Time and frequency resolved XeCl laser-induced mechanical transients in otic capsule bone.

OBJECTIVE This study identifies the presence of photoacoustic waves during excimer laser treatment of porcine otic capsule bone. BACKGROUND DATA Pulsed ultraviolet lasers have been suggested for use in middle ear surgery due to their potential for fiberoptic delivery, decreased thermal trauma, and precise ablation characteristics. However, the short pulse width of excimer lasers (typically 10-150 ns) can create large thermoelastic stresses in the ablation specimen. MATERIALS AND METHODS A XeCl (lambda = 308 nm, tau = 12 ns) excimer laser was used to ablate wafers of bone with energies of 90, 35, 13, 5, and 1.8 mJ/pulse. Custom high-frequency polyvinyldifluoride (PVDF) piezoelectric film transducers were fabricated and attached to the slices of bone. During ablation photoacoustic signals were amplified using a low-noise preamplifier and recorded on a digitizing oscilloscope. RESULTS Photoacoustic waves were clearly identified. Stress wave amplitude increased with laser fluence. CONCLUSION A laser fluence must be found that compromises between an increased ablation rate and increased stress wave amplitude. The acoustic power levels generated during ablation are below maximum exposure limits.