As is well known in the design of lasers, an amplifier
can have either a high gain with poor energy extraction or
a low gain with high energy extraction. A common way to solve
this problem is to use multi-pass amplification, which can
yield high gain and good energy extraction, thereby increasing
the overall efficiency of the system. Even though the benefits
from using multi-pass amplification are straightforward in
theory, implementing them in a system are not. The more elements
that are being added and the more passes a pulse makes through
the amplifier chain the more careful the design needs to control
for de-polarization effects and parasitic oscillations. The
BriteLight amplifier (and pre-amplifier) uses four passes through
each head, which achieves the desired combination of having
high gain and, at the same time, high energy extraction. This
arrangement also allows the BriteLight amplifier to deliver
very high pulse energies at high repetition rates (high thermal
load conditions) with great efficiency.
BriteLight: JMAR's Laser Technology 
