Can interference occur without the use of single slit?

[blue_leaf77]

it would eventually negate the possibility of a case that a(particular) point on source is emitting wave but at that same instant of time no wave is emmeted by one of the other points on the source.

This statement of yours is out of place. If there is such discontinuous wave train, it means the light source is not monochromatic. Monochromatic waves are those having one frequency epxressed mathematically as either sine or cosine function, hence they must be continuous. It's that and must be that.
Well then you may argue that one can have emitters than can be controlled electrically such as that in your last picture. However monochromaticity defines an extremely strict requirement that this wave must start at $t = -\infty$ and ends at $t = \infty$. In spectral domain monochromatic wave has a delta function spectrum located at its oscillation frequency. You can prove it by Fourier transforming such discontinuous wave, you should find the spectrum is not a delta function.

 

[blue_leaf77]

It monochromatic light comes from a diffuse scatterer there is no spatial coherence and an intereference pattern is not visible.

Let's observe a picture I attach. The incoming wave has both perfect temporal and spatial coherence. As I have said the irregularities in the surface only change the structure of reflected wavefronts, it may look as ugly as it can take but as long as there is no change in the surface structure the reflected wavefronts will stay as they are for all times. If one observes what is happening at two points A and B in space, since the reflected wavefront shape that traverses these points is unchanged in time the phase different between those points will also be kept fixed. And now let's remember that what prevents us from seeing interference pattern is that if it fluctuates very rapidly, this rapid fluctuation of interference pattern must have been caused by rapid change in the state of the source. So what if the source state doesn't undergo any change, the emitted wavefronts won't undergo any change either.

 

[siddharth23]

The two slits act as two sources of light, and being from the same source originally, they are coherent.

If you can get two coherent sources, then yes, interference will occur.

 

[Drakkith]

Rightly said sir. I just need one more thing as asked in my earlier post) to be clear with due reason. Once you say something one that I will reflect over it with based with reasoning(perception) that I, why some of my lectures tell and make me feel that still(the picture's situation) will not result sustained interference, so that I may be a good teacher with less doubts.
:)

I can't understand what you've said here.

 

[sophiecentaur]

Let's observe a picture I attach.

Unfortunately, that picture gives the wrong impression of what actually happens to the incident wave fronts. Each piece of the irregular surface will give rise to a set of wavelets (Look up Huygen's Principle) and all those wavelets will add together to give a pattern which is far less 'detailed' than what you have drawn. It will, in fact, produce a smooth looking shape that is curved - showing that the original plane wave front has been diffused. It helps to bear in mind the basic rules of diffraction - the relevant one here is that small structures (i.e. the irregularities) produce broad diffraction patterns and it is only large structures (like pairs of Young's slits, separated by several wavelengths) produce fine structured interference patterns.

 

[Claude04]

Thanks for these infos !

 

[Ahsan Khan]

This statement of yours is out of place. If there is such discontinuous wave train, it means the light source is not monochromatic.

OK so this means that the correct position is that such a source can't be a monochromatic source as earlier also told by diratkkh.

It would be even higlhy appreciable to remove even this trace of doubt from my mind.

A source(with discontinuous wave trains), as shown in my pic can't be a monochromatic one I understand how it can't be monochromatic. Now my question is that if the source is non-monochromatic does it emit discontinuous wave train(of same wavelength) as shown in my picture which eventually cause it to behave as a non-monochromatic source or does it emit continuous wave of different wavelengths from its(non-monochromatic source).
My question is about what causes a source to act non-monochromaticaly based on wave/atomic level.

Drakkith, Sir this is what written above I wanted to say.

Thanks Regards

 

[Drakkith]

Now my question is that if the source is non-monochromatic does it emit discontinuous wave train(of same wavelength) as shown in my picture which eventually cause it to behave as a non-monochromatic source or does it emit continuous wave of different wavelengths from its(non-monochromatic source).

Both.

My question is about what causes a source to act non-monochromaticaly based on wave/atomic level.

The acceleration of charges is not uniform or continuous, giving you a range of wavelengths.

 

[blue_leaf77]

give a pattern which is far less 'detailed'

It is in far field region where the field is given by the FT of the scatterer, in fact diffraction physics guys call these spherical wavefronts in far field as Ewald sphere. But in near field, I think it should still resemble the shape of its scatterer. Anyway the point I uploaded that picture was to emphasize that in that situation any two points in space will always maintain its phase difference all the time.

My question is about what causes a source to act non-monochromaticaly based on wave/atomic level.

There are many kinds of line broadening mechanism, the most natural one is natural broadening caused by the fact that excited electron has finite lifetime. The others include collision broadening, Doppler broadening, etc.

