The Whitest Optical Reflector With High Reflectivity

1. Substrate Selection and Pre-treatment: Substrate materials with low thermal expansion and high mechanical strength are prioritized, such as BK7 optical glass, fused silica, and silicon carbide (SiC). The substrate is cut to the appropriate size according to application requirements, and the edges are polished to avoid chipping. Subsequently, multiple cleaning processes are performed: first, surface oil and dust are removed with detergent; then, a mixture of hydrofluoric acid or chromic acid is used for chemical etching to remove microscopic impurities and optimize surface roughness to improve coating adhesion

2. Surface Modification and Activation (Optional): For special substrates such as silicon carbide, surface modification is required first. A SiₐCᵦOᵧNᵨ coating is deposited using magnetron sputtering, followed by precision polishing to reduce surface roughness (extremely low RMS value) and minimize scattering loss. If a chemical plating process is used, the substrate needs to be sensitized (immersed in stannous chloride solution to adsorb Sn²⁺) and activated (immersed in palladium chloride solution to generate Pd catalytic particles) to prepare for reflective layer deposition.

3. High-Reflectivity Layer Coating: The core processes fall into two categories. High-end products often employ vacuum coating technology: the pre-treated substrate is placed in a vacuum chamber (vacuum degree ≤10⁻⁴Pa), and metals such as aluminum and silver are evaporated through resistance heating or electron beam bombardment, or magnetron sputtering is used to bombard the target material, causing metal atoms/dielectric particles to be uniformly deposited on the substrate surface, forming a reflective film (metal film or metal + dielectric composite film) with a thickness of 50-200nm.

4. Protective Layer Coating and Strengthening: To prevent oxidation and scratches of the reflective layer, a protective layer such as SiO₂, MgF₂, or polyurethane resin is applied, with a thickness controlled at 5-10μm. After curing, a transparent protective barrier is formed. Depending on the application requirements, additional physical tempering (high-temperature air cooling) or chemical strengthening (potassium salt ion replacement) treatments can be performed to improve the substrate's impact resistance and weather resistance.