AbstractWe report a relaxation study of elementary excitations in heavily underdoped Bi2Sr2CaCu2O8+δ (Bi2212) using picosecond Raman Spectroscopy. In B1g symmetry, the two‐magnon peak shows a super‐linear power dependence which is ascribed to excess magnon population. In contrast, the broad feature observed in A1g + B2g symmetry shows a sub‐linear power dependence, suggesting a different origin from the two‐magnon scattering. We could recognize a time response <0.5 ps for the B1g two‐magnon peak. We also observed super‐linear behavior in the power dependence of the 295 and 465 cm−1 anti‐Stokes vibrational modes, in contrast to linear behavior on the Stokes side. We propose to explain the non‐linear behavior in terms of non‐equilibrium phonons. Copyright © 2002 John Wiley & Sons, Ltd.