Laser generation of acoustic waves in the ablative regime

A practical model of acoustic wave generation by a pulsed laser source in the ablative regime is presented. The pressure exerted on the surface during Q-switched laser heating is calculated through a finite difference solution of the vaporization problem. The epicentral displacement is found through summation of the displacement field induced by the vaporization process with that caused by thermoelastic expansion. The model is restricted to the weakly ablative regime in the absence of a backing gas. The results are compared to the epicentral displacements generated in aluminum samples under rough vacuum conditions at generating wavelengths of 532 and 1064 nm. The waveforms compare well over a limited irradiance range. The effects of rough vacuum conditions on the generated acoustic signals are also examined and compared to signals generated in the presence of a backing gas. The divergence in the shape and amplitude of these signals observed under highly ablative conditions is discussed.

[1]  J. M. Khosrofian,et al.  Measurement of a Gaussian laser beam diameter through the direct inversion of knife-edge data. , 1983, Applied optics.

[2]  Lei Wu,et al.  Excitations of thermoelastic waves in plates by a pulsed laser , 1995 .

[3]  M. Allmen,et al.  Laser-beam interactions with materials : physical principles and applications , 1987 .

[4]  W. Duley.  Laser processing and analysis of materials , 1983 .

[5]  J. Miller,et al.  Laser ablation : principles and applications , 1994 .

[7]  J. Monchalin,et al.  Precision laser-ultrasonic velocity measurement and elastic constant determination , 1989 .

[8]  S. Fähler,et al.  Calculations and experiments of material removal and kinetic energy during pulsed laser ablation of metals , 1996 .

[9]  F. Alan McDonald,et al.  Practical quantitative theory of photoacoustic pulse generation , 1989 .

[10]  A. D. Zweig,et al.  A thermo-mechanical model for laser ablation , 1991 .

[11]  Hydrodynamic calculations of surface response in the presence of laser‐supported detonation waves , 1975 .

[12]  M. Allmen.  Laser drilling velocity in metals , 1976 .

[13]  J. Hatch,et al.  Aluminum: Properties and Physical Metallurgy , 1984 .

[14]  J. Ready.  Effects of high-power laser radiation , 1971 .

[15]  L. R. F. Rose,et al.  Point‐source representation for laser‐generated ultrasound , 1984 .

[16]  R. D. Richtmyer,et al.  Difference methods for initial-value problems , 1959 .

[17]  Robert Fedosejevs,et al.  Melting and damage of aluminum surfaces by 80 ps KrF laser pulses , 1994 .

[18]  David A. Hutchins,et al.  Quantitative measurements of laser‐generated acoustic waveforms , 1982 .

[19]  C. Knight.  Theoretical Modeling of Rapid Surface Vaporization with Back Pressure , 1979 .

[20]  J. Narayan,et al.  A novel method for simulating laser-solid interactions in semiconductors and layered structures , 1989 .

[21]  D. E. Gray,et al.  American Institute of Physics Handbook , 1957 .

[22]  W. Arnold,et al.  Calculation and measurement of the ultrasonic signals generated by ablating material with a Q-switched pulse laser , 1996 .