Laser generation of shock waves in different media

When a Q-switched Nd:YAG laser is focused in a medium, breakdown associated with the formation of a plasma occurs, and shock waves are generated in the medium. The appearance of this phenomena has been recorded using ultra-high speed photography the event being illuminated by a dye laser. The measurement of the changes of parameters through the shock region were visualized by using shadowgraph and interferometry techniques and calculated using Abel .inversion, assuming that the thermal conductivity' and the viscosity of the medium were negligible. The velocity of the shock in air was found to be greater than the sound speed, which was in agreement with previous studies. The net peak pressure produced from the passage of the shock wave in air was in the range 0.1 - 0.9 atm (associated with radii between 5 - 1.5 mm). The measured velocity of sound in the liquids being investigated showed good agreement with the accepted values. The pressure produced as a result of the shock transient in water was in the range 10 - 30 atm, corresponding to the radii of the shock wave between 6 - 2 mm. A series of measurements on bovine vitreous humour showed the velocity of sound to be 1510 m/s with 5% accuracy. Spherical shock waves were formed in a range of organic liquids' (chloroform, benzene: and glycerol)when the laser was focused in the body of the liquids. In order to understand the generation mechanism of acoustic waves on solid surfaces, experiments were performed by immersing the solid body (perspex and aluminium plates) in water. The hemispherical shock viwave structure comprising the longitudinal, shear, and Rayleigh (Stoneley) waves was generated as a result of the interaction of the focused laser with.the solid-liquid boundary. These waves were identified by their velocities which were in excellent agreement when compared with the results of previous workers. A series of experiments was carried out to study the shock wave formation in the capsulotomy procedure. In this operation a Q-switched Nd laser is used to rupture the capsule membrane following implantation of an intraocular lens (IOL) in the eye. The effect of the solid lens was studied compared with the free membrane on a model eye structure.