Mirau objective?

[iconoclastica]

I ordered a Nikon M-plan 20x last week, but what I received was a Nikon M-plan 20x DI. Searching for the type learned that this is a Mirau objective used for interferometry. Now I haven't got the least idea what i am talking about now

What is wisdom: send it back for it isn't as advertised, or keep it to make someone happy with it, for it seems to be rare and was not that expensive?

[Macro_Cosmos]

I believe DI stands for Differential Interference (Contrast[?]), something rather advanced, and out of my knowledge. I've looked into this and Confocal Microscopy, Darkfield Epi-Illumination and etc. fascinating and mind boggling at the same time.

They both have an NA of 0.4, requires 210mm extension. I'd say try it out to see the performance. Since it's more expensive, I would personally sell it and buy the correct objective, since spec-wise they only differ from the DI designation.

[Pau]

I have no experience with Mirau interferometers, just googling you can find some useful info:
https://www.microscopyu.com/microscopy- ... rferometry
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5473836/

They are specialized tools and very expensive

Given the extra optics bundled in I guess that they would be inferior for normal work than their normal equivalents because they could add issues at least at the defocused parts and with cross polarization.

Have you tested it?

[iconoclastica]

I tried it by eye only. It has low contrast and DoF. Unless it has unexpected qualities with special (and for me practical) techniques, I will not use it.

[iconoclastica]

I just tried it again, now using epi-illumination. Where the normal Nikon CF 20x 160/0.17 shows a quite interesting image, the field with the M-Plan DI is near featureless and grey. I should add that I still lack a suitable light source for the epi-illuminator and a bright torch is doing the job for the time being.

[iconoclastica]

I believe DI stands for Differential Interference (Contrast[?])

That would be the marking DIC rather than DI. I got a DIC too from the same M-Plan series (100x) which is a very usable objective, even with transmitted light. I don't know what DI stands for, but it is a mirau objective. Looking through it, I can clearly see the mirror.

Since it's more expensive, I would personally sell it and buy the correct objective

Something being expensive and finding someone to buy it off you are two things... I about a month time I have collected a number of surplus parts that when sold for a reasonable price would make up for the parts that I do want to keep. But sofar I only sold one of them and rather low priced too.

[Macro_Cosmos]

Something being expensive and finding someone to buy it off you are two things... I about a month time I have collected a number of surplus parts that when sold for a reasonable price would make up for the parts that I do want to keep. But sofar I only sold one of them and rather low priced too.

Yeah that's the hit, finding a buyer can be very hard. I've only been able to sell some of my surplus stuff at pretty much the amount I paid for it... with ebay fees included it's a loss.

I searched on ebay for that objective, only one listing. In that case, maybe just send it back for being not as advertised. Seller has to pay postage in that case too.

[Smokedaddy]

Here is a short video with my WYKO RX40 Mirau interferometer objective on my Nikon Optiphot microscope, with universal epi illuminator and using bright field setting. The interferometer is contained within the objective. The fringes they produce are used to measure variations in depth within a fraction of a wavelength of light. I'm not smart enough to know 'how' to do that but would love to be.

https://www.youtube.com/watch?v=GpoIXL_BUPo

-JW:

[iconoclastica]

Oops, there's an echo

So if I understand your explanation, the difference between what I did is the interferometer integrated in your objective. Which may be turned and then shows shifting colour patterns depending on differences in object surface distance in the, what, 0.1mu range?

Any idea why I am seeing. a grey field?

[rjlittlefield]

Oops, there's an echo

I deleted the echos. They were caused by the Unicode character set problem, resulting in multiple Submit's.

--Rik

[enricosavazzi]

Oops, there's an echo

So if I understand your explanation, the difference between what I did is the interferometer integrated in your objective. Which may be turned and then shows shifting colour patterns depending on differences in object surface distance in the, what, 0.1mu range?

Any idea why I am seeing. a grey field?

