It's a fairly common laser amplification technique, the lab I work in uses Chirped Pulse Amplification for a lot of our pulsed lasers.

In order to get an ultrashort pulse of light (short in the time domain) it must be made of a large spectrum of frequencies/colors (long in the spectral domain). This is essentially the Fourier transform relationship, similar to the uncertainty principle.

The problem with high energy, ultrashort pulses is that they like to burn optics. You'll toast a lens if you send a beam with enough power through it. So what you do is separate the pulse into its many colors, amplify them individually, and then recombine. It's simple yet brilliant at the same time.