Question on combining beams and more!

Jchad20 · Jun 30, 2012

First question is what would be the result if I would run lets say 2 445nm(just an example) at 500mW through a beam combiner(the ones that you use to produce a white beam)? Would I get a constructive combination and a beam of 1000mW? Or will I be utterly disappointed and get jack squat?

Now onto my other question.

Does the wavelength of a laser play a role into how much energy the laser transfers onto a surface? For instance would a 445nm laser transfer more energy in the same time then a 660nm laser over the same time?

Thanks in advance all you experts out there!:beer:

Machinist Joe · Jun 30, 2012

To combine 2 beams of the same wavelength you need something called a polarized beam splitter (PBS), its name can be deceiving though, because even though it is a splitter, it can also do the opposite, and combine 2 beams, but no more. You can not use 3 PBS cubes to combine 4 beams, it just doesn't work that way. PBS cubes can only combine two of the same wavelengths. To combine two or more beams of different wavelengths you need a dicrotic filter, or mirror. What that does it lets certain wavelengths pass through, but reflect others. These are used to make white beams by combining a Blue, Green, and Red laser, and 2 dicrotic mirrors.

Theoretically, if you were to combine 2 500mW lasers the total output will be 1000mW, but there is some losses in the optics. So plan on losing 10%. So you'd end up with 900mW as an example. With higher end optics and better coatings, the losses decrease.

As for your second question, I believe, but am not sure, wavelengths below 445 have more burning power per mW. Somebody please correct me if I am wrong though.

EDIT: If you are planning on combining 2 445 beams. You should buy this, or something similar http://shop.stanwaxlaser.co.uk/445nm-pbs-cube-310-p.asp

Jchad20 said:
First question is what would be the result if I would run lets say 2 445nm(just an example) at 500mW through a beam combiner(the ones that you use to produce a white beam)? Would I get a constructive combination and a beam of 1000mW? Or will I be utterly disappointed and get jack squat?

Now onto my other question.

Does the wavelength of a laser play a role into how much energy the laser transfers onto a surface? For instance would a 445nm laser transfer more energy in the same time then a 660nm laser over the same time?

Thanks in advance all you experts out there!:beer:

chipdouglas · Jul 1, 2012

Theoretically you would not get 1000mw from 2 500 mw's. Remember that there are stated losses. The higher quality PBS the less loss.but to my knowledge non are 100% efficient

Stryker295 · Jul 10, 2012

no, higher frequency (smaller wavelength) does not equal greater 'energy transfer'. It's really the amplitude that counts. Light isn't like sound, where you have literal cyclical bombardment (okay so it kind of is but it's not the same, in a crucial way). With sound, increasing the frequency (while holding the amplitude constant) results in a perceived volume increase as well, even though the amplitude is not increasing. With light, however, it doesn't happen (sadly). Even if it did, though, I don't think there would really be much of a difference between a red and a violet. Of course, some lasers that use an IR beam with things to change the frequency will be both IR and the main frequency, so those will burn harder/better/faster/stronger.

Make sense?

Oceansoul · Jul 11, 2012

Stryker295 said:
no, higher frequency (smaller wavelength) does not equal greater 'energy transfer'. It's really the amplitude that counts. Light isn't like sound, where you have literal cyclical bombardment (okay so it kind of is but it's not the same, in a crucial way). With sound, increasing the frequency (while holding the amplitude constant) results in a perceived volume increase as well, even though the amplitude is not increasing. With light, however, it doesn't happen (sadly). Even if it did, though, I don't think there would really be much of a difference between a red and a violet. Of course, some lasers that use an IR beam with things to change the frequency will be both IR and the main frequency, so those will burn harder/better/faster/stronger.

Make sense?

Sound: a perceived change does not correspond to an actual change. We have A- and C-weighing for a reason.

Light: Higher frequency light does indeed carry more energy and there's a damn good reason why a gamma ray photon has a sh!ttonne more energy than a violet photon.

c.f. Introduction to Quantum Physics, Hertz and the Photoelectric Effect

What you did get correct was the fact that the difference between red and violet is negligible. And for most purposes, it is. So, to answer the OP's question, higher freq (shorter wavelength) = more energy.

Except energy transfer isn't just dependent on the wavelength of the photon; the wavelength plays a part in how well a photon is absorbed by a surface.

