Flexible delivery of Er:YAG radiation at 2.94 μm with novel hollow-core silica glass fibres: demonstration of tissue ablation

In this work we present the delivery of high energy Er:YAG laser pulses operating at 2.94 mu m through a hollow-core negative curvature fibre (HC-NCF) and a hollow-core photonic crystal fibre (HC-PCF) and their use for the ablation of biological tissue. In HC-NCF fibres, which have been developed recently, the laser radiation is confined in a hollow core and by an anti-resonant or reflection principle (also known as ARROW). Both fibres are made of fused silica which has high mechanical and chemical durability, is bio-inert and results in a fibre with the flexibility that lends itself to easy handling and minimally invasive procedures. The HC-NCF structure consists of only one ring of capillaries around a realtively large core, followed by a protecting outer layer, hence the preform is relatively easy to build compared to traditional HC-PCF. The measured attenuation at 2.94 mu m is 0.06 dB/m for the HC-NCF and 1.2 dB/m for the HC-PCF. Both fibres have a single mode output beam profile which can be advantageous for surgical applications as the beam profile is maintained during fibre movement. We demonstrate delivery of high energy pulses through both fibres, well above the thresholds needed for the ablation of biological tissue in non-contact and contact mode. Delivered energy densities reached > 750 J/cm(-2) after 10 m of HC-NCF and > 3400 J/cm(2) through a 44 cm HC-PCF.

This flexible high energy delivery system offers an alternative to existing beam delivery systems such as articulated arms and large core multi-mode fibres with enhanced capabilities.