|
A Large Aperture, Near-Specular Imaging Reflectometer (LANSIR) was designed and built for performing optical surface quality tests on laminate mirror specimens. LANSIR can quantify the extent of reflective light-scattering from the surface of layered mirrors. It allows real-time examination of scatter from sample areas ranging up to 14 in. in diameter. An illuminated round pinhole as the source, and a video camera with image digitization as the sensor, allows easy detection of directionality (anisotrophy) in the scatter. LANSIR can detect and distinguish the light-scattering con-tributions from surface features which are both directional and widely spaced. These light-scattering contributions can include non-uniform thickness of individual layers, "print-through" texture from reinforcing fibers in composite materials, of and various fabrication flaws such as that caused by extrusion and rol-ling. LANSIR can also control and measure tension in the laminate membrane mirror specimens. Metalized polymer film reflective surfaces laminated to structural metal, or composite material substrates such as those used in stretched membrane heliostats and dishes were investigated. Initial results are encouraging. Mirror samples from most of the recent DOE "membrane mirror" projects have exhibited scatter within the acceptable limits for moderate temperature applications. Even the relatively thick fiber-reinforced polyester structures which are now under initial development come close to passing the test. Nevertheless, our tests have pointed out the need for continued attention, especially of new materials, and of new forming and joining processes.
|
