METHODS TO GENERATE FEMTOSECOND AND ATTOSECOND ELECTRON AND X-RAY PULSES

Short electromagnetic wave pulses of wavelength lambda can be used to modulate the energy of a charged particle beam on a scale of lambda/2, which in turn can generate particle bunching of dimension less than o r similar to lambda/2, in the usual manner. These short bunches can th en radiate correspondingly short photon bunches, including higher ener gy photons. Four types of devices are discussed which can achieve the requisite energy modulation on a scale of lambda/2: Vacuum, Cherenkov, resonator, and klystron modulators. The first is the simplest, and fo r short bunches its performance approaches, or is superior to that of the last two. For broadband short pulses it is generally to be preferr ed.