Abstract
The manufacturing process of large-area, high-precision gratings is a very complicated and time-consuming process. The hardness testing of grating films is an important step in the entire process. In order to simplify the manufacturing process of gratings, we have proposed a new method for testing microhardness based on tool edge indentation. Also, it unified tool adjustment and microhardness testing steps in the grating manufacturing process. First, a mathematical model of the relationship between tool load and indentation contour length is established. The model parameters were then modified using tool indentation experiments with different loads. When measured with a nanoindenter, the average hardness of the grating film was 447 MPa. The hardness value of the grating film obtained by our proposed method is almost the same as that measured by the nanoindenter, and the maximum deviation is about 2.2% of the average hardness value. The experimental results show that our proposed method can replace the microhardness test method of using a nanoindenter. Therefore, the disadvantages of using a nanoindenter to test the hardness of a grating film are avoided, such as the limited sample size, the sensitivity of the indenter to the roughness of the film and the depth of the indentation, and the accuracy of film testing, and the efficiency of grating ruling can be improved.
Highlights
In optics, a diffraction grating is an optical component with a periodic structure that splits and diffracts light into several beams travelling in different directions, and its cross section usually shows a serrated, sinusoidal, or rectangular array
Erefore, the average hardness index C was input into equation (6) that is developed on the relationship between the load on the tool and the length of the tool indentation, and the final microhardness model for grating aluminum films was obtained as follows: P
According to equation (8), the maximum and minimum hardness of the aluminum film are 456.855 MPa and 440.825 MPa, respectively. e difference between the two values is 16.03 MPa, and these values are very close to the average hardness value of 447 MPa measured by the nanoindenter, and the maximum deviation between the two test results was below 2.2% of the average hardness. ese results demonstrate the accuracy and validity of the proposed microhardness model about aluminum films of gratings
Summary
A diffraction grating is an optical component with a periodic structure that splits and diffracts light into several beams travelling in different directions, and its cross section usually shows a serrated, sinusoidal, or rectangular array. During the grating ruling process, to attain the best extruded and polished grating blaze plane and to ensure a regular elastic-plastic uplift in the lateral part of the triangular groove, the consistency of the grating ruling tool main edge and the ruling direction should be strictly guaranteed, and the appropriate load should be optimized according to the hardness of the aluminum film.
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