High power He–Ne laser with flat discharge tube

Abstract

A high-power He–Ne laser with a flat discharge tube has been realized. Its output power can be enhanced by increasing the transverse size of the discharge tube. This high-power flat He–Ne laser tube of 1.4 m discharge length can achieve above 180 mW of output power at a wavelength of 0.6328 µm. Its optimum discharge parameters and the gain characteristics are investigated experimentally. The experiments indicate that the optimum current increases with decreasing total gas pressure. But the increase in the optimum current is almost independent of the gas mixture ratio. The increase in the gain coefficient at the axis of the discharge tube with discharge current is not obvious. The boost in laser output power is mainly caused by the expansion of the lasing gain region. To achieve the higher output power, four of the laser tubes mentioned above are placed into one laser box. The laser beams are coupled into a quartz optic fibre and the output power from the end of the optic fibre can reach above 480 mW. This high-power He–Ne laser has been used in a clinical application, photodynamic therapy (PDT) of cancer, and its effective rate is above 90% in 183 clinical cases. The structure, characteristics and applications of this high-power flat He–Ne laser are introduced and discussed in this paper.