Applied Science - 2015-08-10
Learn how magneto-optical storage discs work, and see how a focused laser can directly alter a material's optical characteristics. Support Applied Science: https://www.patreon.com/AppliedScience Background sources: http://citeseerx.ist.psu.edu/viewdoc/download;jsessionid=E5B999706AB03703B56466094A7B079B?doi=10.1.1.84.4693&rep=rep1&type=pdf https://books.google.com/books?id=RVqeAGKkesEC&pg=PA387&lpg=PA387&dq=cesb+kerr+rotation+euse+euo&source=bl&ots=_vemqlKPhl&sig=dbloCjnRF6qkDY0eMIR94TpTeTk&hl=en&sa=X&ved=0CCUQ6AEwAWoVChMIw8H2l7idxwIVhqWICh3Y-gov#v=onepage&q=cesb%20kerr%20rotation%20euse%20euo&f=false https://books.google.com/books?id=U57RpAaMKgAC&pg=SA2-PA26&lpg=SA2-PA26&dq=magneto+optical+disc+kerr+gauss+constant&source=bl&ots=l-iqbQtogI&sig=nPqEWFlWYilHKmzo81Sva5LB3Lo&hl=en&sa=X&ved=0CEAQ6AEwBWoVChMIh8vX_YudxwIVyT6ICh06-g3R#v=onepage&q=magneto%20optical%20disc%20kerr%20gauss%20constant&f=false https://books.google.com/books?id=e4ntCAAAQBAJ&pg=PA586&lpg=PA586&dq=kerr+rotation+magneto+optical+storage+layer&source=bl&ots=5zOkDcsIyq&sig=-HBUsD5P4s9954jTEbh-syMTLjc&hl=en&sa=X&ved=0CDoQ6AEwBWoVChMImLrd2ZadxwIVVymICh1yXAIL#v=onepage&q=kerr%20rotation%20magneto%20optical%20storage%20layer&f=false http://www.study-on-line.co.uk/whoami/thesis/chap2.html
Thanks Ben, it's always amazing to see you explain complex scientific matters so everybody can understand them. Great channel! Thanks for all the time you keep spending on it. I really wonder who needs to rate down videos like these.
Really fascinating Ben. You keep coming up with these science topics I've never come across before. Keep it up :)
This was really interesting. You described how the magnetic field was flipped while a laser heated the material up to its curie point; is this similar to how re-writable DVDs and CDs work?
I had a MiniDisc back in the day, and it was great. This was shortly before MP3 players were a thing, so being able to carry around hours of music in something half the size of a cassette walkman was revolutionary back then. Plus it ran for ages on a single AA.
These days we just do it all on our smartphones, but you can get MP3 players with 10 times the capacity at a fraction of the size. It's crazy how far tech has come in 15 years. Solid state storage and Li-on batteries are the dog's bollocks.
I still have 7 mini-disk players around the house. They were a brilliant invention for such a short time. I still use mine today. Brilliant video's as ever thank you very much.
Fascinating! I have never seen that type of cassette DVD before. Is it similar to the Mini-Disc? The magnetization part is also new to me - I think! So yes I'm lost. Curie point!? Magneto-optical storage. Mmmm. Done deal now then? Thank you for all that. Very clear and pretty quick, but I can re-run it.
Temporary effect in poly carbonate reminds me of photoelastic ( or elasto-optic) effect that's present in materials like glass, celluloid, gellatin and wide range of resins. It's connected with mechanical stress and some explanations exist like Wertheim law. Your testing setup is very similar to what was used in measuring of mechanical stress in complicated objects before computers were powerful enough to run a simulation like that.
Interesting. Never used one of these magneto-optical drives before, but I've had plenty of experience with Iomega's Zip drives. From their appearance, they've got a similar platter to a floppy disk, but they also include a lattice very similar to an omnidirectional safety reflector. Any idea what those are for?
Very cool! We had a whole backup library of these worm discs. They've got a cool look to the platter/disc
Great stuff! Thanks for sharing your knowledge with us!
Thank you very much for this video and all the others you do. I have been wondering for a time now if you fancy doing a series of videos on defining experiments in science that changed everything, if you will, or defined a constant or established theoretical bases . I would particularly like to see the plank experiment that started quantum theory or the photoelectric effect etc. A somewhat vague question, but i often feel the experiments that started the fields, are lost to syllabuses that teach you what you need to know to do stuff with it, but often not how it came to be. All the best. Colin
Thanks Ben, great explanation of the MO disk operation.
Great presentation. I was very interested in learning about this.
Very cool! Not many people have the problem "My laser is too powerful for this experiment."
Nick Moore A very satisfying inconvenient I must add.
