Ionization is when an an atom loses or gains an electron. This happens to lots of atoms, but it happens so fast that nobody has ever caught ionization in the act. Now, scientists at the Vienna University of Technology have used an attosecond laser pulse to watch as a single electron packs its bags and takes off on its own.
Let's just get one thing straight about attoseconds: they're crazy, wicked, hella fast. The nanosecond, which we normally think of as a fairly short amount of time, is left utterly and completely in the dust by the attosecond, which is a unit of time on the order of 0.00000000000000001 second. Now, three nanoseconds are to one second what one second is to ten years, and in three nanoseconds, light only has enough time to travel one single meter.
An attosecond is more than three billion times faster than this. It's about the amount of time that an electron takes to make one orbit around an atomic nucleus. Unsurprisingly, the only thing that has any hope of operating on such short timescales is light itself.
Back to the atoms: in order to watch an atom being ionized, it's necessary to pinpoint the exact moment that an electron busts out of its orbit. The tricky bit is that an electron isn't just one little round ball like they teach you in school: individual electrons are wave packets that are governed by quantum mechanics, and so they don't leave their parents atoms at one single time, but rather a series of different points in time. What scientists have to measure is how the electron's quantum phase (which describes the oscillation of the wave packet of the electron) evolves over the ten or so attoseconds that it takes the electron to move out of the atom.
By using very, very, very fast pulses from a laser that emits two different wavelength at the same time, researchers at the University of Vienna have managed to actually measure the quantum phase which the electron had inside the atom just before it was knocked out by the laser itself, providing information about about the electron's energy state inside the atom as well as the exact position at which the electron decided to depart. If this is hard to wrap your brain around, no worries: as a species we're not really rigged to comprehend this sort of thing, but the fact that we're able to make it happen at all is fairly remarkable.