What is the Connection Between Excited Atoms and Diffraction?

[masudr]

Look. You do get diffraction from everything. But to be able to measure or quantify it, the range of frequencies you use has to be very very narrow. Of course, it can't be at a single wavlength, like exactly 562.00000000... nm, but whatever equipment we use, there will usually be a small range. Bus as Zz says, depending on the resolution of the image formed etc. it doesn't matter too much.

No one's trying to bust anyone's balls, but the reason this could cause frustration is that this is basic stuff, and trying to make a theory of light (or whatever), without knowing this sort of stuff, and hoping that it will excel quantum electrodynamics is being a bit hopeful, don't you think?

 

[ZapperZ]

Zz,

Now we're going to be practical?? I told you that I have done the experiment both ways, so I have a "practical" understanding. I came here to deepen this understanding.

You said, quote :

"The ONLY way to see clear diffraction pattern IS to use a source with plane, monochromatic light."

and :

"your "white light" isn't white, i.e. not a combination of many spectrum of visible light,.."

I don't have a problem with broadening the definition of "monochromatic" to allow for the limitations of lasers, synchrotrons, etc.
But you also are saying that I could only get the diffraction pattern from white light (light bulb) because it is the combination of MANY frequencies? This is too broad (not monochromatic) to be practical for me.

Then, for what reason did you change the order of the statements between Dex and myself?

He said:

"Probably never walking into a lab...??

Though i have a hunch he's not exactly a theorist..."

and I responded:

"you need to spend some time outside of "the lab", and let some of the air out of your ego."

So, who is not being fair? If you don't want to help, and you have nothing to learn, what are you doing here - trying to bust people's balls?

To theorise something, one must take the risk of being wrong. I don't mind being told I'm wrong, but I don't want to dance in circles with people who are not offering legitimate advice.

TRoc

Read my last posting. Are you saying that in the whole response that I posted, I had NO LEGITIMATE ADVICE?

Question: have you seen the spectrum from an incandescant light bulb using a spectrometer? If you have (and presumably, if you have done diffraction experiment, you'd see such a thing) then you would have notice that the diffraction and interference pattern is CONTINUOUS!

Notice that I said you DO get A diffraction pattern, but this is NOT the diffraction pattern described in standard text because those descriptions are based on a source having just one particular wavelength! All you need to do is plug in all the various wavelength and see for yourself that if you do not have just ONE wavelength, you get multiple patterns that will simply overlap each other! I could have sworn I've said this already.

But somehow, you are now insisting that light sources such as "lasers" and radiation from synchrotrons are not "exactly" monochromatic! What's the point? That such experiments then cannot or should not be done, or the results cannot be believed since there's some finite spread in frequency or wavelength? I will bet you money that you cannot design a typical single-slit experiment whose resolution is SMALLER than the linewidth of the Ti-Sapphire laser that I'm using now.

Moral of the story: In MOST instances, the resolution of your experiment is considerably WORSE than any finite linewidth of light sources such as this. This CLEARLY means that such a spread in wavelength might as well be non-existent. If this is not being "practical", I don't know what is.

Zz.

 

[T.Roc]

Zz,

First, thanks for "hanging in there" with me. 2nd, no I didn't mean you had no legitimate advise to offer, or that everything you said was of no help. Just felt the conversation was starting to go in circles. Dex ruffled my feathers more than your post, you just were in the middle. Sorry.

I realize that you pros are constantly being asked to complete people's homework, or to be drawn into an endless debate with "kooks", and that's got to be frustrating. So is being neither of these, but trying to get answers to questions that will require thoughtful responses, and not reciteful ones.

I'm not saying that the experiments that have been done are not legit, or science is bogus, etc, etc.

