Influence of photon angular momentum on ultrafast demagnetization in nickel

The role of pump helicity in laser-induced demagnetization of nickel thin films is investigated by means of pump-probe time-resolved magneto-optical Kerr effect in the polar geometry. Although the data display a strong dependency on pump helicity during pump-probe temporal overlap, this is shown to be of nonmagnetic origin and not to affect the demagnetization. By accurately fitting the demagnetization curves, we show that demagnetization time tM and electron-phonon equilibration time tE are not affected by pump helicity. Thereby, our results exclude direct transfer of angular momentum to be relevant for the demagnetization process and prove that the photon contribution to demagnetization is less than 0.01%. [on SciFinder (R)]