Cavitation effect of holmium laser pulse applied to ablation of hard tissue underwater.

To overcome the inconsecutive drawback of shadow and schlieren photography, the complete dynamics of cavitation bubble oscillation or ablation products induced by a single holmium laser pulse [2.12 microm, 300 micros (FWHM)] transmitted in different core diameter (200, 400, and 600 microm) fibers is recorded by means of high-speed photography. Consecutive images from high-speed cameras can stand for the true and complete process of laser-water or laser-tissue interaction. Both laser pulse energy and fiber diameter determine cavitation bubble size, which further determines acoustic transient amplitudes. Based on the pictures taken by high-speed camera and scanned by an optical coherent microscopy (OCM) system, it is easily seen that the liquid layer at the distal end of the fiber plays an important role during the process of laser-tissue interaction, which can increase ablation efficiency, decrease heat side effects, and reduce cost.

Asymmetric Fabry-Pérot fiber-optic pressure sensor for liquid-level measurement.

It is demonstrated that an asymmetric Fabry-Pérot fiber-optic pressure sensor is capable to precisely measure liquid levels. They are directly proportional to pressures that can modulate cavity length of Fabry-Pérot cavity. As a result, the sensor can operate over a linear region of an interference fringe that enables liquid-levels interrogation by measuring the reflected intensity. Experimental results show the resolving power of 0.4 mm, sensitivity of 2.4 mV/mm, and precision of 1 mm over range of 2.3 m (water) can be achieved. The sensor can measure liquid levels accurately, continuously, and automatically in flammable and explosive circumstances.