Atomic Sodium Sonoluminescence Features during Bubble Collapse in a Cavitation Cloud by Time-Correlated Single Photon Counting

The pulse width of multibubble sonoluminescence flashes in an aqueous NaCl solution was measured by a correlation method for the spectral range of 300–800 nm. The flash pulse width had a maximum value of 21 ns in the spectral region adjacent immediately to the Na D-line peak (589 nm) and decreased to 2 ns with distance from the line peak. The measured dependence of the flash pulse width on the wavelength agreed with the dynamic Na line shape model proposed by us earlier, where the spectral line width and shift were governed by a fast change in the emitting medium density during bubble collapse. Using the correlation method, the sequence of metal and continuum flashes was determined to measure the relative delay between them. The results showed that Na emission takes a longer time as compared to continuum emission and occurred almost symmetrically in time around a continuum flash with a vanishingly small delay of 0.21 ns after the continuum flash. Using the same method for a CeCl₃ solution, a cerium line flash (350 nm) was revealed to occur after a continuum flash with a delay of 31 ns close to the Ce emission lifetime of 33 ns to be indicative of essential distinction between the mechanisms of Na and Ce emission under multibubble sonoluminescence.