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InvisibletrendalM
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Question about some pics I made with a laser...
    #4398944 - 07/13/05 08:45 AM (11 years, 4 months ago)

Ok I posted these pics in the Pub last night, but I also want to post them in here because I don't really know how these pictures were produced!

The setup involves reflecting the laser beam off one and then a second rapidly-rotating mirrors. Imagine taking a small circular mirror and attaching a motor to the back of it, in the middle. Then you can turn on the motor and the mirror will spin.

Well as it turns out, if you shine a laser beam on to this spinning-mirror the reflection will be an ellipse. Something like this:


My question is, why? Does the rotating mirror "push" the beam around in a circular motion or something?

I've been wracking my brains over this one for a week now and can't figure it out!

Anyway, the REALLY neat pictures start when you add the second mirror:



--------------------
You're here because you know something.
What you know you can't explain,
But you feel it;
You've felt it your entire life.
That there's something wrong with the world.
You don't know what it is, but it's there....
Like a splinter in your mind...
Driving you mad.


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Invisibleroby000
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Re: Question about some pics I made with a laser... [Re: trendal]
    #4399077 - 07/13/05 10:37 AM (11 years, 4 months ago)

i bet you could change it from an elipse to a diffrent shape if the mirror rotated diffrently its probably an elipse because thats how the mirror rotates try making it go up and down only... that is cool though ad another mirror, some pink floyd and charge hippies 5 bucks at the door.


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InvisibletrendalM
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Re: Question about some pics I made with a laser... [Re: roby000]
    #4399085 - 07/13/05 10:44 AM (11 years, 4 months ago)

A rotating mirror always produces an ellipse. Whether the result is a perfect circle or an oval depends on the angle you reflect the beam at.


--------------------
You're here because you know something.
What you know you can't explain,
But you feel it;
You've felt it your entire life.
That there's something wrong with the world.
You don't know what it is, but it's there....
Like a splinter in your mind...
Driving you mad.


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Invisibleroby000
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Re: Question about some pics I made with a laser... [Re: trendal]
    #4399094 - 07/13/05 10:50 AM (11 years, 4 months ago)

right but i mean instead of roatating have it move in right angles.


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InvisibletrendalM
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Re: Question about some pics I made with a laser... [Re: roby000]
    #4399108 - 07/13/05 10:59 AM (11 years, 4 months ago)

I've done that already, it just produces a cicle AROUND the mirror, instead of REFLECTED from the mirror.

I'm going to try gluing a small mirror to the center of a speaker cone, then see what kind of patterns different songs make :wink:


--------------------
You're here because you know something.
What you know you can't explain,
But you feel it;
You've felt it your entire life.
That there's something wrong with the world.
You don't know what it is, but it's there....
Like a splinter in your mind...
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Invisibleroby000
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Re: Question about some pics I made with a laser... [Re: trendal]
    #4399133 - 07/13/05 11:08 AM (11 years, 4 months ago)

that sounds like an awsome idea.


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InvisibleautomanM
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Re: Question about some pics I made with a laser... [Re: trendal]
    #4399194 - 07/13/05 11:34 AM (11 years, 4 months ago)

try to rig a cd player to spin with the lid off. put in a cd upside down and shine the laser on it. i am curious if it will produce the same effect.


--------------------
No, no, you're not thinking, you're just being logical. ~ Niels Bohr


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InvisibletrendalM
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Re: Question about some pics I made with a laser... [Re: automan]
    #4399200 - 07/13/05 11:38 AM (11 years, 4 months ago)

Oh that's another good idea!

I'll have to try that one out tonight when I get home.


--------------------
You're here because you know something.
What you know you can't explain,
But you feel it;
You've felt it your entire life.
That there's something wrong with the world.
You don't know what it is, but it's there....
Like a splinter in your mind...
Driving you mad.


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OfflineSeussA
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Re: Question about some pics I made with a laser... [Re: trendal]
    #4399307 - 07/13/05 12:34 PM (11 years, 4 months ago)

> I'm going to try gluing a small mirror to the center of a speaker cone, then see what kind of patterns different songs make

Produces an image similiar to what your pictures show, but it changes shape with the music. Pretty neat effect.

What axis is the mirror spinning with respect to the beam? Can you post a picture of your setup?


--------------------
Just another spore in the wind.


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InvisibletrendalM
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Re: Question about some pics I made with a laser... [Re: Seuss]
    #4399323 - 07/13/05 12:41 PM (11 years, 4 months ago)

I'll post a pic later of the setup.

The motor spindle is attatched to the BACK of the mirror, so the reflective surface is always facing the same direction (with the beam reflecting off it). It rotates about this axis.


--------------------
You're here because you know something.
What you know you can't explain,
But you feel it;
You've felt it your entire life.
That there's something wrong with the world.
You don't know what it is, but it's there....
Like a splinter in your mind...
Driving you mad.


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OfflineChuangTzu
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Re: Question about some pics I made with a laser... [Re: trendal]
    #4402477 - 07/14/05 06:49 AM (11 years, 4 months ago)

It's definitely some kind of dynamic interference effect--but from where??? Imperfections in the mirror's surface perhaps?

