Note: Longitudinally excited N₂ laser with low beam divergence

We developed a longitudinally excited N2 laser (337 nm) with low beam divergence without collimator lenses. The N2 laser consisted of a 30 cm long Pyrex glass tube with an inner diameter of 2.5 mm, a normal stable resonator formed by flat mirrors, and a simple, novel driver circuit. At a N2 gas pressure of 0.4 kPa and a repetition rate of 40 Hz, the N2 laser produced a circular beam with an output energy of 2.6 μJ and a low full-angle beam divergence of 0.29 mrad due to the uniform discharge formed by the longitudinal excitation scheme, the long cavity with the small aperture, and the low-input energy oscillation.