MRF Applications: Measurement of Process-dependent Subsurface Damage in Optical Materials using the MRF Wedge Technique

Conference · Wed Nov 02 04:00:00 EST 2005

DOI:https://doi.org/10.1117/12.638839· OSTI ID:883569

Menapace, J A; Davis, P J; Steele, W A; Wong, L L; Suratwala, T I; Miller, P E

Understanding the behavior of fractures and subsurface damage in the processes used during optic fabrication plays a key role in determining the final quality of the optical surface finish. During the early stages of surface preparation, brittle grinding processes induce fractures at or near an optical surface whose range can extend from depths of a few mm to hundreds of mm depending upon the process and tooling being employed. Controlling the occurrence, structure, and propagation of these sites during subsequent grinding and polishing operations is highly desirable if one wishes to obtain high-quality surfaces that are free of such artifacts. Over the past year, our team has made significant strides in developing a diagnostic technique that combines magnetorheological finishing (MRF) and scanning optical microscopy to measure and characterize subsurface damage in optical materials. The technique takes advantage of the unique nature of MRF to polish a prescribed large-area wedge into the optical surface without propagating existing damage or introducing new damage. The polished wedge is then analyzed to quantify subsurface damage as a function of depth from the original surface. Large-area measurement using scanning optical microscopy provides for improved accuracy and reliability over methods such as the COM ball-dimple technique. Examples of the technique's use will be presented that illustrate the behavior of subsurface damage in fused silica that arises during a variety of intermediate optical fabrication process steps.

• Research Organization: Lawrence Livermore National Laboratory (LLNL), Livermore, CA
• Sponsoring Organization: USDOE
• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 883569
• Report Number(s): UCRL-PROC-217271
• Country of Publication: United States
• Language: English

Related Subjects

42 ENGINEERING
ACCURACY
DIAGNOSTIC TECHNIQUES
FABRICATION
FRACTURES
GRINDING
OPTICAL MICROSCOPY
OPTICS
POLISHING
RELIABILITY
SILICA