I can’t give you practical advice but I have a background with lasers. Historically many used Invar (Nickel / Iron alloy) rods for laser resonators because of low thermal coefficient of expansion. Many companies switched to carbon composites as lower CTE and much lighter. Found this paper which might be of interest. https://www.researchgate.net/publication/241529927_Long-term_and_thermal_instability_of_carboncarbon_composite
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