Control light with heat and magnets (Magneto-optical Kerr effect)----make money online

in my previous video I said that a

magnetized object will actually affect

the light that is reflected off its

surface and I've spent a lot of time

searching for a way that I can capture

this on video and show it to you and so

today I was finally successful here's

the setup we've got a polarized light

source shining down on this computer

storage disk and then the camera is

looking down through another polarizer

at the spot on the disk and the two

polarizer is are oriented such that very

little light is making it through

so the polarizer is are crossed and then

I've got one of those evil scary magnets

underneath the disc so that the field is

facing up through the disc and then I've

got a laser pointer with a lens that's

purposefully skewed on it so that when I

shine the laser through here I end up

with sort of like a cat's eye spot like

an elongated dot okay so now take a look

what happens when I shine the laser on

the disc pretty cool right I mean you

can see there's a temporary effect so

the laser is actually heating up the

disc which is polycarbonate and

thermally stressing it which is what's

causing that temporary effect but check

it out there's actually a permanent

effect do so after the laser spot has

moved on you'll see that the disc

actually retains a sort of a track of

where the laser has been pretty neat now

I tried to control very carefully for

this at first I thought it's probably a

thermal effect it's probably not the

real magneto-optical Kerr effect so I

removed the magnet and repeated exactly

the same thing as the same setup the

same laser same lens at the same angle

everything and as you can see without

the magnet in place when I bring the

laser over the disc there's no permanent

effect so you can still see the

temporary effect so it's still heating

the disc up because the laser is focused

to a tight spot but it's not creating

tracks like it was with the magnet in

place and I've gone back and forth many

times and I have convinced myself that

this is the real magneto optical effect

but I wouldn't be too surprised if there

was something else going on here because

the magneto optical effect is so weak so

let's talk about what's actually going

on with this storage disk let me just

get the magnet out of the way and we can

talk about what this disc is so as you

can see it is a magneto optical disc and

this was developed

before DVDs were out and you know at the

time two point six gigabytes was

actually pretty good

in fact these came up to five point two

gigabytes in size which was massive I

mean you can almost put your whole hard

drive on that so the designers of this

format were trying to accomplish

something else so unlike a cd-rom or a

DVD drive that have spiral-cut tracks

this disc actually has a bunch of

concentric individual tracks and so this

functions a lot more like a hard drive

than it does a CD or a DVD disc it's

random access so you can put this in the

drive and then treat it just as if it

were like a hard drive just very you

know it's just slower but again at the

time the storage was just great in fact

I have a lot of experience with these

when I was an intern I spent many many

hours copying files on and off of these

discs so it's it's not the first time

that I've held one of these although I

did get this off eBay for five bucks or

something like that the problem of

course is that we want a really robust

format so the the disc is very easy to

put in and out of the drive it's not

very sensitive to dust and all that kind

of stuff but we also want to store a lot

of data on this so at the time there was

something called the Jazz Drive which

was made by I Omega and that was like a

removable hard drive for the platter it

was actually just like a hard disk

platter you'd pull it out of the drive

and you know put another one in and that

was pretty expensive and prone to

failure so an optical storage method

would beat it in terms of robustness and

reliability but then the density wasn't

quite as high and the rewrite ability

was really difficult so the reason that

they went through all the trouble of

coming up with this magneto-optical

style is to have random access and high

density and robustness

here's a cross-section of the disk and

pretty much all the magic happens in

this magneto-optical layer so let's

first talk about what we do to read out

of the disk so let's pretend the disk

already has data on it the data is

stored in bits just sort of like pits

and lands on a CD in this layer and they

are set up such that some of the

magnetization is up or down so pretend

each one of these is a bit domain so we

have up magnetization and then down down

and then up so as we just saw at the

beginning of the video if we shine a

polarized light on here

if the magnetization is in a different

is up let's just say the amount of light

we get back through the polarizer is

different so it basically works just

like a CD and if we focus our light down

we can read just one track at a time

just like a CD and we get you know

flickering light so the fact is that the

this changes the polarization you know

that light comes in and if the

magnetization is up or down the

polarization will shift direction a