Nick Moore Yeah, you should get some of those "5mW" laser pointers from eBay. The set of three (R, G, and B) is down to $8! www.ebay.com/itm/3PCS-Green-Blue-Violet-Red-Light-Beam-Powerful-5MW-Laser-Pointer-Pen-/191194556037
+Applied Science US shipping only >_< I'll have to find a seller who will ship to New Zealand. FedEx is gonna make a killing when I ship my "vacation lab" back to Canada.
+Nick Moore 1st world problems :P
prices dropped to 4,5-5$ if you buy them seperate, Red=1$ Green=2$ Blue=1,5$ :D
Your an inspiration Ben, amazing work.
Awesome experiment. Really enjoyed watching it.
Great video. This is slightly OT... We've seen electron microscope images showing the relative size of the features on CD, DVD, Bluray. Can you do a video about NAND flash? If the memory elements are laid out in 2D, they would be way more dense and tiny compared to Bluray and current HDDs.
Great explanation - thanks! I have a couple of MO drives, both for 130 mm (5.25 in) and 90 mm (3.5 in) discs. And also hifi and portable minidisc recorders. I have found this technology to be very reliable. Sony effectively killed off the minidisc format by designing the most inept software for transferring music from computers to their their NetMD recorders.
Indeed great! Sony, and every digital media manufacturer faced the fear of uncontrollable, non-licenced digital (= original quality) copying cutting down the sales. I have a NetMD, which is, when thinking it from this perspective, probably one of the greatest stretches since the Big Bang. They have the copy protection and user base demand for high speed digital copying. Haha. Digital copy protection was spread everywhere making life difficult. For example, I can transfer any music onto MD, digitally. Encoded, but still. What I cannot do is to record my own singing or playing or nature with my own microphone and load that via the USB cable. I have to make an analog copy of my digital recording. And I've done that. Fortunately, things have changed :)
best option for coping recordings from md to computer was via optical SPDIF - my dad had an optical SPDIF input port added to his computer.. (thats all long long time ago...)
I had a personal minidisc thingy when I was a kid, near CD quality and you could also record from a live line or SPDIF source, great for bootlegs :) ATRAC3 I believe the codec was.
Just to clarify, random access means that you can access arbitrary data on the storage without the need to go through the rest of it. For example magnetic tape is not random access since you have to scroll it to where you want to read or write which takes time proportional to the distance from where the head is.
The term you wanted is rewriteable.
mina86 I would say when writing is is randomly placed; when reading, it is reading the scattered data as opposed to adjacent.
I never used MO tech but I remember it being said that they were very reliable. I also remember that it was the removable media used on the Steve Jobs NeXT computer.
"you could almost get your whole hard drive on one" Had to chuckle at that one. Depending on the time period (MO disks had a fairly long life as a technology), you could put several copies of your hard drive on one.
I really appreciate your work for these interesting subjects!
Btw if there was just normal paypal donation option, one would not be required to link credit card to patreon or paypal.
We stopped using our MO disks many years ago, but before ditching the drives I harvested a couple of strong 60x45x3mm magnets from them.
MiniDiscs were great. I bought a MD recorder when Sony introduced the HiMD version in 2004. Better sound quality than the MP3 players in that time, exchangeable storage and the retro factor. Really nice system, but ancient compared with modern players.
(Still have my recorder and tons of MDs.)
***** You do realize the sound quality depends on the bit rate encoding of the MP3, not the storage medium, right?
***** It depends on the bitrate, the codec and the hardware. At that time flash memory was expensive, MDs were cheap. The Atrac3+ codec is much better that MP3 (same bitrate). And the hardware of Sony MD recorders was better than most other MP3 players.
Today flash memory is cheap. Now I use FLAC, AAC or opus and high quality players with micro SD cards.
Oh, Sony used a different CODEC than MPEG.
Good stuff, done with simple means
Probably a dumb question, but what is the difference between this and a rewritable CD/DVD? Storage capacity? Thanks! I really enjoy your channel.
William White Rewritable CDs and DVDs have a single spiral groove that has no bits etched into (it is smooth). There is a dye layer that is deposited on the smooth groove, which contains the data, and it allows a strong laser to melt the dye and change its reflectivity based on how much power is deposited. There are no magnetics involved. The alteration of the dye is done entirely with a thermal process. The problem is that the whole disk must be erased because of the spiral groove -- no random access filesystem.
Great, thank you for the explanation.
absolutely awesome!
My father in law, Dr. Bernell Argyle, was (from what I remember) a trailblazer in magneto-optics. He worked for IBM in NY.
Correct me if I'm wrong, but @1:52 doesn't temperature affect magnets? Isn't the heat actually demagnetizing the disc in that zone?
