Method for designing three-blazing-surface echelle grating capable of broadening detection spectrum range

[0015] like figure 1 The schematic diagram of the three-blazed échelle grating is shown, and the specific design steps of the three-blazed échelle grating are as follows:

[0016] a. In the echelle grating groove, design three blaze surfaces with different blaze angles, blaze surface 1 is in the middle, blaze surface 2 and blaze surface 3 are on both sides of blaze surface 1, and the blaze angle of blaze surface 1 is θ b1 , the blaze angle of blaze surface 2 is θ b2 , the blaze angle of blaze surface 3 is θ b3 , and the blazed surface decreases in turn from the grating base along the clockwise or counterclockwise direction after the design, θ b3 b1 b2.

[0017] b. According to the grating equation d(sinα+sinβ)=mλ b , for the same beam of parallel incident light A, B, C, incident perpendicular to the blazing surface 1, blazing surface 1 meets the Littrow self-collimated incident condition, and the principal maximum direction of diffraction of blazing surface 1 is the direction of reflected light perpendicular to blazing surface 1 (A' direction in the figure), the corresponding diffraction wavelength is the blaze wavelength of blazing surface 1; since the incident light is not perpendicular to blazing surface 2 and blazing surface 3, the main diffraction maximum directions of blazing surface 2 and blazing surface 3 are The direction of incident light relative to the reflected light of blazing surface 2 and blazing surface 3 (such as figure 1 In B' and C'), the corresponding diffraction wavelengths in the main diffraction maximum direction are the blazing wavelengths of blazing surface 2 and blazing surface 3, respectively, and the diffraction wavelengths of each blazing surface in the main diffraction maximum direction are different.

[0018] c. According to the band range used by the ladder spectrometer, design the blaze surfaces corresponding to the three blaze angles.

[0019] d. The magnitude relationship of the blaze angle difference of each adjacent blaze surface shall be subject to the fact that the superposition peaks of the diffraction energy tend to be equal.

[0020] e. According to the condition that the light energy of the three blazed wavelengths is equal on the image plane, design the blazed surface width t of the three blazed surfaces 1 , t 2 and t 3.

[0021] f. When there are three blazed surfaces, the distribution of the diffraction energy of the echelle grating on the image plane is the superposition of the blazed wavelength of the three blazed surfaces as the spectral energy distribution of the central wavelength. Diffraction wavelengths are different, which broadens the spectral range of diffraction energy distribution on the image plane, and can detect wavelength information that cannot be detected at the edge of spectral energy on the image plane by a single blazed surface échelle grating spectrometer.

[0022] like figure 2 The schematic diagram of the diffracted light intensity distribution of the echelle grating in the three blazed surfaces shown, according to the grating equation (d(sinα+sinβ)=mλ b ), since the blaze surface (1, 2, 3) corresponds to the blaze angle (θ b1 , θ b2 , θ b3 ) are different, so the central wavelength of their diffraction is also different. In the figure λ m1 , lambda m2 , lambda m3 (m=1, 2, 3, 4.....) is the diffraction intensity distribution of the center wavelengths corresponding to blazed surfaces 1, 2, and 3 on the image plane, and it is also the mth-order blaze corresponding to the three blazed surfaces The intensity distribution of diffracted light at the wavelength on the image plane. The intensity distribution of the diffraction spectra of the three blazed planes is cross-superimposed on the image plane, which broadens the spectral energy distribution of the echelle grating on the image plane, thereby achieving the purpose of having a strong spectral intensity in a wide spectral range and broadening the spectrum on the detection plane It can detect the wavelength information that cannot be detected by the edge of spectral energy on the image plane of the single blazed surface échelle grating spectrometer.