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Potting Optical Elements in Cells Eric Booen December 8 th , 2008 OPTI 521

Potting Optical Elements in Cells Eric Booen December 8 th , 2008 OPTI 521. Objective. Introduce Concept of Potting Optical Components Present Adhesive Material Properties Describe Failure Modes of Adhesives Suggest Design Criteria and Assembly Processes. Potted Optical Assemblies.

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Potting Optical Elements in Cells Eric Booen December 8 th , 2008 OPTI 521

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  1. Potting Optical Elements in Cells Eric Booen December 8th, 2008 OPTI 521

  2. Objective • Introduce Concept of Potting Optical Components • Present Adhesive Material Properties • Describe Failure Modes of Adhesives • Suggest Design Criteria and Assembly Processes

  3. Potted Optical Assemblies • Glass Optic rests on machined surfaces • Metal cell or mount • Adhesive Creates Bond • Can reduces part count, weight, cost, and ease of assembly when compared to mechanical mounts

  4. Applications • Applications with small temperature ranges • Optics with low LOS sensitivity (mrad/mrad) • Tolerance Required • Additional testing should be completed to verify assumption in tolerance analysis

  5. Adhesive Materials • Epoxies • High to moderate stiffness and strength • Rule of thumb: E = 150 ksi, Shear strength = 2000 psi • Urethanes • Not recommended for use at high temperature • Commonly used for staking • Acrylics • Quick bonds, high strength, UV cure on occasion • Silicone Elastomers • Flexible, RTVs, high CTE • For more information see References 2 and 3

  6. Bond Failure • Adhesive Failure • Critical damage across the bond interface1 • Decreased by surface preparation, use of primer, proper curing process • Cohesive Failure • Critical damage to bulk material of bond1 • How you design your bonds to fail

  7. Design • CTE mismatch causes shear stress • See Reference 1 alternate stress calc. • Bond size must also prevent shear due to shock loading • F = mgashock • =F/A • Vibration environment may drive bond stiffness requirements

  8. Assembly • Hole size tolerances should be determined based on gap requirement for adhesive material and optic tolerance • Gap tolerances recommended by manufacture or based on experience • Maintain gap through cure temperature • Compliant shims • Spacer Balls added to adhesive • Cure adhesive as recommended then temperature cycle through operating temperature range • Cell is ready for system integration

  9. References • Blain Olbert, “Adhesive Selection and Characterization – What you don’t know can kill you,” USAO Engineering Seminar (Aug 2004) • Daniel Vukobratovich, “Introduction to Opto-Mechanical Design,” Notes, (2008). • Paul R. Yoder, Opto-Mechanical Systems Design, 3rd, CRC Press (2006).

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