Robin Hegenbarth

Milliwatt-level mid-infrared (10.5–16.5 μm) difference frequency generation with a femtosecond dual-signal-wavelength optical parametric oscillator

We demonstrate the generation of mid-infrared radiation using a femtosecond dual-signal-wavelength optical parametric oscillator and difference frequency generation in an extracavity gallium selenide or silver gallium diselenide crystal. This system generates up to 4.3 mW of average mid-infrared power. Its spectra can be tuned to between 10.5 μm and 16.5 μm wavelength (952  cm(-1)-606  cm(-1)) with more than 50  cm(-1) spectral bandwidth. We demonstrate that the power and spectra of this system are temporally very stable.

High-power femtosecond mid-IR sources for s-SNOM applications

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 AgGaSe2 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.

Broadly tunable femtosecond near- and mid-IR source by direct pumping of an OPA with a 41.7 MHz Yb:KGW oscillator

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.

Watt-level optical parametric amplifier at 42 MHz tunable from 1.35 to 4.5 μm coherently seeded with solitons

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.

Two-color femtosecond optical parametric oscillator with 1.7 W output pumped by a 7.4 W Yb:KGW laser

We demonstrate a high-power two-color femtosecond near-infrared optical parametric oscillator synchronously pumped by a 7.4 W femtosecond Yb:KGW laser. This system is almost gap-free tunable with signal wavelengths ranging between 1445 and 1880 nm, with up to 1.7 W average signal output power at femtosecond pulse durations. At wavelengths near the point at which the cavity group-delay dispersion equals zero, dual-signal-wavelength operation occurs due to equal group delay at two wavelengths.

Milliwatt-level mid-infrared difference frequency generation with a femtosecond dual-signal-wavelength optical parametric oscillator

We report on mid-infrared difference frequency generation with a dual-signal-wavelength femtosecond optical parametric oscillator. We achieved up to 1.2 mW average power at 42 MHz at wavelengths tunable between 11 and 18 μm.

Broadly-tunable near- and mid-IR source by direct pumping of an OPA with a 42 MHz femtosecond multi-Watt Yb:KGW oscillator

Laser sources delivering high repetition rate broadband mid-IR radiation enable a number of key applications [1], for example in near-field and FTIR spectroscopy [2]. Here, we present an OPA that is directly pumped by a diode-pumped solid-state oscillator without the need for any amplifier or cavity dumping, generating tunable radiation in the near- and mid-IR spectral region.We employ a passively mode-locked dual-crystal Yb:KGW oscillator delivering up to 7.4 W average power with 425 fs pulse duration and 41.7 MHz repetition rate at 1040 nm as pump source [3]. A fraction of the light is used to generate the supercontinuum seed in an 8 cm long tapered fiber with 4 μm waist diameter, whereas the remaining light is used to pump the parametric amplifier. Pump and signal beam are combined with a dichroic mirror and focused separately into the crystal with a collinear interaction geometry. Using a 5 mm long PPLN crystal for frequency conversion, the OPA signal wavelength is continuously tunable between 1380 and 1830 nm, which corresponds to idler wavelengths from 2.41 to 4.22 μm, by changing the poling period of the crystal (28.0 to 31.0 μm in 0.5 μm steps) and by changing the crystal temperature between 20 and 200 °C. The signal and idler spectra measured at room temperature are shown in Fig. 1(a) and 2(b), respectively. We exceed 325 mW over the whole signal range with a maximum power of 540 mW at 1400 nm and we exceed 140 mW over the whole idler range with a maximum power of 220 mW at 3.06 μm. The pump power was set to 2 W in order to remain well below the damage threshold of the PPLN crystal. Using the maximum available pump power of 4 W, signal powers up to 800 mW were achieved. To generate mid-JR radiation at longer wavelengths we used a 2 mm long GaSe crystal instead of the PPLN crystal. We performed type J phase matching (e - o → o). The pump power was set to 4 W. Broadband mid-JR pulses tunable from 4.85 to 9.33 μm were generated with up to 830 μW average power at 6.46 μm, see Fig. 1(c).Power and spectra are temporally stable with power fluctuation of 0.9 % rms in the NJR and 3.3 % rms in the MJR region. We numerically model the parametric process using a χ(2) Nonlinear Envelope Equation [4] and show good agreement between simulations and experiments. Our source is compact and cost efficient and has the potential to replace more complex Ti:sapphire/OPO systems for ultrafast spectroscopy and mid-JR applications.

Stable MHz-Repetition-Rate Passively Q-Switched Microchip Laser Frequency Doubled by MgO:PPLN

We present a passively Q-switched microchip laser generating 460 ps pulses at 1064 nm with up to 1.1 MHz repetition rate and a jitter < 1%. The IR-light was frequency doubled in an MgO:PPLN crystal with up to 75% conversion efficiency.

1.5 W output two-color femtosecond optical parametric oscillator pumped by a 7.4 W femtosecond Yb:KGW laser

We report on a 42 MHz femtosecond two-color MgO:PPLN OPO pumped by a mode-locked 7.4 W Yb:KGW fs laser. Up to 1.5 W average output power and tunability from 1.45 to 1.88 μm have been achieved.