Dependence of acoustical characteristics of laserinduced breakdown in dielectric materials on shape of inelastic region
Abstract
Generation of acoustic waves in a transparent dielectric material following its breakdown by a laser beam is analyzed theoretically, taking into consideration the real ellipsoidal rather than ideal spherical shape of the inelastic region and its prolateness in the direction of the laser beam. The boundary conditions at the surface of this region are stipulated in terms of zero shear strains and pressure or normal stress decreasing exponentially with time over duration of the laser pulse, assuming that the surfaces of the specimen are so far from the inelastic region inside as to have a negligible effect on the process. The corresponding wave equations for the displacement vector are solved in Legendre series, after this vector has been resolved into a longitudinal component which is the gradient of a scalar potential and a transverse component which is the curl of a vector potential. In an ellipsoidal system of coordinates each term of the series is the product of two Legendre functions, with a coefficient, one of the first kind of a circular trigonometric argument and one of the second kind of a hyperbolic trigonometric argument. At far distance from the inelastic region the solution simplifies, inasmuch as shear waves do not reach the detector before longitudinal waves have already been recorded.
 Publication:

JPRS Report Science Technology USSR Space
 Pub Date:
 June 1987
 Bibcode:
 1987RpScT....R..46I
 Keywords:

 Acoustics;
 Breakdown;
 Dielectrics;
 Ellipticity;
 Laser Damage;
 Sound Waves;
 Wave Generation;
 Inelastic Collisions;
 Legendre Functions;
 Trigonometry;
 Wave Equations;
 Lasers and Masers