Patent ID: 8772708

Claim:
A time-of-flight mass spectrometer including an ion ejector for accelerating target ions by imparting a certain amount of energy to the ions, an ion reflector for reflecting ions ejected from the ion ejector and turning the ions around by an effect of an electric field, an ion detector for detecting the ions reflected by and exiting from the ion reflector, and a reflector driver for driving the ion reflector so as to create a reflecting electric field inside the ion reflector, wherein: with X denoting a coordinate along a central axis of the ion reflector, the reflector driver applies a voltage to the ion reflector so as to create, inside an inner hollow area of the ion reflector and along the central axis of the ion reflector, a predetermined potential distribution U A (X) in which the potential monotonously changes over the entire ion reflector and therefore an inverse function X A (U) can be uniquely obtained, thus creating an N-th order focusing position at a position with coordinate X 0 and potential E 0 inside the ion reflector; and the reflector driver also applies a voltage to the ion reflector within a space having the N-th order focusing position with coordinate X 0 as a starting point and extending into a deeper region, so as to superpose, on the predetermined potential X A (U), a predetermined correcting potential X C (U) which can be approximated by a formula proportional to {U(X)−E 0 } N+3/2 in a vicinity of the coordinate X 0 and which is expressed as a smooth function continuing from the coordinate X 0 into the deeper region.