In vivo three- and four-photon fluorescence microscopy using a 1.8 $\mu$m femtosecond fiber laser system

TL;DR

This paper introduces a novel femtosecond fiber laser system emitting at 1.8 μm, enabling in vivo three- and four-photon fluorescence microscopy beyond the typical wavelength range of commercial lasers.

Contribution

Development of a 1.8 μm femtosecond fiber laser system with sufficient pulse energy for in vivo multiphoton imaging, expanding the accessible excitation wavelengths.

Findings

Achieved ~150 fs pulses at 1.8 μm wavelength.

Generated ~1 μJ pulse energy suitable for in vivo imaging.

Extended multiphoton microscopy capabilities beyond 1040 nm.

Abstract

Multiphoton microscopy has enabled us to image cellular dynamics in vivo. However, the excitation wavelength for imaging with commercially available lasers is mostly limited between 650-1040 nm. Here we develop a femtosecond fiber laser system that produces $\sim$150 fs pulses at 1.8 $\mu$m. Our system starts from an erbium-doped silica fiber laser, and its wavelength is converted to 1.8 $\mu$m using a Raman shift fiber. The 1.8 $\mu$m pulses are amplified with a two-stage Tm:ZBLAN fiber amplifier. The final pulse energy is $\sim$1 $\mu$J, sufficient for in vivo imaging.