Patent ID: 7321377

Claim:
A method for laser marking in which a predetermined array of dots for forming a marking pattern are formed by irradiating a photosensitive material with a laser beam oscillated through a laser oscillation device, wherein when a wavelength λ of the laser beam is within a range of equal to or larger than 9 μm and smaller than 10 μm, and a pulse width t for driving the laser oscillation device in order to form one dot is within a range of equal to or larger than 3 μsec and smaller than 30 μsec, an energy density E (kw/cm 2 ) of the laser beam on the photosensitive material and the pulse width t are set in an area defined by the following relations: E=− 10 t+ 330, and E=− 15 t+ 1000; wherein said irradiating a photosensitive material deforms said photosensitive material to form dots having a convex surface; and said dots comprise a plurality of small bubbles beneath the surface of the photosensitive material.