Doping dependent study of non-equilibrium quasiparticle dynamics in the superconducting and normal state of La$_{2-x}$Sr$_{x}$CuO$_{4}$ thin films

We report on measurements of non-equilibrium quasiparticle dynamics in La$_{2-x}$Sr$_{x}$CuO$_{4}$ thin films via ultrafast optical pump probe spectroscopy. Quasiparticles are excited into the thin films using ultrashort laser pulses. The transient change in the quasiparticle density causes a corresponding change in the reflectivity of the sample, allowing time resolved measurements of quasiparticle recombination. We describe the doping dependence of these measurements both above and below Tc and discuss their implications on the nature of the electron-boson coupling in the cuprates.