5 K, slightly increases with increasing temperature below 200 K. Above 200 K, where artifacts due to subtraction of component A start to be significant, τ$_{1B}$ steeply in- creases towards 1 ps. The amplitude of component B, A$_{B}$ , stays almost constant up to ∼ 70 K and then drops monoto nously. nent relaxation. To separate contributions from different components we use 41,42 the fluence dependence of the reflectivity transients. The data can be consistently de- scribed by three distinct components A, B and C, which are tightly connected with three observed temperature regions. The temperature-independent linear scaling of the transients with F above ∼ 150 µ J/cm 2 suggests the de- composition of the raw Δ R/R into component A which scales linearly with F and a residue which saturates at finite F (see Fig. 7). Component A dominates at high temperatures and has to originate in at least three dis- tinct relaxation processes due to the relatively complex time evolution. (i) The slower dynamics, which is vir- tually the same as in undoped SmFeAsO at high tem- peratures (see Fig. 6), could be attributed to the band renormalization due to the lattice expansion. (ii) The sub-ps decay, also having a similar decay time as in un- doped SmFeAsO at high temperatures, will be discussed in more detail below. (iii) The oscillatory part of com- ponent A is attributed to a coherent phonon oscillation which appears softer as in undoped SmFeAsO. Except for the shift of the coherent phonon frequency all show only a minor T -dependence. The residue shows an unipolar single-exponential de- cay (see Fig. 8) above T$_{c}$ , which we name component B. Component B dominates in the raw transients in the intermediate temperature range, above T$_{c}$ . Below T$_{c}$ the residue changes to a bipolar multi-exponential decay, ev- idently due to the appearance of an additional relaxation process associated with the superconducting state named component C. Component C saturates at lower F ≈ 10 µ J/cm 2 than component B, which saturates above ∼ 70 µ J/cm $^{2}$. The decomposition to the three components is further supported by comparison of the raw Δ R/R at different ℏ ω$_{P}$ shown in Fig. 6 where components A and B show much smaller amplitudes at ℏ ω$_{P}$ = 1 . 55 eV in comparison to ℏ ω$_{P}$ = 3 . 1 eV, while the amplitude of component C shows a negligible ℏ ω$_{P}$ dependence. Above T$_{c}$ we fit the residue with a single exponential decay (component B ) 43 (see Fig. 8), Figure 8: Temperature dependence of Δ R/R transients with component A subtracted. Thin lines are single exponential decay fits (component B) above T c and multi-exponential de- cay fits (a sum of component B and C) below T c . Figure 9: Temperature dependence of the component-B re- laxation time (a) and amplitude (b) in superconducting SmAsFeO 0 . 8 F 0 . 2 obtained from the fits. The thin line is the fit for the case of a relaxation over a T -independent gap 16,41 with 2Δ$_{PG}$ = 120 meV. For comparison, the temperature de- pendence of the relaxation time and the transient amplitude in undoped SmAsFeO is also shown. where τ$_{rC}$ represents the rise time and τ i C the decay times. The resulting fit parameters for component B are shown in Fig. 9. The decay time, τ$_{1B}$ ≈ 0 . 25 ps at 4 where σ corresponds to the effective width of the excita- tion pulse with a Gaussian temporal profile arriving at t$_{0}$ and τ$_{B}$ the exponential relaxation time. Below T$_{c}$ addi- tional exponential decays representing component C are needed to fit the residue , Δ R$_{C}$ R = A$_{1C}$ ( e − t$_{−}$$^{t}$0 $^{τ}$1C − e − t$_{−}$$^{t}$0 $^{τ}$rC ) + A$_{2C}$ e − t$_{−}$$^{t}$0 $^{τ}$2C − e − t$_{−}$$^{t}$0 $^{τ}$rC (4) Δ R$_{B}$ R = A$_{B}$ 2 e − t$_{−}$$^{t}$0 $^{τ}$B erfc ( σ 2 − 4( t − t$_{0}$ ) τ$_{B}$ $_{2}$√$_{2}$$_{στ}$$_{B}$ ) , (3)