All-fiber ultrafast amplifier at 1.9\xa0\u03bcm based on thulium-doped normal dispersion fiber and LMA fiber compressor

Vasilii Voropaev,Andrey Voronets,Daniil Batov,Mikhail Tarabrin,Aleksandr Donodin,Vladimir Lazarev,Rana Jafari,Dmitrii Vlasov,Rick Trebino

doi:10.1038/s41598-021-02934-4

Abstract

The duration reduction and the peak power increase of ultrashort pulses generated by all-fiber sources at a wavelength of 1.9,upmu hbox {m} are 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 to 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 central wavelength of 1.9,upmu hbox {m}, the repetition rate of 23.8 MHz, the energy per pulse period of 25 nJ, the average power of 600 mW, and a random output polarization. The pulse intensity and phase profiles were measured via the second-harmonic-generation frequency-resolved optical gating technique for a linearly polarized pulse. The linearly polarized pulse has a duration of 71 fs and a peak power of 128.7 kW. The maximum estimated peak power for all polarizations is 220 kW. The dynamics of ultrashort-pulse propagation in the amplifier were analyzed using numerical simulations.

Highlights

Ultrafast thulium-doped fiber-laser sources at the wavelength of1.9 μm have attracted great interest due to their wide range of potential a pplications[1], including remote sensing, precision frequency-domain s pectroscopy[2], and breath analysis[3]
For the first time to the best of our knowledge, we present a system for ultrashort pulse amplification and compression based on the combination of an active germanosilicate thulium-doped fiber with a normal group-velocity dispersion (GVD) and an LMA fiber with an anomalous GVD
The actual shortest pulse had a much more complex shape than a Gaussian, so it was necessary to measure the true temporal intensity profile using frequency-resolved optical gating (FROG) to estimate the peak power and clarify the nature of the pulse pedestal of the autocorrelation trace associated with pre-pulses and post-pulses

Summary

Introduction

Ultrafast thulium-doped fiber-laser sources at the wavelength of1.9 μm have attracted great interest due to their wide range of potential a pplications[1], including remote sensing, precision frequency-domain s pectroscopy[2], and breath analysis[3]. In thulium-doped fiber-laser systems, various techniques and their combinations are used to achieve such pulse characteristics, including the use of large-mode-area (LMA) active fibers[8], nonlinear pulse c ompression[9,10,11], the chirped-pulse amplification technique[4,10,11], etc. Laser systems based on thulium-doped normal dispersion fibers have been experimentally embodied[18,19] These setups feature durations of more than 600 fs, which are less promising for coherent supercontinuum generation. The use of a germanosilicate thulium-doped fiber with normal GVD as an active medium significantly expands the pulse spectrum during the amplification process This broadening helps to achieve a shorter pulse duration than that fundamentally achievable at the input of the amplifier. The pulse intensity-and-phase profile was measured via the secondharmonic-generation (SHG) frequency-resolved optical gating (FROG)[20]

Results

Discussion

Conclusion