The switching of a magnetic tunnel junction (MTJ) using femtosecond laser pulses enables a possible path for nonvolatile, ultrafast, and low-dissipative memories. In this work, we demonstrate successful field-free 50-fs single-laser-pulse-driven magnetization reversal of a [Tb/Co]-based storage layer in a perpendicular MTJ with a estimated absorbed energy of 68.6 fJ/bit. The nanofabricated MTJ devices have an optimized bottom reference electrode and show tunnel-magnetoresistance-ratio (TMR) values up to 74% after patterning down to sub-100-nm lateral dimensions. Experiments on continuous films reveal peculiar reversal patterns of concentric rings with opposite magnetic directions, above a certain threshold fluence. These rings have been correlated with the patterned-device switching probability as a function of the applied laser fluence. Moreover, the magnetization reversal is independent of the duration of the laser pulse. According to our macrospin model, the underlying magnetization-reversal mechanism can be attributed to an in-plane reorientation of the magnetization due to a fast reduction of the out-of-plane uniaxial anisotropy and a magnetization precession around the local effective-anisotropy axis. These aspects are of great interest both for the physical understanding of the switching phenomenon and their consequences for all-optical-switching memory devices, since they allow for a large fluence operation window with high resilience to pulse-length variability