Workgroup Prof. Aeschlimann

High harmonic generation

For the high harmonic generation, we use the output of a regenerative Ti:Sapphire laser amplifying system providing <50 fs pulses at a fundamental wavelength of 780 nm. We then use the second harmonic of the fundamental light to create the high harmonics by focussing the beam into a hollow waveguide perfused by a noble gas. Because of the high peak intensity of the laser pulses, the atomic Coulomb potential of the noble gas atoms is bent, allowing electrons to leave them in a tunnel ionization prozess. These free electrons are then accelerated in the strong electric field of the laserlight and have a probability to recombine with the mother ion, thus radiating their additionally gained kinetic energy in form of odd numbered multiples of the initial laser light. By using the frequency doubled light for the high harmonic generation process, we get a free spectral range of 6.4 eV between each order in the harmonic spectrum.

 

  • Output photonenergy 16eV - 72eV
  • HHG pulse duration ~ 20 fs
  • Energy resolution <150 meV

Sub-Femtosecond Phase Control and Stabilization

With the Pulse-Shaper setup it is possible to generate arbitrary pulse sequences. In the so-called 4f-setup, the pulse gets spectrally seperated by gratings and a LCD can manipulate the spectral amplitude in the fourier space. The backfolded pulse is thereby seperated into the desired number of sub-pulses with changable relative phase in respect to eachother. This setup was used to introduce a novel 2D spectroscopy measurement scheme for PEEM called 2D Nanoscopy. By removing the polarizer after the LCD,  the Pulse-Shaper is capable of generating abritrarily chirped and polarized pulses.
 

Nonlinear frequency conversion

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