N132-137 TITLE: Low-loss Optical Polymer Materials in Multi-kilogram Quantities for Optical Lens Development

TECHNOLOGY AREAS: Materials/Processes, Sensors, Weapons

OBJECTIVE: We seek a source of thermoplastic polymer materials (e.g. Polymethyl methacrylate (PMMA), Styrene Acrylonitrile (SAN), et al) with internal scattering losses <0.5 dB/m in quantities (kilograms) suitable for the fabrication of extrusion processed and/or molded near diffraction-limited optical devices.

DESCRIPTION: Polymers have been used as optical materials for over 50 years, mostly in applications where low cost and light weight are a critical issue. The light weight and impact resistance of polymer lenses could provide a significant advantage in more demanding DoD applications. However, the use of polymers in optics with demanding specifications has been limited primarily by scattering losses. The haze and transmission specifications for commercial polymers are described in ASTM D1003 and/or the International Organization for Standardization (ISO) 14782 procedure. In the American Society for Testing and Materials (ASTM) D1003 measurement, only light scattered outside of a cone of ~8 degrees is reported as haze. In commercial polymers there is usually a specification for haze rather than one for scattering. Forward scattered light remaining within an 8 degree cone is included in the transmission. The light scattered within a small angle in the forward direction will have a deleterious effect on the imaging properties, Modulation Transfer Function of, for example, the night vision goggle. The level of scattering is not due to the intrinsic optical properties of the polymer, but rather to losses introduced into the polymer source materials during their manufacturing processes. For example, PMMA and perflourinated polymers have been synthesized with scattering levels more than three orders of magnitude lower than those usually specified by bulk manufacturers. More acceptable scattering levels are found in polymers produced under more careful conditions albeit in quantities smaller than that needed for the production of optical devices.

Low-loss polymers are produced by insuring extrinsic defects and impurities are excluded and by insuring the production conditions preclude the formation of localized inhomogeneities. A program to develop the science and manufacturing capability to produce polymer materials with specifications for higher end optical applications could have a substantial impact on the use of polymer materials in demanding optical applications and would have an excellent chance of transitioning into high end optical devices.

PHASE I: Define and if possible develop a concept for a cost effective method to scale up the synthesis and optimize the quality/volume/cost tradeoffs of polymer materials suitable for the fabrication of diffraction limited optics. Demonstrate the feasibility of producing one high optical quality thermoplastic polymer material with losses <0.5dB/m. This effort will define and if capable demonstrate the production to >1kg of thermoplastic polymer(s) suitable for the fabrication of extrusion processed and/or molded diffraction-limited optics.

PHASE II: Based on Phase I approach, demonstrate production on a scale up to >5kg or larger batch(s) of thermoplastic polymers that have losses <0.5dB/m with coextrusion rheology which is compatible with PMMA or SAN17. Provide test measurements suitable for specifying materials for high quality optics. Tests used by optical glass manufacturers and/or in ASTM E1653 - 94 (1999) could provide a starting point. Internal losses and on-axis stray light of <0.5dB/m (~ 0.5% in a 1 cm thick lens) over the 350-1650nm spectral range (2) will be demonstrated. These materials will have index of refraction within the range 1.35 to 1.72 and Abbe numbers within the range of 20-80. The materials will be thermoplastic and coextrudable with PMMA and/or SAN17.

PHASE III: Demonstrate the development of 10Kg batches of a set of optical polymers that have indexes of refraction across the range 1.35 to 1.72 and Abbe numbers across the range 20-80. The materials will be thermoplastic and coextrudable with PMMA and/or SAN17 and a centimeter thick sample will have an internal optical transmission >99.5 % and on-axis stray light of <0.5% for the 350-1650nm spectral range2 which is sufficient to permit a demonstration of the feasibility of near diffraction-limited polymer optical systems.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: High quality polymer optics will improve the performance, reduce the size and weight, and increase the durability of household and commercial optical devices, such as telephones, surveillance and web cameras and binoculars.

REFERENCES:
1. Y. Koike, T. Tanio, and Y. Ohtsuka; Macromolecules 22, 1367 (1989)

2. J. Stevens, Proc. of SPIE Vol. 5442 Helmet- and Head-Mounted Displays IX: Technologies and Applications,73-82.

3. N. Tanio and Y. Koike; Jpn J. Appl. Phys, 36, 743 (1997)

4. Y. Koike and K. Koike; J. Polym. Sci. Part B: Polym. Phys. 49, 2 (2011)

5. N. Tanio and Y. Koike; Polymer J. 32, 43 (2000)

KEYWORDS: Thermoplastic Polymers; Optical Fibers, Lens systems, optical design, optical scatter, coextrusion

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