| 摘要 |
PROBLEM TO BE SOLVED: To provide a long-focus laser beam generation apparatus which can suppress the ripple of optical power in the direction of the optical axis by using an optical filter which can be manufactured at low cost and with good accuracy. SOLUTION: A long-focus laser beam generation apparatus is provided with a first lens 2 by which a laser beam 11 from a laser light source 1 is converted into a plane-wave laser beam 12, with a slit plate 3 which converts the laser beam 12 into spherical waves by a ring-shaped slit 3a and with a second lens 4 by which the spherical waves from the ring-shaped slit 3a are converted into a plane-wave laser beam 15. An optical filter 5 which is formed on the basis of a cosine function-shaped amplitude transmittance distribution and which has a step-shaped amplitude transmittance distribution radially outward with reference to an optical axis Z is arranged between the slit plate 3 and the second lens 4. The optical filter 5 is manufactured at low costs and with good accuracy by a photolithographic technique or a vapor deposition technique. Then, the ripple of optical power in the optical-axis direction of a Besssel beam 16 generated on the optical axis Z is suppressed. |
