Patrick J. Hood

Processing of alignment layers for glassy liquid crystals

This paper presents the current status of alignment techniques for a new class of liquid crystalline material being developed for both passive optical filtering/polarizing and latching electro-optic applications. This new glassy liquid crystal (GLC) material has the unique property of being electro-optic and fully latching. That is, in one state, the material has the properties of a conventional nematic liquid crystal, capable of being aligned with either an electric or magnetic field; while in its other state, it is an optical quality solid that maintains the molecular alignment set while in the fluid state. Molecular alignment of nematic GLC films is a critical technology necessary to develop high-performance, novel latching devices. The alignment of the nematic pendant component of GLCs directly correlates to the optical contrast, switching speed (turn-on time), and decay speed (turn-off time) of an active latching device. There has been little prior research conducted to assess conventional LC alignment techniques for use with GLCs. The processing and effectiveness of multiple alignment techniques will be discussed.

Multicomponent composites and their application in replica mirrors for lightweight space-based optics

Research and development in multi-component composites demonstrated new material and fabrication concepts for mirrors for space-based optics. Cornerstone Research Group, Inc., effort, conducted under contract to the Air Force Research Laboratory, developed new organic and inorganic composite materials and investigated their potential for application as light-weight, low-cost alternatives mitigating the drawbacks of conventional materials (glass and metals) and fabrication processes for space-based mirrors. This development demonstrated the feasibility of multi-component organic composites integrating cyanate ester resin with several reinforcements, especially carbon fabric and nanofibers. It demonstrated feasibility of high-quality cyanate ester-based syntactic composite (structural foam composed of microspheres embedded in resin). The development also demonstrated initial feasibility of multi-component inorganic composites integrating a proprietary inorganic resin with particulate and nanofiber reinforcements. These new materials (both organic and inorganic composites) show strong potential for achieving major reduction in mirror areal density (compared with current operational mirrors) while achieving strength, stiffness, and thermal properties required for space applications. Finally, this project demonstrated feasibility of a replication approach to mirror fabrication. With this fabrication technology, a composite mirror is cast directly to net figure and finish. This dramatically simplifies the mirror fabrication process, thereby enabling less expensive tooling than conventional practice for glass or metal mirrors. In production lots of identical mirrors (e.g., spacecraft constellations), the replication approach will provide radical reduction in mirror costs by eliminating the lengthy, expensive grinding and polishing processes for individual units.

Fabrication and performance of chiral liquid crystal polymer membranes

The materials and process technology necessary to fabricate free-standing, circularly-polarizing thin films based on chiral polymer liquid crystalline materials has recently been demonstrated. Free-standing membranes with thicknesses on the order of 10 microns and diameters in excess of 7 cm have been fabricated. The spectrally selective films possess exceptional optical and mechanical properties, exhibiting polarization contrast in excess of 250 with out-of-band transmissions greater than 95%. The theory, materials, processing techniques and spectral performance of these filters are presented.

Polymer liquid crystal membrane filters in space applications

The materials and process technology necessary to fabricate free- standing, circularly-polarizing thin films based on chiral polymer liquid crystalline materials has recently been demonstrated. Free-standing membranes with thicknesses on the order of 10 microns and diameters in excess of 7 cm have been fabricated. The spectrally selective films possess exceptional optical and mechanical properties, exhibiting polarization contrast in excess of 250 with out-of-band transmission greater than 95%. The theory and performance of these filters are presented with specific attention given to the predicted effects of space environments on the durability of this materials technology. Environmental effects to be discussed include wide temperature cycling, radiation and atomic oxygen scavenging.

Effects of stereochemistry on the static and dynamic performance of glassy liquid crystals

Glass-forming liquid crystals (GLC) are a new class of materials suitable for use in a wide variety of latching optical and photonic applications. Applications range from physically small devices for latching fiber optic devices, such as switches and attenuators, to physically large devices, such as corrective optics for deployable space-based optical systems. Previously, we demonstrated the ability to electronically change and then latch the birefringent characteristics of an optical device. Recent data indicates that not only does the chemical design of a GLC material impact the electro-optic properties of a latching device, but stereochemistry also plays a significant role. This paper presents static and dynamic optical data taken on a set of four similar GLC materials. Based on the results of this study, we have developed a qualitative understanding of the structure-property relationships, leading to GLC materials that are suitable for use in latching electro-optic devices.

New materials technology for latching electro-optic devices

This paper presents the current status of a new class of liquid crystal material being developed for latching electrooptic applications. This new material has the unique property of being electrooptic and fully latching. That is, in one state, the material has the properties of a conventional liquid crystal, capable of being aligned with either an electric or magnetic field; in its other state, it is an optical quality solid that maintains the molecular alignment set while in the fluid state. Experiments have shown that current materials can be switched on the order of milliseconds, as is the case with conventional nematic liquid crystals. In the solid state, the electric field can be removed with no change to the previously set optical properties because the molecular alignment is frozen in place, which should last for an extended period of time. In addition, the material exhibits broad temperature stability in the solid state, enabling devices to be developed that operate from cryogenic temperatures to 80 degrees C without the use of a temperature controller. This new material is ideally suited for applications where the size and mechanical robustness of an electrooptic device is desired, along with the latching capability of optomechanical devices. This materials technology alone will currently not meet high-speed switch requirements. However, this technology can be integrated with other state-of-the-art high-speed materials to provide a high-speed latching device. Devices currently under investigation using this materials include optical switches, optical attenuators and tunable filters.