The output of a picosecond cascade-pumped controlled transient oscillation (CTO) dye laser has been amplified to the millijoule level. Single-mode operation and frequency selection with a spectral width of 0.2 nm were achieved by using an angle-tuned narrow-band interference filter. A plasma shutter was employed as a pulse clean-up device for these high-power laser pulses. This device had a transmission of 86 percent and provided background-free operation for the laser system. Sychronizable output pulses with an energy of 2 mJ and a duration of 20 ps at 10 pps were routinely produced. The gain of the amplifier chain was about .