Spacecraft design relies upon contamination control plans that specify proper material handling and material choices. Typical manufacturing areas employ control plans that monitor air quality for particulate contamination. All individual materials of construction are controlled for outgassing and purity and are required to comply with ASTM E595 vacuum outgassing requirements. Recently, ASTM E1559 test methods are being used to characterize outgassing of entire systems. However, there is still a significant gap in testing for interactions of multiple materials that may cause a variety of problems, including contamination. Requirements for assemblies such as electronics, circuit cards, and sensors are passed on to subcontractors, often without details beyond meeting ASTM outgassing requirements and particulate standards and neglecting information on design compatibility. Guidance typically is not provided on how to execute assemblies, manage material interactions, or restrict materials that should not be used in manufacturing. Significant contamination can occur during manufacturing from manufacturing tooling aids, fixtures and fixturing designs, accidental or incidental contact, instability of in-use materials (e.g., adhesives), or incompatible material choices in the system design. This contamination may not be detected until failures occur at final assembly or vacuum bake-out because typically limited sampling is specified for cleanliness verification during assembly operations. As innovations to system designs continue, designing and controlling the manufacturing of components and assemblies will require improvements and detailed guidance to minimize material compatibility issues and contamination. Examples of manufacturing tooling aids or material interactions that can lead to contamination will be provided along with recommendations to mitigate the contamination.
Langmuir-Blodgett (LB) films have been fabricated from a preformed acrylate amphiphilic copolymer with nonlinear optical (NLO) active chromophores covalently attached to the polymer backbone. By alternate deposition of this NLO active polymer with an NLO passive amphiphilic polymer, high quality multilayer films have been obtained with sufficient thickness to allow waveguiding in the LB films. The observed optical attenuation is between 1 and 3 dB cm-1. The linear and nonlinear optical characteristics of these films have been determined, both in transmission (or reflection) and in waveguide format. The high degree of order in LB films makes this type of supramolecular structure attractive for NLO applications. Based on the observed parameters (dispersion of the refractive indices, birefringence, tilt angle of the chromophore, hyperpolarizability), different phase-matching schemes can result in efficient second harmonic generation.
Langmuir-Blodgett films have been fabricated of a prepolymerized amphiphile containing a chromophore of high second-order nonlinear optical activity. Thick films, containing as many as 262 layers of noncentrosymmetric structure have been prepared by alternate deposition of the dye polymer and several different materials. In contrast to previous literature reports on Langmuir-Blodgett films of other polymeric dyes, these films show the theoretically expected quadratic dependence of second harmonic generation with film thickness. Polarization studies of the second harmonic generation demonstrate that the chromophores are highly ordered in these films. In addition, by using all-polymeric materials it has been possible to fabricate a waveguide of these films with optical attenuation of about 1 dB cm-1, substantially lower than has been previously reported for Langmuir-Blodgett films even without a noncentrosymmetric structure.