little bit but if we have our polarizer

is crossed so that it's very dark then

that changes the amount of light going

through okay fair enough

so you know at this point it works just

like a CD now we want to go to write to

it we have a couple options what we can

do is submerge this entire thing in a

bulk magnetic field like a huge magnetic

field like I was doing with the the big

scary neodymium magnet and then what we

can do is shine a laser in here a much

more powerful laser than the reading

laser and if the laser heats up this MO

layer to its Curie point which is the

point at which it loses magnetism and

it's in this giant magnetic field when

it cools down again it will assume the

magnetization direction that this big

field is pushing on to it so let's say

we wanted to turn all this into up

magnetization we would set up the

external field so that everything is

going up and then we would turn on this

a powerful laser and burn all this heat

it up past the Curie point which is

about 200 C for this material and then

as it cools back down all of these would

be facing up so to get a little bit more

fancy what

we could do is flip the magnet field

back and forth as we're burning along

with this powerful laser and we could

actually flip the domains into the spots

we want them as we're going along

alternatively what we could do is also

first just level the track so we could

have constant magnetic field and then

come along with our laser that's just

constantly on and make all these face up

or down then what we could do is flip

the magnetic field once and then come

back and just turn on the laser just

where we want to alter the field so as

this thing is going along let's say

they're all starting off in the up

direction we would have laser off and

then turn the laser on here and here to

flip these to the down direction so the

benefit of this of course is that we

don't have to change the magnetic field

very quickly what we can do is just

first clear the track and then flip the

magnetic field and come back and just

turn the laser on and off very quickly

so this actually solves a lot of

problems even though it seems like kind

of a complicated system the material in

the magneto-optical layer is quite

special indeed in fact it's even

probably more than one layer inside here

and one layer takes care of this

magneto-optical readout so not not many

very many materials have this correct

that's easy to see it's a very small

effect and so the material has to be

chosen so that it will give a nice big

polarization rotation but then we also

want a material that's easy to magnetize

kind of like a floppy disk so they

actually use multiple materials in here

to get both parts storage and readout

and then I believe the silicon nitride

layers are just insulators basically

since we have to get this middle layer

up to you know 200 degrees C for it to

change magnetization direction we sort

of have to insulate it from the stuff

around it and also prevent the

polycarbonate from melting if it's in

direct contact this is a 5 mil elazer

from ebay i've actually measured these

at about 250 milliwatt and so the reason

that I've slanted the lens off to one

side is to make a more oblong spot if

the lens is straight on the spot is

truly you know round it's very well

focused and it actually burns the disc

it literally melts it and destroys the

in

structure of the disk so I don't want to

do that I just want to heat it up to the

Curie point so I tilted the lens off at

an angle so that my focal spot is

stretched out ones that it's easier to

see because it's a bigger spot but also

the energy density is a bit lower so

that I don't physically melt the disk I

tried to demonstrate the magneto optical

effect with just ceramic magnets and I

tried a lot of different magnets with

many different materials and coatings

and everything and I couldn't get any of

it to work not too surprising like you

see the compounds that they used to make

this disc are not at all common and I'll

put the link in the description with

more info but if you could do this was

just plain old nickel or whatever the

designers would not go through all the

trouble to make this very interesting

layer that works in the disc another

interesting example of the magneto

optical storage technique is the Sony

mini disc some of you a prior to

remember that I think it was actually

more popular in Japan but anyway the

bitrate was so low on those that one

worked just by turning the laser on

constantly and then flipping the

magnetic field back and forth but the

mini disc along just like this is a

random access device you could actually

record over it and you know change the

tracks later unlike a CD this was

invented in the days before thumb drives

of course so as soon as you were able to

get multiple gigabytes on a solid-state

device and just plug it into your

computer this thing pretty much became

useless okay see you next time byeTop Search Keyword : online earning, , make money online, earn money online, online earning, online earning sites, make money online free, online money income, earn money online free, money online, best way to earn money online, online income site, money earning websites, best online earning sites, easiest way to earn money online, earn money payment bkash, online money income site