PURPOSE: To enlarge an oscillation wavelength range of variable wavelength laser by covering at least one of an excitation light source and a laser medium with a fluorescent glass tube of SiO2 glass doped with Tb and Al.

CONSTITUTION: A sol obtained by hydrolyzing ethyl silicate with an aqueous solution of hydrochloric acid is mixed with TbCl3 and AlCl3 in a given molar ratio to prepare colloidal SiO2. Then the colloidal SiO2 is adjusted to proper pH by adding an aqueous solution of NH3, gelatinized, heated and dried to give a dry gel, which is heated to a given temperature to give a fluorescent quartz glass doped with Tb and Al. A Ti/Al2O3 rod 41 is covered with a quartz glass tube 44 by a laser device, cooling water 46 is made to flow in the tube. On the other hand, xenon flash lamps 42 are covered with doped quartz glass tubes 45, the cooling water 46 is made to flow in the tubes, light rays from the xenon lamps 42 are reflected from a condensed light reflecting mirror 43, passed through a fluorescent glass tube, light rays at ≤300nm short wavelength are cut to double luminance of light rays in 400-550nm wavelength. An oscillation wavelength range of variable wavelength laser can be widened.