Characterization of prompt flash signatures using high-speed broadband diode detectors

Impact flash is a brief, intense flash of light released when a target is impacted by a hypervelocity particle. It is caused by emissions from a jet of shocked material which is thrown from the impact site. Impact flash phenomenology has been known for decades, and is now being considered for applications where remote diagnostics are required to observe and diagnose impacts on satellites and space craft where micrometeoroid and orbital debris impacts are common. Additionally, this phenomena and remote diagnostics are under consideration for missile defense applications. Currently, optical signatures created from hypervelocity impact can be utilized as the basis for detectors (spectrometers, pyrometers), which characterize the material composition and temperature. More recent interest has focused on study of hypervelocity impact generated debris and the physics of the associated rapidly expanding and cooling multiphase debris cloud. To establish this capability technically in the laboratory, we have conducted a series of experiments on a two-stage light gas gun at impact velocities ranging from 6 to 19 km/s, which is representative for light emissions resulting from hypervelocity impacts in space. At these high impact velocities jetting is no longer the dominant mechanism for observed impact flash signatures. The focus of this work is to develop fast, inexpensive photo-diodes for use as a reliable prompt flash, and late time radiating debris cloud diagnostic to: (a) characterize material behavior in the shocked and expanding state when feasible; (b) ascertain scaling of luminosity with impact velocity; (c) determine the temperature of the impact flash resulting from radiating emissions when multiple silicon diodes are used in conjunction with narrow band pass filtering at specific wavelengths as a pyrometer. The results of these experiments are discussed in detail using both a metallic target, such as aluminum, and an organic material such as Composition-B explosive.