| 摘要 |
PURPOSE:To extend the working distance between a light emitting face and an objective lens by using a retrofocus lens, where a concave lens having a negative refracting power is arranged in the exit side of a luminous flux, as the first lens. CONSTITUTION:Luminous fluxes emitted from a beam waist position 6a in a plane vertical to the joint surface of a laser 7 and a beam waist position 6b in a plane parallel with the joint surface are received by an objective lens 8, and the luminous flux emitted from the objective lens 8 is converted to parallel rays by a cylindrical lens system 9. What is called a retrofocus lens is used as the objective lens 8, whose luminous flux exit side a concave lens having a negative refracting power is arranged on, for the purpose of extending the working distance between the light emitting face of the laser 7 and the objective lens 8. This method is effective to extend the working distance in comparison with the focal length of the objective lens 8 when the focal length is shortened. If the focal length may be long, it is possible to eliminate the concave lens on the exit side.
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