Applied Science - 2018-12-10
A plain laser diode can easily measure sub-micron vibrations from centimeters away by self-mixing interferometry! I also show how this technique can be used for range-finding. http://sci-hub.tw/http://iopscience.iop.org/article/10.1088/1464-4258/4/6/371/pdf https://www.jameco.com/Jameco/Products/ProdDS/2120428.pdf https://www.spiedigitallibrary.org/journals/optical-engineering/volume-57/issue-05/051506/Overview-of-self-mixing-interferometer-applications-to-mechanical-engineering/10.1117/1.OE.57.5.051506.full?SSO=1 Nerd Thunder! Check them out! Dean Segovis: https://www.youtube.com/user/HackaweekTV Jeri Ellsworth: https://www.youtube.com/user/jeriellsworth Becky Stern: https://www.youtube.com/user/bekathwia Ben Krasnow: https://www.youtube.com/user/bkraz333 John Schuch: https://www.youtube.com/user/HackersBenchTV Darren Landrum: https://www.youtube.com/user/dmlandrum Joe Grand: https://www.youtube.com/user/kingpinempire Mark VandeWettering: https://www.youtube.com/user/brainwagon Alan Wolke: https://www.youtube.com/user/w2aew/ https://www.patreon.com/AppliedScience
When an Applied Science video comes out, you know it's time to drop everything else
Yes, sleep is overrated any way.
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The Japanese company Keyence makes commercial laser sensors based on a multi wavelength refinement of the basic interferometric technique you demonstrate so nicely here. They can get down to 1 nanometer resolution!
Only vocalzoom managed to develop such a commercial sensor
slab of granite would be better. It won't change with weather, metal will.
pool of mercury on top...... Then you only need to worry about the dam moon, and rotation of the earth.
My bench legs were 200 lb cast iron, so I was close at 800 lbs. With the 2" slab of wood on top it made it.
@Phillip Salisbury Excuse me! Is this 2019 or 2543? :)
I did my PhD on this exact topic. Yes, it is true that you can get the signal using just the laser diode itself, you need an extremely stable current source for the laser and then a very high gain amplifier with low noise on the terminal voltage of the laser. Even in academia, few people try to do it because using the photodiode is way easier. There is also some semiconductor noise which shows up in the terminal voltage signal which is hard to get rid of. You can determine the direction of movement in your piezo speaker example by just looking at the slope between the fringes.
Also, the quality of the signal you get back using the terminal voltage depends strongly on the structure of the laser itself (ie VCSEL, DFB, etc)
I did my Master's on SMI, shake hands :)
look at vocalzoom. they did this sensor and it's for sale. extremely robust and can also work as laser mic
Excellent Macro Videography on this one.
I see you're in early! Subscribed to this channel with alerts too? Good move. There's another channel I do that with, can't remember the name of it though...
there was this report on seeker a week ago about the fastest camera able to capture propagation of light, hmm
I missed this - where exactly is the macro videography? Destin and Ben, you both create amazing content, but this comment just seems patronizing.
@Aditya he probably refers to what the oscilloscope makes visible - very cool indeed!
Was the piece of paper picking up your voice as you were speaking? Could this be used as a very sensitive microphone by turning the distance measured into a wave function?
I noticed the same thing, particularly the “ess” sibilant sounds seemed to be picked up the best. I wouldn’t call it so much of a microphone as an effect of the pressure waves from speech modulating the movement of the speaker cone. Very cool though, and just another indication of how sensitive this laser/circuit is.
@Kalanchoe1 Ben Krasnow actually has a video on this: https://www.youtube.com/watch?v=1MrudVza6mo
Kept thinking the same thing.
Glad to see I wasn't the only one who noticed his voice picking up on the interferometer setup at the end. I was totally blown away with the technique used to measure distance, too.
@Felix Cyberius It was picking up his voice from 8:11 onwards. Every different setup he made simply depicts them into a waveform in different manners.
I believe that the movement of the reflective target by 1/4 of a wavelength results in a path difference of 1/2 wavelength which changes the light from constructive to destructive (or visa versa).
Next on applied science, making a desktop gravitational wave detector
Does make me wonder if you could just loop a TON of fiber optic cables instead of shining the light a very far distance.
@Alan Ball yes, yes you could
Make you wonder, if monitoring the sum collections of errors rate on a high speed fibre optic back bone trunk of a communication provider, will be of used?
Nahh, eavesdropping on the space station.
@Robert Slackware Holy shit I think that's totally possible. If you could direct a beam up that high and then back from there without the beam dispersing so much.
The offset between constructive and destructive interference is indeed half a wavelength, but since the wave has to travel both to and back from the reflector, the displacement of the reflector has twice the effect on the offset of the wave. The difference in reflector displacement between full constructive and full destructive interference is therefore the quart of a wavelength, not half a wavelength.
