An equilateral prism is an optical prism whose cross-section is an equilateral triangle, with all three apex angles equal to 60°. It is one of the most fundamental and widely used dispersive optical elements.
| Parameter | Typical Value | Description |
|---|---|---|
| Apex angle $A$ | 60° | Fixed by equilateral geometry |
| Material | BK7, F2, fused silica, SF11 | Determines index & dispersion |
| Refractive index $n_d$ | ~1.52 (BK7), ~1.72 (SF11) | At 587.6 nm |
| Abbe number $V_d$ | ~64 (BK7), ~25 (SF11) | Higher = lower dispersion |
| Surface flatness | λ/4 – λ/10 | Optical quality spec |
| Surface quality | 40-20, 60-40 (scratch-dig) | Per MIL-PRF-13830B |
| Clear aperture | 80–90% of face | Usable optical area |
| Angle tolerance | ±3′ to ±30″ | Apex angle precision |
| Coating | AR, HR, or uncoated | Optional |
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