (Ra).


Example of small-diameter complex shaped mirror:
Square aspherical mirror for laser beam intensity profile transformation

(Joint research by the Central Research Institute of Electric Power Industry,
Osaka University Mori Research Laboratory and Nikon)

If the electrode is changed to match the specific shape requirements, such as for generating a very narrow plasma "pencil," it is possible to fabricate small and complex shapes that are not possible using mechanical grinding and polishing.
For example, the complex shape of this small-diameter mirror is only possible with plasma CVM.
Moreover, because Plasma CVM is a non-contact method, ultra-precise fabrication of thin-wall and minute materials without deflection or contortion is possible.
With these characteristics, Plasma CVM is expected to be used not only in lens and mirror processing but also in nanotechnologies, including micromachinery, and the aerospace field.


Renewed April 2007

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