| 摘要 |
PROBLEM TO BE SOLVED: To read the bar code with minimum line width over wide range by expressing a curved line, which expresses the ridge line of a cross section including an optical axis while being rotationally symmetrical to the optical axis, as a non-linear function which can not be differentiated on the optical axis, increasing the inclination at the part of the ridge line closer to the optical axis and providing an optical element having a little inclination of the ridge line away from the optical axis. SOLUTION: The curved line of ridge lines D' and D" of the cross section cut by a plane including an optical axis 4 while being rotationally symmetrical to the optical axis 4 uses an optical element 3 for laser beam generation in the form expressed by the non-linear function which can not be differentiated on the optical axis 4. The light to be made incident to this optical element 3 for laser beam generation is divided to the optical axis 3, two light flux C' and C" emitted from the element 3 is mutually interferred and light intensity is gradually attenuated. Therefore, this element 3 generates the long focus laser beam similar to a Bessel beam. Besides, the inclination of ridge lines D' and D" of the element 3 closer to the optical axis 4 is increased but the inclination away from the optical axis 4 is decreased and a condensed light spot diameter is reduced. |
