All-fiber ultrafast amplifier at 1.9 μm based on thulium-doped normal dispersion fiber and LMA fiber compressor

The duration reduction and the peak power increase of ultrashort pulses generated by all-fiber sources at a wavelength of
1.9 µm are an urgent tasks. Finding an effective and easy way to improve these characteristics of ultrafast lasers can allow a
broad implementation of wideband coherent supercontinuum sources in the mid-IR range required for various applications. As
an alternative approach of sub-100 fs pulse generation we present an ultrafast all-fiber amplifier based on a normal-dispersion
germanosilicate thulium-doped active fiber and a large-mode-area silica-fiber compressor. The output pulses have the following
characteristics: the pulse duration of 71 fs, the central wavelength of 1.9 µm, the repetition rate of 23.8 MHz, the energy per
pulse period of 25 nJ, the average power of 600 mW, the maximum estimated peak power of 220 kW, and a random output
polarization. The pulse intensity and phase profiles were measured via the second-harmonic-generation frequency-resolved
optical gating technique. The dynamics of ultrashort pulses propagation in the amplifier was analyzed using numerical
simulation.