Optical Interferometry Part 1: Introduction & ZYGO GPI layout
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- เผยแพร่เมื่อ 15 พ.ค. 2024
- The video discusses the principles of optical interferometry using glass interfaces and a ZYGO GPI LC interferometer from the 1990s.
0:00 intro
2:13 What can you do with interferometry?
3:06 Optical wave fronts explained
12:41 Inside the ZYGO GPI LC interferometer
20:45 Example of visual fringe evaluation
The clip featuring a wave at 3:12 min was taken from this FailArmy video:
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Expansion would cause convexity and your finger-heat caused a curvature that goes against the rest of the pattern, so the rest of the surface is concave.
I see a wide area of constructive interference on the left of the image, so this would mean an area of less slope in reference to the flat surface.
That would mean answer A.
(As it is concave and a 'flatter' area relative to the flat surface is on the left)
Love the video. :)
We have a winner!
I was thinking it was D as I was thinking the opposite of you.
in situations where the measured curvature is so small that few or even no lines are visible. When heated enough, the interference pattern inside the convexity caused by an expanding heated spot would always create a continuous loop of a fringe which has a thicker belly facing down the slope if the surrounding surface is concave, as the surface facing up the slope would have a change in the gradient from horizontal in relation to the rest of the surface in cross section, while the surface facing down the slope would appear continuous. This would also make the loops of fringes appear to generate off centre from the heated spot towards the higher side.
Good explanation. I imagine the fringes as height lines of a sphere with a decentered vertex due to the tilt. That's how I can rule out B) and C). The extra info comes from the convex thermal expansion. Digital interferometers usually use phase shifting to determine the correct sign of the surface.
BTW a good analogy is cutting an onion far from the center which yields a similar pattern to the interference of a plane and a spherical wave because of the constant shell thickness.
I watch a lot (too much) of YT, but for some reason whenever this channel has new content I get most exited. It's all just so fascinating.
Same! Honestly optics was the only section of physics I enjoyed when I took it, so this channel is my little guilty pleasure to binge watch every once in awhile😂 it’s a nice break from the other fast paced stuff I watch
I do like this channel for the reason that the content when it comes is well done and not part of the daily information flood. Quality over quantity. Another similar channel is Brainiac75, and I also like the LockPickingLawyer where you'd almost can see the quality of the lock picked featured by the length of the video.
But I think that Google has considered that quantity is more important than quality.
Project Farm and Mustie1 are channels with weekly content, which is a decent frequency for regular, much like the weekly magazines that used to exist. And for those that don't mind a bit colorful language then AvE is a channel with high and low parts of a lot of hands on stuff. So there are a number of channels there with pretty good quality content.
I do a few videos myself at random intervals, and I try to make stuff that do show things that might interest at least someone.
Nailed it!
You can't be watching more than me
Excited*
What a great video! I've been working at Zygo for over two years now in our precision lens assembly division that focuses on telescopes. Love seeing these deep dives into the tools we use every day
The "elite" is exploiting you and want you docile and brainwashed 👉 The Connections (2021) [short documentary] 💖
This is the kind of scientific content I open youtube for. True, real, practical science, and, the best of it all, it's about the very closed and obscure field of precision optics.
Thanks for treating us with this stuff.
The "elite" is exploiting you and want you docile and brainwashed 👉 The Connections (2021) [short documentary] 💖
At my job, I used to work on a few interferometer test stands using similar instruments, so this was a bit nostalgic and it made for a nice refresher course.
I appreciate the attention to detail at 16:39, where the reference flat is shown with a significant wedge. Although not explained in the voiceover, I'm sure this is intentional, not a video production glitch. The wedge is necessary because light will reflect off both sides of the optic-not just the reference surface, but the opposite surface too. The wedge puts this unwanted reflection out of alignment so it doesn't pick up in the interferogram.
The "elite" is exploiting you and want you docile and brainwashed 👉 The Connections (2021) [short documentary] 💖
The tiny "bye bye" at the extreme end of the video caught me off guard. Thank you for explaining all these concepts so thoroughly and clearly. I enjoy all of your videos and happily await the next one.
Fantastic video, thank you! The temperature coefficient of Zerodur's *refractive index* is two orders of magnitude greater than its thermal expansion coefficient, so in transmission (as here) the expansion effect is in fact negligible. You're seeing entirely the effect of dn/dT. As it happens, dn/dT is positive, so given your assertion about the sign, your winner will still get the right answer; but for the wrong reason.
Very interesting, what's the reason for that, my understanding was that thermal effects on refractive index were driven mostly by density changes which is related to the thermal expansion, maybe thats not correct here.
