Page 489 - Tunable Lasers Handbook

9 Tunable Free-Electron Lajers 449

pme into macropulse(arb. units)
T

Micropulse
\

I I I I
2.73 2.81 2.89 2.97 3 05 3.12
Time into macropulse(arb. units)
FIGURE 4 A typical rime structure is shown for a laser pulse from a EL based on a pulsed rf
linear accelerator. The laser macropulse consists of hundreds of short micropulses. In most FELs
operating to date, the micropulses are 1 to 10 ps in length and the macropulse is from 1 to 100 ps in
length. The macropulses repeat at a repetition rate limited by the accelerator: usually in the range of
several hertz up to 120 Hz. The micropulse repetition rate can be anywhere from several megahertz
up to several gigahertz. The ripple on the pulse is due to modulations in the arrival time and energy
of the elecnons caused by effects in the microivave power source in the accelerator.

dreds of milliwatts or more) or a picosecond time structure may find that the
FEL provides just the laser light source they need.