X. Fan, K.K. Murray, “UV laser irradiation of IR laser generated particles ablated from nitrobenzyl alcohol,” Appl. Surf. Sci. 255 (2009) 6297–6302. doi:10.1016/j.apsusc.2009.02.005.

Abstract: Particles generated by 2.94 µm pulsed IR laser ablation of liquid 3-nitrobenzyl alcohol were irradiated with a 351 nm UV laser 3.5 mm above and parallel to the sample target. The size and concentration of the ablated particles were measured with a light scattering particle sizer. The application of the UV laser resulted in a reduction in the average particle size by one-half and an increase in the total particle concentration by a factor of nine. The optimum delay between the IR and UV lasers was between 16 and 26 µs and was dependent on the influence of the IR laser: higher influence led to a more rapid appearance of particulate. The ejection velocity of the particle plume, as determined by the delay time corresponding to the maximum two-laser particle concentration signal, was 130 m/s at 1600 J/m^2 IR laser influence and increased to 220 m/s at 2700 J/m^2. The emission of particles extended for several ms. The observations are consistent with a rapid phase change and emission of particulate, followed by an extended emission of particles ablated from the target surface.

Particle size distribution for IR laser ablation and UV post-irradiation of 3- nitrobenzyl alcohol at UV laser delay times of (a) 0, (b) 18, (c) 20, (d) 28, (e) 100, (f) 1000 µs and (g) 15 ms. The IR and UV fluences were 1900 and 2400 J/m2, respectively.