Table 3. Summary of characteristics of CBXFEL diamond crystal mirrors C₁–C₄ measured after laser machining, ablation and annealing.

			COM (r.m.s.) in working area and drumhead membranes (µrad)
Crystal	Sample thickness (µm)	Miscut angle (°)	2 mm × 2 mm	1 mm × 1 mm	M1 0.3 mm × 0.3 mm	M2 0.3 mm × 0.3 mm	RMS wavefront phase error
C1 (drumhead)	508	0.30	0.21	0.18	0.17	0.19	λ/109
C2	550	0.10	0.16	0.13	–	–	λ/131
C3	378	0.22	0.14	0.12	–	–	λ/68
C4	546	0.14	0.16	0.13	–	–	λ/77