Cleaning wave plates

[viktor j nilsson]

Earlier this year I bought an Olympus Vanox AH. I mostly wanted it for its DIC capacity, but I was also happy to see that it came with a complete polarizing setup (rotating stage, pol condenser, pol intermediate tube, pol objectives, two wave plates). A full presentation of this microscope will be posted on this site when I get everything working.

The wave plates are a 530nm (full wave) and a 147.3nm quarter wave plate (a millimicron, mµ, is an older name for nanometer).



I believe these wave plates are made of either mica or gypsum.

I haven't cleaned wave plates before. Are they particularly sensitive? What solvents would be best to use, and what solvents are best to avoid?

[Element 56]

I clean mine with an aqueous solution and lens wipes. I loosely wrap a piece of the wipe around a small swab with plenty of cushion between the end of my wrap and the swab. That way there's no hard backing so it's more like a brush. Saturate the makeshift swab/brush so you can sweep the surface in a circular motion from the center out toward the edge. Use once and repeat until its clean. If you have spots remaining from whatever detergent you use repeat the same process with distilled or deionized water. Don't linger and don't fuss. It's better leave a little behind rather than scratch the surface.

I use a low alcohol content (actually I've been leaning towards acetone more and more) in my lens cleaner relying on the detergent to do most of the work.

Kirby

[viktor j nilsson]

Thanks, Kirby! Are they really soft, these older mica/gypsum plates?

[Element 56]

Yes it would be much softer, however, I don't know for sure that in your case you will actually be cleaning the mica. I could be wrong but you may actually have a mica disc sandwiched between two pieces of optical glass. May be someone else can chime in here that is more familiar with the Japanese equipment of that period. Cheaper instruments like Unitrons were definitely laminated and I'm guessing Olympus is the same but that is just a guess. I never worked on one branded Olympus. Earlier wave plates are a different story.


Kirby

[PeteM]

It's easier to get a nice clean wet wipe across the entire prism if you disassemble the plate. Trying to swirl around inside the viewing aperture is more likely to leave debris and scratch the surface.

[Element 56]

It's easier to get a nice clean wet wipe across the entire prism if you disassemble the plate. Trying to swirl around inside the viewing aperture is more likely to leave debris and scratch the surface.

I agree but those might be glues in place or there could be a snap ring. Must be careful not to break it on the way out!

[abednego1995]

Those wave plates are usually a sandwitch of optical glass and mica, if not quartz. Normal protocol with objectives will work Ok, just be careful not to immerse the edges with solvents that may attack the optical bonding. And dissassembling wave plates are a big nono. You'll never get the axes right.

Cheers,
John

[PeteM]

Just to be clear, the idea is to take off the cover (if screwed on) to get a nice clear shot. Not to separate the optical elements (which in my experience have often been cemented - and as John noted don't want to be wet along the edges).

[viktor j nilsson]

Thanks for great input, all of you.

Upon closer inspection, it does look like the wave plate is cemented together, so it makes a lot of sense that it would be mica sandwiched between optical glass.

Removing the cover is not an option, the holder is solid metal. The wave plate is inserted into a threaded hole. Well, at least you can see threads on one side. Strange enough, there's no retainer ring or anything. So either the wave plate itself has threads on its side (which seems unlikely) or rests on a 'shelf' inside the hole that is formed by the threads. Kind of weird. But maybe that's a way of ensuring that it rests at a very slight angle? I know olympus often does that with flat surfaces in the image forming pathway?

[abednego1995]

rests on a 'shelf' inside the hole

Exactly. Ever seen stress lines in polarized light? The last thing you would want to subject an element in a pol train is stress. Minimum amount of "soft" adhesive holds them in place.