Patent ID: 8774247

Claim:
An Echelle diffraction grating comprising a plurality of gratings, each of which has an asymmetrical triangular shape on a section in which the plurality of gratings are arranged, wherein each grating includes a resin layer made of light curing resin, and a reflective coating layer formed on the resin layer, wherein each grating receives and diffracts incident light on a blazed surface corresponding to a short side of the asymmetrical triangular shape, wherein an apex angle between the blazed surface and a counter surface corresponding to a long side of the asymmetrical triangular shape is between 85° and 90°, wherein a second blaze angle, which is a blaze angle between the blazed surface and a lattice plane, is smaller than a first blaze angle that maximizes diffraction efficiency of a set blazed order for incident light of a wavelength of 193.3 nm, wherein the following conditional expression is satisfied where bd denotes the first blaze angle, and ba denotes the second blaze angle: 0.25 °≦bd−ba≦ 1.2°, wherein the second blaze angle maximizes the diffraction efficiency of a set blazed order for incident light having a wavelength of 248.4 nm, wherein the set blazed order for the incident light having the wavelength of 248.4 nm is set between 77 th order and 86 th order, and wherein combinations of the blazed order that is set for the incident light having the wavelength of 193.3 nm and the incident light having the wavelength of 248.4 nm include a 102 nd order and a 79 th order, a 107 th order and a 83 rd order, and a 111 st order and a 86 th order.