But pretty impressive stuff!
Came to comment on the same topic.
Indeed the path-length difference in the reflected ray is double the displacement of the surface; but the destructive interference would only result in an intensity maximum every half wavelength if counterpropagating relative to the non-reflected reference beam. If the reference and reflected beam are coaxial and traveling in the same direction (which seems more likely), then a full wavelength shift of the reference beam is required to cycle the intensity pattern once.
So assuming the reflected and reference beam hit the diode from more or less the same direction, id say 2 maxima per single wavelength displacement of the reflective surface.
But it really depends on how the beams meet, and if that is in a nontrivial way, all bets are off; though 4 maxima per displacement is indeed a theoretical maximum.
Best to get out a micrometer and measure it!
You need to take into account the distance between the LD and PD as well, right? Or is that to be ignored because it's a constant?
@Fons Knaapen Yeah pretty much. Should you vary that distance, you would not observe any variation if the light bundles are travelling in the same direction; or two maxima per wavelength if they are travelling in opposing directions. But as long as you dont vary it the actual distance does not matter since the light forms a periodic pattern.
I noticed that also and saw you already had commented. Important detail.
15:46 "...because the physics is slightly over my head." Sure, right! HA! :)
Right, this is one of the smartest guys on youtube when it comes to this stuff.
Wohoo! Every day when Ben releases a new video is like christmas and birthday party at the same time.
So you feel like Jesus?
Jesus that scope is huge.
Just looked it up, it's a Tektronix MSO58....bout $35,000...and that probe is $1,800.
@trombre Yep, it was a gift from Tektronix.
This video makes me want to buy another oscilloscope
So if I understand this correctly, the distance measurement is the same thing as modulated continuous wave radar, except in the visible spectrum? Really cool!
Fantastic as always!
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ASPERGERPORNHUB
"How It's Made" is porn for mathematicians, engineers, construction guys.
great video! I want to know what the signal sounds like! and can you use the self-mixing interferometer as a laser microphone? or a distortion pedal? :D
@Pixl Rainbow Probably, but the idea is that the glass, being a thin rigid sheet w/ high surface area, would vibrate at higher amplitude than, say, a wall behind the glass. Certainly still feasible, but even in the near laboratory conditions shown in this vid, the noise floor is pretty high. But you're right; it still would work, in theory.
All speakers are weak microphones by default. Most motors are weak generators when ran in reverse. Ergo, a laser diode is a laser measurement system if you monitor it using a low driver current.
VocalZoom sells such laser microphones used for cars and first responder applications. the sensors are very small and low cost
Lossanaught , do you watch disney movies backwards as well? LOL
I would think certain sounds move air more, so would disrupt the laser beam when talking with it in front of you.
I didn't notice. I was to busy drooling over the scope.....
I was thinking of a laser mic to see which jerk is blasting your hood...
ahhhhh, why midnight? Sleep or this?
False dichotomy, you can sleep and watch the video when you wake up.
sleep, trust me
Turn off your notifications.
@Wolfin... they are 😅
@Poptart McJelly 😜
Holy crap. I can imagine this might form the basis of an optical servo tweeter. Or a new way of characterizing drivers at least.
I remember this on "Tomorrow's World".
http://celestion.com/speakerworld/patech/4/114/Advanced_Cone_Measurement_and_Analysis/
Also the basics of a Doppler radar.
where have u been man i miss ur pretty channel
@vk2zay Dude are you the guy who invented the vive base stations? I think i stalk you on reddit (young EE, you're a legend)
@Jon Davis what is the vice basestation...
You can see if your AC electroluminescent displays are actually oscillating at the driving frequency. It would make sense that the width between the top and bottom electrode is expanding and contracting due to the strong applied electric field.
If you make the laser light bounce off both the top and bottom of the EL strip at the same time, you may get double the amplitude, and see double the count of interference fringes. Comparing that measurement to single-sided will provide a nice double check on results.
On the square wave you are hearing the sharp rise and not the small ringing.
Basic fourier stuff, a rapid change requires high frequencies.
The steeper the change, the higher the frequencies produced. This is why the "ramped" square wave was not audible.
That's correct. Might I add that the driver used, or pretty much any driver will have a hard time reproducing a clean square wave at anything other than low midrange and down without a great deal of jiggery pokery in phase compensation techniques.
@Kravchenko Audio Fortunately that doesn't really matter too much, as we are only sensitive to the magnitude of the spectrum and not phase distortion.
this would be really cool if you use this laser diode to read vinyls and play it back over a speaker, laser diode vinyl player nice!
It's done. Google laser vinyl player.
@zole yeah, i see a "LASERPHONE" haha.
