Seminar
Tuesday, 11 May, 2010
Group seminar MPQ: XUV frequency comb metrology
Dr. Christoph Gohle
Tuesday, 11.05.2010 10 a.m. (s.t.) in Herbert-Walther-lecture room, MPQ Garching
We report on an approach to transfer the remarkable precision of comb lasers to the extreme ultraviolet (XUV), a frequency region previously not accessible to these devices. This is demonstrated by direct XUV frequency comb excitation of 4Helium atoms from the 1s2 ground state to the 1snp (n ∈ {4, 5}) excited states. The required XUV comb at wavelengths below 52 nm is generated by amplification and coherent upconversion by high order harmonic generation (HHG) of a pair of pulses originating from a near-infrared femtosecond frequency comb laser. Signal in the form of stable Ramsey-like fringes with high contrast is observed when the comb laser is scanned over the nP states of helium. This is the first proof that frequency combs survive the HHG process below 100 nm wavelength. The accuracy of the measured XUV frequencies (6 MHz, 10−9 relative accuracy) represents an improvement of almost an order of magnitude over previous results, and challenges these as well as current theoretical calculations. As far as we know, this is the first demonstration of an absolute frequency
measurement in the XUV spectral range.