Laser-induced superintensive bubble boiling

Superintensive bubble boiling (SBB) is implemented in water in the absence of degassing at the end surface of a laser fiber using 100-ns laser pulses. A thulium fiber laser with a radiation wavelength of 1.94 $\mu$m and moderate power is used as a radiation source. The generation of bubble microjets in the vicinity of the end surface of the laser fiber is studied with the aid of high-speed photography and acoustic methods. After a threshold transition to the SBB regime, the energy of acoustic emission is predominantly concentrated in an acoustic interval of 10–30 kHz. The acoustic signal is generated due to thermal cavitation. Record-high thermal fluxes of up to 0.16 MW/cm$^2$ are reached in the SBB regime. Parameters of the resulting convective fluxes, microbubbles, and broadband acoustic oscillations are determined.