Mamyshev oscillators are at the forefront of parameter scaling of ultrafast fiber oscillators. This talk focuses on the prospects of Mamyshev oscillators in the spectral 2 µm region based on thulium-doped fibers. Recent studies have reported pulse energies up to 15 nJ at a duration of 140 fs by a large normal dispersive cavity. Moreover, higher order soliton dynamics hold promise to scale the peak power into the MW-class for ultrafast fiber oscillators in the short wavelength mid-infrared.
Gain dynamics play a crucial role in the design of laser oscillators and amplifiers. In order to expand
the understanding of gain dynamics into the spectral 2 μm region, this study presents the experimental characterization of transfer functions in thulium-doped fiber amplifiers associated with the 3F4 → 3H6 transition that governs emission in this spectral range. The transfer functions for both the signal and pump are thoroughly investigated, providing detailed information on their magnitude and phase. We find a damped high-pass and a low-pass filtering behaviour for the respective signal and pump transfer function of thulium-ions in silica glass.
We report on our recent results of the numeric evaluation of the gain evolution inside a thulium-doped fiber Mamyshev oscillator in the spectral 2 μm region, comparing the core pumping scheme with the double-clad pumping scheme in order to further optimize the output parameters in the experimental setup. By comparing the two pumping schemes, we find spectral gain channeling around 1950 nm for the double-clad pumping scheme owing to a three orders of magnitude lower pump intensity and an order of magnitude higher doping concentration. The found gain distribution is highly effective to suppress amplified spontaneous emission at the maximum emission cross section of thulium ions in silica glass and thus enables operation beyond the water absorption lines. Furthermore based on the gain evolution model, also a novel broadening mechanism inside the gain fiber of Mamyshev oscillators is numerically evaluated. The pulse evolution is determined by the interplay between the anomalous dispersion and self-phase modulation inside the gain fiber and allows to self-compress the pulse, while simultaneously monotonic spectral broadening arises during the amplification. This novel pulse evolution inside a Mamyshev oscillator shows nearly transform limited high peak power pulses with a pulse duration below 100 fs directly at the output without any additional compression stage.
We report on our recent results for output scaling by a Thulium-doped fiber Mamyshev oscillator in the spectral 2 µm region. In order to further scale the output, a highly Thulium-doped double-clad fiber was implemented in the Mamyshev oscillator. A stable pulse train at a repetition rate of 19.7 MHz with an average power of 220 mW was observed. This corresponds to a pulse energy of 11 nJ at a pulse length of 2.4 ps. Further scaling of the output parameters was limited by soliton fission, which will be mitigated by introducing normal dispersive fiber sections in future experiments.
The principle of a Mamyshev oscillator depends on alternating spectral filtering between sections of spectral broadening by self-phase modulation. In the 2 µm wavelength range, this concept faces the difficulty that standard fibers are anomalous dispersive which limits the possible pulse energy to the pJ-regime without proper dispersion management. We applied ultra-high numerical aperture fibers with normal dispersion in order to achieve up-chirped pulses in an anomalous dispersive Thulium-doped gain fiber. With that design, we achieved mode-locked pulses with energies of 6.4 nJ and a compressed autocorrelation duration of 195 fs at a repetition rate of 16 MHz.
Conference Committee Involvement (2)
Fiber Lasers XXI: Technology and Systems
29 January 2024 | San Francisco, California, United States
Fiber Lasers XX: Technology and Systems
30 January 2023 | San Francisco, California, United States
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