Instrumentation of Ultrafast Sagnac Interferometry for Simultaneous Detection of Lattice and Spin Dynamics

We built ultrafast Sagnac interferometer to simultaneously measure the lattice and the spin dynamics. Although the pump-probe magneto-optical Kerr effect (MOKE) instrument is most widely used in Femtomagnetism to measure reflectivity and Kerr responses, it is considerably hard to analyze fundamental interactions of electron-spin or lattice-spin due to the complex nature of the reflectivity. The ultrafast Sagnac interferometer has the great advantage of obtaining the real and imaginary parts of MOKE as well as the reflectivity and the lattice displacement at the same time. Therefore, through the rigorous investigation of temporal sequences of electron, lattice, and spin systems, we expect this instrument to play an leading role in unraveling interaction mechanisms between systems.