Three-photon Excited Autofluorescence Microscopy with a Gain-managed Nonlinear Fiber Amplifier

Three-photon excited fluorescence (3PEF) microscopy enables deeper imaging in scattering tissues like the brain. It uses a longer excitation wavelength and nonlinear excitation, offering advantages over two-photon techniques [1]. However, it demands ultrashort pulses with high peak power, often requiring complex setups like optical parametric or regenerative amplifiers. While Yb:fiber lasers <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(\sim 1\mu \mathrm{m})$</tex> offer a promising alternative for imaging endogenous fluorescence, gain narrowing during amplification typically limits pulse durations to over 150 fs [2]. We present a compact, fiber-based laser system integrating a gain-managed nonlinear (GMN) amplifier with a pulse-picking unit. This system delivers 39 fs pulses with a high peak power of 0.83 MW and an adjustable repetition rate ranging from 0.3 to 15.2 MHz at a wavelength of 1070 nm. For the first time, we demonstrate the application of the GMN amplifier in 3PEF microscopy, enabling enhanced performance for imaging applications.