Multimodal nonlinear endomicroscopic imaging probe using a double-core double-clad fiber and focus-combining micro-optical concept

Multimodal non-linear microscopy combining coherent anti-Stokes Raman scattering,second harmonic generation,and two-photon excited fluorescence has proved to be a versatile and powerful tool enabling the label-free investigation of tissue structure,molecular composition,and correlation with function and disease status.For a routine medical application,the implementation of this approach into an in vivo imaging endoscope is required.However,this is a difficult task due to the requirements of a multicolour ultrashort laser delivery from a compact and robust laser source through a fiber with low losses and temporal synchronization,the efficient signal collection in epi-direction,the need for small-diameter but highly corrected endomicroobjectives of high numerical aperture and compact scanners.Here,we introduce an ultra-compact fiber-scanning endoscope platform for multimodal non-linear endomicroscopy in combination with a compact four-wave mixing based fiber laser.The heart of this fiber-scanning endoscope is an in-house custom-designed,single mode,double clad,double core pure silica fiber in combination with a 2.4 mm diameter NIR-dual-waveband corrected endomicroscopic objective of 0.55 numerical aperture and 180µm field of view for non-linear imaging,allowing a background free,low-loss,high peak power laser delivery,and an efficient signal collection in backward direction.A linear diffractive optical grating overlays pump and Stokes laser foci across the full field of view,such that diffraction-limited performance is demonstrated for tissue imaging at one frame per second with sub-micron spatial resolution and at a high transmission of 65%from the laser to the specimen using a distal resonant fiber scanner.

Hybrid multimode - multicore fibre based holographic endoscope for deep-tissue neurophotonics

In-vivo microendoscopy in animal models became a groundbreaking technique in neuroscience that rapidly expands our understanding of the brain.Emerging hair-thin endoscopes based on multimode fibres are now opening up the prospect of ultra-minimally invasive neuroimaging of deeply located brain structures.Complementing these advancements with methods of functional imaging and optogenetics,as well as extending its applicability to awake and motile animals constitute the most pressing challenges for this technology.Here we demonstrate a novel fibre design capable of both,high-resolution imaging in immobilised animals and bending-resilient optical addressing of neurons in motile animals.The optimised refractive index profile and the probe structure allowed reaching a spatial resolution of 2μm across a 230μm field of view for the initial layout of the fibre.Simultaneously,the fibre exhibits negligible cross-talk between individual inner-cores during fibre deformation.This work provides a technological solution for imaging-assisted spatially selective photo-activation and activity monitoring in awake and freely moving animal models.