A gas discharge laser crystallization apparatus and method for performing a transformation of a crystal makeup or orientation in a film on a workpiece is disclosed, which may comprise a master oscillator power amplifier MOPA or power oscillator power amplifier configured XeF laser system producing a laser output light pulse beam at a high repetition rate and high power with a pulse to pulse dose control; an optical system producing an elongated thin pulsed working beam from the laser output light pulse beam. The apparatus may further comprise the laser system is configured as a POPA laser system and further comprising: relay optics operative to direct a first output laser light pulse beam from a first laser PO unit into a second laser PA unit; and, a timing and control module timing the creation of a gas discharge in the first and second laser units within plus or minus 3 ns, to produce the a second laser output light pulse beam as an amplification of the first laser output light pulse beam. The system may comprise divergence control in the oscillator laser unit. Divergence control may comprise an unstable resonator arrangement. The system may further comprise a beam pointing control mechanism intermediate the laser and the workpiece and a beam position control mechanism intermediate the laser and the workpiece. Beam parameter metrology may provide active feedback control to the beam pointing mechanism and active feedback control to the beam position control mechanism.