Asking this because I’ve been thinking about resin printing and how a small layer of said liquid could, in theory, be used to make the prints faster and negate any problems regarding the FEP film (which can wrinkle, tear and be a hassle to clean when small pieces are stuck to it). The ideal liquid would have to be:
- Inert to UV light
- Not miscible with the resin
- Denser than 1.25g/cm³
Maybe the liquid doesn’t even need to have a small refraction, so long as the light doesn’t diffuse too much after going through ~1mm of it. That or doing some compensation on the print.
Assuming we’re talking about refractive index here, metals technically still have a refractive index despite being reflective (light can penetrate a very short distance through metals). In the UV, the refractive index of mercury is <1 and of course it’s very dense. But that’s probably not going to be useful to you.
For transparent materials, water actually has a lower refractive index than most liquids (around 1.34 in the UV). You can check this website to see if there’s anything better (probably an organic), but I doubt it would be by much.
I don’t know much about 3D resin printing, but I assume you a focus an image (in the UV) onto a resin layer to selectively cure it. As you suggest, the presence of a liquid would refract the focusing light rays and change the position of the focal plane. This could in principle be accounted for by changing the distance from the focusing optic, though there could be some (perhaps minor) blurring of the image.