Toward endoscopic ultrafast laser microsurgery of vocal folds

Vocal fold scarring is one of the predominant causes of voice disorders yet lacks a reliable treatment method. The injection of soft biomaterials to improve mechanical compliance of the vocal folds has emerged as a promising treatment. Successful implementation of this method may benefit from improved localization of the injected material. Here, we create sub-surface vocal fold microsurgeries with a goal of eventually creating a plane in dense sub-epithelial scar tissue into which biomaterials can be injected. Specifically, we demonstrate the ablation of sub-epithelial voids in porcine vocal fold tissue within 100 μm below the surface such that a larger void in the active area of vocal fold mucosa (~3 × 10 mm2) can eventually be ablated in about 2 minutes. We use sub-μJ, 776 nm pulses from a compact, commercially available amplified femtosecond laser system operating at a 500 kHz repetition rate. The use of relatively high repetition rates, with a small number of overlapping pulses, is critical to achieving ablation in a very short period of time while still avoiding significant heat deposition. Additionally, we use the same laser for nonlinear optical imaging to provide visual feedback of tissue structure and confirm successful ablation. The ablation parameters, including pulse duration, pulse energy, spot size and scanning speed, are comparable to the specifications in our recently-developed miniaturized femtosecond laser surgery probe, illustrating the feasibility of developing an ultrafast laser surgical laryngoscope. We aim to further develop this clinical tool through demonstration of laryngeal microsurgery using a compact laser system in conjunction with a larynx-specific fiber-based surgery probe.