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Conical Wave pulses for phase-matched frequency conversion into the eXtreme-UV region (conicx)
Start date: 01 Aug 2008, End date: 31 Jul 2009 PROJECT  FINISHED 

One of the most promising applications envisaged in the near future for LASER physics in the ”extreme” nonlinear optical regime is efficient frequency conversion from the visible or near-infrared region into the extreme UV region (EUV). Table-top laser sources of EUV light give ready access to attosecond pulses and wavelengths in the 1-50 nm range, of great importance for example for applications in ultrafast spectroscopy, microscopy and high-density photo-lithography. However to date there is no broad-range phase matching mechanism that allows to achieve the maximum allowed (limited by absorption) conversion efficiency to EUV light. Hollow waveguides may be used at low intensities and gas pressures. Modulated waveguides have been used at higher intensities. Both these methods lack the possibility to arbitrarily choose the operating conditions (e.g. gas pressure or laser intensity) and they have an extremely limited tunability. We propose a novel phase-matching technique based on the use of conical pulses that allows to reach the absorption limit for any gas, pressure or EUV wavelength desired. Tunability is obtained by simple tuning of an imaging telescope. Conical pulses, for example the Bessel pulse or the X Wave, offer the possibility to tune the effective wave-vector of the laser pulse over an extremely broad range and thus phase-match any nonlinear interaction of interest - in this case, frequency conversion into the EUV region. Preliminar simulations using a propagation code for the laser pulse and based on an estimation of the coherence length, have already demonstrated the validity of the technique. Now we need to validate the idea experimentally and eventually with further simulations that also properly account for the full quantum nature of the EUV generation process. The goal therefore is to introduce a new technology that will lead to a significant advance in EUV physics and related applications.
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