The "elite" is exploiting you and want you docile and brainwashed 👉 The Connections (2021) [short documentary] 💖
Hi it also felt extremely unlikely that with rise of temperature of temperature 0.5 - 2 Celsius Zerodur had expanded so gravely! (Too lazy to count)
So you wanted to say that it was a refraction index that affected the light transmission in Zerodur ? But it was not the thermal expansion.
I think it's a testament to the sensitivity of interferometry that the distortion due to temperature change from touching a piece of _Zerodur_ is so easily observed.
Need to get Tom Lipton and Robin Renzetti to see this!
And Spencer Webb!
The heat from your finger warping the lens blew my mind. Great video. I had a vague understanding of how this worked before but this was so easy to understand.
I winced when he said, "Let's touch the surface."
that collimating lens is a work of art
Ladies and gentlemen, the Oscar for the most amazing scientific video 2023 goes to... Huygens Optics!
Nice Interferometer! Amazing visualisation of thermal lensing too :) a perfect way to get a sense of how important temperature control is for ultra-high performance optical systems. Cant wait to see more!
Your channel is consistently well produced, informative, deliciously technical, yet reasonably approachable and absolutely fascinating. Thank you for your hard work putting these videos together, they are truely the work of a master.
I can't wait to see you jam a real ccd in that thing!
I just started a project related to phase-measurement interferometry this week, so the timing of his video could not be any better!
i never went to school, i have absolutely no idea what you are talking about 90% of the time, yet for some reason, i watch every single one of your videos without fail
I have been building many displacement and surface measuring (mainly Fizeau) interferometers over the last 25 years as wel as teaching. This presentation is the best introduction video I ever saw. Thanks for your great explanation: a must see for students!
New videos from @HuygensOptics are always the best part of my day
I gotta say your practical knowledge & experience with optics and the equipment is the solid foundation needed to really understand the theory behind it. It gives you an intuitive edge over pure theoretical book learning as taught in universities. Thanks for another solid presentation
I work in a metal workshop and we have a lot of old precision measuring tools. In some of the kits there are these glass pucks that have an arrow on the side that points to one face and 0.2mkm written next to it. Can these be test glasses that were used to measure surface flatness?
I'm pretty sure they are. The arrow generally indicates the flattest side. If you clean then and put two on top of each other under fluorescent light you will probably see straight fringes.
This type of channels and videos - one of the reasons why i'm still believe in youtube. It's just amazing information, thank you again for the video.
I like how this video also tests the YT compression very nicely 😄
Where was this channel when i was in grad school? Students have it so easy now (if they can find such good information in an ocean of garbage)!!!
Yet another clear and digestible explanation of complicated optical principles for the non-physicist. Bravo!!!
I don't work in a field anywhere adjacent to optics or interferometry. However, your videos are so thorough and well-explained, I am able to follow what you're saying with just my the undergraduate physics education I got as part of my engineering degree. I don't know why it works so well but you method of delivery makes this extremely complex topic very interesting!
This is one of my favorite channels on YT. Always happy when I see a new video come out!
Your videos always leave me with a powerful sense of how much there is to learn. I can't wait to see these tests you tease us with!
Great video, I am SO excited for the next one!
Love your videos! (Can’t wait to see you finish the catadioptric lenses too)
Thanks for this fascinating video! I've been interested in interferometers, since I first heard of the Michelson-Morley Experiment. Later, I worked on ambient air quality and stack gas monitoring and came across interferometry again, this time to measure individual gases in a sample or continuous flow.
The solution is A !
warming the spot increases the thickness between the interfaces:
1. The fringe moves to the left, away from the region of higher thickness. So the thickness has to be higher at the right side (A or B).
2. The fringes incircle minima or maxima of thickness. So the left edge has to be a global maxima. Using the first conclusion it has to be a global minima, so the surface is concave (A or C).
Dude...this is AWESOME! Amazing presentation
Awesome piece of tech! Thanks for sharing!!
one of those super high-qual channels. always a pleasure.
Finally a pure optics video again, very nice! Really looking forward to the follow ups! It is super interesting, how precise optical metrology is.
This was the perfect video to follow your Coherence series.
❤❤ Much Love, hope you never stop making videos ❤❤
This is great. Really interesting. Thanks for posting and explaining so well
Very well done video! I appreciate the effort you put into the explinations and production quality!
Awesome work!
Aaaah, this tickled the mind in just the right way 😊
Science is awesome, and your way to explain and visualise everything is excellent.
Your content is so articulate and clear! Thank you for sharing your work.
Absolutely phenomenal, thank you so much for sharing! Your presentation style and the subjects you discuss are excellent.
This video is an outstanding piece of reference material!
I came to learn about optics but stayed until the very end and heard the sensual goodbye and now I'm more confused than ever. To be clear, the optics explanations were first class....
Thank you very much for great video!
Very informative. Thank you!
