The temporal contrast is classified into two main regimes, the
nanosecond-scale and the picosecond-scale contrast prior to the main
pulse. The Lund terawatt laser system is shown to be improved on the nano-
and picosecond-scale by a factor of 10 and 50, respectively, when it was
optimized for contrast but not for energy. Calculations are also presented
to emphasize the role of angular dispersion on the picosecond contrast.
Finally we show a compromise between the duration and contrast of
femtosecond laser pulses amplified in an optical parametric (chirped