Since the period of the mirror's rotation is astronomical compared to that of the laser beam, it must have something to do with differences in local velocities of the mirror's surface; have you tried pointing the beam at different distances from the mirror's center? What effect does the speed of the mirror's rotation have on the shape/size of the ellipse?

Cool pics! Too bad I won't be taking QCD until the fall... :/

[Edit: I started thinking about this more and it almost certainly has absolutely nothing to do with classical interference or any kind of classical optics whatsoever. I'm betting on needing QCD to solve this one. Classically, rotations should be totally irrelevant.

Does the thickness of the mirror glass have any effect?]


Edited by ChuangTzu (07/14/05 07:31 AM)


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OfflineSeussA
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Re: Question about some pics I made with a laser... [Re: trendal]
    #4402515 - 07/14/05 07:46 AM (11 years, 4 months ago)

Quote:

the motor spindle is attatched to the BACK of the mirror, so the reflective surface is always facing the same direction (with the beam reflecting off it). It rotates about this axis.




My guess...

The mirror is not purely orthagonal to the axis of spin. In other words, as the mirror spins, it wobbles slightly on the axis' perpendicular to the spin. The slight wobble translates into a cyclic angle change between the surface of the mirror and the laser beam causing an ellipsoid to be projected (or traced). Vibrations cause the beam to shift slightly with time causing the projection to spread out. (The path traced is offset a bit due to vibrations, thus you get the appearance of several ellipsoids rather than one being traced over top of itself.)


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OfflineChuangTzu
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Re: Question about some pics I made with a laser... [Re: ChuangTzu]
    #4411056 - 07/16/05 10:00 AM (11 years, 4 months ago)

What's the word Trendal? Are you going to give us an update?


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InvisibletrendalM
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Re: Question about some pics I made with a laser... [Re: ChuangTzu]
    #4411113 - 07/16/05 10:37 AM (11 years, 4 months ago)

I think seuss (and anyone else who mentioned the mirror being off-axis) is correct on this one!

I tried reflecting the beam off of a spinning hard-drive surface, which SHOULD be perfectly balanced/centered. It only reflects a solid dot, not a circle.

I bent the HDD disk so it would be slightly lopsided and it instantly started creating an ellipse.

I also managed to lose one of my mirrors when it came detatched from the motor spindle while at high speed :frown:


--------------------
You're here because you know something.
What you know you can't explain,
But you feel it;
You've felt it your entire life.
That there's something wrong with the world.
You don't know what it is, but it's there....
Like a splinter in your mind...
Driving you mad.


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Offlinedebianlinux
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Re: Question about some pics I made with a laser... [Re: trendal]
    #4411221 - 07/16/05 11:34 AM (11 years, 4 months ago)

Quote:

trendal said:
I also managed to lose one of my mirrors when it came detatched from the motor spindle while at high speed :frown:




How much speed? Considering the relative speed of the optic nerve you shouldn't have to spin it very fast to generate the illusion of being solid.


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OfflineChuangTzu
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Re: Question about some pics I made with a laser... [Re: trendal]
    #4417811 - 07/18/05 04:45 AM (11 years, 4 months ago)

Now I'm really starting to think that all this school is making me stupider. Of course I was influenced early on when I started thinking about this, when I read a website that said rotating mirrors are used for making patterns in light shows. The never said anything about wobbly mirrors! *slap*

When you slow down the motors, can you see the dot tracing out the patterns?


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InvisibletrendalM
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Re: Question about some pics I made with a laser... [Re: ChuangTzu]
    #4418183 - 07/18/05 09:45 AM (11 years, 4 months ago)

When you slow down the motors, can you see the dot tracing out the patterns?

Yeah, easily!


--------------------
You're here because you know something.
What you know you can't explain,
But you feel it;
You've felt it your entire life.
That there's something wrong with the world.
You don't know what it is, but it's there....
Like a splinter in your mind...
Driving you mad.


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OfflineSeussA
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Re: Question about some pics I made with a laser... [Re: trendal]
    #4418513 - 07/18/05 12:26 PM (11 years, 4 months ago)

> I think seuss (and anyone else who mentioned the mirror being off-axis) is correct on this one!

When is Seuss ever wrong?  Well, there was that one time when I claimed that matter/antimatter results in 0 energy... and that one other time when I claimed... oh, and don't forget about that time ... ok, shut up, I get the idea... :grin:


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InvisibletrendalM
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Re: Question about some pics I made with a laser... [Re: Seuss]
    #4418827 - 07/18/05 02:05 PM (11 years, 4 months ago)

:lol:


--------------------
You're here because you know something.
What you know you can't explain,
But you feel it;
You've felt it your entire life.
That there's something wrong with the world.
You don't know what it is, but it's there....
Like a splinter in your mind...
Driving you mad.


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InvisibleautomanM
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Re: Question about some pics I made with a laser... [Re: Seuss]
    #4420462 - 07/18/05 09:06 PM (11 years, 4 months ago)

Quote:

When is Seuss ever wrong?




remember that one time drinking mescal with that puerto rican hooker you thought .... erm... was a... nevermind....


--------------------
No, no, you're not thinking, you're just being logical. ~ Niels Bohr


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