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High Harmonic Generation

The generation of high-order harmonics of a laser fundamental is mainly motivated by the application of time-resolved photoelectron spectroscopy for studies of ultrafast dynamics in solids and at solid surfaces. This technique is well established in the visible or near ultraviolet range but would benefit greatly from an extension into the XUV regime. A main advandtage is the high kinietic energy of photoemitted electrons since with an electron spectrometer of a certain acceptance angle a wider range of the electrons parallel momentum becoms accessable. A high repetition rate is hereby important in order to maintain good statistics while keeping the number of photoelectrons per pulse at a very low level.

We generated high-order harmonics by focussing the relatively weak (up to 6 μJ) laser pulses of the fundamental into a tight rare-gas jet at a high repetition rate of 100 kHz. Usually, as the generation of high-order harmonics requires intensities in the range of 1014 W/cm2, high-power laser systems are employed to drive this highly non-linear light conversion process. A tight focus geometry, however, opens the possibility to generate high-order harmonics using low pulse energies and therefore with currently available laser systems at up to MHz repetition rates. This is of great importance for a variety of applications.

 

hhg_setup.png

 

hhg_spectra.png

By changing the type of rare-gas and adjustng the laser-intensity, the nozzle baking presuere and the postion on the nozzle relative to the laser focus, we are able to optimize the photon gain of a certain order H. Furthermore the stability of the tempral stability of the high-order gernration apparatus is impressive as shown in (d).


Literature

  • C. M. Heyl, J. Güdde, A. L. L'Huillier, and U. Höfer

High-order harmonic generation with µJ laser pulses at high repetition rates
J. Phys. B: At. Mol. Opt. Phys. 45, 074020 (2012). DOI: 10.1088/0953-4075/45/7/074020 Abstract Reprint (PDF) (© IOP)

see also: Labtalk "Scaling up the repetion rate of high-order harmonic sources"

Zuletzt aktualisiert: 26.02.2016 · armbrusn

 
 
 
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