Fiber-based sources delivering high-energy few-cycle pulses at high repetition rates are currently being developed in the near-infrared spectral range, thanks to the wide availability of telecommunication-grade optical fibers and components. Similar sources in the middle-wave infrared (mid-IR) spectral domain, however, are scarce, although such sources are of high interest for applications such as high-precision frequency metrology and molecular spectroscopy or as a seed source to reach further into the mid-IR via coherent nonlinear processes. Here we report on the design of a fiber-based source of 50-nJ energy 90 fs duration pulses up to 2950 nm, corresponding to 500 kW peak power. To obtain this level of peak power we exploit multi-solitonic fission and soliton self-frequency shift in large mode area fibers excited by picosecond pulses emitted at 2 µm from a megahertz repetition rate fiber laser. We leverage mature silica-based fiber technology up to 2.4 µm and restrict the use of fluoride fiber to the very last frequency-shifting stage. The level of instantaneous power and ultra-short duration achieved in this Letter pave the way to all-fiber format generation of an ultra-broadband coherent continuum in the mid-IR with profound implications for applications such as high-resolution molecular spectroscopy and imaging.
The spectral window around 1700 nm is interesting for in-depth multiphoton microscopy of intact tissues due to reduced scattering and absorption in this wavelength range. However, wide adoption of this excitation range will rely on the availability of robust and cost-effective high peak power pulsed lasers operating at these wavelengths. Here, we report on a fiber-based femtosecond laser providing up to 95 nJ, 85 fs pulses at 1800 nm. The laser system makes use of a fiber-based chirped pulse amplifier emitting at 1560 nm followed by an in-house fabricated very large mode area antiresonant fiber for soliton self-frequency shift. Megawatt-peak power pulses at the repetition rate of 1 MHz are available directly at the output of the flexible fiber. We illustrate the potential of the source for biological microscopy by recording three-photon-excited fluorescence images of mouse nervous tissue. The flexible fiber tailored to propagate megawatt solitons in the biologically relevant window around 1700 nm opens the way to deep brain imaging of freely moving animals via miniaturized endomicroscopes.
We report on the generation of 35 kW, 180 fs pulses above 4 μm by soliton self-frequency shift from a 2 µm fiber-based laser and their application to the generation of two-octave mid-infrared supercontinuum in chalcogenide fiber.
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