Transient optical polarization response of aluminium at an interband transition

Femtosecond optical pump-probe measurements have been performed upon a 500 Angstrom polycrystalline Al film at an interband transition at a wavelength of 800 nm. The dependence of the intensity and polarization of the reflected probe pulse upon the polarization of the pump pulse has been determined. A sharp peak was observed in the polarization signal at zero time delay that contains contributions from both the specular inverse Faraday effect (SIFE) and the specular optical Kerr effect (SOKE). The SIFE and SOKE are associated with the optical orientation of angular and linear momentum, respectively. The dependence of the peak height upon the pump polarization has allowed us to deduce values of chi(xxyy) = (1 + 0.6i) x 10(-8) rad cm(3) erg(-1) and chi(xyyx) = (0.5 - 0.1i) x 10(-8) rad cm(3) erg(-1) for the non-vanishing components of the local cubic susceptibility tensor. A distortion of the peak was observed when the pump was elliptically polarized. Its detailed shape shows that the characteristic relaxation time for the SOKE is about 30 fs longer than that for the SIFE in measurements of ellipticity. This suggests a similar difference in the relaxation times for the angular and linear momentum of the optically excited hot electrons. The initial peak was generally followed by a tail that decayed with a time constant of several picoseconds, which we attribute to an ultrafast anisotropic excitation of the lattice.