I've been wondering, with today's lab grown diamonds, if a 10-15mm long, 2mm diameter single-crystal diamond tube, would not be the summum of combining "fibre optic frontsight light gathering technology" with more classy materials like diamond.
I had Grok look into it, and it said the following:
Yes, a straight tube made of
pure single-crystal diamond can act as an extremely efficient light pipe or light concentrator, very similar to (and in most ways vastly superior to) a classic fiber-optic sight used on firearms or bow sights.
Here’s why and how it works in practice, based on the real physics of diamond:
1. Total Internal Reflection (TIR) in diamond
Light that enters the sidewall of the tube at a sufficiently shallow angle will undergo total internal reflection because diamond has an exceptionally low refractive index for a transparent material — but wait, no: diamond has a
very high refractive index
n ≈ 2.417 at 589 nm.
The critical angle for TIR at a diamond–air interface is:
θ_c = arcsin(n_air / n_diamond) ≈ arcsin(1 / 2.417) ≈
24.4°
This is an
extremely small critical angle. That means almost any ray that enters the sidewall and is heading even slightly along the length of the tube will be trapped by TIR and will bounce down the tube with essentially
zero loss per reflection (diamond is virtually non-absorbing from ~225 nm out to >10 µm).
2. Light collection and concentration
If the outside of the tube is polished and clean (or even slightly roughened in a controlled way), ambient light hitting the lateral surface over the entire length enters the diamond. Every time a ray meets the inner wall at >24.4° to the normal, it is totally reflected and continues down the tube.
At the exit end you therefore get:
- A very bright spot or ring of light
- Light coming from a huge solid angle (essentially the whole environment around the tube)
- Geometric concentration ratio roughly equal to (length / diameter) in the simple case, and potentially much higher because of the very low critical angle
Real-world numbers: A 50 mm long, 3 mm diameter diamond rod can easily concentrate ambient daylight at the exit face to >50–100× the brightness of the surrounding illumination — enough to be clearly visible even in bright sunlight, exactly like the best tritium + fiber-optic sights, but without needing tritium.
3. Comparison to plastic fiber-optic sights
| Property | Acrylic/plastic fiber | Diamond tube/rod |
|---|
| Refractive index | ~1.49 | 2.417 |
| Critical angle | ~42° | ~24.4° |
| Acceptance angle | Moderate | Extremely high |
| Transmission loss (visible) | 0.2–0.5 dB/m | <0.001 dB/m (negligible) |
| Scratch/abrasion resistance | Poor | Highest of any material |
| UV and thermal stability | Degrades | Essentially forever |
| Brightness in practice | Good | Blindingly bright |
