From a physorg article (the forum won't let me post the link since I don't have enough posts yet):
"The power contained in a single pulse from the LCLS is estimated to be in the neighborhood of a few billion watts—a tremendous amount to be sure. However, that power will be compressed into an unimaginably tiny sliver of time: around 100 femtoseconds, or one-tenth of a quadrillionth of a second. Because the pulses are so short, the total energy of the beam is relatively low, about 2 millijoules.
Despite their brevity, the momentary burst of X-rays still packs enough punch to instantaneously destroy most materials, a critical consideration for sensor design. Additionally, the sensor must be able to measure pulses at the full repetition rate of 120 per second. "
So if your CW power meter were sensitive to this beam it would read about 240 mW for the average power.
