- #1

anvoice

- 16

- 3

Would I be better served using a single fused silica ball lens, or 2 hemispherical lenses in this scenario? If I understand correctly in air, the focal point for a hemispherical lens will be Radius / (n - 1), whereas for a ball lens it is Radius / 2(n-1) where n is the refractive index (close to 1.5 for fused silica at 275nm). If so, that works out to about 10mm for a 10mm radius hemispherical lens (giving me about 5mm of distance from the lens surface), or 5mm for a spherical lens. If above is correct, I can't use spherical lenses as they will focus at the surface of the sphere. Then there is the fact that the light source isn't an ideal point, so the calculations wouldn't apply perfectly. A final factor to consider is that a 20mm diameter hemispherical fused silica lens costs four times that of a 10mm diameter, so if possible I was hoping to get away with a smaller lens. Would this work at all? Will I need to switch to larger radius of curvature lenses?

I am currently vigorously reading various sources to try to figure this out, but it would be nice to order the materials sooner rather than later. I was also hoping to buy the correct lenses on the first try, as they are both not cheap and take a while to arrive. Thanks in advance for any insight!