Microscopy: Diffraction (Jeff Lichtman)

[@fplasil]

I absolutely loved the XEM magnification story :) I am teaching high school physics online. We are just talking about diffraction of light. I was looking for some video about diffraction limitations of optical microscopes. Thanks for your video!

[@SahinKupusoglu]

Excellent video Professor Lichtman; a thousand thanks...

[@aatt3209]

excellent, concise & to the point visual.

[@brendansullivan4872]

WOW the goat of microscopes right here

[@imagination7710]

At 15:00: amplitude (m) is analogous to displacement (r). So for amplitude to increase whilst f (Hz) remains constant, this requires an increase in both r and v by the same factor (square).

[@kaleemullah8142]

Thank you very much dear professor for this video.

[@irisobobo]

Brilliant explanation! Thank you!

[@hachemelouggouti1967]

Let us take this process into the pre-digital photolabor. We enlarge a negative until the emulsion grains become visible, and then take another negative, from the same object, but taken with a more powerful telelens, or microscope, and enlarge the negative again. Obviously more details will show. We may entertain the illusion that we have reached the limit of light, but the only thing we can be certain about is the limit of the information each image contains. After that we are left with the illuminated substrate

[@al1383]

Excellent presentation, thanks

[@anonviewerciv]

Diffraction limits. (9:09,18:48) 3:13 Based on an analog interpretation of the technique used in CSI.

[@hachemelouggouti1967]

using extension rings with a pinhole camera give a pseudo telelens effect. A smaller portion of the field of view gets more and more blown up. It looks like the decreasing sharpness has something to do with light, while it is really a technical artifact. A similar issue is why a large aperture gives less sharp pictures than a smaller ones This is, once again, the same problem as with the pinhole and the extension tubes, but this time the field of view is determined not by the distance between the hole and the reflecting surface, the focal length, but by the width of the opening. A larger aperture means a wider field of view, but since the reflecting or light sensitive surface remains the same, and is usually much smaller that the complete field of view, a smaller portion of the view is captured by the screen, just as if the focal length had been lengthened in a pinhole camera. Therefore, the matter of the so-called diffraction limit becomes the question why blowing images up create unsharp pictures. Is it a technical matter, or is it a property of light? Maybe it is both, since the same amount of light has to be smeared thin on a relatively larger surface. We can imagine that at some point the image will cease being visible because each element would be separated from the other by ever growing distances. In fact, if that were not the case the night sky would be completely illuminated. Okay, but what about the lower limit, when the opening is so small as to let pass a single photon of light, what happens then? Well, first I would like to point out that such a case is highly speculative since we have no way of observing it actually happen. One thing is certain, if we are still able to observe diffraction effects, then there is light enough to go around and therefore no reason not to obtain a sharp image. If we do not, I do not think we should blame the light, we should blame it on the fact that an ever smaller portion of space is being projected on the same surface as before. We are in fact blowing up what amounts to a few atoms to fill the whole sensor area. Add to that the magnification needed to see the image on paper or on a screen and you can imagine the extent to which reality has been magnified. So, maybe the so-called diffraction effects are simply the authentic rendition of a minuscule point in space blown up out of proportions! After all, just like large apertures give a large field of view, point-like apertures, pinholes, give point-like views, and these get projected on the same area that is used for much larger views.

[@user-xb2sg5zv3k]

excellent!

[@robelbelay4065]

Great lecture! Thanks

[@AdolfoCarloni]

what do you think about exciting subdiffractive nanoparticles with a light source at lambda/4 and at lambda/10 ? It would be probabilistic photon detection, but with modern software is possible to do that. Diffraction does not mean more all, because chemistry grew up and is able to produce around the captured analytic molecule of interest some over-diffractive supramulecular structures so big (300 nm) that those can be seen from a normal transmission microscope or maybe a simplfied laser one. The importance stands on the chemical protocol, especially if you know that. Thanks for your lesson :-)

[@Chris-ng9zi]

Re: plane and spherical waves. Can plane waves be thought of as an infinitely small section of a spherical wave? Similar to the idea that a straight line is an infinitely small section of a circle.

[@anirudhgangadhar6158]

Yes, I believe it can. What its saying then is that due to an infinite radius of curvature, things don't really matter in the 3rd direction, hence the name. Cheers

[@Yunpree]

Thank you so much 💖

[@reshmabhagat8054]

Excellent!

[@user-fi9ef7ec2l]

So well explained, really appreciate it!

[@shreyagupta983]

thank you!!!!! so helpful.

[@koltonjones866]

How the heck did that get published. I have this weird ass phobia of publishing. i guess this a good enough reason to give that up phobia.

[@hachemelouggouti1967]

Going back to the view you so justly attacked, if, by some miracle, or disaster, the theory were accepted that one can enlarge copies indefinitely, then I am sure that scientists would find perfectly reasonable explanations for the phenomena that would then appear. Those explanations could then be used to justify further assumptions and it might take a while before such a theory would lead to enough inconsistencies as to be considered as erroneous. This scenario is certainly not implausible, there are enough examples to be found in the history of science that followed such a scenario, and I will only mention the ether and the phlogiston, the first one having survived for more than two centuries, much longer than the first one. The fact therefore that experiments seem to confirm the validity of the current views on light should be seen as a practical reason to keep believing in them and using them, as long as one does not forget that current practice is no guarantee for future validity.

[@hachemelouggouti1967]

I find your critique of the view that one could indefinitely copy an enlargement and enlarge a copy very justified. It is a very simplistic assumption which photographers, among others, have long know to end up with a very large grain with no information whatsoever. Still, I find your argumentation not really convincing. Without realizing it you adopt the same attitude when you explain the results given by a small hole as coming from the nature of light and not of the material used to project the image. You are of course, as is almost any scientist, convinced of the validity of Huygens wave theory, and that makes you somewhat rely too much on its logic. I do not believe in its validity but I will concede to you that the wave theory is a powerful explanation tool that cannot be lightly ignored. I will leave it to that for now. Once you stop assuming that what we see on a screen in such cases must necessarily be explained by the wave theory of light ( I certainly do not deny that it can!) you ignore the possibility that the resolution of light rays, or waves if you prefer, can be much higher than what can be possibly represented by a reflecting surface, at least those surfaces manufactured by humans until now. You maybe of course completely right and maybe diffraction phenomena are inevitable at some point. The only thing is, you have not proven it but made an appeal on the authority of a well known theory.