Explosive boiling of water after pulsed IR laser heating

Abstract

By focussing 1 J of 1064 nm Nd ∶ YAG beam into 30 atmospheres of hydrogen we could Raman shift to produce a 10 ns, 300 mJ, 1.9 µm laser pulse. This pulse can directly heat water by more than 100 K (average), during the laser pulse, inducing vaporisation. Vaporisation was studied using time-resolved shadowgraphy and Raman spectroscopy to obtain macro and molecular level information. The O–H stretching Raman bands of water are sensitive to temperature allowing us to measure the average temperatures during the boiling process. After the T-jump, explosive boiling occurred within 100 ns during which time the bulk temperature decreased, indicating that the vaporising water molecules deprived heat from their surroundings. Shadowgraphs confirmed the timescale for this phenomenon visually. After 10 µs, vaporised gas molecules condensed and formed droplets, which were observed by a morphology-dependent resonance (MDR) Raman.