Long-duration nano-second single pulse lasers for observation of spectra from bulk liquids at high hydrostatic pressures

AbstractThe influence of laser pulse duration on the spectral emissions observed from bulk ionic solutions has been investigated for hydrostatic pressures between 0.1 and 30MPa. Transient pressure, shadowgraph imaging and spectroscopic measurements were performed for single pulses of duration 20 and 150ns. The transient pressure measurements show that for hydrostatic pressures up to 30MPa, propagation of the high-pressure shockwave generated by the focused laser causes the local pressure to reduce below ambient levels during the time frame that spectroscopic measurements can be made. The pressure impulse and subsequent reduction in pressure are larger, with the latter lasting longer for the 150ns pulse compared to a 20ns pulse of the same energy. The 150ns pulse generates larger cavities with significant enhancement of the spectral emissions observed compared to the 20ns duration pulse for pressures up to 30MPa. The results demonstrate that laser-induced breakdown using a long ns duration pulse offers an advantage over conventional, short ns duration pulses for the analysis of bulk ionic solutions at hydrostatic pressures between 0.1 and 30MPa