My question is better said in 2 parts:

1. HAS an experiment been done to anyones' knowlegde that had a truly mono-chromatic wavelength through a slit? (hydrogen n=2, 658nm for instance)

2. IF this hasn't been done, and IF it were possible to devise a test (so we're only left with opinions) do you think we would get a "washed out" pattern, or just a slit shaped dot? (assume a 658nm slit)

thanks
TRoc

 

[ZapperZ]

Zz,

First, thanks for "hanging in there" with me. 2nd, no I didn't mean you had no legitimate advise to offer, or that everything you said was of no help. Just felt the conversation was starting to go in circles. Dex ruffled my feathers more than your post, you just were in the middle. Sorry.

I realize that you pros are constantly being asked to complete people's homework, or to be drawn into an endless debate with "kooks", and that's got to be frustrating. So is being neither of these, but trying to get answers to questions that will require thoughtful responses, and not reciteful ones.

I'm not saying that the experiments that have been done are not legit, or science is bogus, etc, etc.

My question is better said in 2 parts:

1. HAS an experiment been done to anyones' knowlegde that had a truly mono-chromatic wavelength through a slit? (hydrogen n=2, 658nm for instance)

2. IF this hasn't been done, and IF it were possible to devise a test (so we're only left with opinions) do you think we would get a "washed out" pattern, or just a slit shaped dot? (assume a 658nm slit)

thanks
TRoc

In return, I will say that you have not offended me at all. I have much thicker skin than that after being on the 'net for more than a dozen years.

To answer your question, are you restricting a "monochromatic" source as being a H transition line? If it is, then I can tell you that even this isn't that good. There are line widths even for this, and depending on your source (arc lamp? discharge tube?), the line width can be quite worse than, for example, a YAG laser (we won't get even get to a mode-locked Ti-Sapphire laser). If this is all that you want (i.e. something as good or better than an H transition line), then yes, such an experiment has been done. In fact, I can easily stick a slit anywhere in the beam path and see the diffraction/interference pattern. I don't know why this would be new though...

What I don't understand is why would this be any different than what you get from, let's say, a He-Ne laser (which is very common), or the one from an ordinary laser pointer? Are you able to look at the diffraction pattern from such sources and actually SEE the finite linewidths from these sources? I would find that very hard to believe.

Zz.

 

[Antiphon]

To the original poster:

Diffraction happens because wave amplitudes (of almost any type of wave)
can add or subtract (called superposition), and because waves tend to spread
out from a particular location as they travel.

These two features will cause diffraction to occurr whenever a wave of any
type meets an obstruction of any type.

 

[T.Roc]

Zz

I was thinking of a single hydrogen atom being excited 1 level past ground state, producing 1 monochromatic photon. (I realize the difficulty here, hence "IF" in the question.)

I wonder what the relationship, if any, with this aproach, would the wavelength and the slit width have on the diffraction, if any.

TRoc

 

[ZapperZ]

Zz

I was thinking of a single hydrogen atom being excited 1 level past ground state, producing 1 monochromatic photon. (I realize the difficulty here, hence "IF" in the question.)

I wonder what the relationship, if any, with this aproach, would the wavelength and the slit width have on the diffraction, if any.

TRoc

And I will have to repeat my puzzlement from before. Why would you want to do this? Why aren't you satisfied with using, for example, a simple He-Ne laser?

You do know, of course, that a SINGLE transition producing a SINGLE photon, will not produce a diffraction pattern on anything. A diffraction pattern (and interference pattern) only occurs after a gazillion photons hit a detector or a screen.

Zz.

 

[Antiphon]

Zz

I was thinking of a single hydrogen atom being excited 1 level past ground state, producing 1 monochromatic photon. (I realize the difficulty here, hence "IF" in the question.)

I wonder what the relationship, if any, with this aproach, would the wavelength and the slit width have on the diffraction, if any.

TRoc

I understand T.Roc's pain. He hasn't yet figured out that a single quantum
behaves exactly the same way as the many others coming from a HeNe laser.

The single Photon interferes with ITSELF and diffraction is inevitable.
Maxwell's equations correctly describe the photon's diffraction through the slits
and QM per se is not necessary to analyze the diffraction.