Abstract
Here, we firstly utilize a newly explored 1.6 μm harmonic dissipative soliton resonance (DSR) pulses as a pump source to realize a highly efficient gain-switched thulium fiber laser at 1719.52 nm. The 1.6 μm DSR pulses with a fundamental repetition rate of 360 kHz were produced from a nonlinear amplifying loop mirror (NALM) ring cavity, which directly output high power mode-locking pulses due to freedom of soliton-area limitation and pulse breaking. The harmonic mode-locking (HML) operation was achieved by properly adjusting the polarization controllers (PCs). The thulium fiber laser cavity constructed by a Fiber Bragg Grating (FBG) pair was resonantly (in-band) pumped by the 1.6 μm harmonic DSR pulses. Taking the merit of the strong absorption of Tm<sup>3+</sup> at 1.6 μm and the laser cavity having a low insert loss, the 1.7 μm gain-switched fiber laser with the maximum repetition rate of 2.16 MHz, corresponding to the average power of 2.826 W and the pulse energy of 1.33 μJ, was obtained at a high slope efficiency of about 71.9%. The maximum output power could exceed 3 W with a high slope efficiency of over 70%, which is the record in 1.7 μm all-fiber pulsed thulium lasers.
Highlights
The development of 1.7 μm lasers has raised great interest in recent years
A. 1.6 μm dissipative soliton resonance (DSR) laser When the 915 nm pump power was increased to 1.5 W, the continuous wave (CW) 1.6 μm laser became the mode-locking state with a fundamental repetition rate of 360 kHz
It can be seen that the pulse exhibited a rectangle-shaped profile, which was the typical feature of DSR laser
Summary
The development of 1.7 μm lasers has raised great interest in recent years. Within this wavelength regime, the human tissue with rich lipid has a strong absorption. The scattering loss of biological tissue is proportional to ω4, in comparison with the light source in 1000 nm ~ 1400 nm, 1.7 μm laser can achieve a deeper penetration depth and reduce non-resonant background. These advantages make 1.7 μm laser being a promising light source for biomedical imaging. High power 1.7 μm lasers can be high brightness pump sources for Dy: fluoride to generate midinfrared lasers [8]
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