Page 344 - High Power Laser Handbook

312 So l i d - S t at e La s e r s Ultrafast Solid-State Lasers 313

Figure 12.8 Grism stretcher for downchirped pulse amplification (DPA)
ultrafast laser system. The stretcher is capable of chirping a pulse from
15 fs to greater than 40 ps.

the beam from a CPA laser must also typically be expanded to avoid
damage to the gratings.
One advantage of DPA is the ability to use grisms as the stretcher
for the amplifier system. Grisms, a combination of prisms and grat-
ings, have a very high dispersion. (Figure 12.8 shows a diagram of a
commercially available grism stretcher.) The GVD:TOD ratio of a
grism pair is also an exact match for most bulk materials, which means
28
that phase distortion in the system can be corrected for up to TOD.
For a full description of grism pairs, see Durfee, Squier, and Kane. 29
Although DPA is attractive because it is simple and highly efficient,
its main drawback is the large amounts of material in the system, which
can lead to a substantial B integral. However, this technique has been
very useful for ultrafast systems in the hundreds of microjoules to
1 millijoule range of energies at very high repetition frequencies. 30,31
A DPA system’s compressor usually consists of a pair of mirrors and
a block of glass, preferably one of the short flint glasses available
from Schott. Figure 12.9 shows the layout of such a compressor,

Positively chirpped mirror
Telescope SF6 Power compressor Final compressor +100fs GVD

SF6/SF57HT Glass precompressor
Output

Input Positively chirpped mirror
+100fs GVD
Figure 12.9 Glass compressor for DPA ultrafast laser system. Compressors can
handle up to ~1 mJ, while keeping the B integral to ~1. GVD: group-velocity
dispersion.