High power, ultrashort pulse control through a multi-core fiber for ablation

Abstract

Ultrashort pulse ablation has become a useful tool for micromachining and biomedical surgical applications. Implementation of ultrashort pulse ablation in confined spaces has been limited by endoscopic delivery and focusing of a high peak power pulse. Here we demonstrate ultrashort pulse ablation through a thin multi-core fiber (MCF) using wavefront shaping, which allows for focusing and scanning the pulse without requiring distal end optics and enables a smaller ablation tool. The intensity necessary for ablation is significantly higher than for multiphoton imaging. We show that the ultimate limitations of the MCF based ablation are the nonlinear effects induced by the pulse in the MCFs cores. We characterize and compare the performance of two devices utilizing a different number of cores and demonstrate ultrashort pulse ablation on a thin film of gold.

Learning to see through multimode fibers

“…The transmission of images through a MMF was first presented in 1967 by Spitz and Wertz [3] who demonstrated experimentally that the distortion introduced by modal dispersion can be undone by phase conjugation. In the intervening years numerous publications have described methods for transmitting image information through MMFs or scattering media [4][5][6][7][8][9][10][11][12][13][14][15]. These methods rely on coherent (holographic) recording of the speckle pattern detected at the distal end of the fiber and they use phase conjugation or the transmission matrix method to compensate for the effects of modal dispersion and either focus the light at the distal end or project focused images.…”

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

“…We have previously reported on the delivery of ultrashort pulses via a multicore fiber (MCF) for laser ablation purposes [25]. We achieved a maximum peak intensity delivery of 4x10 12 W/cm 2 with a MCF fiber of 10,000 cores (460 μm core diameter) [25].…”

“…The TM is calculated using 12,000 and 46,000 input angles for each of the fibers respectively [32]. More details concerning the TM recording and processing have been previously reported [24,25,33]. The pulse energy used for measuring the TM (E p = 0.2 μJ) was below the level that nonlinearities arise along the GRIN fibers.…”

“…We have previously reported on the delivery of ultrashort pulses via a multicore fiber (MCF) for laser ablation purposes [25]. We achieved a maximum peak intensity delivery of 4x10 12 W/cm 2 with a MCF fiber of 10,000 cores (460 μm core diameter) [25]. The segmented (grating-like) core shape of the MCFs results in the formation of a diffraction circle around the focus spot even after wavefront shaping, which reduces the light power in the focus to about 14% of the total power [25,[34][35][36].…”

“…The addition of distal end optical and/or mechanical components significantly increases the size and complexity of the endoscope. To avoid this, wavefront shaping techniques (digital-phase conjugation (DPC), transmission matrix (TM), iterative optimization) have been proposed to focus and scan the laser beam digitally by encoding the wavefront at the proximal end of a multimode fiber (MMF) [20,[23][24][25][26][27][28][29]. In this work, we use the TM technique to focus and scan the light through ultrathin GRIN fibers.…”