High-repetition-rate laser ultrasonic generation in carbon-fiber-reinforced plastics excited by a 3.2-3.4  μm ZGP...

In this paper, we demonstrate 1-kHz-repetition-rate laser ultrasound in carbon-fiber-reinforced plastics (CFRPs). A ZGP master oscillator and power amplifier (MOPA) system was used to generate high-repetition-rate laser radiation in the spectral range 3.2-3.4 μm. At the output wavelength of 3.4 μm, the maximum output energy of the ZGP MOPA system is 5.62 mJ with a pulse width of 24 ns, corresponding to a peak power of approximately 233.9 kW. The ultrasound was generated by the laser converted from 3.2 to 3.4 μm in the graphite/epoxy composite. The maximum ultrasonic signal amplitude in the CFRP sample was 36.2 mV in the condition of thermoelastic excitation at 3.4 μm. Ablation occurred in the CFRP sample when the energy fluence was over 90  mJ/cm². Compared in different samples, laser-ultrasound generation was influenced by the wavelength of the laser.