Beatsy wrote: ↑
Mon Mar 07, 2022 3:04 pm
Scarodactyl wrote: ↑
Mon Mar 07, 2022 1:22 pm
If you ever get an SIL objective working you will be a true hero. I think any enthusiast who has run across them has been curious what those marvelous NAs might reveal, but so far nobody's had the gumption as far as I know. I sure haven't anyway.
Won't be me. The RI of the substrate (which would be the mountant in/around a diatom in my case) has to be at least as high as that of the SIL material or NA is limited to the RI of the substrate. Tough call to match the 2.35 of the lens linked! Probably meant for imaging deeper metal layers through silicon on ICs, or something related to that (RI of silicon is 3.4).
Zrax, a high-RI diatom mountant has an RI of 1.7+ when properly hardened. This is a good match for glass and sapphire SILs (hemispheres). There is a better shape for the SIL too, the super-sphere, which is simply a bit more than half a sphere, say 3/5ths. This increases NA by up to RI squared
I can envisage a way of starting with a sphere and grinding/polishing a flat like that.
This is a very intriguing little rabbit hole that I'm going to continue exploring anyway - independently of the UV stuff.
Just a bit of teaser at this point as this is a very fragmented project that I'm only visiting sporadically - but I hit a milestone. Since the idea started here, it seemed the best place to put this (one-off) report.
I do not claim to have made proper SuperSILs here (Super Solid Immersion Lenses) but they're definitely good "working models" of SuperSILs. I need to learn more about handling during fabrication and in-use before spending serious money on real spherical lenses to make SuperSILs from - which is why I'm going the cheap and crude route for now. After a few false starts trying to make spheres (beads) from scratch I found some low/mid grade glass ball bearings for pennies each and bought a selection of sizes from 1mm-3mm. Easier to make glass spheres if you start with glass spheres
I fire polish these (chefs blowtorch on ceramic surface), pick out the clear spherical successes (about 1 in 2 or 3 is "good enough), glue 4 to a glass slide (to keep them level when lapping), grind and polish the flat on ascending-grit lapping papers stuck to glass (sphere diameter to height ratio dependent on RI), then cook them out of the glue. Quick clean and they're done.
These are 2mm diameter SSILs. A bit grubby from the glue and far from optically perfect, but they actually work surprisingly well under visual inspection (no photos yet). I placed one "dry", flat side down, on various bits of an open diatom strew and was immediately able to see far more detail in the magnified images through the SIL than I could just looking directly at the diatoms - even if I added higher power oculars for extra magnification with the scope alone. Resolution was subjectively better, I'm convinced of it, but I fully intend to photograph and measure the improvement objectively once the process is less manual and fiddly. I have spare manipulator parts laying around that should help improve that.
So although this still looks very promising I'm not yet ready to spend >£70 each on optically perfect, high-RI, 1mm spheres to turn into SSILs. I intend to try more of these home made ones to find the best size for my needs first (diatoms) and the practicality in use. The diatoms in my early tests had to be squashed flat (WD<50nm in air) but I think mountant will improve working distance by 200nm or so. I need to be more accurate with the grinding too as I usually only get one of the four that is exactly the right height (+/- 10 microns). That's partly because of size variation in the source balls, but partly technique too. I welcome the variation for experimenting, but once I find the sweet spot, I want to hit it for all the spheres being "modified" thereafter. Which means I have quite a bit more sporadic tinkering to do before I'll have anything else worthwhile to report. That should be with visual results (pics) too - but I'll start a new thread for that...