Scattering properties and femtosecond laser ablation thresholds of human and canine vocal folds at 776-nm wavelength

Ultrafast laser ablation may provide a treatment for vocal fold (VF) scarring. Optical properties of VFs must be known prior to clinical implementation to select appropriate laser surgery conditions. We present scattering lengths of epithelium ℓ_{s, ep}, superficial lamina propria ℓ_{s, SLP}, and ablation thresholds F_th of human and canine VF tissues. Our experimental approach involves an image-guided, laser-ablation-based method that allows for simultaneous determination of ℓ_s and F_th in these multilayered tissues. Studying eight canine samples, we found ℓ_{s, ep} = 75.3 ± 5.7 μm, ℓ_{s, SLP} = 26.1 ± 1.2 μm, F_{th, ep} = 1.58 ± 0.06 J/cm², and F_{th, SLP} = 1.55 ± 0.17 J/cm². Studying five human samples, we found ℓ_{s, ep} = 42.8 ± 3.3 μm and F_{th, ep} = 1.66 ± 0.10 J/cm². We studied the effects of cumulative pulse overlap on ablation threshold and found no significant variations beyond 12 overlapping pulses. Interestingly, our studies about the effect of sample storage on the scattering properties of porcine VF show a 60% increase in ℓ_{s, ep} for fresh porcine VF when compared to the same sample stored in isotonic solution. These results provide guidelines for clinical implementation by enabling selection of optimal laser surgery parameters for subsurface ablation of VF tissues.