Congratz on your new interferometer , you deserve it! , The content and perspective you provide is amazing! ✨✨✨
i love to see your videos. thank you so mutch. there is no place to become such good information like you. thanks.
What a remarkable video! Thank you so much for your explanation!
it kind of makes sense that the components of a measuring instrument are built to higher precision than mass consumer product
What a great apparatus and while the resolution of that old camera is nothing remarkable, it still offers a massive amount of functionality as a tool. Incredible stuff thanks for showing
Very nice. Thank you!
Very informative video, thank you for sharing your knowledge.
I just wanted to say "thanks" for making such wonderfully informative content.
Always a good day when I get a dose of optics theory from you, I barely understand some of the things but I find it extremely interesting nonetheless
This is an excellent and informative video.
Thank you for sharing
Only a few minutes in and I’m enjoying the video. Thank you 😊 ❤
Very interesting and enlightening video! I'm using interferometry frequently when checking the flatness of lapped/polished surfaces of metallic sealing discs for industrial safety valves. Our setup is a lot more barebones though, with just a monochromatic lamp and the prisms.
Im just wanted to say how much I appreciate this channel!
Probably its my favorite channel on whole TH-cam! Im saying it without any exaggeration!
After I started studying cinematography in uni I just got obsessed with physics of light. Thank you!
Really nice videos, thanks so much!
excellent video. very understandable - I've learned something new!
brilliant, thank you!
New optics video, know its gunna be a good day
Really enjoyed this
Another awesome video about a subject that is not well explaned anywhere I know. Thanks
This is so incredibly cool
Love these vids.. I learn something new EVER.. SINGLE.. VIDEO :)
Thank you for showing and explaining us insides of such great and rare instrument! Most of us have no chance to work with them by ourselves.
In my experiments with interferometry for evaluating the surface roughness I was limited to use cheap laser diode, DSLR and UV photo filter as reference surface to get interferograms)) Working with high quality interferometer is just totally different level. Thank you!
Love your video's...cheers!
I used it a lot to aline fixturing for polishing and machining.
waiting for an update on mirror lenses
Thanks for this video. 50+ years ago I worked in a calibration lab using optical flats. In our case we were often calibrating the accuracy of working gauge blocks (device under test) compared to the reference gauge block. We would place them a known distance apart and bridge the 2 blocks with an optical flat. Using a monochromatic light (or course) we looked at the interference pattern and calculated the difference in length between the 2 gauge blocks. We also reported on the surface deviation of the block under test. Of course, being so long ago, I remember nothing of the calculations, only that the procedure was quite demanding, and accurate if done well! And by "calibration", I don't mean any adjustment was performed, only that we reported the precise length and surface characteristics of the block under test.
I love your videos! I am working now since 11 years in the field of experimental quantum optics, and I leaned something in every video of yours. Whenever you upload a video i tell my wife that i need to watch it and she needs to take care of the baby and that I am not available for lunch/dinner or whatsoever until i watched it!
Maybe I remember this incorrectly, but shouldn't there be a part 3 of the mirror lenses series?
Cheers
Yes, that is correct, I did not get to that. But now I have a good instrument so hopefully I 'll find tye time for it in the near future.
Cool, looking forward to the next Videos... i actually dont care abou the topic :)
Amazing video.
Very nice video--contained the core of an 'introduction to optical testing' course. In my career, I never did have the opportunity to open a Zygo, so that was fun to see. By the way, the alignment system was the subject of a rather vicious patent suit between Zygo and Wyko--unfortunate, because we used that technique in graduate school long before either company used it in their commercial devices. (I'm kind of biased, though, because I was a grad student of JC Wyant.) Looking forward to subsequent videos!
Interesting stuff.
thank you for this. never change
I remember (a long time ago) swimming front crawl against a slightly taller boy in a short course pool. Every tumble turn he got an advantage of twice the difference in height (assuming the difference in leg length was proportional to the difference in height). That must totally explain the difference in our speed.:-). Anyway, just thinking about the factor of two at 22.48
Your maximum speed is actually 1.34 x sqrt(body length). So yes, being longer helps, but I'm afraid it's not quadratic with the difference :-).
ty for the lecture!
I use an optical parallel and a monochromatic light to identify imperfections in a polished surface. Lines, some curved, indicate that the surface is not smooth and flat. It's simpler but it helps me understand the topic of your discussion. Thank you for posting.
The glass gets thicker due to the higher temperature, and this region will be more convex. The original interference pattern shows opposite curvature of the disturbance, so the orginal surface must be concave. The line movement shows that the higher side is to the right, so the correct answer should be A.
Thank you very much for yours videos there are super and full of knowledge and experience,
I think that the right answer is D because the thermal expansion from the back side of the material tries to correct the center in the interferometer path.
Have a nice weekend, Always the best.
