Spatiotemporal beam self-cleaning for high-resolution nonlinear fluorescence imaging with multimode fibres

Figure 1: Experimental setup and characteristics of the output self-cleaned beam. a, Schematic representation of the experimental setup as detailed in Methods section. b, Output beam diameter evolution vs. input peak power (Insets: 3D representation of the output beam pattern for low and high peak powers, respectively). c, Output autocorrelation (left) and pulse duration (right) versus the input peak power. d, supercontinuum generation vs. input peak power (insets: near field pattern of the output beam for different wavelengths). Optical 50/125 µm GRIN fibre, 3 m for BSC, 18 m for supercontinuum generation.

Beam self-cleaning (BSC) in graded-index (GRIN) multimode fibres (MMFs) has been recently reported by different research groups. Driven by the interplay between Kerr effect and beam self-imaging, BSC counteracts random mode coupling, and forces laser beams to recover a quasi-single mode profile at the output of GRIN fibres. Here we show that the associated self-induced spatiotemporal reshaping allows for improving the performances of nonlinear fluorescence microscopy and endoscopy using multimode optical fibres. We experimentally demonstrate that the beam brightness increase, induced by self-cleaning, enables two and three-photon imaging of biological samples with high spatial resolution. Temporal pulse shortening accompanying spatial beam clean-up enhances the output peak power, hence the efficiency

of nonlinear imaging. We also show that spatiotemporal supercontinuum generation is well-suited for large-band nonlinear fluorescence imaging in visible and infrared domains. We substantiated our findings by multiphoton fluorescence imaging in both microscopy and endoscopy configurations.

Figure 2: Nonlinear fluorescence images obtained in a microscopy configuration of mouse kidney labelled with Alexa 488, Alexa 568 and Dapi, revealing tubule, actin and nucleus, respectively. a, two-photon fluorescence imaging of tubule and actin, three-photon imaging of nucleus by using a self-cleaned pump beam at 1064 nm. b, two-photon fluorescence imaging of tubule, actin and nucleus by using visible/IR light between 700 nm and 950 nm. c, three-photon fluorescence imaging of tubule, actin and nucleus by using IR light between 1300 nm and 1500 nm and 1200 nm for Dapi; Dwell time: 5µs/px, averaged traces for 1 image: 20, image size: 1024×1024 pixels.


N.O. Moussa, T. Mansuryan, C.H. Hage, M. Fabert, K. Krupa, A. Tonello, M. Ferraro, L. Leggio, M. Zitelli, F. Mangini, A. Niang, G. Millot, M. Papi, S. Wabnitz and V. Couderc, “Spatiotemporal beam self-cleaning for high-resolution nonlinear fluorescence imaging with multimode fibres,”