Accession Number : ADA138483

Title :   Laser Generation of Ultrasound.

Descriptive Note : Final rept.,

Corporate Author : BOLT BERANEK AND NEWMAN INC CAMBRIDGE MA

Personal Author(s) : Rudd,M J ; Doughty,J A

PDF Url : ADA138483

Report Date : Feb 1983

Pagination or Media Count : 67

Abstract : The purpose of this report is to demonstrate a technique to generate high level, focused ultrasound by laser excitation of a material. The application is for ultrasonic nondestructive testing of components and possibly structures. The principle is that the laser energy is absorbed by a material and heats it, and the resulting thermal expansion generates a pressure wave in the material. An experimental and analytical study has been conducted into the use of carbon dioxide TEA lasers to generate ultrasonic waves. When the laser is fired at a plastic target, waves with a peak-to-peak pressure of 10 bars are generated. Teflon and Mylar were the most effective. There was no damage to the plastic, even after several hundred shots. This was not the case for glass or aluminum with a much smaller absorption depth and lower conversion efficiency. The sound wave could be directed by using an off-axis zone plate. This generated a 10 MHz tone burst, 45 deg, off-axis with a duration of 4 microsecs. A theoretical analysis of the phenomena is given which accounts for the waveforms and peak pressures measured.

Descriptors :   *Ultrasonic tests, *Ultrasonics, *Laser applications, *Nondestructive testing, *Laser weapons, Excitation, Surface properties, Laser damage, Carbon dioxide lasers, Tea lasers, Thermal expansion, Thermoelasticity, Targets, Plastics, Aluminum, Glass, Shock waves, Stress waves

Subject Categories : Lasers and Masers
      Test Facilities, Equipment and Methods
      Acoustics

Distribution Statement : APPROVED FOR PUBLIC RELEASE