Abstract:We generate over half a watt of tunable near-IR (1380-1830 nm) and several hundred milliwatts in the mid-IR (2.4-4.2 µm) as well as milliwatt level mid-IR (4.85-9.33 µm) femtosecond radiation by pumping an optical parametric amplifier directly with a 7.4 W Yb:KGW oscillator at 41.7 MHz repetition rate. We use 5 mm PPLN and 2 mm GaSe as downconversion crystals and seed this process by a supercontinuum from a tapered fiber. The system is extremely simple and very stable and could replace more complex OPOs as tunable light sources. repetition rate tunable femtosecond pulses and broadband amplification from fiber laser pumped parametric amplifier," Opt. Express 14(11), 4765-4773 (2006). 12. C. Schriever, S. Lochbrunner, P. Krok, and E. Riedle, "Tunable pulses from below 300 to 970 nm with durations down to 14 fs based on a 2 MHz ytterbium-doped fiber system," Opt. Lett. 33(2), 192-194 (2008). Chu, "Broadband tunable optical parametric amplification from a single 50 MHz ultrafast fiber laser," Opt.
We report on an optical parametric amplifier at high repetition rate of 41.7 MHz seeded by an optical soliton from a tapered fiber. Gap-free signal tuning from 1.35 μm to 1.95 μm with corresponding idler wavelengths from 2.2 μm to 4.5 μm is demonstrated. The system provides up to 1.8 W average power at 1.4 μm, more than 1.1 W up to 1.7 μm, and more than 400 mW up to 4.0 μm with a signal pulse duration of 200 to 300 fs. It is directly pumped by a solid-state oscillator providing up to 7.4 W at 1.04 μm wavelength with 425 fs pulse duration. Soliton-seeding is shown to lead to excellent pulse-to-pulse stability, but it introduces a timing-jitter on the millisecond timescale. Using a two-stage concept the timing-jitter is efficiently suppressed due to the passive synchronization of both conversion stages.
We demonstrate two high-power femtosecond mid-infrared (mid-IR) sources that can be combined with a scattering-type scanning near-field optical microscope (s-SNOM). The first one is based on difference frequency generation (DFG) between the two signal wavelengths of a high-power dual-signal-wavelength periodically poled lithium niobate (PPLN) optical parametric oscillator (OPO) and covers the spectral range from 10.5 μm to 16.5 μm. The second one is an AgGaSe 2 OPO pumped by the PPLN OPO. With this mid-IR OPO we obtained up to 113 mW average idler power at 4857 nm with more than 40 cm −1 FWHM spectral width. We demonstrate mid-IR near-field spectra and near-field images that we obtained by combining the broadband femtosecond mid-IR DFG source with an s-SNOM.
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