Would like to see more lens making.
fascinating
I’m a carpenter and through have developed an interest in precise measurements. I really appreciate your clear descriptions of these natural phenomena and how the instruments are able to detect and display them. It’s , shall we say, unlikely that I’ll be cutting any boards with this level of precision, but I really enjoy knowing the outer limits of what’s possible with relatively common materials and relatively inexpensive instruments.
Sometimes I miss working with White Light Interferometers... Then I remember what a pain it was to align the test surface well enough for the first fringes to show up.. Good times.
it always hurts seeing a new video, because I KNOW after almost 30 minutes I'll be left thinking "MORE!!!", and have to wait another prolonged time for the next video :(
I paused at 25:50 for this: Assuming your glass is BELOW body temperature (a probably reasonable, but not trivial assumption), the heat of your finger causes deviation in a material with a positive temperature coefficient indicates the surface is nominally concave. For clarity, the heat of your finger causes the glass to expand causing a deviation in the Z curve. That the deviation is opposite the general trend indicates the glass is concave (so A or C). That the curve is opposite the general trend of the curves points to C - if the curve were A, heating the middle would emphasize/exaggerate the curves. IFF (if, and only if) the lens is ABOVE your body temperature such that touching the lens cools (and shrinks) it, the B surface would be the best fit.
That only the middle curve is influenced by touch is very interesting, but makes sense if the touch is not too long in time.
That you touch your lenses with your fingers at all seems heretical, blasphemous, and deprecated! But thank you for sacrificing your lens(es) to educate us!
I dream of creating a laser measuring system for machining. Something based on interference, that's able to immediately measure fine structures in real time while machining. I'm certain that one or two lasers can achieve more than we know so far.
There are laser measuring systems for machining. They're just unjustifiably expensive. Well, I'd love to make one too.
Interferometry is a holy grail of precision. If you have imprecise optics, using an interferometer and a bunch of fourier computations you can figure out source of that imprecision, and machine the lens further. One linear measurement of distance is encoded over several million extremely sensitive pixels of a modern camera, greatly increasing the precision. After you have a better set of lenses, you put them into your interferometer and continue process ad nauseam until you hit the bottleneck of stability of your laser. Then you can machine a better laser, better invar housing, iodine vapor chamber...
The few things needed are a computer, a web camera, some low expansion ratio glass, some non-expensive nickel alloys and a few grams of silver. If you count only the materials, it's less than $100.
In the past it was all about good hardware and patience. Now it's about software and automation. Want your precision to go up a few orders of magnitude? Make a heterodyne interferometer, it's only some more trigonometry and least squares to do on GPU. It's a shame we don't deploy interferometry literally everywhere.
Respect for such a strong passion and congratulations on your new acquisition!
The right answer is A.
1) The interval between the fringes decreases from left to right, which means that the thickness increases in the same direction => A or D = true.
2) A local increase in thickness leads to a shift of the fringe to the left => A or B = true.
1),2) => A is true.
Incidentally, the following question arose. Where is the focus of the CCD1 sensor lens? It looks like the optical system must transform the flat front on the input of the interferometer into a flat front at CCD1? It doesn't form the optical image of the testing surface, right?
Yes A is correct. About the focus, this is realized with the lens in front of the camera. Standard it is sufficiently focused between 0.1 and 1 m ( I think). A correct interferogram can only be recorded if the surface under test is in focus on the ccd.
@@HuygensOptics
Understood, thanks. Probably, stable interference occurs in any cross section of the overlapping beams, since the coherence length is quite large. But to see the surface, we must look at the surface)
Cool! What do you think of the reflectance of dielectric materials, which can be used to make 'Enhanced Specular Reflector Film'. Could you do that with glass as well?
Think ill give up the idea of making a lens haha. Nice video and nice equipment.
Genius piece of equipment that
Jeroen, have you ever tried making a germanium lens for a thermal imager? All I know so far is that some of them look amazing. I wonder how different the lapping process might be compared to glass, or even whether lapping is still a suitable process in this application.
I have lapped Germanium. It's softer and requires you to work very cleanly. Also, you use Al2O3 rather than CeO as a polishing agent. I've never done a video about it though.
tom lipton did a video on this years ago. very cool analog tech! (i didnt know this was basis of any digital imagery!)
awesome!
10:00, Is it like moiré fringes used in subsampling of position encoders? So you have 2 gratings that differ slightly. (for example one has 10 lines per mm, and the other 11 lines per mm and if you look through both grated stencils, you can see 0,01 mm instead of 0,1 mm).
Very nice animations in the beginning. How did you make them?
I'm not sure which animations you are referring to but everything was either done in Powerpoint or in the video editor (ShotCut). In ShotCut I used images with a black background that were superimposed while using the filter "blend mode" either set to add or subtract.