At the 26 th AIRAPT conference in 2017, a task group was formed to work on an International Practical Pressure Scale (IPPS). This report summarizes the activities of the task group toward an IPPS ruby gauge. We have selected three different approaches to establishing the relation between pressure (P) and ruby R1-line shift (Δλ) with three groups of optimal reference materials for applying these approaches. Using a polynomial form of the second order, the recommended ruby gauge (referred as Ruby2020) is expressed by: P[GPa] = 1.87(+0.01) × 10 3 Dl l 0 1 + 5.63(+0.03) Dl l 0 ,where λ 0 is the wavelength of the R1-line near 694.25 nm at ambient condition. In June of 2020, the Executive Committee of AIRAPT endorsed the proposed Ruby2020. We encourage highpressure practitioners to utilize Ruby2020 within its applicable pressure range (up to 150 GPa), so that pressure data can be directly compared across laboratories and amended consistently as better scales emerge in the future.

We measured the longitudinal sound velocity in Mo shock compressed up to 4.4 Mbars on the Hugoniot. Its sound speed increases linearly with pressure up to 2.6 Mbars; the slope then decreases up to the melting pressure of ∼3.8 Mbars. This suggests a decrease of shear modulus before the melt. A linear extrapolation of our data to 1 bar agrees with the ambient sound speed. The results suggest that Mo remains in the bcc phase on the Hugoniot up to the melting pressure. There is no statistically significant evidence for a previously reported bcc→hcp phase transition on the Hugoniot.

Plate impact experiments were conducted to produce two and three step shock wave loadings in [100] ultrapure, lithium fluoride (LiF) crystals to examine the role of loading history on optical window response in laser interferometry measurements. Peak compressive stresses ranged between 5.0 and 17.5 GPa, and the window response was characterized by measuring the difference between the apparent and actual velocities of reflecting surfaces by using a velocity interferometer. In some experimental configurations, this velocity correction was obtained independently from the projectile velocity. Our results show that the velocity correction in [100] lithium fluoride windows can be described in all cases by a single linear relation, Δu=(0.2739±0.0016)u. Because this correction is independent of the loading history, it is applicable to arbitrary loading, which includes ramp-wave or shockless compression. By using the velocity correction and the measured particle and shock velocities, we have also determined the density dependence of the refractive index for [100] lithium fluoride at 532 nm to be n=(1.2769±0.0024)+(0.0443±0.000 82)ρ.

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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