Once the accelerator is in place, it looks like a big old pipe. The accelerator excites the electron beam up to about 100 million volts to prep it for lasing. In a conventional laser, an energy source such as another laser or a power supply excites atoms so that they lase. With a free electron laser, it's the accelerator that gives the electron beam the boost it needs to directly emit photons. If the Navy gets its way, this contraption will be in the hull of a ship someday.