The Mirau interferometer requires light to be sent out through the objective and toward the subject. Interference then takes place when light returns from the subject and passes a second time through the objective. This is a simplified explanation, in reality the interferometer contains a small total-reflection mirror in addition to a larger semi-transparent mirror.

If you are using the objective on a normal transmitted-light microscope, there is no light source behind the objective, so there is no interference.

[Smokedaddy]

Oops, there's an echo

So if I understand your explanation, the difference between what I did is the interferometer integrated in your objective. Which may be turned and then shows shifting colour patterns depending on differences in object surface distance in the, what, 0.1mu range?

Any idea why I am seeing. a grey field?

No.

This might help if you're interested. Mike (mtuell) is a member here. The DI is double-beam interferometry.

https://lavinia.as.arizona.edu/~mtuell/ ... rence.html

-JW:

[iconoclastica]

In James' video the colours move about. Something is being adjusted and judging from the images of that objective, I'd say it's the ring of its integrated interferometer. In the link to mtuelas explanation it says

Using the 10x M Plan DI, the following images were obtained on the Optiphot with an epi-illuminator.

That is close to what what I am using. But the result is very different:

in transmitted light:


in incident light:

(I couldn't make the shades out by eye).

Shouldn't there be some kind of 'analyzer' (the interferometer?) in the path?

[Smokedaddy]

What is the specimen? Try it on a shiny chrome ball bearing, something reflective.

[mtuell]

Hi, sorry, they've "upgraded" the server my site is on, and it is currently only sort of working...

Anyway, in the video made by James, he is adjusting focus, which changes the path length between the specimen and the reference mirror in the objective. This goes from no fringes (out of the range of the coherence length of the source), through pastel shades (multiple order interference), through bright single frequency colors, to the zero order (perfect focus) which is white with black fringes on either side, and through to the other side again - bright colors, pastel and finally no fringes.

To achieve this, you need the epi-illuminator with it's lamphouse. It is really hard to do if you don't have the style with field and aperture stops built in, since you use those for alignment. You also benefit by having a phase telescope (like what is used to align the phase ring on a phase contrast objective). It is also really fairly finicky to do without a tilting specimen stage. Having a very stable system is critical as well - vibrations of 50 nm will destroy your fringes if they are high frequency and at least move them around if they are low frequency vibrations.

The basic procedure is to align your lamp for Kohler, then stop down the field stop. When you are at the correct focus, you will see a halo around the field aperture collapse to the edges of the aperture. Then open up that field stop and close down the aperture stop. Use the phase telescope to image the aperture stop, where you should see a double image of the stop. Tilt the specimen to get those overlapping.

At this point, open back up the aperture stop and at least partially close down the field stop. In the normal eyepiece (if you haven't removed the phase telescope), by very slight adjustments to focus, you should find a set of interference fringes. Fine adjust the tilt of the specimen, while keeping it in focus, to get the desired number of fringes in the field. You can go all the way to a null fringe (a single shade of grey or other color) if you have good enough control of the specimen tilt.

To get quantitative analysis, it is generally much easier to use a monochromatic source, say by inserting a GIF filter in the path. That has a wavelength of around 546 nm, and each fringe represents a half-wave, so about 273 nm. If you can pick out by eye deviations of say 1/5th of a fringe, then you can measure surface height errors at around the 50 nm level. Computer software and phase shifting can get you down in the single digit nm easily. With software, we routinely measure surface roughness in the less than 2 nm rms range with an accuracy (based on a average measurement, not a single) in the 0.01 nm range.

Vertical scanning white light inteferometry, as the name implies, uses the full polychromatic source. By moving the focus stage a known amount, it is possible to use the central white fringe to know really accurately how large a step feature is. A single interferogram can't get you the height of a 100 micron step, for example - but combining interferometry with mechanical stage motion, you can get that measured to the 10's of nm.

Sorry this isn't easy to explain quickly, but hopefully there are a few things here that may help you out.

Mike