Transcript Kathrin
Two-Color-Interferometer and Coherent Focusing FRED project course, LTH Kathrin Klünder Motivation: HHG in a Two-Color-Field red only • High-order harmonic generation (HHG) by focusing an intense laser field (800nm) into an atomic gas • Properties of the harmonics determined by fundamental driving field • Adding a second field to the generation process by frequency doubling a fraction of the fundamental laser frequency => now wavelengths of 800nm and 400nm • Ability of changing properties of harmonics and pulse train itself • Standard procedure in our lab red and blue Experiment Theory Setup: HHG in a Two-Color-Field Ti:Sapphire, 800nm, 35fs, 4mJ focusing mirror doubling crystal interferometer delay plate Brewster window (55.47˚ for 800nm) probe beam •Changing the relative phase by rotation of delay plate HHG generation (gas inlet) The FRED project Procedure for aligning interferometer: • two beams overlap spatially and in time directly after passing interferometer • No further check after propagation though rest of the setup => Works fine, BUT what are the possible problems or what should one keep in mind? Use FRED to model influence of delay plate and investigate standard procedure when aligning/working with the Two-ColorInterferometer. Our setup in FRED… Defining the Light Source desired properties: • coherent • polarized • pulsed (35fs) => in FRED not possible • define spectral bandwidth of ≈ 30nm Properties of the Delay Plate new materials can added from a huge range of cataloged materials Using FRED Scripting built-in functions to get ray informations and control optical components: create variables ray-tracing and drawing the rays define and open output file #1 access delay plate coordinates get infos about ray j for angle i if rays ended up on right detector: print infos in #1 close output file #1 Performance of Interferometer thickness of delay plate 510µm 340µm 170µm analysis surface delay of red arm as a function of angle delay plate red arm blue arm Interferometer works fine. Influence of Brewster Window focusing mirror (f=75cm) vacuum Brewster window (1mm) blue arm delay of red arm as a function of angle red arm • Brewster window introduces dispersion for both colors – relative delay of the two arms changes – temporal spread of the two pulses; bigger influence on blue pulse (approx. 10fs for spectral bandwidth) Influence of Brewster Window beam in focal plane: no Brewster window: with Brewster window: offset 6µm foci positions red and blue beams: – 3µm offset in direction of beam propagation – 6µm offset in Y-direction Some Words about the Focusing spherical focusing mirror x decrease distance x: before focus in focus some other bad example… • focus size and astigmatism depends on incoming angle • for better focusing conditions spatial offset gets more important • perturbation of wave fronts due to focusing mirror In the End FRED is... – easy to get started with – convenient to model small questions – good to get an idea what happens in the setup