title: Tunable fibre-coupled multiphoton microscopy with a negative curvature fibre.
abstract: Negative curvature fibre (NCF) guides light in its core by inhibiting the coupling of core and cladding modes. In this work, an NCF was designed and fabricated to transmit ultrashort optical pulses for multiphoton microscopy with low group velocity dispersion (GVD) at 800 nm. Its attenuation was measured to be <0.3 dB m(-1) over the range 600-850 nm and the GVD was -180 ± 70 fs(2)  m(-1) at 800 nm. Using an average fibre output power of ∼20 mW and pulse repetition rate of 80 MHz, the NCF enabled pulses with a duration of <200 fs to be transmitted through a length of 1.5 m of fibre over a tuning range of 180 nm without the need for dispersion compensation. In a 4 m fibre, temporal and spectral pulse widths were maintained to within 10% of low power values up to the maximum fibre output power achievable with the laser system used of 278 mW at 700 nm, 808 mW at 800 nm and 420 mW at 860 nm. When coupled to a multiphoton microscope, it enabled imaging of ex vivo tissue using excitation wavelengths from 740 nm to 860 nm without any need for adjustments to the set-up.
authors.affiliation: Department of Physics, Imperial College London, London, SW7 2AZ, UK. b.sherlock@imperial.ac.uk.
authors.forename: Ben
authors.initials: B
authors.lastname: Sherlock
authors.affiliation: Department of Physics, University of Bath, Bath, BA2 7AY, UK.
authors.forename: Fei
authors.initials: F
authors.lastname: Yu
authors.affiliation: Department of Physics, University of Bath, Bath, BA2 7AY, UK.
authors.forename: Jim
authors.initials: J
authors.lastname: Stone
authors.affiliation: Department of Physics, Imperial College London, London, SW7 2AZ, UK.
authors.forename: Sean
authors.initials: S
authors.lastname: Warren
authors.affiliation: Department of Physics, Imperial College London, London, SW7 2AZ, UK.
authors.forename: Carl
authors.initials: C
authors.lastname: Paterson
authors.affiliation: Department of Physics, Imperial College London, London, SW7 2AZ, UK.
authors.forename: Mark A A
authors.initials: MA
authors.lastname: Neil
authors.affiliation: Department of Physics, Imperial College London, London, SW7 2AZ, UK.
authors.forename: Paul M W
authors.initials: PM
authors.lastname: French
authors.affiliation: Department of Physics, University of Bath, Bath, BA2 7AY, UK.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Knight
authors.affiliation: Department of Physics, Imperial College London, London, SW7 2AZ, UK.|Centre for Histopathology, Imperial College London, London, SW7 2AZ, UK.
authors.forename: Chris
authors.initials: C
authors.lastname: Dunsby
mesh_terms: D000818:Animals; D008027:Light; D051379:Mice; D036641:Microscopy, Fluorescence, Multiphoton; D012867:Skin / Q000000981:diagnostic imaging
keywords: Photonic crystal fibre; multiphoton; negative curvature