Frank Noack

Tunable femtosecond pulses in the near vacuum ultraviolet generated by frequency conversion of amplified Ti:sapphire laser pulses.

Frequency transformation of high-power Ti:sapphire laser pulses in three β-barium borate crystals resulted in 180-fs optical pulses tunable from 189 to 200 nm. UV pulses with energies of as much as 4 μJ at 200 nm with a 1-kHz repetition rate and pulses with energies of more than 2 μJ at 193 nm with a 20-Hz repetition rate were produced.

Difference-frequency generation of intense femtosecond pulses in the mid-IR (4–12 μm) using HgGa2S4 and AgGaS2

Abstract We compare the properties and the performance of HgGa2S4 and AgGaS2 in a high-power difference-frequency generation scheme mixing the signal and idler from a travelling wave optical parametric generator at 1 kHz. Femtosecond pulses from 3.7 to 12 μm with quantum efficiency of 40–80% are generated with HgGa2S4 which is about 1.2 times higher than with AgGaS2 typically used in that wavelength range. The maximum single pulse energy obtained exceeds 9 μJ near 4 μm and 1 μJ in the whole tunability range which represents about an order of magnitude improvement in comparison with previous results. The mid-infrared pulses are almost bandwidth limited with durations of the order of 200 fs and less (minimum 165 fs).

Application of the nonlinear crystal SrB4O7 for ultrafast diagnostics converting to wavelengths as short as 125 nm

We used non-phase-matched second-harmonic generation (SHG) in the highly nonlinear but low-birefringence crystal SrB4O7 for temporal characterization (autocorrelation) of femtosecond UV pulses to convert these pulses to wavelengths as low as 125 nm, close to the transparency limit of SrB4O7. The sensitivity of this method was approximately 1 microJ at the fundamental for a repetition rate of 1 kHz. We also used SHG at longer wavelengths to estimate the three nonlinear coefficients of SrB4O7.

Femtosecond parametric generation in ZnGeP(2).

We report traveling-wave optical parametric generation in short (2-mm) ZnGeP(2) samples with reduced anomalous absorption, using femtosecond pump pulses near 2 mum . The signal and the idler waves generated could be tuned from 2.5 to 10 mum , and they extend the tunability of the beta-barium borate optical parametric generator used as a pump source to the mid-infrared. At a single-pass internal conversion efficiency of 2.5% we estimate pulse durations of 75 fs (signal near 3 mum) and 200 fs (idler near 6 mum).

Generation of tunable femtosecond pulses to as low as 172.7 nm by sum-frequency mixing in lithium triborate.

A tunable 1-kHz repetition-rate regenerative Ti:sapphire amplifier system is used to produce 200-fs vacuum-ultraviolet pulses in the range of 172.7-187 nm by phase-matched sum-frequency mixing in lithium triborate of the Ti:sapphires fourth harmonic and a parametrically generated infrared pulse.

Two-octave supercontinuum generation in a water-filled photonic crystal fiber.

Supercontinuum generation in a water-filled photonic crystal fiber is reported. By only filling the central hollow core of this fiber with water, the fiber properties are changed such that the air cladding provides broadband guiding. Using a pump wavelength of 1200 nm and few-microjoule pump pulses, the generation of supercontinua with two-octave spectral coverage from 410 to 1640 nm is experimentally demonstrated. Numerical simulations confirm these results, revealing a transition from a soliton-induced mechanism to self-phase modulation dominated spectral broadening with increasing pump power. Compared to supercontinua generated in glass core photonic fibers, the liquid core supercontinua show a higher degree of coherence, and the larger mode field area and the higher damage threshold of the water core enable significantly higher pulse energies of the white light pulses, ranging up to 0.39microJ.

Generation of high-energy sub-20 fs pulses tunable in the 250-310 nm region by frequency doubling of a high-power noncollinear optical parametric amplifier

We report on the generation of powerful sub-20 fs deep UV pulses with 10 microJ level energy and broadly tunable in the 250-310 nm range. These pulses are produced by frequency doubling a high-power noncollinear optical parametric amplifier and compressed by a pair of MgF2 prisms to an almost transform-limited duration. Our results provide a power scaling by an order of magnitude with respect to previous works.

The nonlinear coefficient d36 of CdSiP2

The new nonlinear crystal for the mid-IR CdSiP2 was discovered only very recently but the interest in this chalcopyrite is enormous because it possesses most of the attractive properties of the related ZnGeP2 but allows in addition pumping at 1064 nm without two-photon absorption and uncritical phase-matching for 6 μm generation with maximized effective nonlinearity. The last feature is due to the fact that this crystal is negative uniaxial in contrast to ZnGeP2 which shows positive birefringence. We now measured its nonlinear coefficient using SHG of femtosecond pulses generated near 4.6 μm from a seeded KNbO3 optical parametric amplifier. The SHG efficiency was compared for uncoated samples of CdSiP2 and ZnGeP2, both ≈0.5 mm thick, in the low conversion limit (<10% internal conversion efficiency) which justifies the use of the plane wave approximation. Taking into account the experimentally determined phase-matching angles for type-I SHG (oo-e type in CdSiP2 and ee-o type in ZnGeP2), which were in good agreement with the existing Sellmeier approximations, we arrived at d36(CdSiP2)~d36(ZnGeP2) which is rather unexpected having in mind the larger band-gap of CdSiP2. The reliability of the measurement was tested at the same wavelength by comparing ZnGeP2 with HgGa2S4 which led to the result d36(ZnGeP2)~3d36(HgGa2S4), in very good agreement with previous estimations.

High repetition rate traveling wave optical parametric generator producing nearly bandwidth limited 50 fs infrared light pulses

A 1 kHz Ti:sapphire femtosecond regenerative amplifier system is used to pump a lithium triborate optical parametric generator in a type II noncritical phase matching configuration and a β‐barium borate parametric amplifier. Infrared pulses near 1460 nm as short as 50 fs are achieved with a pulse duration/bandwidth product of only 0.44.

Optical parametric generation of femtosecond pulses up to 9 μm with LiInS2 pumped at 800 nm

We demonstrate direct access to the 4.8–9 μm spectral region with 800 nm, 1 kHz pumping of a femtosecond optical parametric amplifier based on the wide-gap wurtzite-type LiInS2. LiInS2 did not exhibit two-photon absorption at 800 nm and seems applicable at this pump wavelength with intensities of the order of 100 GW/cm2 for down-conversion of high energy ultrashort pulses up to its mid-IR edge at ≈12 μm.