Laser apparatus including two different, pulsed MOPAs, one having a fundamental wavelength of 1064 nm and the other having a fundamental wavelength of 1564 nm, provide trains of optical pulses. The 1064-nm pulses are frequency tripled to 355 nm and the 1564-nm pulses are frequency doubled to 782 nm. The 355-nm and 782-nm pulses are mixed to provide 244-nm pulses. The 244-nm pulses are mixed with residual 1064-nm pulses to provide 198-nm output pulses of the apparatus. The output pulses can be either digitally modulated or amplitude modulated by controlling the phase relationship between the 1064-nm and 1564-nm pulses.