Terahertz Spectrocopy of Ultrafast Demagnetization in iron

We use ultrafast terahertz transmission and emission spectroscopy to study ultrafast demagnetization in ferromagnetic iron. We show that the emitted THz pulse results from both the demangetization process and the time-dependent induced conductivity of the sample. Using the experimentally determined time-dependent optical conductivity, we determine that ultrafast demagnetization proceeds with a $1.7\,\mathrm {ps} \pm 0.5\,\mathrm{ps}$ lifetime in single crystal ferromagnetic films at room temperature.