Method of manufacturing a foraminous plate

A method is shown to make a relatively thick foraminous plate wherein the inside of each one of the foramina is treated as desired, the disclosed method comprising the steps of working a strip of a metallic or plastic foil to form transverse grooves, treating the worked strip to cause the surfaces of such grooves to have desired qualities and then rolling the strip (or stacking portions thereof) to form the desired foraminous plate.

BACKGROUND OF THE INVENTION 
This invention pertains generally to the fabrication of optical elements 
and particularly to a method of making elements wherein the optical 
characteristics are controlled. 
It has been known for some years in the field of fiber optics that certain 
lens-like elements (sometimes referred to as "channelplates" or 
"collimators") may advantageously be used to filter light. For example, in 
my copending application Ser. No. 726,079 entitled "Optical Apparatus", 
filed Sept. 23, 1976 U.S. Pat. No. 4,183,664 and assigned to the same 
assignee as this invention, a foraminous plate wherein the walls of the 
individual foramina are rendered opaque may be used to pass light 
originating in a small selected field and to reject light from any point 
outside such field. 
Unfortunately, when the above-mentioned foraminous plate is made according 
to any known method, it is very difficult and expensive to fabricate a 
satisfactory plate. The dimensions of the individual ones of the foramina, 
coupled with the requirement that the inner wall of each foramen be 
substantially the same as each other one, explain why known methods are 
difficult and expensive. For example, in a typical case where it is 
desired to define a field of view with an angular size in the order 
1.degree. and each foramen is cylindrical, with a diameter say of 
400.times.10.sup.-6 inches, the length of each foramen must be 
approximately 22,800.times.10.sup.-6 inches or 0.023 inches in length. For 
proper operation, the optical characteristics of the wall of each foramen 
must be the same along its length, i.e. the wall must be totally 
nonreflective or reflective or have some other desired characteristic. It 
is manifest, then, that any treatment of the walls of the literally 
thousands of foramina making up a channelplate of modest size (there being 
about 202,800 foramina in a channelplate of 1" diameter) is most difficult 
when, as is now the practice, such foramina are made by drawing bundles of 
hollow optical tubing or by treating photosensitive glass. 
SUMMARY OF THE INVENTION 
With the foregoing in mind it is a primary object of this invention to 
provide an improved method of fabricating a channelplate wherein the 
surfaces of the foramina in such plate are exposed during fabrication. 
Another object of this invention is to provide a method as above wherein 
the foramina may be formed in materials other than glass or other plastic 
material. 
Still another object of this invention is to provide a method of 
fabricating a channelplate as above wherein the wall of each foramen may 
be covered with materials of differing optical characteristics. 
The foregoing and other objects of this invention are attained by following 
the method generally characterized by scribing parallel indentations 
across the complete width of a tape-like base of a selected material, then 
treating the surfaces of such tape-like base in accordance with an optical 
characteristic desired for a completed channelplate and then either 
winding a scribed and treated strip or stacking a plurality of such strips 
to form a channelplate of a desired size.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to FIG. 1, it may be seen that a tape-like base, hereinafter 
referred to as a strip 10, is pulled from a feed roll (not shown) in any 
convenient manner (not shown) to a position on a platen 12 under a 
scribing tool 14. For expository reasons it will be assumed here that the 
strip 10 is aluminum foil with a thickness of 100 microns and a width of 5 
centimeters. It will be obvious, as the description of the invention 
proceeds, that materials other than aluminum foil may be used and that the 
dimensions of the strip 10 may be changed. That is to say, depending upon 
the chosen way in which the strip 10 is to be worked and the desired 
configuration of the final product, other materials (including various 
kinds of plastics) having appropriate characteristics may be used and the 
dimensions of the strip 10 may be changed. The platen 12 preferably 
incorporates a conventional vacuum holding arrangement whereby a partial 
vacuum is drawn in any convenient way (not shown) under the strip 10 near 
the scribing tool 14. The latter preferably is a conventional 
