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Old 08-10-2007, 11:19 PM #1
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Default Bizzare Phenomenon ??(Added Pics)

While mucking around burning a match I noticed what I thought was pretty weird. *When I aimed the beam at the wooden match shaft(which was completely terminated on it) and looked at it's shadow on the wall there was a green dot smack bang in the middle of the shadow !!! *How is this possible ?? *Is the laser light SO intense that it passed right throught the match ?? *I have a couple of theories but I didn't, possibly, want to give it away if I am right. *Though I'm probably not.

What do ya's think ??

EDIT: I was using a 90 odd mW CNI style laser.


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Old 08-11-2007, 02:12 AM #2
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Default Re: Bizzare Phenomenon ??

Hmmmm Well, light does not bend under normal circumstances, so that cannot be it - unless the light from the laser was so intese, it LOOKED like it rejoined into a single dot on the other side of the match ?
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Old 08-11-2007, 02:29 AM #3
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Default Re: Bizzare Phenomenon ??

I'm pretty sure 90 mW didn't go right through a match - probably some sort of "lensing effect" at the edges of the matchstick caused it.

Look at the same thing through through laser glasses and (with an unlight match) place a dark nonflamable object immediately behind the matchtsick - there should be a shadow of the matchstick. Further away it will probably vanish at some point.
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Old 08-11-2007, 06:05 AM #4
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Default Re: Bizzare Phenomenon ??

im bout to leave but its fringing effect i think. light bend around objects to a degree that why if u write on high power lighting gel's the shadow doesn't appear on ground .......bad explanation... anyway off too snow
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Old 08-11-2007, 08:42 AM #5
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Default Re: Bizzare Phenomenon ??

Because it is hard to explain properly I took some pics of it. *See below:


The set up




Match closer to laser(20mm?)




Match further away from laser(120mm?)




NOTE: I probably should have used a tripod so the camera was in the same spot, but you get that.

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Old 08-11-2007, 09:02 AM #6
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Default Re: Bizzare Phenomenon ??(Added Pics)

Light is a wave like any other, the only diference between it and waves like waterwaves and soundwaves is that its wavelength is just under a micron. Sound is about 1m and shorter in air, with the low frequency being around the 1m mark.

All waves will diffract (bend) around an object, the level of diffraction depending on the wavelength of the wave and the size of the object it is passing. Take sound for example. The average doorway is around 1m accross. Low frequency sound is about 1m wavelength. The low frequency sound is therefore able to bend through the doorway and fill the space beyond it whilst the high frequency sound casts a shadow. You can hear it easily if you stand in line with the doorway, but move to the sides and it drops off quickly. This is why you hear low frequency sounds before you hear high frequency.

You can achieve the same with light, just that your object generally has to be quite small for any noticable effect. For a matchstick, the process is straight edge diffraction, also called knife edge diffraction. h t t p : / / w w w.oberlin.edu/physics/catalog/demonstrations/optics/knifeedge.html

Notice on the picture on that site that there is the large amount of light to the right. This is the laser that was not blocked by the razorblade. To the left is the "bent" waves that have interfered to produce the pattern seen. With a matchstick, this happens for both edges if the laser beam is wide enough and the interference adds for both sides. Because of this, you can get light where you do not expect it...in the middle of the shadow.

It could however be a defect in the match that allows part of the light through, or the match could jus be transparent enough.

Edit: Seeming that you posted pics just before i submitted my post, it looks as if it is more that the laserlight is just passing through match, not that it is diffracting. You should be able to check this by looking at the oposite side of the match. If you can see the light coming through, then it is just transparency. Diffraction is not going to effect the back of the match.
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Old 08-11-2007, 07:03 PM #7
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Default Re: Bizzare Phenomenon ??(Added Pics)

That was a very neat explanation. I enjoyed reading that

Thanx;
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Old 08-11-2007, 09:52 PM #8
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Default Re: Bizzare Phenomenon ??(Added Pics)

I think Ben covered it (assuming there wasn't a hole in the match stick :P).

One word, diffraction. Specifically what you've found is commonly referred to as a 'Poisson's Spot'. See two links below, the second link has a picture created using a laser and a ball bearing.
http://en.wikipedia.org/wiki/Arago_spot
http://www.phys.unsw.edu.au/PHYS1241...t2/poisson.htm

It just shows how incomplete our understanding of light is. There are several different models used to describe it (wave, particle, quantum) - they all have uses, but none really reach the heart of the matter (or should I say light?).

Laser's make what are normally subtle phenomenon, like diffraction and interference effects, easy to see. Every time you reflect the laser spot off a reflective surface you can see interference patterns in the reflected patch, caused by roughness in the surface.