@Riaan Schoeman I forgot the name and brand, only remember it's Japanese and was shown to me by a HiFi enthusiast.
@Riaan Schoeman Here: watch?v=W_4sooWCh_Y
As some one wrote, it is already done, and it is able to play even the dust over the disk. The idea and pattents were developes in usa around 1980's but then the CD player did come on scene and nobody were wanting a vynil player. A japanese company but the rights, and now you can have a laser vynil player for about 10.000 dollars after a 4 month delivery time.
Nice... similar to the principle that I co-developed for a microwave motion detector back in the late 1970's. It just used a simple/cheap Gunn diode microwave source (10GHz), high-impedance power supply, and detect Doppler shift as AC/audio across the Gunn diode. It used about a 6" parabolic dish antenna, which was also the reflector for the light... as this was an automatic motion sensing yard-light.
Did it fry the neighbors cat?
You can now buy the same thing for a couple dollars, most seem to just connect the RF circuit to a board designed for a PIR sensor and it works well enough.
I'd like to know more about this I find unpublished development history fascinating
Big Clive shows the modern version https://youtu.be/FgdXRLjYkc4
I watch these videos hoping to pick up even one percent of what this guy knows.
"The physics is over my head" I'm out.
I think your voice was affecting the measurements and disrupting the paper!
8:42
"I want to measure uA" EEVBlog: Here's my uCurrent. Applied Science: hold my beer.
Any reason you can't use FFT to extract "the number of steps" per cycle in the final experiment/measurement setup?
I'm going assume from the ❤ that there isn't any obvious reason...
Well at least it's only midnight and not 3am this time so I won't have to call in to work for lack of sleep.
"without any external components" he says as he hooks up everything in his shop to the laser diode XD 27:31
I wonder how far can you still get a relatively good sensitivity with this setup?
The technique presented at the end of the video, sweeping the wavelength and measuring the interferometric fringe spectrum is essentially Swept Source Optical Coherence Tomography (SS-OCT). The axial resolution is proportional to the sweep bandwidth, i.e. the higher the bandwidth, the higher the resolution. If you scan the laser over a sample, and for each scanning point take the spectrum of the fringe signal you get depth resolved reflectivity. Do this with large enough bandwidth, and with fast enough sweeps and you can create volumetric scans like this: https://www.youtube.com/watch?v=vEgrpwtP0UQ
This is clearly awesome, but what I'm most excited about is the unintentional tip of sandblasting your third hand, bet it's so much less useless afterwards!
You can also use solder to fill the opening portion of the "jaws." That can help create more rigidity overall and adds a slightly better texture in some instances. After adding solder it is also easy to use a file to alter the jaw faces without deformation.
-Jake
This is way out of my pay grade
Thank you! Very interesting.
"Pretty cool," you say. I say this is absolutely brilliant, probably my favourite project of yours yet.
I'm happy that I understood 4% of what you said, keep it coming! BTW do a demonstration about light speed, and how its unimaginably fast. That will help
I like it how we can easily see the vibrations caused by your voice too.
When you start showing the signal on the scope the wave form is influenced by your voice! Very interesting video btw, as always.
Best thing on the internet! I love your videos so much, thank you <3
This must be the best YT channel, thank you for this demonstration, incredibly cool!
First, wow amazing :)
Second, its also a laser based microphone 😂 especially in the last bit, just by talking you can notice the changes
Wow. Great work! One of the first projects I worked on back in the early 80's was programming a laser dilitometer we built. It used a laser interferometer to measure the change in length of dental material samples in a precisely controlled optical furnace.
What beautiful physics.
You know you're going to witness cool stuff when you get notifications from Applied Science
"signal massaging" - I might steal that one!
This is great, I work with interferometers for research, this is rather cool demo and explanation of a really cheap but great tool!
Time for a DIY gravity wave detector
My favorite part was seeing the gold bonding wires.
Absolutely fascinating (and relevant to me), thank you for sharing.
wow, I'm always impressed by your videos! Thank you so much
Brilliant - thanks, as always a real treat. Could this be used with a closed path - say triangular -
to measure rotation ?
John Pattillo - 2018-12-10
Holy jeez that is a big oscilloscope screen.
Ahron Wayne - 2019-11-24
@Dan Nguyen I just have these old coathangers, will those work instead?
Dan Nguyen - 2019-11-24
@Ahron Wayne One thing is for sure, having coat hangers and no oscillscope is better than having no coat hangers and no oscilloscope.
Rex Baird - 2019-12-25
@robert hamilton what about ultra violet rays?
Tellurium - 2020-06-08
First I thought you were talking about the KEITHLEY one but then he suddenly showed this moster
Z80 - 2020-06-14
@ebulating I'm lazy buying 7$ scope