Helium is useful as a carrier gas for some experiments in photochemistry and photophysics (the study of laser-created nanoclusters, for example); these experiments benefit from laser sources capable of ionizing neutral atoms but falling short of the helium (He) photoionization threshold. One such source has been developed by researchers at Colorado State University (Fort Collins, CO). They have demonstrated a tabletop laser using neonlike chlorine as a gain medium that emits at 52.9 nm, just below the He ionization threshold. The laser emits 10-mJ pulses at 1 Hz, producing a beam with a divergence of 4 mrad.
The gain medium is produced by rapidly exciting a 3.2-mm inside-diameter capillary channel filled with preionized chlorine gas; a current pulse produces a plasma column 18.2 cm long. The fast current pulse compresses the column, causing collisional electron excitation and thus a population inversion. The optimum pressure for lasing was found to be 224 mTorr. The device produces pulses having a full-width-at-half-maximum duration of 1.46 ±0.25 ns and a peak power of 7 kW. The far-field pattern has a Gaussianlike shape. Contact Jorge Rocca at [email protected].