Pump-probe experiment in LaMnO3/SrTiO3 superlattices and thin film

We present the time dependent transmittance of LaMnO3 thin film and [(LaMnO3)n/(SrTiO3)8]20 (n=2 and 8) superlattices grown on SrTiO3 substrate. We used the laser pulse pump-probe technique. We observed two phonon oscillation in the LaMnO3 film at 8 THz and at 15 THz. In the superlattices, 8 THz mode seemed obliterated. The phonon oscillation damping time constant was also different. In LaMnO3 thin film, we could observe the oscillation until $\sim$ 1.5 ps. In the superlattices, the damping time constant was smaller: $\sim$ 0.7 ps for n=8 superlattice and $\sim$ 0.3 ps for n=2 superlattice. We will discuss number of phonon mode and the damping time constant in terms of the sample geometry and the electronic struncture.