Patent ID: 7348517

Claim:
A laser cutting apparatus comprising: a gas laser oscillator; and an optical system including a collective lens and transmitting and collecting a laser beam generated in said gas laser oscillator to irradiate a workpiece with the laser beam; wherein a beam quality index M 2 of the laser beam emerging from said optical system, with which the workpiece is irradiated, is in a range of 2.8 to 4.5; while the index M 2 is defined by a formula: M 2 =π×( dm ) 2 /(4 ×λ×Zr ) in which λ is a wavelength of the laser beam; dm is a minimum beam diameter of the laser beam in a predetermined optical-path range including a focal point of said collective lens; and Zr is a distance between a first position on an optical axis, at which said minimum beam diameter dm is established, and a second position on said optical axis, at which a beam diameter “2 1/2 ×dm” is established, in the laser beam in said predetermined optical-path range, wherein said optical system includes a beam-quality modifying optical element affecting a value of said index M 2 .