Fig. 1. Steps of two-flats refractive index uniformity test

Fig. 2. The original simulation wave

Fig. 3. Recovered refractive index uniformity wavefront results and its residual comparison

Fig. 4. Experimental setup for two flats refractive index uniformity test

Fig. 5. Wavefront of refractive index uniformity of transmission flat by two flats method

Fig. 6. Experiment of transmission method for refractive index uniformity test

Fig. 7. Steps for measure refractive index uniformity by transmission method

Fig. 8. The result of refractive index uniformity

Fig. 9. Relationship between the rotation angle error and the residual error

Fig. 10. Relationship between the pixel offset and residual error