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Author Topic: Can I make myself a white laser?  (Read 12655 times)

Offline chris

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Can I make myself a white laser?
« on: 15/07/2012 10:47:30 »
If red, white and blue laser light were combined, would it be possible to create a white laser? And would would be the practicalities of doing so?


 

Offline syhprum

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Re: Can I make myself a white laser?
« Reply #1 on: 15/07/2012 11:34:24 »
You could of course use three lasers to produce an approximation of white light but lasers are sources of single wavelengths of light while white such as you obtain from the sun or other thermal sources is a continuous spectrum of wavelengths. 
 

Offline yor_on

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Re: Can I make myself a white laser?
« Reply #2 on: 15/07/2012 11:58:57 »
White light is the combination of all wavelengths there is right? So, following up on Chris idea, how many wavelengths are there? How small can we make the 'jumps' between each wavelength/frequency?

Or :)

What the he* is white light?
 

Offline RD

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Re: Can I make myself a white laser?
« Reply #3 on: 15/07/2012 12:02:28 »
Apparently it can be done ...

Quote
This laser kit allows you to mix your Red, Green and Blu-Ray (Violet) lasers to produce any color you like. Even white!
http://laserpointerforums.com/f64/fs-white-fusion-laser-mixing-kit-42013.html


 

Offline chris

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Re: Can I make myself a white laser?
« Reply #4 on: 15/07/2012 13:41:07 »
But could you make a white laser? Or would you need to fire the beams at a target where the reflected result looks white...?
 

Offline syhprum

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Re: Can I make myself a white laser?
« Reply #5 on: 15/07/2012 14:03:58 »
You would not get proper white light if you tried to use it for colour matching you would get a most un-satisfactory result.
 

Offline imatfaal

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Re: Can I make myself a white laser?
« Reply #6 on: 15/07/2012 14:29:45 »
Chris - you cannot see light until it hits something.  If you think you can see a light beam what you are actually seeing is light hitting motes of dust, smoke, water vapour etc.

Even with more normal lights this is the case - everyday reflected light is rarely monochromatic.  Our eyes see everything by relative amounts of firing of three different colours - I cannot see how you couldn't make any colour; with enough hard work  calculating and testing. 

But that said - the laser is not white, its a mixture of colours.  White is a completely human and subjective quality (ie there is no such thing as a white photon or a white wavelength) - and you could get it subjectively correct.
 

Offline syhprum

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Re: Can I make myself a white laser?
« Reply #7 on: 15/07/2012 15:05:13 »
"What the he* is white light?"

White light is light with a continuous distribution of frequencies such as you would get from a thermal source commonly specified as about 5000°K in no way could a combination of light from three monochromatic lasers be considered white this light illuminating and object that only reflected light of a frequency in a gap between the emissions of these three lasers would appear black whereas if it was illuminated with true white light it would show its natural colour. 
« Last Edit: 15/07/2012 15:07:15 by syhprum »
 

Offline yor_on

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Re: Can I make myself a white laser?
« Reply #8 on: 15/07/2012 15:13:09 »
Ahhh, physics :)
Gotta love it-

Think you're right Syhprum. Although white light is a subjective definition for the direct observation it still has a strict definition physically. But I'm still wondering how many frequencies and wavelengths one can get, assuming black body radiation and the rest of the 'jumping' radiation does? Or am I bicycling in the great younder here? Never thought of that one actually but assuming discrete energies it seems to logically follow that you must have a limited number of 'energy levels', at least as directly measurable for us, and from that?
 

Offline Geezer

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Re: Can I make myself a white laser?
« Reply #9 on: 15/07/2012 17:26:21 »
But I'm still wondering how many frequencies and wavelengths one can get,

You'd need to have all of them  :)

The frequency bands in a spectrum are a consequence of the atoms that produced the light, but there is no quantization of light frequencies.
 

Offline JP

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Re: Can I make myself a white laser?
« Reply #10 on: 15/07/2012 18:40:55 »
There is such a thing as a supercontinuum laser: http://en.wikipedia.org/wiki/Supercontinuum
 

Offline syhprum

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Re: Can I make myself a white laser?
« Reply #11 on: 15/07/2012 19:36:57 »
Thank you JP for drawing my attention to a field of research that I did not know existed, I do not think it has much relevance to the question asked by the original correspondent Who asked "Can I make myself a white laser?" who probably does not have access to 700Kw pico second lasers but it is an interesting field of research never the less.

PS Geezer, I believe that the energy levels of light photons are quantized but the steps are to small to be measured
« Last Edit: 15/07/2012 20:56:39 by syhprum »
 

Offline Bored chemist

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Re: Can I make myself a white laser?
« Reply #12 on: 15/07/2012 21:46:28 »
True, but, since the OP probably doesn't have a lot of rather odd science gear, the answer to "Can I make myself a white laser?" is simply "No" which is rather dull.

In principle you can get a laser to turn white by switching it on and off really quickly.
It might not behave much like a laser beam when you do that.
 

