Novel gas target for use in laser harmonic generation

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Abstract
A novel gas target was developed for use in laser-atom harmonic-generation experiments. It operates on the principles of free molecular flow rather than those of fluid flow as does a gas jet. This allows much lower gas pressures to be achieved. The device is a small, cylindrical, double-ended hole through which the focused laser beam passes. Gas enters from the middle of the cylindrical wall and quickly disperses as it emerges out the hole openings. As with the gas jet, the purpose of the gas target is to provide a very narrow and localized distribution of gas for laser interaction. Some of the advantages of the target relative to the jet are that it is easier to systematically align to the laser beam and it can operate at much lower pressures. Results of a Monte Carlo simulation of the gas density and flow rate within the target and experimental measurements of the density profile made by imaging the recombination emission are presented herein. It is found that the gas density decreases rapidly once outside the target hole openings along the symmetry axis. The calculations are in good agreement with experimental measurements. The gas target continues to function without serious deviation at pressures up to ten times above the molecular flow range.