Performance of Silicon Carbide Mirrors for Advanced Light Source Devices

doi:10.15541/jim20250354

Abstract

Abstract:

The rapid development of advanced light source technologies, such as synchrotron radiation and X-ray free electron lasers, especially for high-energy and high-brightness X-ray facilities, has become one of the key factors restricting the further improvement of beamline performance. When high-energy beams are irradiated onto the surface of mirrors, the absorption of such energy can cause radiation damage and thermal deformation of the mirrors. This study provides an in-depth exploration of various aspects, including the structural design of mirrors, material selection, performance simulation, prototype fabrication, optical processing, and performance testing. By combining solid-state sintering with precision optical processing technology, a silicon carbide (SiC) planar mirror with high optical properties was developed. The influence of different materials on the thermal deformation of the reflective mirror surface, as well as the impact of surface shape accuracy and roughness control on the optical surface quality of the reflective mirror, was discussed. The research shows that under an absorbed power of 200 W, the modified SiC mirror exhibits approximately 25% reduction in normal deformation along the meridional direction compared to conventional single-crystal silicon mirrors. After optical processing, the peak to valley (PV) value of its mirror surface reaches 24.294 nm, the root mean square (RMS) value reaches 1.680 nm, the surface roughness RMS reaches 0.168 nm, and the gas release rate is 2.40×10⁻⁷ Pa∙L/(s∙cm²). These results meet the requirements for ultra-smooth mirrors in advanced light source facilities, demonstrating the potential of high-performance silicon carbide ceramics as an ideal choice for next-generation mirror applications, instead of single-crystal silicon.

Key words: synchrotron radiation, X-ray free electron laser, silicon carbide mirror, surface shape accuracy, roughness

CLC Number:

TH743

LIU Leimin, LUO Hongxin, HE Yumei, JIN Limin, LI Yongjie, LIU Jingwen, WEI Yuquan, SUN Anle, CHEN Zhongming, LIU Xuejian, YIN Jie, HUANG Zhengren. Performance of Silicon Carbide Mirrors for Advanced Light Source Devices[J]. Journal of Inorganic Materials, 2026, 41(6): 805-813.

Figures/Tables 16

Fig. 1 Preparation process of silicon carbide mirror

Fig. 2 Model diagram of mirror cooling system

Table 1 Physical parameters of materials

Physical parameter	SiC	Si	Cu
Elastic modulus/GPa	440	112	115
Poisson’s ratio	0.18	0.28	0.32
Bulk density/(g·cm^-3)	3.12	2.33	8.94
Thermal conductivity/(W·m^-1·K^-1)	180	100	320
Coefficient of thermal expansion/(×10^-6, K^-1)	2.20	4.00	16.5

Fig. 3 Distribution of heat power absorbed on the mirror surface (a) 200 W; (b) 50 W. Colorful figures are available on website

Fig. 4 Thermal-structure numerical simulation results of two types of material mirrors Temperature distribution: (a) Si-200 W, (b) SiC-200 W, (c) Si-50 W, (d) SiC-50 W; Thermal deformation distribution: (e) Si-200 W, (f) SiC-200 W, (g) Si-50 W, (h) SiC-50 W. Colorful figures are available on website

Fig. 5 Meridian surface shape of mirror under thermal load impact (a) Normal deformation curves of center line of the spot region; (b) Slope curves

Table 2 Thermal-structure simulation and analysis results of mirror

Thermal power/W	Material	Maximum temperature/ ℃	Meridian slope/ μrad	Residual meridian slope after deducting the fitted circle/μrad	Fitting the radius of the circle/ km
200	Si	47.1	7.3	4.8	8.7
200	SiC	45.5	5.5	2.8	18.2
50	Si	34.3	1.8	1.2	34.7
50	SiC	33.9	1.4	0.7	72.6

Fig. 6 Silicon carbide mirror blank

Fig. 7 Fracture morphology of silicon carbide ceramics

Table 3 Physical properties of silicon carbide ceramics

Physical property	Result
Bulk density/(g·cm^-3)	3.12±0.01
Flexural strength/MPa	491±56
Elastic modulus/GPa	439±3
Thermal conductivity/(W·m^-1·K^-1)	180.0±7.5
Coefficient of thermal expansion/(×10^-6, K^-1)	2.22±0.02

Fig. 8 Surface roughness of silicon carbide mirror (a) Polished SiC; (b) Polished Si film. Colorful figures are available on website

Fig. 9 Optical processing and surface shape detection of silicon carbide mirror (a) Ion beam fine polishing; (b) Surface shape detection; (c) Convergence process of silicon carbide mirror shape error. Colorful figures are available on website

Fig. 10 Final surface shape of silicon carbide mirror (a) Meridian direction; (b) Arc vector direction. Colorful figures are available on website

Table 4 Comparison of optical surface shape of this study with internationally developed mirrors

Country	Year	Device	Material	Size/(mm×mm×mm)	Surface shape accuracy	Roughness/nm
France^[26]	2018	ESRF BM08/LISA	Si	900×35	Slope error: 0.5 μrad RMS	0.2
Germany^[27]	2014	PETRA III	Si	100×50×15	Height error: <0.1 nm Slope error: 0.041 μrad RMS	0.2
Japan^[28]	2025	SPring-8	Si	400×50×50	Height error: 1 nm	0.15
China^[29]	2020	HEPS/SSRF	Si	200×50×50	Slope error: 0.26 μrad RMS	0.3
China	2025	This work	SiC	440×50×50	Height error: 1.3 nm Slope error: 0.166 μrad RMS	0.13

Fig. 11 Detection results of outgassing rate of SiC mirror (a) Outgassing spectrum; (b) Extractor gauges. Colorful figures are available on website

Table S1 Comparison of the key performance stability of mirror materials[4]

Material	Elastic modulus/ GPa	Density/ (g·cm^-3)	Thermal conductivity/ (W·m^-1·K^-1)	Coefficient of thermal expansion/ (×10^-6, K^-1)	Ratio stiffness/ (MPa·m³·kg^-1)	Thermal stability/ (×10⁶, W·m^-1)	Maximum weight loss rate^***/%
Diamond	880	3.50	2000	1.50	251	1333	0
SSiC^*	440	3.12	180	2.20	138	81	90
RB-SiC^**	360	3.03	130	2.50	119	52	90
ULE	67	2.20	1.30	0.03	30	43	75
Si	112	2.33	100	4.00	48	25	-
Be	303	1.84	216	11.50	165	19	60

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