Offline Geezer

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Re: Can I make myself a white laser?
« Reply #13 on: 15/07/2012 22:57:46 »

PS Geezer, I believe that the energy levels of light photons are quantized but the steps are to small to be measured


Would that not also mean that radio frequencies are not continuous?
 

Offline yor_on

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Re: Can I make myself a white laser?
« Reply #14 on: 16/07/2012 05:37:55 »
It's the light quanta that are discrete, meaning that they have different 'jumps' of energy levels, but you can pack them as tight as you like in a beam. And if described as waves? I don't know? The main stream definition of a wave is dependent on what time is seen as, and if you think that time is a continuous process without 'breaks' then a wave should be one too. Weird stuff, and once again the particle/wave duality.
=

Or am I wrong there?

Is light discrete when it comes to light quanta? And does discrete mean that they have different defined energies, and does it then mean that there is 'jumps' between those energy levels? I'm not sure?
=

No, it should be correct. A light quanta is a discrete 'particle', but does it answer if there is jumps between their energy levels, or if you could imagine that there is a infinite procession of energy levels creating a 'smooth' procession?

Eh, it can't be smooth :)
Da*

Ah well.
=

Or maybe it can?
It all depends on how you think of it, doesn't it?

Assume you superimpose photons, do the energy then jump in steps or do they gradually, ever so smoothly, ahem, increase their energy?

How about a laser?
=

It would still be 'breaks' involved, wouldn't it? But how tight would it be between them? Plank scale?
=

I better stop, I'm getting myself confused here :)
« Last Edit: 16/07/2012 06:17:41 by yor_on »
 

Offline syhprum

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Re: Can I make myself a white laser?
« Reply #15 on: 16/07/2012 06:36:09 »
Geezer
Although we do not think of radio frequency emissions as photons they must be although of much lower energy than the 1 to 2 ev of visable light IMHO the smallest increment of photon energy must be the 6.63x10-34 Joule-sec of Planck's constant.
Could the most high resolution spectrum analyser display this ? , not a hope but I wonder if we examined the the electromagnetic radiation of a rotating galaxy the discrete nature of the energy levels might be resolvable.
Bored Chemist
If you you switched your laser on and off rapidly you would be modulating it with a square wave and generating side bands although to generate white light your switching frequency would have to be quasi random. 
« Last Edit: 16/07/2012 06:44:05 by syhprum »
 

Offline JP

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Re: Can I make myself a white laser?
« Reply #16 on: 16/07/2012 13:58:12 »
The reason that lasers tend to emit a very narrow range of frequencies is the way in which they work.  A thermal source, such as the sun or an incandescent light bulb emits light when the electrons that are inside the heated material jiggle about fast (due to heat).  Moving charged particles emit light, so these jiggling electrons emit radiation.  This radiation has a continuous spectrum because the electrons can jiggle with a continuous range of motions.

Lasers on the other hand work in a completely different manner.  You put two mirrors facing each other and bounce light back and forth between them.  One of the mirrors is slightly less reflective, so a tiny amount of light leaks through it at each bounce.  Then you put what's called a "gain medium" between the mirrors.  This is a medium where you can pump energy into the electrons to raise many of them to a precise higher energy state.  Because of the laws of quantum mechanics, when they drop back down to a given lower state,
they release a very precise amount of energy as a photon.  This alone isn't enough to create a laser, however.  The light bouncing between the two mirrors has to match that energy as well, so you have to place the mirrors just the right distance apart, so the wavelength of the light fits inside the space between the mirrors (actually it can be a full or a half wavelength).  "Lasing" happens when the light bouncing back and forth interacts with the electrons in the gain medium, causing them to drop down and emit photons which are identical to the photons bouncing back and forth.  The fact that they are identical is what gives lasers their very unique properties (known as coherence).  This emission is called "stimulated emission," which is a quantum phenomenon, where you need to have a photon pass by the excited electron to cause it to emit another identical photon.  Hence Light Amplification by Stimulated Emission of Radiation (LASER).  As another aside, you have to continually pump energy into the gain medium to continually re-excite those electrons. 

At any rate, if you followed all or part of that, the photons coming out have a very narrow band of frequencies, given by the matching of the mirror cavity length with the properties of the gain medium.

The problem with coming up with a way of broadening the spectrum of a laser is that you generally want to preserve much of the coherence properties of the light.  The ways to preserve coherence while making a broader spectrum are to chop up your laser into short pulses (pulses by definition have a range of wavelengths) as BC said (the primary techniques are called Q-switching or mode locking) or to send it into a nonlinear medium, which can shift laser frequencies while maintaining coherence.  The supercontinuum lasers I mentioned use this technique.
 

Offline syhprum

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Re: Can I make myself a white laser?
« Reply #17 on: 16/07/2012 15:53:12 »
I have struggled maintaining just the type of lasers you describe mercifully you don,t have to adjust the distance between the mirrors to the nearest half wavelength (which would be bloody nye impossible)  the light frequency adjusts to suit the distance between the mirrors.
 

