Linear Propagation Model for Laser-Induced Ultra-Sound in Water.
Abstract
The long-range propagation of acoustic transients produced experimentally from absorption of laser energy by water is examined theoretically. The linear theory, which it is argued, applies for ranges r > r sub O where viscosity effects will dominate, results in a diffusion equation for the transient pulse form. The solutions exhibit solitonic behavior, the linear l/r peak pressure falloff law going over eventually to the l/r-sq law rather than the much more severe exponential law which applies to pure tone (harmonic) waves. The scale distance for the cross-over to 1/r sq. behavior (fresh water), (r sub 1) = 0.33 km (2t sub 1)-sq, where 2t sub 1 is the transient pulse width (one-half the period) in microseconds, is predicted to be 14 meters for carbon dioxide laser induced pulses observed below threshold for vaporization. Necessary generalizations are described briefly for taking account of salinity in sea water, and of non-linear acoustic effects.
Document Details
- Document Type
- Technical Report
- Publication Date
- Aug 01, 1982
- Accession Number
- ADA157199
Entities
People
- R. Cawley
Organizations
- Naval Ordnance Laboratory