Optical: systems and elements – Lens – With support
Reexamination Certificate
2000-04-14
2001-10-16
Epps, Georgia (Department: 2873)
Optical: systems and elements
Lens
With support
C372S034000
Reexamination Certificate
active
06304392
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to a method of matching the coefficient of thermal expansion of a plurality of structural members in an optical assembly and, more particularly, to a method of providing a thin spacer element at the end of one or more composite structural members associated with a laser optical assembly, where the combination of the coefficient of thermal expansion of the spacer element and the coefficient of thermal expansion of the structural member matches the coefficient of thermal expansion of a target structural member.
2. Discussion of the Related Art
Laser systems include structural elements that hold and mount optical components, such as mirrors, lenses, etc., in precise alignment with each other for proper laser operation. For example, certain laser systems include a resonant optical cavity where opposing mirrors are mounted to end plates of the cavity in very precise alignment with each other to maintain the lasing process. The laser system may be subjected to various disturbances, such as g-loads, shock, vibration and acoustical loads. These disturbances may act to misalign the optical components, thus degrading the operation of the laser system. Thus, the structural elements need to be rigid enough to prevent misalignment of the optical components under these disturbances.
In addition to the various disturbances mentioned above, environmental heat or heat caused by the operating temperature of the laser system can also cause misalignment of the optical components. Thermally induced misalignment is caused by certain structural support members associated with the laser system expanding at different rates in response to the heat. This thermal induced misalignment can be the result of the structural members having different lengths, the structural members having the same length but different coefficients of thermal expansion (CTE), or a combination of both. In one laser system, the end plates of the resonant cavity are connected together by four separate structural support members. If the CTE of the structural members are not matched, the heat may cause one member to expand in length more than the others. This length mismatch induces a tilt on the mirrors, which can cause optical misalignment, thus degrading the laser performance.
For those laser systems that need to be light-weight, for example, laser systems used in missile guidance systems on aircraft, the structural members are typically made of composite materials, such as carbon and graphite, to meet the weight requirements. The composite structural members must meet stringent coefficient of thermal expansion requirements for proper laser operation. The CTE of a composite structural member is controlled by material selection (fiber/resin system) and ply orientation. Presently, these types of composite structural members are made by wrapping a ply layer made of the composite material around a suitable substrate. The orientation of the fibers in the ply layer determine the CTE of the resulting member, and thus the ply layer must be accurately wound to meet the CTE tolerances of the laser system. The present manufacturing processes of these types of composite structural members for optical assemblies can not ensure proper orientation of the material to the degree required to meet CTE requirements, which are dictated by optical alignment requirements. Therefore, those structural members that do not meet the proper CTE requirements are discarded, thus incurring waste.
What is needed is a technique for controlling the CTE of composite structural members used to support optical components in a laser system. It is therefore an object of the present invention to provide such a technique.
SUMMARY OF THE INVENTION
In accordance with the teachings of the present invention, a technique for controlling the coefficient of thermal expansion (CTE) of composite structural members in an optical assembly is disclosed, that maintains precise alignment between optical components. This technique includes removing a narrow end portion of the structural member and replacing the removed portion with a metal shim member. The metal shim member is made of a material having a CTE that compensates for the overall CTE mismatch between the composite structural members.
In one embodiment, the apparent CTE of the several composite structural members used in a particular optical assembly can be made identical or nearly identical by the following procedure. First, each of the structural members are cut to the same length and the CTE of each structural member is measured. The structural member with the highest CTE is selected as the “target” member having the ‘target’ CTE. Then, the other structural members are modified, if necessary, by replacing an end portion of each member with a metal spacer having the appropriate thickness. The material and thickness of the spacer is selected so that the CTE of the combination of the spacer and the structural member matches the “target” CTE, and the original length of the structural member is retained.
Additional objects, advantages and features of the present invention will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 4613972 (1986-09-01), Bettman
patent: 4696010 (1987-09-01), Eastman
patent: 4989217 (1991-01-01), Ostler
patent: 5031189 (1991-07-01), Stuhler et al.
patent: 5309282 (1994-05-01), Feldman et al.
Bell Doug M.
Florentino Caesar C.
Rahhal Waleed F.
Tinti Robert
Epps Georgia
Harness Dickey & Pierce
Seyrafi Saeed
TRW Inc.
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