A laser system includes a resonator having two gain modules generating pulses, coupled with intra-cavity polarization into a single beam line, using a single output coupler. A laser controller controls the laser heads to emit pulses in rapid succession, such as pulse pairs separated by a time interval of less than about 1 millisecond, and in some embodiments in a range from about zero (overlapping) to about 100 microseconds. Also a system adapted for metrology using particle image velocimetry PIV uses the resonator. For PIV, optics are provided in the output beam paths which expand the beam to form pulsed illumination sheets. A camera is used to capture images of the pulsed illumination sheets for analysis.