The letter reports the first use of laser ablation of trace impurities into a reversed field pinch (RFP) similar to that used in tokamaks, but selecting different impurity elements appropriate to the confinement times of present RFPs. The ionization rates from helium-like carbon and boron are sufficiently slow to allow measurements of particle confinement times from line intensity decay rates of the near UV transitions. A zero-dimensional treatment, incorporating impurity ionization and confinement, is used to interpret the temporal behaviour of the line intensity. The results obtained yield typical particle confinement times of about 1 ms.