Kagome fiber based ultrafast laser microsurgery probe delivering micro-Joule pulse energies

Abstract

Abstract:We present the development of a 5 mm, piezo-actuated, ultrafast laser scalpel for fast tissue microsurgery. Delivery of micro-Joules level energies to the tissue was made possible by a large, 31 μm, air-cored inhibited-coupling Kagome fiber. We overcome the fiber's low NA by using lenses made of high refractive index ZnS, which produced an optimal focusing condition with 0.23 NA objective. The optical design achieved a focused laser spot size of 4.5 μm diameter covering a 75 × 75 μm 2 scan area in a miniaturized setting. The probe could deliver the maximum available laser power, achieving an average fluence of 7.8 J/cm 2 on the tissue surface at 62% transmission efficiency. Such fluences could produce uninterrupted, 40 μm deep cuts at translational speeds of up to 5 mm/s along the tissue. We predicted that the best combination of speed and coverage exists at 8 mm/s for our conditions. The onset of nonlinear absorption in ZnS, however, limited the probe's energy delivery capabilities to 1.4 μJ for linear operation at 1.5 picosecond pulse-widths of our fiber laser. Alternatives like broadband CaF 2 crystals should mitigate such nonlinear limiting behavior. Improved opto-mechanical design and appropriate material selection should allow substantially higher fluence delivery and propel such Kagome fiber-based scalpels towards clinical translation.

Preclinical evaluation of porcine colon resection using hollow core negative curvature fibre delivered ultrafast laser pulses

“…The laser was transmitted through a kagome fibre optic probe, which was used to generate a lissajous pattern on the tissue surface at a frequency of approximately 1 kHz. However, no histology results are provided with this work so it is not possible to evaluate the impact on underlying tissue in a clinically relevant context and in particular assess the extent of the thermally damaged region . Earlier research has shown a significantly larger width of thermal necrosis induced by conventional surgical devices such as electrocautery (456 μm) , harmonic scalpel (690 μm) and CO 2 laser (300 μm) .…”

“…Researchers have used multicore and graded index multimode fibres for the delivery of ultrashort pulse (USP) to demonstrate the laser ablation. Prior work has established pig tissue as an efficient medical model for several studies related to human diseases and is consequently applied in porcine vocal fold tissue resection using 1.5 ps laser pulses delivered through kagome lattice hollow core photonic crystal fibre for microsurgery . The microsurgery laser ablation on the vocal fold tissue has a depth and width of ablation of around 43 and 40 μm, respectively, at a pulse energy of 1.2 μJ.…”

“…In contrast to previous work in fibre delivered USPs for microsurgery of tissue the work reported here focuses on using longer, 6 ps, pulses for larger, millimetre scale, ablation of tissue. These pulses are delivered using a HC‐NCF which has favourable performance in terms of minimizing nonlinear effects and bend losses.…”

Selective femtosecond laser ablation via two-photon fluorescence imaging through a multimode fiber

“…Our results show that the 400 μm diameter GRIN fiber can provide a focus spot with peak intensities reaching up to 1.5x10 13 W/cm 2 . The peak intensity delivered by our system is comparable to that of a HC-PCF [17,18], while maintaining the size of the final probe below 1mm by avoiding the need of distal components.…”

“…Most commercially available tools use either single mode fibers (SMFs) combined with optical components to focus the light at the distal side and scanning mechanisms to steer the light around the region of interest or fiber bundles that result in pixelated images [1,17,[19][20][21][22]. The addition of distal end optical and/or mechanical components significantly increases the size and complexity of the endoscope.…”