A technique for sampling negative ions in hollow‐cathode and hollow‐anode discharges of strongly electronegative gases is presented. The negative ions were mass analyzed to be Cl−, Cl−2, and Cl−3for the discharge of Cl2/N2mixture and Cl−for HCl/N2. The dependence of negative ion intensity on gas pressure and discharge voltage was investigated. Photodetachment of negative ions was used to induce photoelectron transient signals that probe ion concentrations. The transient signal indicates that negative ions originate in discharge, but not in the mass‐analyzer region. Time dependence of the negative ion signal induced by laser irradiation was measured by a quadrupole mass analyzer and used to study the kinetics of charged particles responsible for the transport of laser‐induced perturbation. The observed negative ion transient signal is a useful means for studying negative ion kinetics in plasma.