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Abstract POLAR is a compact wide-field space-borne detector for precise measurements of the linear polarisation of hard X-rays emitted from gamma-ray burst and solar flares in the energy range of 50 keV to 500 keV. It consists of a 40 × 40 array of plastic scintillator bars used as a detection material. POLAR was launched into a low Earth orbit on-board the Chinese space-lab TG-2 on September 15, 2016. To achieve high accuracies in polarisation measurements it is essential to perform a precise energy calibration both before and during the flight. Such calibrations are performed with four low activity 22Na radioactive sources placed inside the instrument. Energy conversion factors are related to Compton edge positions from the collinear annihilation photons from the sources. This paper presents the main principles of the in-flight calibration, describes studies of the method based on Monte Carlo simulations and its laboratory verification, and provides some observation results based on the in-flight data analysis. [ABSTRACT FROM AUTHOR]

Abstract: This paper shows how a scanning laser Doppler vibrometer (LDV), an instrument designed to measure vibrations of structures or objects, can be used in a non-traditional fashion to identify acoustical sources. This is achieved by measuring the changes in the optical path induced by local fluctuation of the air refraction index to which the LDV is sensitive. The acoustical signal used is sinusoidal and may be recovered by scanning at a uniform rate over a subject area (continuous scan) parallel to the source axis and demodulating this signal. Due to the fact that the measured scan area is in fact a line integral over a measurement volume between the laser head and a rigid object needed to reflect the laser beam, multiple view planes around the axis of the acoustic source are usually measured. These are then passed through a tomographic algorithm, thereby reconstructing the full sound field. In this article however, only one view plane is measured, but the acoustic source is placed on a rotating surface with fixed rotational frequency, thereby imposing a modulation on the measured spectrum. Demodulation will allow reconstruction of the three-dimensional sound field. [Copyright &y& Elsevier]