Optical Activitiesin Industry

reported by FRANK COOKE, 59 Summer Street, North Brookfield, Mass. 01535. Mr. Cookewelcomes letters, news and comments for this column which should be sent to him at the above address

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Toroidal mirror of evaporated silicon carbide

Frank Cooke, Stephen Fantone, and Ben Fuchs

Frank Cooke is with Frank Cooke, Inc., North Brookfield,Massachusetts 01535; S. Fantone is with Polaroid Corpo-ration, Cambridge, Massachusetts 02138; and B. Fuchs iswith Lawrence Livermore National Laboratory, Liver-more, California 94550.

Making this evaporated silicon carbide toroidal mirror was a joint effort. Stephen Fantone furnished theexpertise to test the mirror optically. Ben Fuchs provided the inspiration and polishing knowledge. FrankCooke devised and made the special machinery needed and kept the ball rolling.

1 The short radius of the mirror is 16.5 in., the long 4510 in.A steel wheel with a crown of 0.002 in. was plated withdiamond by the Norton Company. This crown took care of theshort radius; a cam below dictated the long. The pictureshows this form wheel just above the mirror. Over an hour wasneeded to travel the length, because of the hardness.

2 The long radius was controlled by a cam on an asphericgenerator. The picture shows the follower resting on the cam.As it moves slowly along, the entire assembly carrying thediamond wheel rises and falls. This procedure gave sagittalaccuracies of +0.0002 in.

0003-6935/87/112050-04$02.00/0.© 1987 Optical Society of America.

2050 APPLIED OPTICS / Vol. 26, No. 11 / 1 June 1987

3 Preparation for polishing was achieved by lapping on a33-in. diam steel drum which had a 0.014-in. convex crown.The pencil points to the mirror resting on this lapping drum.The drum rotates slowly while the mirror is moved from left toright. All drives are variable speed. Boron nitride was thelapping compound used.

5 A special polishing machine was built; it rocks the work intwo directions while the mirror rests on a preformed pitch lap.More than 200 carats of various diamond powders were neededover a polishing time of some 500 h. The picture shows theconvex polishing lap and the mirror beside it.

4 The polishing machine shows work on the lap and theweights on it to speed stock removal. The eccentrics andconnecting rods can also be seen.

6 The pencil points to the convex Pyrex pressing lap. Thislap was made on the large drum.

1 June 1987 / Vol. 26, No. 11 / APPLIED OPTICS 2051

7 The pressing lap rests on the pitch polishing lap. 10 A Tropel SMI interferometer is shown with the mirror at agrazing angle and two auxiliary lenses in place. This testingmethod came from Stephen Fantone and worked well.

8 The depth of the long radius (4510 in.) is measured by abar spherometer.

11 The interferogram shows the mirror to be irregular andzone free but concave. How nice it is when physical andoptical tests agree. The surface smoothness was better than10 A.

9 The sagittal depth of the short radius is determined to +0.000010 in.

2052 APPLIED OPTICS / Vol. 26, No. 11 / 1 June 1987