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

Maximum relative height of elastic interfaces in random media

The distribution of the maximal relative height (MRH) of self-affine one-dimensional elastic interfaces in a random potential is studied. We analyze the ground state configuration at zero driving force, and the critical configuration exactly at the depinning threshold, both for the random-manifold and random-periodic universality classes. These configurations are sampled by exact numerical methods, and their MRH distributions are compared with those with the same roughness exponent and boundary conditions, but produced by independent Fourier modes with normally distributed amplitudes. Using Pickands' theorem we derive an exact analytical description for the right tail of the latter. After properly rescaling the MRH distributions we find that corrections from the Gaussian independent modes approximation are in general small, as previously found for the average width distribution of depinning configurations. In the large size limit all corrections are finite except for the ground-state in the random-periodic class whose MRH distribution becomes, for periodic boundary conditions, indistinguishable from the Airy distribution. We find that the MRH distributions are, in general, sensitive to changes of boundary conditions.Comment: 14 pages, 10 figure

Wavelength-Dependent Third-Harmonic Generation in Plasmonic Gold Nanoantennas: Quantitative Determination of the d‑Band Influence

Plasmonic gold nanoantennas are highly efficient nanoscale nonlinear light converters. The nanoantennas provide large resonant light interaction cross sections as well as strongly enhanced local fields. The actual frequency conversion, however, takes places inside the gold volume and is thus ultimately determined by the microscopic gold nonlinearity, which has been found to significantly surpass common bulk nonlinear materials. While the influence of the nanoantenna geometry and hence the plasmonic resonance has been studied in great detail, only little attention has been paid to the microscopic material nonlinearity. Here we show that the microscopic third-order nonlinearity of gold is in fact a resonant one by virtue of interband transitions between the d- and sp-bands. Utilizing a large set of resonant nanoantennas and a fiber-feedback optical parametric oscillator as a broadband-tunable light source, we show that the radiated third-harmonic signals significantly increase at the onset of interband transitions, namely, as soon as the third harmonic becomes resonant with allowed interband transitions. With the help of an anharmonic oscillator model and independent reference measurements on a gold film we can unambiguously demonstrate that the observed third-harmonic increase is related to a strongly wavelength-dependent microscopic third-order gold nonlinearity, which is additionally underlined by quantitative agreement between simulation and measurement. This additional tuning parameter allows further manipulation and optimization of nonlinear nanoscale systems and thus renders the investigation of other plasmonic materials, especially with interband transitions located in the ultraviolet range, highly intriguing