Time-resolved resonant absorption study of 532-nm laser-generated plumes over YBa₂Cu₃O₇ targets

The number densities n(t) of the atomic species produced by pulsed-laser (532-nm) interaction with YBaCuO targets were measured using time-resolved resonant absorption spectroscopy. At ∼5 J/cm² fluence and 0.8 mm above the target, the peak n(t) ranged from 10¹³ to 10¹⁵ cm^-3. The distributions of the normal z-velocity component could be modeled by Gaussian functions, in agreement with the theory of supersonic nozzle beams and the more recent theory of Knudsen layer formation. Such theoretical fits gave most probable z velocities in the km/s range and Mach numbers as high as 7. Ba-ion z velocities were better fitted by a 4:7 mix of fast (∼3-km/s) and slow (∼2-km/s) components.