A mass spectrometer includes: an accelerator for receiving ions travelling in a drift direction and accelerating the ions in an acceleration direction orthogonal to the drift direction; a detector downstream of the accelerator with respect to the drift direction; and an ion mirror assembly intermediate the accelerator and the detector. The ion mirror assembly includes at least a first ion mirror and a second ion mirror spaced apart from each other in the acceleration direction. The accelerator, detector, and ion mirror assembly provide a folded ion path between the accelerator and the detector for separating the ions according to their mass-to-charge ratio so that a flight time of the ions is substantially independent of ion energy. The first and second ion mirrors each apply an electrostatic potential to the ions that is curved in both the drift direction and a lateral direction orthogonal to both the drift and acceleration directions.