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

Abstract

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.

Highly Nonlinear Multimode Tellurite Fibers: From Glass Synthesis to Practical Applications in Multiphoton Imaging

“…In such configuration and using this multimode optical fiber details as small as 1.2 μm have been observed by lighting the sample with an infrared beam (1100–1700 nm): this corresponds, on average, to a resolution close to the wavelength dimension (Figure 6d), which is only twice times larger than the half‐wavelength minimum resolution reported with a single‐mode polychromatic beam. [ 6 ]…”

“…[ 2 ] In particular, SC generation with wavelengths covering all the visible domain and a large part of the silica transparency window has been demonstrated [ 3 ] : the spatially single‐mode polychromatic beams have widely been employed for linear and nonlinear fluorescence imaging using femtosecond, picosecond, or subnanosecond pulses. [ 4,5 ] More recently, multimode optical fibers have also been considered for efficient imaging processes demonstration in the visible and near‐infrared domain [ 6 ] ; in particular, two and three‐photon fluorescence measurements have been demonstrated. Although coupling laser light into a multimode fiber is a relatively easy task, the output beam suffers from spatial and temporal distortions that bring severe limitations to the imaging resolution.…”

Single-mode spatiotemporal soliton attractor in multimode GRIN fibers

“…In addition, there is a significant industrial interest in the use of large-area fibers for up-scaling the power of fiber lasers, for high-power beam delivery, and for biomedical imaging applications. In these applications, it is very important to maintain the high beam quality of single-mode fibers even when transporting a beam via an MMF [11,12].…”

Singlemode spatiotemporal soliton attractor in multimode GRIN fibers

“…In addition, there is a significant industrial interest in the use of large-area fibers for up-scaling the power of fiber lasers, for high-power beam delivery, and for biomedical imaging applications. In these applications, it is very important to maintain the high beam quality of singlemode fibers even when transporting a beam via an MMF [11,12].…”