Another experiment, a classic, is known as 'the double slit' diffraction experiment. This is an easy experiment anyone with a laser can duplicate. To understand the very strange implications of this experiment see the animation below
http://video.google.com/videoplay?do...91949403496551
also, wiki:
http://en.wikipedia.org/wiki/Double-slit_experiment

Here are a couple pictures I took of interesting interference patterns, caused by reflecting a red laser off a frosted incandescent bulb:



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Old 08-11-2007, 11:51 PM #9
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Default Re: Bizzare Phenomenon ??(Added Pics)

Ahh, Poisson's spot. It's an interestng read for those interested h t t p : / / w w w.dctech.com/eureka/short-stories/poisson.php

The same diffracting technique is what i thought may have been used on the match, only with two straight sides and the finite width of the laser beam providing the final dimmensions. If it were bigger, it would look more like a line than a dot.

Curse this inability to post links!
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Old 08-12-2007, 12:49 PM #10
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Default Re: Bizzare Phenomenon ??(Added Pics)

Hey thanks alot for the answers guys, it is a very intriguing effect for sure. *Certainly something I would not have expected from light. *And it's definately not what I thought was happening in the beggining

Here is your link ben *http://www.dctech.com/eureka/short-stories/poisson.php * You will be able to post links after you have 25+ posts.


I decided to try it with some alluminium plate that was a little thicker and deeper than the match and not at all transparent. *You can see that the effect is trying to happen but it just can't get around that much depth.

Set up:




Shadow:




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Old 08-12-2007, 04:17 PM #11
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Default Re: Bizzare Phenomenon ??(Added Pics)

if the wall was further away, you may have the same effect as with the match...
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Old 08-12-2007, 05:47 PM #12
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Default Re: Bizzare Phenomenon ??(Added Pics)

I tried it the same and got the same shape as the one pictured with the aluminum plate. I tried is with a match too. I used a focusable red laser and focused the dot on the match stick. The further I went the more the 2 curves drew closer together. At one point they just stopped and there was a dot. It's kind of neat... "When the top of one wave hits the bottom of another wave, they cancel each other out!"

I'm glad you brought this up. I learned something new.

Thanx guys;
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Old 08-12-2007, 05:49 PM #13
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Default Re: Bizzare Phenomenon ??(Added Pics)

Quote:
Originally Posted by Morepower
Hey thanks alot for the answers guys, it is a very intriguing effect for sure. Certainly something I would not have expected from light. And it's definately not what I thought was happening in the beggining
Well, diffraction, or the wave nature of light, is the reason why it's impossible to design a laser beam that does not diverge, at least a little bit. Every time light passes through an aperture there's some divergence, just as when water or sound waves pass through a narrow opening the expand out. Diffraction is also the reason it's impossible to magnify something an arbitrary amount with a microscope or a telescope.
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Old 08-13-2007, 08:04 AM #14
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Default Re: Bizzare Phenomenon ??(Added Pics)

Quote:
Originally Posted by flogged
[quote author=Morepower link=1186787981/0#9 date=1186922976]Hey thanks alot for the answers guys, it is a very intriguing effect for sure. *Certainly something I would not have expected from light. *And it's definately not what I thought was happening in the beggining
Well, diffraction, or the wave nature of light, is the reason why it's impossible to design a laser beam that does not diverge, at least a little bit. Every time light passes through an aperture there's some divergence, just as when water or sound waves pass through a narrow opening the expand out. Diffraction is also the reason it's impossible to magnify something an arbitrary amount with a microscope or a telescope.
[/quote]

Yep, if you point the most perfect laser pointer at the moon, your beam it still going to be several kilometers in diameter. That might be an under-estimate though.
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Old 08-13-2007, 03:25 PM #15
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Default Re: Bizzare Phenomenon ??(Added Pics)

http://www.sciam.com/article.cfm?art...amp;sc=I100322

See the link for a great home experiment where you can see the effects of interference and quantum "erasure". You can actually erase information about a past event within a beam of light. Spooky quantum physics that you can do with a laser pointer!
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Old 08-13-2007, 05:09 PM #16
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Default Re: Bizzare Phenomenon ??(Added Pics)

Quote:
Originally Posted by Justin
http://www.sciam.com/article.cfm?articleID=E20B77CB-E7F2-99DF-33669D92032DFF8C&sc=I100322

See the link for a great home experiment where you can see the effects of interference and quantum "erasure". You can actually erase information about a past event within a beam of light. Spooky quantum physics that you can do with a laser pointer!
Oh, MAN ! That rocks ! You mean, I can get "UNFIRED" if I point all my lasers at the same time ? LOL !!!! Weeeee-hooooo ! I will get my job back ! Muahahahahahaha !
Uhm...wait, maybe I should READ the article first before ASSuming anything, eh ? hahahahaha !
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