a Department of Physics, University of Warwick, Coventry CV4 7AL, UK
b Department of Engineering, University of Warwick, Coventry CV4 7AL, UK
Abstract:
An industrial TEA-CO2 laser, operating at a wavelength of 10.6 μm, has been used to produced broadband ultrasonic pulses in polymers. The generation mechanism falls into three categories. At low power densities ≤ 107 W cm−2 a thermoelastic regime predominates. As the power density is increased in the range (1–5) × 107 W cm−2 ablation of the material surface plays an increasingly important role in the acoustic generation. Thirdly, at greater power densities, plasma breakdown just above the material surface serves as the means of generation. This paper describes the acoustic sources for these types of generation mechanism and presents theoretically calculated acoustic waveforms to match those recorded experimentally.