Fig. 1. Measurement schematic of LTP

Fig. 2. Principle diagram of LTP detects grating. (a) Grating surface shape measurement with normal incidence; (b) detecting deviation of the grating density at Littrow angle of incidence

Fig. 3. Optical path diagram of LTP system

Fig. 4. Image of LTP system

Fig. 5. Schematic of system error calibration

Fig. 6. Result of system error calibration

Fig. 7. Measurement results of 760 line/mm grating. (a) LTP measurement of the grating in the first diffraction order (m=1)and in the zeroth diffraction order (m=0) (average of 6 groups);(b)(c) reproducibility of LTP measurement on the grating in the first diffraction order(m=1) and in the zeroth diffraction order (m=0) (deviations between each result and the average of 6 groups); (d) uniformity of grating groove density

Fig. 8. Measurement results of 2400 line/mm grating. (a) LTP measurement of the grating in the first diffraction order (m=1) and in the zeroth diffraction order (m=0) (average of 6 groups); (b)(c) reproducibility of LTP measurement on the grating in the first diffraction order (m=1) and in the zeroth diffraction order (m=0) (deviations between each result and the average of 6 groups); (d) uniformity of grating groove density

Fig. 9. Diagrams of 760 line/mm grating diffraction wavefront detected by interferometer. (a) The first diffraction order; (b) the zeroth diffraction order

Fig. 10. Comparison of height profiles for a center line trace on the 760 line/mm grating between LTP and interferometer. (a) The first diffraction order; (b) the zeroth diffraction order; (c) the first diffraction order subtracts the zeroth diffraction order