• Digital holography interferometry maps CW laser-induced thermocavitation in liquids. • Non-contact optical metrology enables temperature mapping at the micrometer scale. • Interferometry captures pre-cavitation heating and post-collapse thermal dynamics. • Raman and COMSOL validate heat transfer and concentration effects in solutions. • Advances optical methods for temperature, heat, and fluid flow characterization. Thermocavitation, the nucleation of vapor bubbles generated by continuous-wave (CW) laser heating in absorbing liquids, underlies a range of fluidic and optical processes. However, the transient thermal environment preceding, during, and following cavitation remains poorly characterized due to the limited spatial and temporal resolution of conventional probes. Here, we demonstrate the first use of digital holography interferometry (DHI) for quantitative, two-dimensional temperature mapping of thermocavitation in copper nitrate solutions. Operating at 693 frames per second, the DHI system resolves localized pre-cavitation heating and the rapid post-collapse cooling signature at the laser focus, followed by thermal redistribution into the bulk fluid with micrometer-scale spatial resolution. Raman spectroscopy and viscosity measurements reveal concentration-dependent modifications to solution structure and thermal diffusivity, while COMSOL simulations support the experimentally observed heat transport. Across concentrations, DHI reveals that lower-absorbing solutions exhibit earlier cavitation onset (∼ 0.2 sec vs. ∼ 0.5 sec in concentrated solutions), broader heating zones, larger absolute bubble sizes, and more substantial post-collapse redistribution. In contrast, higher concentrations confine heating near the cuvette wall because stronger optical absorption limits light penetration, producing smaller bubbles in absolute size but proportionally larger relative to the much shorter heated-zone length. Using DHI, we observe temperatures preceding bubble nucleation at the laser focus ranging from ∼ 307 to 355 °C with increasing concentration, consistent with the trend-based nucleation temperature ranges inferred from Raman spectroscopy. High-speed imaging confirms the relationship between bubble size and heated length, complementing the interferometric data. Collectively, these results establish DHI as a powerful non-contact, non-invasive technique for resolving spatiotemporal dynamics of CW laser-induced cavitation and highlight its broader potential for probing rapid, small-scale superheating and heat transfer phenomena in liquids.
Alvarez et al. (Mon,) studied this question.