Quasi-Static Strain Governing Ultrafast Spin Dynamics

The quasi-static strain (QSS) is the product induced by the lattice thermal expansion after ultrafast photo-excitation. Although the QSS and thermal effects are barely distinguishable in time, they should be treated separately because of their different fundamental actions to ultrafast spin dynamics. By employing ultrafast Sagnac interferometry and the magneto-optical Kerr effect, we demonstrate quantitatively the existence of QSS and the decoupling of two effects counteracting each other in typical polycrystalline Co and Ni films. The Landau-Lifshitz-Gilbert and Kittel equations considering a magnetoelastic energy term showed that QSS, rather than the thermal energy, in ferromagnets plays a governing role in ultrafast spin dynamics. This demonstration provides an essential way to analyze ultrafast photo-induced phenomena.

Multi-loop atomic Sagnac interferometry

The sensitivity of light and matter-wave interferometers to rotations is based on the Sagnac effect and increases with the area enclosed by the interferometer. In the case of light, the latter can be enlarged by forming multiple fibre loops, whereas the equivalent for matter-wave interferometers remains an experimental challenge. We present a concept for a multi-loop atom interferometer with a scalable area formed by light pulses. Our method will offer sensitivities as high as $$2\times 10^{-11}$$ 2 × 10 - 11 rad/s at 1 s in combination with the respective long-term stability as required for Earth rotation monitoring.