We report on the utilization of the two-photon induced free carrier generation in a diamond pin-type photodiode to record fringe-resolved second-order autocorrelations of femtosecond pulses in the UV. Measurements in photovoltaic mode are performed at the second and third harmonic of a Ti:sapphire laser (lambda(0)=401 nm and lambda(0)=265 nm) with pulse energies down to about 2 nJ. The band gap of diamond of 5.5 eV sets a short wavelength limit at about 225 nm. Combined with the simultaneously recorded linear autocorrelation the spectral phase is reconstructed employing an iterative algorithm.
The dynamics of excited charge carriers at the graphene/Ni(111) interface has been investigated by means of time-resolved two-photon photoemission spectroscopy, employing femtosecond-XUV pulses with an energy of 39.2 eV produced by high-order-harmonic generation. Due to the interplay of substrate and adsorbate band structures, the dependence of the lifetimes on the energy (E − E F ) of the excited carriers was found to be similar to that of Ni 3d electrons measured for clean Ni in the energy range (E − E F ) < 1 eV, while it resembled that of graphite from 1 eV above E F onwards. This result is suggested to be the effect of the peculiar electronic structure of the interface, which still possesses features belonging to the pristine graphene layer, such as a residual saddle point.
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