We report on the generation of extreme ultraviolet radiation utilizing the plasmonic field enhancement in arrays of bow-tie gold optical antennae. Furthermore, their suitability to support high-order harmonic generation is examined by means of finite-difference time-domain calculations and experiments. Particular emphasis is paid to the thermal properties, which become significant at the employed peak intensities. A damage threshold depending on the antenna length is predicted and confirmed by our experimental findings. Moreover, the gas density in the vicinity of the antennae is characterized experimentally to determine the number of atoms contributing to the measured radiation, which is almost an order of magnitude larger than previously reported.

We report on low-order harmonic generation utilising the plasmonic field enhancement in arrays of rodtype gold optical antennae. Furthermore, we examine their suitability to support high-order harmonic generation (HHG). The low-order harmonics are used as a tool to investigate the nonlinear properties of the antennae. Particular attention is paid to the thermal properties, which become significant at the peak intensities necessary for HHG. A theoretical model explains the experimental findings and enables future improvements. In experiments we observe up to the fifth harmonic order and measure a field enhancement sufficient to support high-order harmonic generation. Moreover, we find a damage threshold for the antennae.

Following the impact of a single femtosecond light pulse on nickel nanostripes, material deformations-or "nanobumps"-are created. We have studied the dependence of these nanobumps on the length of nanostripes and verified the link with plasmons. More specifically, local electric currents can melt the nanostructures in the hotspots, where hydrodynamic processes give rise to nanobumps. This process is further confirmed by independently simulating local magnetic fields, since these are produced by the same local electric currents.

High-order harmonic generation in xenon with oscillator repetition rates is studied. The necessary intensity is reached via plasmonic field enhancement at nanostructured arrays of bow-tie gold antennae. The theoretical analysis focuses on the thermal properties and the damage threshold of the bow-tie antennae. On the experimental side the number of contributing atoms is determined and optimized. Extreme ultraviolet radiation is successfully observed with photon fluxes almost an order of magnitude larger than previously reported.

We demonstrate a chirped-pulse Ti:sapphire laser oscillator with both Kerr-lens and semiconductor- saturable-absorber-mirror-assisted mode locking generating 1.1 microJ pulses at 1 MHz pulse repetition rate. The pulses are coupled out of the laser cavity by means of an acousto-optical cavity dumper, have a spectral width that supports a Fourier limit of 74 fs, and currently have a chirped-pulse duration of 5 ps. After compressing the pulses, this laser will be an ideal tool for efficient high-harmonic generation directly from a laser oscillator.

No abstract

A number of applications ranging from micro-machining to non-linear frequency conversion and high harmonic generation (HHO) would significantly benefit from femtosecond laser sources with pulse energies in the Ill-regime with MHz repetition rate at pulse durations below 100 fs. To this end in recent years several different concepts have been developed [1][2][3].Here we report for the first time to our knowledge on a chirped-pulse Ti:sapphire laser oscillator with acoustooptical cavity-dumping that reaches pulse energies in excess of IIII at a repetition rate of 1 MHz and with a spectral width supporting pulse durations below 80 fs. After the laser, a cw-pumped, cryogenically cooled amplifier is used to further increase the pulse energy up to 1.5 Ill. In this contribution we will discuss possible setups and designs for energy scaling up to several microjoules.A schematic layout of the laser is shown on the left hand side of Fig. 1. The laser oscillator is built in a standard z-configuration with a Herriott-cell to allow for compact design. It has an internal repetition rate of 25.6 MHz from which the pulses are picked with a 1 MHz repetition rate with the help of the AOM. SESAM CoIlerent Verdi 16W@532nm to experiments r ·20 I .JÕ Ĩ~I Lo t Ĩ~I '~I ""9;5 780 790 7'9S 8CX:l 805 810 815 wa\'elength 10m) Fig. 1. (left) Laser setup; (right) Optical spectrum of the laser pulses.The laser is operated with a pump power of 16 Wand a net positive intra-cavity dispersion of 650 fs 2 in order to ensure chirped pulse operation and to avoid detrimental nonlinearities . The right hand side of Fig. 1 shows the spectrum of the output laser pulse which supports a Fourier limit of74 fs. Because of the chirped pulse operation the actual pulse length behind the oscillator is about 5 ps. These out-coupled pulses are subsequently used in a single stage cw-amplifier currently pumped with 10.5 W which is sufficient to further amplify the pulse energy to 1.5 III without any change in the spectral shape or width. With more pump power available, we expect power scaling into the multi-Ill range.References:

No abstract