[Technology] Imaging devices based on superconductors rather than semiconductors could provide the data needed to understand what is speeding up the universe’s expansion (...). In terms of imaging, the output of the two facilities will be extraordinarily high – some 300 million galaxies should be observed by the former and a whopping 10 billion by the latter. The galaxies’ spectra, however, will be obtained simply by capturing the images through a handful of filters of varying colours. While more distant objects tend to be redder, the redshift measurements obtained in this way will not be precise enough to record the universe’s expansion history in detail. The solution to this problem, according to astrophysicist Ben Mazin of the University of California, Santa Barbara, is to carry out spectroscopic measurements not with the conventional charge-coupled devices (CCDs) used in the Dark Energy Camera, LSST and almost every other major telescope in the world, but with a new kind of sensor known as a microwave kinetic inductance detector (MKID). Rather than using semiconductors to convert incoming photons into single electrons, as is the case in CCDs, MKIDs instead employ a superconductor, typically titanium nitride. Each photon breaks Cooper-paired electrons in a pixel of superconductor to produce thousands of excitations known as quasiparticles, with the resulting change in the material’s inductance then measured using a microwave resonator. These devices are ideal for carrying out redshift measurements, explains Mazin, as the number of quasiparticles produced by a photon depends on the energy, and hence frequency, of that photon. In other words, an MKID pixel array can both image and measure the spectra of many objects – potentially as many as tens or even hundreds of thousands – in the sky at the same time. “I think it is the only way that people have thought of so far of getting low-resolution spectroscopic follow-up for the large numbers of galaxies imaged in sky surveys,” says Mazin, who has been developing MKID technology since 2000. “It is a very powerful technique for studying dark energy.” live.iop-pp01.agh.sleek.net/physicsworld/reader/#!edition/editions_Big-Science-2014/article/page-3054
Posted on: Wed, 08 Oct 2014 04:50:32 +0000
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