Page 352 - High Power Laser Handbook

320 So l i d - S t at e La s e r s Ultrafast Solid-State Lasers 321

by light-induced polymerization, because two-photon absorption
may be used to initiate the polymerization reaction. As in their use for
micromachining, femtosecond laser pulses allow significant two-
photon absorption in localized volumes and can produce small, high-
resolution spatial features.
12.6.3 Laser-Based Photon and Particle Sources
Recent experiments have demonstrated that an intense femtosecond
laser pulse focused into a gas-puff target can drive a strong plasma wake
field, which can accelerate electrons to tens of mega-electronvolt
energy in a propagation distance of just a few millimeters. Recent
experiments have shown that under the right conditions, the emitted
electron bunch can be monochromatic, with an energy bandwidth of a
45
few percent at electron energies as high as 80 MeV. In this recent
work, ultrafast laser pulses of peak power ~1 to 10 TW are needed to
effect relativistic self-focusing of the pulse at intensities greater than
18
2
10 W/cm , which is required to generate the wake field. Further
work in ultrafast laser development, as well as continued progress in
optimizing parameters for plasma generation, will allow this type of
electron accelerator to work reliably at higher 100 to 1000 Hz repeti-
tion rates. This would make laser-plasma-based electron sources
practical for such applications as radioisotope production and, even-
tually, for use as much-brighter photoinjector electron sources for
compact free-electron lasers.
An important set of new, high-resolution radiological applica-
tions may soon be possible using these intense lasers. It is well known
that such intense laser pulses can produce copious amounts of radia-
tion of various sorts. These radiation sources range from photons
with energy of 10 eV to greater than 1 MeV to a host of particles,
including neutrons, protons, and electrons. Moreover, the fluxes of
these radiation sources can be quite substantial, even though their
source sizes are small (microns to tens of microns). Therefore, these
new photon and particle radiation sources would have unique appli-
cations in high-resolution probing of materials—for example, to
detect buried voids and cracks in aircraft surfaces or to understand
fuel flow and combustion. Thus, this field has the potential for these
sources of extreme photons and particles to be combined with novel
diagnostic techniques to realize enabling technologies that will have
a major impact on diverse areas of the defense, manufacturing, envi-
ronmental and medical industries.

12.6.4 High Harmonic Generation
One of the major thrusts in modern science and technology has been
to understand and make use of electromagnetic (EM) radiation.
Understanding the interaction of EM radiation with matter led to the
development of quantum theory and, subsequently, of solid-state