FY 2011 Miniature Spherical Retroreflectors - Final Report

Anheier, Norman C. ; Bernacki, Bruce E. ; Qiao, Hong (Amy)

关键词: CHALCOGENIDES;    COMPARATIVE EVALUATIONS;    COMPRESSION;    CROSS SECTIONS;    DESIGN;    EFFICIENCY;    EYES;    FEASIBILITY STUDIES;    GLASS;    GRINDING;    LAWRENCE LIVERMORE NATIONAL LABORATORY;    MOLDING;    PERFORMANCE;    POLISHING;    POLYMERS;    REFLECTIVE COATINGS;    SIMULATION;    THERMAL EXPANSION;    WAVELENGTHS Optical Retroreflectors;    Mid-Infrared;    Remote Sensing;   

DOI  :  10.2172/1034587
RP-ID  :  PNNL-20898
PID  :  OSTI ID: 1034587
Others  :  Other: NN2001000
Others  :  TRN: US201204%%67

学科分类：材料科学（综合）

美国|英语

来源: SciTech Connect

【 摘 要 】

PNNL conducted a systematic optical modeling effort to study and compare retroreflector designs with respect to available optical materials. The optical Strehl ratio (SR) and cross section figures of merit were used to compare the performance of candidate optical designs. Further modeling was conducted to assess the relationships between standoff range and retroreflector diameter and cross section. Analysis showed that small diameter retroreflectors have very high optical link loss, since the net loss scales by retroreflector diameter to the 4th power. Optical retroreflection efficiency is also important, but extracting ideal performance from a complicated design must be tempered by the fact that the effective retroreflector range varies only as the fourth root of the cross section. It's therefore imperative to maintain a reasonable retroreflector diameter, but striving for perfect optical performance may be a costly effort that does not merit the modest performance gain. Several promising designs were developed for visible and mid-infrared applications, which embraced lessons learned in the standoff range study. These designs included a polymer clad glass core approach for visible wavelengths and a concentric shell design using chalcogenide glass for the mid-infrared. Injection molding feasibility studies demonstrated that it was practical to fabricate visible polymer retroreflectors using this approach. Such an approach may be a practical solution for the LLNL project. Our primary focus is to develop mid-infrared designs; therefore compression molding chalcogenide glass was adopted for fabricating mid-infrared retroreflectors. A significant effort was focused on developing practical compression molding methods that provided reasonable device yield. A custom compression molding press was developed in collaboration with a private engineering firm. Many successful molding studies were conducted during this effort, but ultimately the fragile nature of the chalcogenide glass and the unfavorable thermal expansion properties limited the feasibility of fabricating the thin shell structures needed for this design. An alternative Cat's Eye retroreflector design was therefore adopted. This design is constructed using two hemispherical structures that can be fabricated by conventional grinding and polishing methods or by molding with high yield. The cross section of this design is very good (and can be further improved by applying a highly reflective coating to the rear surface), but has reduced field of view as a design trade off as well as the isotropic nature of Luneburg-style retroreflector.