Table 1. Parameters for the two optical substrates, as measured facing sideways by Zeiss’ D100 interferometer.

Parameter	Mirror 1 (C-line)	Mirror 2 (E-line)
Substrate	Silicon	Silicon
Length L (mm)	900	900
Height H (mm)	57.5	57.5
Trapezoidal width W (mm)	76.3–63.7	77.9–62.1
Active area L × W (mm)	700 × 50	700 × 20
Tangential slope error r.m.s. (nrad)	170	140
Tangential radius R (km)	1010	460