Abstract: A disclosed objective lens includes: a lens having an entrance surface and an emission surface; and an anti-reflection coat formed on the emission surface, wherein a transmittance T1—0 [%] of the anti-reflection coat when an incident angle of a first laser beam having a first wavelength ?1 (390 nm??1?430 nm) is 0°, and the transmittance T1—40 [%] of the anti-reflection coat when the incident angle of the first laser beam is 40° satisfy 0.95?T1—0/T1—40?1.05, and a transmittance T2—0 [%] of the anti-reflection coat when an incident angle of a second laser beam having a second wavelength ?2 (630 nm??2?680 nm) is 0° and a transmittance T2—40 [%] of the anti-reflection coat when the incident angle of the second laser beam is 40° satisfy 0.85?T2—0/T2—40?0.97.

Abstract: A disclosed objective lens includes: a lens having an entrance surface and an emission surface; and an anti-reflection coat formed on the emission surface, wherein a transmittance T1—0 [%] of the anti-reflection coat when an incident angle of a first laser beam having a first wavelength ?1 (390 nm??1?430 nm) is 0°, and the transmittance T1—40 [%] of the anti-reflection coat when the incident angle of the first laser beam is 40° satisfy 0.95?T1—0/T1—40?1.05, and a transmittance T2—0 [%] of the anti-reflection coat when an incident angle of a second laser beam having a second wavelength ?2 (630 nm??2?680 nm) is 0° and a transmittance T2—40 [%] of the anti-reflection coat when the incident angle of the second laser beam is 40° satisfy 0.85?T2—0/T2—40?0.97.

Abstract: A transmission diffraction grating body including a base material being substantially transparent with respect to wavelength ?1 and having a refractive index n0; another base material being substantially transparent with respect to wavelength ?1 and having a refractive index n1, which is formed on the base material having a refractive index n0; and a relief diffraction grating formed on the base material having a refractive index n1; wherein the refractive indexes n1 and n0 satisfy the relationship: n1>n0. Thus, the base material having a refractive index n1 can be formed of a high refractive index material, and when the depth of grating of the diffraction grating is set so that the diffraction grating diffracts the light with wavelength ?1 and does not diffract the light with wavelength ?2, the depth of grating of the diffraction grating can be made to be shallow, thus preventing the loss of the amount of the light with wavelength ?1.

Abstract: A transmission diffraction grating body including a base material being substantially transparent with respect to wavelength &lgr;1 and having a refractive index n0; another base material being substantially transparent with respect to wavelength &lgr;1 and having a refractive index n1, which is formed on the base material having a refractive index n0; and a relief diffraction grating formed on the base material having a refractive index n1; wherein the refractive indexes n1 and n0 satisfy the relationship: n1>n0. Thus, the base material having a refractive index n1 can be formed of a high refractive index material, and when the depth of grating of the diffraction grating is set so that the diffraction grating diffracts the light with wavelength &lgr;1 and does not diffract the light with wavelength &lgr;2, the depth of grating of the diffraction grating can be made to be shallow, thus preventing the loss of the amount of the light with wavelength &lgr;1.