diamond-tipped cutting tool of the type used to scribe lines in 
diffraction gratings, adjusted here to scribe a substantially square 
groove 16 in the strip 10 from one edge thereof to the other. It will be 
noted here in passing that, because the final product resulting from the 
process being described is intended to have a very large number of 
accurately positioned apertures corresponding to a similar number of 
accurately machined grooves such as the substantially square groove 16, 
the scribing tool 14 is preferably mounted on gas bearings in a machine 
having tolerances in the order of the tolerances encountered in optical 
work. The strip 10 is then repetitively moved in any convenient manner 
(not shown) along its length a predetermined amount (say 50 microns) and 
the scribing process is repeated until a desired length of the strip 10 is 
scribed. In passing it should be noted that a plurality of scribes to 
scribe 10 could be positioned in a known manner at stations along the 
length of the strip 10 to allow more than one square groove 16 to be 
formed at any particular time. It will also be noted that with the given 
thickness of the strip 10 and the given dimensions and spacing of the 
square grooves, 25% of the original material of the strip 10 is removed 
and maximum dimension of the field of view of the still to be completed 
channelplate will be approximately 1.15.degree. (or 0.020 radians). 
After scribing is completed the strip 10 is passed through a processing 
station 18, here arranged to black anodize the strip 10. Alternatively, 
according to the invention the processing station 18 could be arranged to 
reduce any oxide on the strip 10 and to coat the surface to prevent 
reoxidation if a reflective surface is desired for each foramen of the 
still to be completed channelplate or still alternatively a layer of a 
secondary emitter could be applied. After being passed through the 
processing station, the strip 10 is wound on a takeup spool 20 having a 
round bobbin 21 (to form the channelplate shown in FIG. 2A) or a flat 
bobbin 23 (to form the channelplate shown in FIG. 2B). Alternatively, 
predetermined lengths of the strip 10 may be cut by any convenient means 
(not shown) and the lengths stacked on top of each other (to form, in 
accordance with prior art, the channelplate shown in FIG. 2C). After 
winding or stacking, the final step (not shown) is to secure the almost 
complete channelplate in any convenient manner. That is to say, the rolled 
or stacked lengths of the strip 10 are inserted in a frame (not shown) or 
thermally bonded to provide a finished product which will maintain its 
desired shape. It will now be appreciated that the form of the completed 
channelplate shown in FIG. 2A is similar to the form of the channelplate 
shown in my copending application entitled "Optical Apparatus", Ser. No. 
726,079, filed Sept. 23, 1976 and assigned to the same assignee as this 
application. It will also be appreciated that, because the channelplate in 
the just-cited application was fabricated by joining a large number of 
hollow glass tubes (each of which had to be treated so that its interior 
would be nonreflective), the just-described method of manufacture is 
easier to perform with a more desirable end product. 
A moment's thought will make it clear to one of skill in the art that the 
present concept of forming a channelplate (wherein the entire length of 
each one of a large number of foramina is exposed during the manufacturing 
process) may be carried out in many ways other than the way described. For 
example, if the desired configuration of the final product is such that 
the foramina need not have the degree of straightness attained by 
following the described method, i.e. if it were satisfactory to allow each 
one of the foramina in the final product to be curved, the scribing tool 
14 (or several such tools) could be mounted on rotatable arms and the 
strip 10 could be moved continuously or intermittently during the cutting 
process. Further, of course, it is obvious that the shape of each one of 
the substantially square grooves 16 may be changed to allow grooves to be 
made without scribing. Thus, the grooves may be made using laser cutting 
methods or by selectively melting portions of the strip 10. Still further, 
it will be obvious that the grooves may be filled with, for example, a 
vitreous material transparent (or substantially so) to the particular type 
of radiation to which the completed channelplate will be exposed. In view 
of the foregoing, it is felt that this invention should not be restricted 
to its disclosed embodiment, but rather should be limited only by the 
spirit and scope of the appended claims.