Page 142 - Chalcogenide Glasses for Infrared Optics

CHAPTER 5

Conventional Lens

Fabrication and

Spherical Surfaces

glass composition has been selected for development. The
optical and related physical properties have been determined,
A and the glass has been selected for fabrication into lenses.
A plate of the glass has been compounded, cast, and annealed. The
plate has been ground flat and parallel using a Blanchard Mill and
polished for final inspection. A serial number is assigned and inscribed
on the outside edge of the plate and transferred to the quality control
sheet along with all the evaluation data. The plate is turned over to
production for lens blank fabrication.

5.1 Lens Blank Preparation
In this particular instance, the plate is a 9-kg plate of Amtir 1, with
8 in diameter and 2 in thickness. The plate will be blocked in an oven
on a silicate glass plate using blocking wax. After cooling cylinders of
glass, the correct diameter for the lens will be diamond cored drilled
out of the plate as shown in Fig. 5.1. The plate is shown along with a
glass cylinder. The cylinders have a piece of ceramic epoxied the
length of the core to serve as the last material to be sawed through,
which prevents chipping of the edge of the lens blank. In Fig. 5.2, we
see glass cylinders glued together with epoxy end to end to increase
the number of blanks sawed at one time. For greater efficiency, other
end-to-end cylinders may be added side to side to increase the number
of blanks produced at one time. Figure 5.2 is a photograph of blanks
being sawed. Notice the white ceramic glued to the bottom of the
cylinder. The controls on the saw are set so that the thickness of each
blank is the same. The hole in the ID saw is large, with a 3.5-in diameter
which allows use on larger blanks or more ganged together. After the
sawing is complete, the sawn parts are placed in a container and
soaked in acetone to remove the ceramic and epoxy. Most of the lenses

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