The dependence of the yield of high-order harmonic generation (HHG) on several important experimental parameters
has been successfully modeled in the last 20 years by taking into account the single atom response and propagation
effects. We extended this description by adding a stimulated emission process and named it x-ray parametric
amplification (XPA). Beyond the super-quadratic increase of the XUV signal, which can be explained only in a limited
pressure range by HHG theory, other observed characteristics like exponential growth, gain narrowing, strong blue-shift,
beam divergence, etc. and their dependence on laser intensity and gas pressure can be explained accurately only by the
new XPA model. We experimentally demonstrated XPA in Argon in the spectral range of 40-50 eV in excellent
agreement with the theory. XPA holds the promise to realize a new class of bright x-ray sources for spectroscopy.
We report on the realization towards a compact, pulsed XUV source for high temporal and spatial resolution pumpprobe
spectroscopy. The system will be based on intracavity high harmonic generation in a Ti:sapphire oscillator. An
oscillator with repetition rate of 20 MHz has been realized, which operates in the net negative (near zero) dispersion
regime with intracavity pulse energy up to 280 nJ. The cavity has been extended with a secondary focus, where the high
harmonic generation can take place. In the recent state, the oscillator is capable to generate XUV harmonics up to 35 eV.
We report on the generation of sub-30fs pulses from a mirror-dispersion-controlled (MDC) Ti:sapphire oscillator, containing a multiple-pass Herriott-cell for increasing the cavity length. Using that scheme, repetition rates down to some few MHz could be achieved. To avoid multiple pulsing instabilities, we operate the laser in a regime of slight positive group-delay dispersion (GDD) over a very broad wavelength range. This results in the formation of strongly chirped light pulses, reducing the otherwise very high peak-intensity inside the laser crystal, which would limit the maximum output energy. We have investigated the spectral phase associated with these pulses with the help of the well known SPIDER-technique, and, based on the results, have constructed an optimized compressor.
When pumped with the full 10 W of a frequency-doubled Nd:YVO4 laser (Coherent Verdi V10), output energies well above 200 nJ could be obtained. As no signs of instabilities were observed, we believe, that our approach is scaleable to even higher energies if more powerful pump lasers are used. Thanks to the excellent beam profile, high-resolution micromachining of various materials, including transparent dielectrica could be demonstrated.
Results on sub-micrometer surface modification of transparent materials will be presented.