Contributed Review: Absolute spectral radiance calibration of fiber-optic shock-temperature pyrometers using a coiled-coil irradiance standard lamp

Abstract

Development of a fast fiber-optic two-color pyrometer for the temperature measurement of surfaces with varying emissivities Rev. Sci. Instrum. 72, 3366 (2001); 10.1063/1.1384448 This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitationnew. We describe an accurate and precise calibration procedure for multichannel optical pyrometers such as the 6-channel, 3-ns temporal resolution instrument used in the Caltech experimental geophysics laboratory. We begin with a review of calibration sources for shock temperatures in the 3000-30 000 K range. High-power, coiled tungsten halogen standards of spectral irradiance appear to be the only practical alternative to NIST-traceable tungsten ribbon lamps, which are no longer available with large enough calibrated area. However, non-uniform radiance complicates the use of such coiled lamps for reliable and reproducible calibration of pyrometers that employ imaging or relay optics. Careful analysis of documented methods of shock pyrometer calibration to coiled irradiance standard lamps shows that only one technique, not directly applicable in our case, is free of major radiometric errors. We provide a detailed description of the modified Caltech pyrometer instrument and a procedure for its absolute spectral radiance calibration, accurate to ±5%. We employ a designated central area of a 0.7× demagnified image of a coiled-coil tungsten halogen lamp filament, cross-calibrated against a NIST-traceable tungsten ribbon lamp. We give the results of the cross-calibration along with descriptions of the optical arrangement, data acquisition, and processing. We describe a procedure to characterize the difference between the static and dynamic response of amplified photodetectors, allowing time-dependent photodiode correction factors for spectral radiance histories from shock experiments. We validate correct operation of the modified Caltech pyrometer with actual shock temperature experiments on single-crystal NaCl and MgO and obtain very good agreement with the literature data for these substances. We conclude with a summary of the most essential requirements for error-free calibration of a fiber-optic shock-temperature pyrometer using a high-power coiled tungsten halogen irradiance standard lamp. C 2015 AIP Publishing LLC.[http://dx

Thermodynamically complete equation of state of MgO from true radiative shock temperature measurements on samples preheated to 1850 K

“…Third, the initial temperature of MgO was monitored at the back surface of the capsule and, therefore, was most accurately known there. Fourth, our detailed calibration studies [26] revealed that the difference between the static and dynamic response of our amplified photodetectors decreased as the input light pulse duration increased. Therefore the errors in the corresponding correction factors are minimized at the end of useful radiance records.…”

“…[33]. A comprehensive review of the Caltech sixchannel pyrometer operation and calibration can be found elsewhere [26]. Therefore we give only a brief description of the most essential issues, shock target parameters, and newly developed procedures for the data acquisition and analysis.…”

“…[33]), (3) an average 22 ± 4% reflectivity of the MgO shock front measured at 220 and 248 GPa shock pressure (see Sec. IV B), (4) up to ≈21% lower electronic output response of the pyrometer photodetectors to short, approximately 10 −8 to 10 −7 s, optical pulses from shock experiments compared to long, approximately 10 −3 s, calibration pulses [26], and (5) formation of an 18 ± 2-μm-thick (as measured at room T ) black layer of Ti-doped MgO at the impact side that reduced the shock travel distance "seen" by the shock pyrometer in all experiments with Ti foil (shots 389-411). After correcting the systematic errors induced by these effects, we report herein fairly good agreement between the results of our model prediction and experimental values.…”

“…Laser-driven shock wave loading in their experiments was not completely steady. As in all other laser-driven pyrometry experiments to date, their temperature measurements were calibrated to shock-compressed quartz, which is not a primary standard and has been shown to give poor accuracy [26]. The range of their reported B1-B2 and B2-melt transition pressures was more than 50 GPa and the lowest shock temperature uncertainty was ≈1000 K.…”

“…McWilliams et al [22] had poor constraints on the mechanical state of their MgO samples at shock speeds below ≈17.3 km/s (i.e., pressures below ≈525 GPa) due to loss of VISAR reflectivity, high uncertainties on all pressures due to sparse calibration assuming a linear Hugoniot despite the [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] and conventional shock temperature data [25,26]. Typical uncertainties of the predicted melt lines are 100-200 K. Thicker lines indicate several melting curves that are close enough to be grouped and shown together.…”