A doping dependent study of nonequilibrium quasiparticle dynamics in electron and hole doped BaFe$_2$As$_2$

We report on measurements of the doping dependence of quasiparticle dynamics in single-crystals of Ba$_{1-x}$K$_{x}$Fe$_2$As$_2$ and Ba(Fe$_{1-x}$Co$_{x}$)$_2$As$_2$ in the superconducting state via ultrafast pump-probe spectroscopy. Quasiparticles are injected into the samples by ultrashort laser pulses. Once injected, they cause a reflectivity change of the sample at the laser frequency, allowing time-resolved optical measurements of their density. Our measurements reveal band-dependent quasiparticle recombination which provide clues on gap symmetry and electron-boson coupling.