Spontaneous Boiling-Up Onset: Activation Effect of Laser Pulses

Miniature fiber optic sensors were used for detection of initial boiling-up of uniformly superheated liquid in the capillary of a bubble chamber. The possibility of local boiling-up activation by a laser pulse at a single-mode fiber end with a diameter of 9 mu m was shown. The object of the study was n-pentane superheated at 82 K with respect to the liquid-vapor equilibrium temperature at atmospheric pressure. The control sensor recorded a signal similar to that of spontaneous macroscopic boiling-up. The activation threshold value for the radiation intensity at the end of the fiber was found. This value varies for different fibers. The minimum pulse energy required for activation was 6 nJ, which was insufficient for triggering of the thermal activation mechanism. An assumption is made about the mechanical effect of laser pulse on the fiber-liquid interface.