At Los Alamos National Laboratory (LANL), a high-speed, four-wavelength, infrared (IR) pyrometer has been used for surface temperature measurements in shock-physics experiments for several years. The pyrometer uses solid-state detectors and a single fiber-optic cable for transmission of light from the target surface to the detectors. This instrument has recently been redesigned for an upcoming experiment at the Nevada Test Site (NTS). Three different IR detectors (two HgCdTe variants as well as the existing InSb chip) were compared for sensitivity, signal-to-noise ratio, and bandwidth. Of major concern was detector amplifier recovery time from overload saturation. In shock-physics experiments, a short but very bright precursor frequently accompanies shock breakout (often from trapped air). This precursor can saturate the amplifier and may "swamp-out" the signal of interest before the amplifier recovers. With this in mind, we evaluated two new amplifier designs by the Perry Amplifier Company for linearity, signal-to-noise characteristics, gain, and saturation recovery time. This paper describes experimental setup for detector comparison and results obtained. Furthermore, we discuss new amplifier design and suitability for high-speed infrared pyrometry in shock physics experiments.
In an effort to understand the influence of different surface finishes and the effect of ejecta mass on free surface temperature measurements, we performed a series of high-explosively (HE) shocked tin experiments. In this series of experiments the surface finish (i.e, specular, shallow grooves (16 μinch), deep grooves (200 μinch) and "ball-rolled" surfaces) and the ambient atmosphere (from 1.2 torr, to atmospheric air, as well as 1 atm helium) were varied. With a ~180 kbar shock pressure the temperature results agreed for all but the very deep groove (>200 μinch) surfaces investigated.
In addition to the standard problems associated with contactless temperature measurements, pyrometry in shock physics experiments has many additional concerns. These include background temperatures which are often higher than the substrate temperature, non-uniform sample temperature due to hotspots and ejecta, fast sample motion up to several km.s-1, fast-changing sample emissivity at shock breakout, and very short measurement times. We have designed a four channel, high speed near-infrared (NIR) pyrometer for measurements in the 400 to 1000K blackbody temperature range. The front end optics are specific to each experiment, utilizing preferably reflective optics in order to mitigate spectral dispersion. Next-generation instruments under development are also discussed.