Lasers that Flash in a Quintillionth of a Second Could 'Film' Electrons as they Interact | Popular Science: Attosecond laser pulses have been demonstrated before, but they were too weak to actually measure electron dynamics. For that, you need something both fast and intense. This new laser system satisfies both requirements, and does so with a relatively simple setup.
To get super-short bursts of laser light, you need to combine light waves of different frequencies in a very precise way such that they reinforce each other. This is easier said then done, particularly because it’s hard to get two different laser beams synchronized precisely. To overcome this, the researchers constructed a setup that runs a single laser beam through a beam splitter, producing two beams of different frequencies that are nonetheless the same beam.