Browsing by Author "Hegenbarth, Robin"

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    Broadly tunable femtosecond near- and mid-IR source by direct pumping of an OPA with a 41.7 MHz Yb:KGW oscillator
    (2013) Krauth, Joachim; Steinmann, Andy; Hegenbarth, Robin; Conforti, Matteo; Giessen, Harald
    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.
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    High-power broadband femtosecond near- and mid-infrared sources based on optical parametric oscillators and difference frequency generation at 40 MHz repetition rates
    (2014) Hegenbarth, Robin; Gießen, Harald (Prof. Dr.)
    The goal of this dissertation was the generation of femtosecond sources in the near- and mid-infrared spectral range with repetition rates in the 40 MHz range. The approach was based on nonlinear frequency conversion based on an Yb:KGW laser oscillator with up to 7.4 W output power as a pump source. Output powers on the Watt level for the near-infrared and in the 100 mW region in the mid-infrared around 5 µm, as well as several mW between 10 and 20 µm, were the goal. With the Yb:KGW laser oscillator an optical parametric oscillator (OPO) based on a 1 mm long magnesium-oxide-doped periodically poled lithium niobate (MgO:PPLN) crystal has been pumped. The signal of this OPO is almost gap-free tunable between 1446 and 1896 nm with up to 1.7 W average signal output power at femtosecond pulse durations. At wavelengths close to the point at which the intracavity group-delay dispersion equals zero, dual-signal-wavelength operation occurs due to equal group delay at two wavelengths. Due to the high pump power available, very high signal output coupling rates in excess of 50% are beneficial. In order to obtain a spectrally broadband mid-infrared (mid-IR) source, the difference frequency between the two OPO signals was generated outside the cavity by means of either a gallium selenide (GaSe) or silver gallium diselenide (AgGaSe2) crystal. The specifications of this system were characterized with a selection of different crystal lengths. This system generates up to 4.3 mW of average mid-IR power. Its spectra can be tuned between 10.5 and 16.5 µm (952 – 606 cm-1) with more than 50 cm-1 spectral width. Power and spectra are temporally very stable. Thus, it was demonstrated that it is feasible to combine this system with a scattering-type scanning near-field optical microscope. Even more power in the mid-IR spectral region was obtained with an AgGaSe2 OPO that was synchronously pumped by the MgO:PPLN OPO at single-signal-wavelength operation. With this device up to 113 mW average idler output power at 4857 nm (2059 cm-1) were obtained. By adjusting cavity length, phase-matching angle, and pump wavelength, its idler wavelength could be tuned between 4570 and 5121 nm (2188 – 1953 cm-1) with more than 40 cm-1 spectral width.
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    ItemOpen Access
    Watt-level optical parametric amplifier at 42 MHz tunable from 1.35 to 4.5 μm coherently seeded with solitons
    (2014) Steinle, Tobias; Steinmann, Andy; Hegenbarth, Robin; Giessen, Harald
    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.