I would like Ben to take a slice of one of these and stick it in the scanning electron microscope. Might not see anything but would be interesting.
brilliant, thanks Ben :)
Im not convinced that this is the magneto optical effect. Do you think that there is a possibility that the strong magnet forces a significant realligning of the magnetic particles when it is heated u by the pointer, ie its kind of "melting" the optical surface temporarily. Without the magnet it doesnt do it as there isnt a sufficient magnetic force on the particles so they just stay where they are.
Im not saying this is what happens for definite, its just my take on your cool experiment!
***** It's certainly possible there is some other effect causing the alteration. Without crossed polarizers, there is no visible evidence of the altered area, but I agree, it could still be some kind of weird stress effect in the polycarbonate caused by the magnet pushing on the magnetic layer.
Applied Science I wonder how you could verify it?
Applied Science can you verify the magneto-optic kerr effect is occurring by flipping the polarity of the neodymium magnet beneath the disk and reheating the area? Shouldn't this reverse the magnetic domains of the heated region and produce reflected light with a different polarization than what you are seeing here?
Alex Gibbs It's a good idea. I tried this, and the result was surprisingly inconclusive. The track width created by the laser pointer is super narrow, and flipping the magnet involves disturbing the orientation of the disc relative to the polarizers, so the whole setup needs to be re-adjusted, and this makes it difficult to see if the new tracks have different polarization rotation. I should get a much better setup with a more reliable magneto-optical material.
Could you tell us how did you measure the output power of the laser ? I bet a lot of us would like to know.
Periode-ik I used a commercial optical power meter at work. Kinda cheating, I know. The cheapo eBay laser pointers vary a lot, but they are all way over 5mW.
Periode-ik Cheap way to get ballpark (I guess error is few %) figure of laser power is to take solar cell with known absolute spectral response. It tells you how many A you get per W of incident light power at specific wavelength. Then you measure short circuit current of solar cell when you shine laser on it. From there is very easy to calculate power of used laser. This method is proven to work even for near IR lasers with few W of power.
If you have any more questions I will be glad to answer.
And always remember to wear safety glasses when looking at laser with remaining eye :)
p.s. I figure you can use photo-diode or photo-transistor instead of solar cell for weak lasers.
Applied Science And why is that the power output is way higher? If it's cheap, I'll expect less power than anounced, not the other way around.
dsiefus It is the opposite the actual laser power output is less than specified.
Michel PASTOR No, he said (quote) "but they are all way over 5mW.", and the video he said it is 250 mW.
Dang! I do not have a clue what I just seen , but it was amazing :)
i wish they'll make something like that with appropriate capacity for nowadays. Flash drives are compact, redundant and small, but they are a little boring
I don't think this is the Kerr effect. You explain how this storage disc needs two parts: a laser and a magnetic field. Without a magnetic field, the magneto-optical layer will cool to a random orientation, what I would assume would be the manufactured state. When burning CD's you can physically see the burn. This too is an optical format.
I bet if you shined the laser around using a small magnet you would be able to see the magnetic field lines.
very cool, thanks Ben.
I wonder if minidiscs would also show the effect.
If I was Dave Jonson I would definitely employ you in Aperture Science
Awesome video!
Ohh yea! Almost forgot about those. We used to call them "Floptical" drives..Like floppy+optical.
I think Nintendo's experimental N64 Disk Drive add-on used these magneto-optical disks as well.
Great video!
Funny that HAMR (futuristic hard drives 100 G/in2) are using the same technique on a different materials
Have you thought of building a ring laser gyroscope?
This looks very much like a DVD-RAM disc. They were popular in DVD camcorders about ten years ago.
+Dishmopo DVD-RAM discs were purely optical, like CD-RW, DVD-RW, & DVD+RW. They were also more reliable as the drive hardware verified what was being written to the disc. Often housed in caddys, which afforded them greater protection.
This is a thing again! Check out Heat-Assisted Magnetic Recording (HAMR), Seagate announced commercial scale production capacity in February of 2019.
Is this the same basic idea on re-writable CD's and DVD's?
very informative .... thanx
If I recall we just skipped those and went from floppies straight to cds/dvds. The exponential technology availability after fall of iron curtain lol.
jb listener - 2015-08-11
That brings back memories! The computer store I used to work at had a contract with EDS, so we always had at least one in stock, but they were so expensive (about $2000 for the drive, $100/disk, in 1993), that we never sold one to our retail customers.
None of us liked handling them, because nobody wanted to be responsible for something that was half the price of a barebones Hyundai, much less testing one for fun. Even now, I cringed a little watching you take a laser to the obsolete disk, lol.