Can normal light penetrate a laser beam

[paulF]

Hey everyone,
might be a silly question here but just wondering if anyone has an idea if normal light emissions can penetrate a laser beam. For example, can photons in a flashlight penetrate a laser beam.

Cheers

[bojan]

???
Photons normally do not interact with each other in vacuum.. or in the air.
So, yes, they can.

[paulF]

Thanks for the reply Bojan :)
I always had this wild idea in my mind to overcome light pollution but based on what you explained, it won't work :sadeyes: .
The idea is to have a tunnel of visible lasers around the OTA of the scope which would stop the outside light from distorting the light gathered by the telescope and thus overcoming light pollution.And since a laser's light is concentrated, it shouldn't in theory affect the light gathered by the scope.

I think if i manage to save some money on the side, i will still test the idea on my small 2.5 inch refractor to see the outcome!Would probably need around 10 cheap laser pens....

Regards,
PaulF

[bojan]

And all you will create will be what will appear as a bright spot in the sky, right in the centre of your FOV (laser light reflected from dust particles in the atmosphere)...

[multiweb]

Ooooo...I see... a "laser gatling" system pointed at the sky... hmmm... I can hear the police sirens already :lol:

[wasyoungonce]

If light is a wave then when the waves interact there will be constructive interference as the waves pass. Once passed they will settle back to what they previously were & carry on their happy way.

If light is a particle....then it gets more complicated.

A LASER is just coherent light...meaning it's just a pure wavelength of light.

[Robh]

Simple experiment ...
In a dark room, shine a torch onto a blank wall. Turn a laser collimator or pointer on and direct it across the face of the torch. Don't shine it into someone's face! You will not see any shadow of the beam on the wall.

Regards, Rob.

[RobF]

Better yet, what every amateur will want and need in 2110 is the new Orion FFAEA (force field air evacuation assembly) mounted on their OTA.

Evacuated forcefield running from scope through to upper atmosphere will eliminate poor seeing. All powered from the household "Mr Fusion" reactor of course....:whistle: :D

[paulF]

Bojan,wasyoungonce,Robh thanks for clearing that out for me and Robh i did the experiment and you were right :) thanks again !
multiweb, extremely good point, pointing one laser would be like asking for trouble, imagine around 10 at the time!!!!!!!!!!!!!!!!
RobF, i will aim to wait till 2110 and for the Orion FFAEA to go out :rofl:

Cheers everyone

[TrevorW]

Not that simple this may throw some light on it for you

http://www.wiziq.com/tutorial/59391-Interference-amp-Diffraction-of-Light

[Robh]

A bit of light reading! The best part was page 38 in bold. :lol:
Seriously though ...
I assume you are referring to my simple experiment and it is a valid point (diffraction).
I had thought about diffraction but assumed it would not be significant with the width of the laser beam.
If you do a torch test with a 2mm piece of wire across its face, it can be established that it will throw a shadow on the wall. Only a very bright torch will noticeably diffract light around the wire to reduce the shadow in the central region and this effect can be pretty much eliminated by holding the wire further from the torch face. The emergent beam on my pointers are around 2mm and diverge gradually over distance. So, using the wire as a control, it can still be established the laser beam throws no shadow.

Regards, Rob.

[paulF]

TrevorW, thanks for the link. Reminded me of my second year at Uni with all the formulas and not done reading yet it !!!!!!!!!!

[TrevorW]

Rob this what happens when sh.. hit's the fan it gets scattered

Not that I'm really that smart it seemed logical considering whether light be a wave or particles that when two beams interact that at some point the waves would intersect or the particles collide resulting in something happening whether minuscule or not

If my logic is floored then please correct me

[bojan]

The vacuum being optically linear medium, there is NO interaction between photons and/or optical waves, however you look at this. (there is some theoretical work about possible interactions between very high energy photons and radio-waves (when I dig the paper out, I will post it here.. http://en.wikipedia.org/wiki/Two-photon_physics) , but I am not sure if this was ever confirmed by experiment or observation).

However, photon-photon interactions will occur only in optically non-linear media, like some crystals, and this effect is used in lasers, optical (EDFA) amplifiers, optical frequency doublers and so on. Of course, in such environments the atoms in crystal lattice play the important role in those interactions.

[Robh]

As Bojan stated, photons don't interact with each other. Photons have no rest mass but they do have energy (momentum) and can react with particles that have mass.
Consider this ...
The Sun emits radiation (photons). On Earth, energy is absorbed (and/or reflected) by various surfaces around us. The reason we can see these bodies is from re-emitted photons. However, photons are transmitted in essentially random directions and are crisscrossing each other continually from surrounding bodies. If photons were to interact or interfere with each other, we could make no visual sense of our environment. As it is, our eye processes direct and apparently un-interfered light from each object and this is confirmed by our sense of touch.
The brighter the light energy, the more strongly an object re-emits energy and the brighter everything appears. A green laser illuminates small particles in air. At right-angles to the beam at any point there are much fewer particles and the laser appears transparent i.e. invisible.

I think I read somewhere that bosons, which include photons, can occupy the same space i.e if their paths intersect, they simply pass through each other. Anyone know if this is a correct assumption?

Regards, Rob.

[bojan]

It is.. fermions obey Pauli's principle (no two fermions at the same energy level) while bosons do not ...
http://theoncologist.alphamedpress.org/cgi/content/full/11/1/62

[AJohnston]

A very elegant way of showing that light does not scatter.

[Robh]

Bojan, thanks for that!
Pauli Exclusion Principle. That's a revisit from a long time ago!

Regards, Rob.