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" ... What they've done here is the first real spectroscopy of antihydrogen atoms, though in hard-core spectroscopy terms, it's kind of a baby step. They collected a bunch of antihydrogen-- about 14 atoms per trial, which may not seem like much but is a tenfold improvement over past experiments-- and hit them with a laser tuned to match the frequency needed to excite ordinary hydrogen atoms from the lowest energy state (the "1S" state, in the notation we use for such things) to the first excited state (the "2S"). Actually, the 1S-2S transition is forbidden for a single photon (and also at a massively inconvenient ultraviolet wavelength), so they tuned their laser to half the necessary frequency (which is a slightly easier-to-work-with color of light, anyway); this lets the atoms absorb two photons at once to make the jump from 1S to 2S, a process that's allowed but highly unlikely. They need a huge amount of laser power to make anything happen, but they manage to get about a watt of laser power onto the trap, which is pretty respectable. ... "