Accession Number : ADA119903

Title :   Photoacoustic Microscopy.

Descriptive Note : Final rept. 16 Aug 81-15 Aug 82,


Personal Author(s) : Thomas,R L ; Favro,L D ; Kuo,P K

PDF Url : ADA119903

Report Date : 14 Sep 1982

Pagination or Media Count : 5

Abstract : Considerable improvements have been achieved in the design of the photoacoustic microscope, including new sample cells, and better microcomputer hardware, firmware, and software for the scan control and data acquisition. The ND:YAG laser system has been made operational and has been used to obtain preliminary data in the development of a time-domain phtoacoustic microscope (pulse-echo themal wave imaging). Scan control instrumentation has been developed for this instrument, as well as electronics for data acquisition in the time domain. Theoretical calculations of pulsed thermal wave propagation and scattering have been carried out for comparison with experiment. Calculations for photoacoustic signals (cw) from model subsurface defects have been carried out and compared with experimental results. A key result is the theoretical prediction, and experimental verification that closed subsurface lateral cracks have a very characteristic photoacoustic phase signature which allows their discrimination form subsurface voids (or open cracks). Calculations have also been carried out for subsurface shpericl voids and tilted closed cracks. These calculations themselves were made possible because of our development of a very general theorem for SPAM using gas-filled cells, which greatly simplifies the theoretical calculations of the effects of thermal wave scattering from arbitrarily shaped flaws in solids.

Descriptors :   *Microcomputers, *Photoactivation analysis, *Acoustic microscopes, *Nondestructive testing, Data acquisition, Defects(Materials), Models, Thermal properties, Image processing, Wave propagation, Computer programs, Voids, Cracks, Shape, Time domain, Theory, Predictions

Subject Categories : Radiation and Nuclear Chemistry
      Computer Programming and Software
      Computer Hardware
      Test Facilities, Equipment and Methods

Distribution Statement : APPROVED FOR PUBLIC RELEASE