An improved electric-discharge-excited mercury halide dissociation laser operable on the (B-X) transitions in HgCl, HgBr and HgI at 558, 502 and 443 nm respectively. The laser discharge cell is elongated and made from temperature-resistant silicon-glass laminate or any other suitable material and includes separate ceramic crucibles for containing mercuric dihalide crystals. A pair of electrodes, each having external terminals, extend along the linear axis of the cell in parallel relationship with the linear axis and each other. Ultraviolet discharge means is also provided for preionizing a buffer gas of helium to which nitrogen has been added. The improvement comprises the addition of about 10% nitrogen to the buffer gas of helium which is admitted to the laser cell prior to excitation. The addition of nitrogen may act to selectively remove the terminal levels of the mercury halide laser transitions, thereby permitting more efficient extraction of the optical energy from the laser media. Thus improvements in both efficiency and output energy are obtained. The laser cavity is completed by a fully and a partially reflective surface for the wavelength of operation. The gases are preionized and excited by pulsed electrical energy from separate sources.