Seismic excitation using a high power CO2 laser

Abstract

Lasers provide one method of remotely exciting propagating waves in soil. The absorption of optical energy results in plasma formation, a dynamic change near the soil surface, and excitation of propagating waves. Experiments were performed using a high power CO2 pulsed laser to determine the pressure waveforms generated in desert sand and caliche clay. The laser energy ranged from 400–750 J with a pulse duration of 35 μs. The resulting pressure pulse was observed for duration of at least 400 μs and had a peak pressure of 100 kPa. The duration increased at greater depths, while the peak pressure and energy in a pulse decreased rapidly at these depths. Surface velocity reached a peak of 35 mm/s as acquired on geophones placed in proximity to the laser plasma event. This system, in combination with a laser Doppler vibrometer, has the potential to be a useful component of non‐invasive mine detection equipment.