Offline Geezer

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Re: Can I make myself a white laser?
« Reply #18 on: 16/07/2012 18:53:03 »

Geezer
Although we do not think of radio frequency emissions as photons they must be although of much lower energy than the 1 to 2 ev of visable light IMHO the smallest increment of photon energy must be the 6.63x10-34 Joule-sec of Planck's constant.
Could the most high resolution spectrum analyser display this ? , not a hope but I wonder if we examined the the electromagnetic radiation of a rotating galaxy the discrete nature of the energy levels might be resolvable.


This is where frequency of light (EMR) might become a bit dodgy, so I suppose we need to talk in terms of wavelengths. In that case, does the wavelength of monochromatic light have to be an integer number of Planck lengths or something? If that's the case, it would set an upper limit on the shortest possible wavelength.
 

Offline Geezer

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Re: Can I make myself a white laser?
« Reply #19 on: 16/07/2012 18:59:25 »
It's the light quanta that are discrete, meaning that they have different 'jumps' of energy levels, but you can pack them as tight as you like in a beam. And if described as waves? I don't know? The main stream definition of a wave is dependent on what time is seen as, and if you think that time is a continuous process without 'breaks' then a wave should be one too. Weird stuff, and once again the particle/wave duality.
=

Or am I wrong there?

Is light discrete when it comes to light quanta? And does discrete mean that they have different defined energies, and does it then mean that there is 'jumps' between those energy levels? I'm not sure?
=

No, it should be correct. A light quanta is a discrete 'particle', but does it answer if there is jumps between their energy levels, or if you could imagine that there is a infinite procession of energy levels creating a 'smooth' procession?

Eh, it can't be smooth :)
Da*

Ah well.
=

Or maybe it can?
It all depends on how you think of it, doesn't it?

Assume you superimpose photons, do the energy then jump in steps or do they gradually, ever so smoothly, ahem, increase their energy?

How about a laser?
=

It would still be 'breaks' involved, wouldn't it? But how tight would it be between them? Plank scale?
=

I better stop, I'm getting myself confused here :)

Aren't the jumps that we see with light a consequence of the energy level jumps in atoms? Light is EMR and you can produce any arbitrary EMR frequency so, in theory, you could produce light of any arbitrary frequency (with a very exotic radio transmitter).
 

Offline syhprum

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Re: Can I make myself a white laser?
« Reply #20 on: 16/07/2012 19:25:17 »
I am open to correction on both these points I do not know if it accepted that the frequency/energy levels of photons are quantitized but it seem logical to me that they should be, as you say this would put an upper limit on the energy that photons could have again this seems reasonable but I do not know if it is generaly accepted.
We must talk about photons in a general sense not only light a rotating galaxy with a magnetic field is emitting photons all be it of a very low frequency and energy 10^-31 Hz
« Last Edit: 16/07/2012 19:31:48 by syhprum »
 

Offline Bored chemist

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Re: Can I make myself a white laser?
« Reply #21 on: 16/07/2012 20:04:30 »
Geezer
Although we do not think of radio frequency emissions as photons they must be although of much lower energy than the 1 to 2 ev of visable light IMHO the smallest increment of photon energy must be the 6.63x10-34 Joule-sec of Planck's constant.
Could the most high resolution spectrum analyser display this ? , not a hope but I wonder if we examined the the electromagnetic radiation of a rotating galaxy the discrete nature of the energy levels might be resolvable.
Bored Chemist
If you you switched your laser on and off rapidly you would be modulating it with a square wave and generating side bands although to generate white light your switching frequency would have to be quasi random. 

If I shorten the pulse far enough then the uncertainty relation will broaden the bandwidth  to an extent that makes the light "white"

Also, in my not very humble opinion, you can have photons with any energy and any separation you want. Planck's constant isn't a limit here.
Apart from anything else the units don't tally up for the assertion that " the smallest increment of photon energy must be the 6.63x10-34 Joule-sec of Planck's constant"
 

Offline JP

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Re: Can I make myself a white laser?
« Reply #22 on: 16/07/2012 21:52:30 »
There isn't a low-frequency cutoff for photons.  Even a constant background EM field is made up of photons.  Photons are a way of writing how the energy of an EM field groups itself into packets on a quantum level.  There are (relatively easy) rules for how the energy of a plane wave of a single fixed frequency splits up into photons.  The rules are less easy when your EM field isn't a nice monochromatic plane wave, but they still exist.
 

Offline Geezer

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Re: Can I make myself a white laser?
« Reply #23 on: 16/07/2012 21:56:06 »
There isn't a low-frequency cutoff for photons.

I was wondering if there is a short-wavelength (high-frequency) cutoff?
 

Offline JP

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Re: Can I make myself a white laser?
« Reply #24 on: 16/07/2012 23:27:53 »
I don't think anyone knows.  As I understand it, the theory breaks down at Planck energies because we would have to measure time so precisely that quantum gravity fluctuations in space-time would become significant.  This would correspond to some Planck frequency for photons (E=hf).  But we don't know if this breakdown signifies that nothing exists higher than that limit or if some new theory of quantum gravity will explain ultra-high-energy photons and other particles.
 

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Re: Can I make myself a white laser?
« Reply #24 on: 16/07/2012 23:27:53 »

 

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