NONLINEAR SPECTROSCOPY OF Y-BA-CU-O AND NI THIN-FILMS BY A BIHARMONIC PUMPING TECHNIQUEстатья
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Дата последнего поиска статьи во внешних источниках: 9 ноября 2013 г.
Аннотация:High temperature superconducting (HTSC) (Y-Ba-Cu-O, critical temperature T(c) = 87 K) and metal (Ni) thin films are investigated by a picosecond spectrometer with two tunable dye lasers. The self-diffraction process efficiency-eta versus the biharmonic pumping component detuning-OMEGA has been measured at temperatures-THETA = 300 and 80 K. For the HTSC films at THETA = 80 K a well-defined dip on the dispersion curve-eta(OMEGA) for - 10 > OMEGA > - 50 cm-1 is found. The upper limit of the region of this dip corresponds to a value of 2-DELTA of the superconducting energy gap. At 10 < OMEGA < 50 cm-1 no such effect is found. In other respects all obtained dispersion curves resemble each other. These curves consist of a central peak (eta approximately 10(-7), [OMEGA[ < 10 cm-1) and wide wings (eta approximately 10(-9), [OMEGA[ > 10 cm-1) with a complex interference structure. The Y-Ba-Cu-O film resonances coincide with the phonon mode frequencies (120, 335 and 580 cm-1). It is also shown that the photoexcitation kinetics must consist of some components. The characteristic time of the most "ultrafast" component below 5 fs has been estimated and a complex subpicosecond quantum beat presence has been predicted.