 

[Ahsan Khan]

Both.

Wow good. Please do also teach me which one of the above limitation is easier to control. I mean if we were to make a close monochromatic source which of the above problem come more as a hurdle or to say what scientists actually do, in coming technology by which they are able to make sources close to monochromatic one like laser(I am not sure is laser a close to monochromatic source)

The acceleration of charges is not uniform or continuous, giving you a range of wavelengths.

When you say acceleration of charges is not uniform what it actually referring to?

Does it mean the various charges in the bulk of the source do not have same acceleration at any point of time causing different wavelengths(at a single point of time) or does it mean that any time all charges have same uniform acceleration but that acceleration of different charges can keep same value with the passage of time.

May be you will say, O May God how many questions do he ask? :) I am so sorry for that but I hope you will answer them. Lol

 

[Ahsan Khan]

There are many kinds of line broadening mechanism, the most natural one is natural broadening caused by the fact that excited electron has finite lifetime. The others include collision broadening, Doppler broadening, etc.

Sir you have explained a lot of good things I really appreciate it. But I do not understand the above terms like broadening mechanism, role of finite life time of excited electrons etc. It would be very helpful further if they may be explained simply so that I can have a clear idea.

Regards

 

[blue_leaf77]

line broadening = broadening of spectrum from delta function (monochromatic) to something else w/ nonzero width (polychromatic). Google can help you a lot further.

 

[brianhurren]

You need a source of coherent light. The single slit is by far the cheapest, easiest, and lowest-tech coherent light source, but any coherent light source will do.

It is a coherency filter, much like a pin hole.

 

[Drakkith]

Wow good. Please do also teach me which one of the above limitation is easier to control. I mean if we were to make a close monochromatic source which of the above problem come more as a hurdle or to say what scientists actually do, in coming technology by which they are able to make sources close to monochromatic one like laser(I am not sure is laser a close to monochromatic source)

A laser is not a monochromatic source. It has a very narrow bandwidth, but still has a bandwidth. Bandwidth means it emits a range of wavelengths. For example, a laser may emit light within a range of 499-500 nm. Or perhaps 499.9 - 500.1 nm.

It's not about which one is 'easier' to control. The fact is that a real source is both discontinuous (since you have to turn it off and on) and emits a range of wavelengths. We cannot get rid of either one, so we can't make a perfectly monochromatic source.

When you say acceleration of charges is not uniform what it actually referring to?

Does it mean the various charges in the bulk of the source do not have same acceleration at any point of time causing different wavelengths(at a single point of time) or does it mean that any time all charges have same uniform acceleration but that acceleration of different charges can keep same value with the passage of time.

The former I think. I'm not quite sure what you're trying to say with the second half of that sentence. In a bulk material you will have charges moving at difference velocities, in difference directions, and undergoing different acceleration at any point in time. The acceleration isn't constant or continuous for any individual charge either. It's a real mess down there.

 

[Ahsan Khan]

It's not about which one is 'easier' to control. The fact is that a real source is both discontinuous (since you have to turn it off and on) and emits a range of wavelengths. We cannot get rid of either one, so we can't make a perfectly monochromatic source.

Thank you Drakkith. OK we can't get rid of anyone. I still need to know what actually Young did by placing the single slit between source and double slits. I mean by using it did he corrected the discontinuity of wave trains which is also a cause of phase change(and not letting coherence) or it corrected the changing frequency problem of the sodium source or both. I again want to take you back at the statement of textbook where it says that their is "abrupt" phase changes in the phase if waves and that Young uses an indigenous techniques of "locking" the phase. I want to know (1).if the text talking about "abrupt" phase change due to discontinuity of wave fronts or due to fluctuating wavelengths or both,(2) when they say Young " locked" the phases by using single slit do they mean by doing this discontinuity in wave trains get eliminated or do they mean by doing this problem if fluctuating phase is removed or both.

I am attaching the pages of the textbook in the next post.

The former I think. I'm not quite sure what you're trying to say with the second half of that sentence. In a bulk material you will have charges moving at difference velocities, in difference directions, and undergoing different acceleration at any point in time. The acceleration isn't constant or continuous for any individual charge either. It's a real mess down there.

Thank you. I am sorry that the second portion of my that post was written with a mistake and that's why you couldn't get it. I apologise for this. I must make that only change which was written wrong rest you can go back to it to see it.

The mistake was in last sentence its can't keep(instead of can keep) the same value of wavelengths with passage of time.

Regards

 

[Ahsan Khan]

Pictures

 

[Ahsan Khan]

Typed, just to get into discussion the forgotten post. It would be very helpful if my last two posts be responded as the earlier ones were done. It's really feel very good that people here in our PF are very helpful.