Patent ID: 7801008

Claim:
A diffractive optical element comprising a first optical part and a second optical part bonded to each other with a bonded surface therebetween formed as a diffraction surface for diffracting a plurality of kinds of laser beams of different wavelengths on said diffraction surface, wherein: diffracted light with the largest quantity of light out of diffracted light for at least one of said plurality of kinds of laser beams obtained on said diffraction surface has a second or higher diffraction order, wherein said plurality of kinds of laser beams include a first laser beam of a first wavelength and a second laser beam of a second wavelength different from said first wavelength, and the following conditional formula (1) is satisfied in a region where at least said first laser beam and said second laser beam enter: 0.7<( m 1 ·λ 1 ( n 1 (λ 2 )−( n 2 (λ 2 ))/( m 2 ·λ 2 ( n 1 (λ 1 )−( n 2 (λ 1 ))<1.3 Formula (1): wherein m 1 is a diffraction order of diffracted light with the largest quantity of light out of diffracted light for said first laser beam obtained on said diffraction surface; m 2 is a diffraction order of diffracted light with the largest quantity of light out of diffracted light for said second laser beam obtained on said diffraction surface; λ 1 is said first wavelength; λ 2 is said second wavelength; n 1 (λ 1 ) is a refractive index of said first optical part to said first laser beam; n 1 (λ 2 ) is a refractive index of said first optical part to said second laser beam; n 2 (λ 1 ) is a refractive index of said second optical part to said first laser beam; and n 2 (λ 2 ) is a refractive index of said second optical part to said second laser beam.