Crystal changes laser wavlength

[Antharak]

Was not sure where to post this as I thought the more people that saw it the better for opinions as to what's going on.
Here is the setup:
Jug of tap water with pink highlighter ink.
Amethyst crystal, cut like a gem for a ring, suspended in the water.
A Qtech 532nm unknown wattage( says<5mw, but it lights matches).
Nikon Coolpix camera, in total auto mode.

Here is the pic.




Since I thought lasers were one wavelength, why is the light coming out of the crystal yellow? When the reflected beam is still green and where the yellow hits the side of the jug it's a green dot.. Is it that the 532nm is a mix of blue and yellow wavelengths?, I doubt this. Or is it that the crystal is absorbing the 532nm and readmitting it closer to 589nm. Or is it just the dye reacting to the emissions from the crystal?( my choice) Or am I just being an idiot? If so feel free to point and laugh.
Thoughts? Opinions?. Ideas? :thinking:
Ed

 

[norbyx]

well when light goes through a material like glass or a liquid it is more or less like putting a filter. Light frequency may shift because light propagation is not the same from one matter to another, at least that is how I remember it from a sience class. But that was a long time ago, I might be wrong...

 

[Cyparagon]

^That is indeed incorrect. You're thinking of refraction. While this does technically change the wavelength, the frequency remains the same. The photon's energy (color) depends on frequency. Frequency is the same as speed divided by wavelength, but wavelength AND speed reduce when in a denser medium, so this again has no effect on the color. Even if it did, it would change back immediately after exiting the material and you would never know it changed to begin with.

The phenomenon is called fluorescence.

 

[DrSid]

Yep .. fluorescence .. If you used prism or diffraction grating , you would see that the wavelength (or frequency, or just color) did not CHANGE. New wavelengths were added. And the resulting mix APPEAR to have different color. Color is totally subjective thing, and same looking color can be achieved by many combinations ow wavelengths.
And there are colors which do not have any wavelength, because they can only be achieved by combining two or more wavelengths .. like most violets and white.

This is btw. how while LED is made .. there is blue LED which emits single blue wavelength (well, not as single as laser can, but let's say rather narrow spectrum) with fluorescent filter over it .. which converts some of the blue light into wide orange spectrum line. Together they mix into white.

Green lasers do this on some substances .. but blue do it on almost everything. Most of the time a material glows at predefined set of wavelengths .. and it must be 'energized' by more energetic photons - shorter wavelength. So green can make things only shine yellow, orange and red .. blue can also make things glow green and cyan. UV can for even blues and purples out, which widens the amount of materials which will react somehow.

 

[Antharak]

Green lasers do this on some substances .. but blue do it on almost everything. Most of the time a material glows at predefined set of wavelengths .. and it must be 'energized' by more energetic photons - shorter wavelength. So green can make things only shine yellow, orange and red .. blue can also make things glow green and cyan. UV can for even blues and purples out, which widens the amount of materials which will react somehow.

Well you guys will love this, I was just trying some changes and I found that the angle that the beam is seen at determines the color. If you are looking at the beam at 90deg you see yellow, if you look at the beam at 30deg you see green. So the reflected beams coming from the front side of the crystal are green because of their angle to the lens? I'll post two pics later after dark to show the effect. Around 8:00 pm EDT or if you prefer -5:00 UTC.

Thank You all I learned a lot from your replies.
I really love this place

Ed
:thanks:

 

[Hydroas]

I think too it's fluorescence. On time I pointet a green 5mW Pointer on yellow powder from highlighter and it fluorescence very bright!

 

[DrSid]

Well you guys will love this, I was just trying some changes and I found that the angle that the beam is seen at determines the color. If you are looking at the beam at 90deg you see yellow, if you look at the beam at 30deg you see green. So the reflected beams coming from the front side of the crystal are green because of their angle to the lens? I'll post two pics later after dark to show the effect. Around 8:00 pm EDT or if you prefer -5:00 UTC.

Thank You all I learned a lot from your replies.
I really love this place

Ed
:thanks:

The fluorescence will usually glow in all directions uniformly. But they green laser will disperse heavily around the original direction. So the ratio of dispersed green to fluorescent color will vary with angle. The medium may actually glow in red, and the yellow is just combination of the original green and this red. Try to setup the experiment so everything is fixed and safe, then try to observe the scene in reflection of a CD, that should show the spectrum. You should see green reflection .. and different color slightly offset .. yellow, orange or red ..

 

[Antharak]

The fluorescence will usually glow in all directions uniformly. But they green laser will disperse heavily around the original direction. So the ratio of dispersed green to fluorescent color will vary with angle. The medium may actually glow in red, and the yellow is just combination of the original green and this red. Try to setup the experiment so everything is fixed and safe, then try to observe the scene in reflection of a CD, that should show the spectrum. You should see green reflection .. and different color slightly offset .. yellow, orange or red ..

Ok I'll try that later. I have lab stands to use for holding things so I can do a very safe setup. The stand that the laser goes in is heavy duty. I have a small diffraction grating I'll use rather than the CD.
Holographic Diffraction Grating

 

[Cyparagon]

Holographic Diffraction Grating

Where do I start?? Do they even know what holography is, or is it just a word that came up a lot when they googled "laser"? There is no holography involved here. One ancient method to make gratings is to use holography, but for $3, that certainly isn't happening.

Our replica diffraction grating

Replica? As in fake?

Most low-cost diffraction gratings are
photographically reproduced replicas of real diffraction grating.

Photographically? That sounds like BS, but correct me if I'm wrong.

This is the only point where they sell themselves short. Low-cost diffraction gratings ARE real diffraction gratings.

Previously dim lines are now visible!

And... dim lines are also visible. Dim does not mean invisible.

the most efficient grating ever offered.

That's just a plain lie. It's $3; Give me a break. Efficiency has no effect on how bright the relative spectral lines are anyway, because our eyes will adjust. If the weak lines are brighter, the strong lines will also be brighter, and our eyes adjust to the increased brightness and weak lines do not appear any brighter. Besides, acetate gratings pass a good >90% of the light. Even if these passed 99% (and they don't), the difference would be imperceptible. Fail squared.

I'm sure there's nothing wrong with the product itself, and $3 isn't too bad for a price. But I expect better descriptions and less BS from something that calls itself a science supply site.

 

[Antharak]

I agree, I just wanted to show what I was using. They can be over the top a lot. Should have " AS SEEN ON TV" at the top of their page.
But it does work, somewhat.


I,ll see if I can catch the effect , more pics to come.

 

[Antharak]

The great diffraction grate was useless for this, so I used the CD and got this shot.



As you can see in the lower right corner, green to yellow to red then on to darker reds. Sorry about the focus but the camera had a hard time with the CD.

 

[DrSid]

Great !