Simple example: 808nm (NIR) is not absorbed by white paper while 445nm (indigo) is. You can have many watts of 808nm not do anything to white paper, while a 500mW 445nm laser is sufficient to mark/burn it.

Shorter wavelengths are more readily absorbed by substances than longer wavelengths. If it were a perfect blackbody, it wouldn't make a difference, but as most objects aren't, the wavelength does play a role in energy transfer insofar as it is the reason why blue and violet lasers are, to use forum terminology, such good burners.

Stryker295 · Jul 11, 2012

Oceansoul said:
Sound: a perceived change does not correspond to an actual change. We have A- and C-weighing for a reason.

Light: Higher frequency light does indeed carry more energy and there's a damn good reason why a gamma ray photon has a sh!ttonne more energy than a violet photon.

c.f. Introduction to Quantum Physics, Hertz and the Photoelectric Effect

What you did get correct was the fact that the difference between red and violet is negligible. And for most purposes, it is. So, to answer the OP's question, higher freq (shorter wavelength) = more energy.

Except energy transfer isn't just dependent on the wavelength of the photon; the wavelength plays a part in how well a photon is absorbed by a surface.

Simple example: 808nm (NIR) is not absorbed by white paper while 445nm (indigo) is. You can have many watts of 808nm not do anything to white paper, while a 500mW 445nm laser is sufficient to mark/burn it.

Shorter wavelengths are more readily absorbed by substances than longer wavelengths. If it were a perfect blackbody, it wouldn't make a difference, but as most objects aren't, the wavelength does play a role in energy transfer insofar as it is the reason why blue and violet lasers are, to use forum terminology, such good burners.

*takes notes*

Bionic-Badger · Jul 11, 2012

Oceansoul said:
Except energy transfer isn't just dependent on the wavelength of the photon; the wavelength plays a part in how well a photon is absorbed by a surface.

Simple example: 808nm (NIR) is not absorbed by white paper while 445nm (indigo) is. You can have many watts of 808nm not do anything to white paper, while a 500mW 445nm laser is sufficient to mark/burn it.

Shorter wavelengths are more readily absorbed by substances than longer wavelengths. If it were a perfect blackbody, it wouldn't make a difference, but as most objects aren't, the wavelength does play a role in energy transfer insofar as it is the reason why blue and violet lasers are, to use forum terminology, such good burners.

Ummm? Why are you spreading this disinformation?

The ability for a substance to absorb a particular wavelength is dependent on the substance itself--its absorption spectrum. This depends on the atomic and molecular structure of the substance, which governs its ability to absorb certain wavelengths. It is not a simple function of a wavelength being shorter. For example, most objects will readily absorb long-wave infrared--i.e. heat--while they may reflect shorter visible wavelengths. This is why you can use cheap plexiglass goggles to protect your eyes from CO2 lasers where you may need special filters for visible wavelengths. On the other hand, plexiglass will pass most UV, so don't use it for protecting your eyes from the sun.

Another contradiction to the short-wavelength-absorption assertion is that gamma/X-rays have the shortest of wavelengths but can penetrate materials far better than visible light. It all depends on whether the light can interact with (be absorbed by) the substance or not.

As for paper or other things that burn better with shorter visible wavelengths, it is, again, just a function of the material's absorption spectrum. Cellulose probably absorbs UV/near-UV wavelengths better than longer visible wavelengths, maybe because of its organic nature. You can easily affect your paper's visible wavelength absorption by coloring the paper (you know, like sharpieing matches).

Oceansoul · Jul 12, 2012

Bionic-Badger said:
Ummm? Why are you spreading this disinformation?

The ability for a substance to absorb a particular wavelength is dependent on the substance itself--its absorption spectrum. This depends on the atomic and molecular structure of the substance, which governs its ability to absorb certain wavelengths. It is not a simple function of a wavelength being shorter. For example, most objects will readily absorb long-wave infrared--i.e. heat--while they may reflect shorter visible wavelengths. This is why you can use cheap plexiglass goggles to protect your eyes from CO2 lasers where you may need special filters for visible wavelengths. On the other hand, plexiglass will pass most UV, so don't use it for protecting your eyes from the sun.

Another contradiction to the short-wavelength-absorption assertion is that gamma/X-rays have the shortest of wavelengths but can penetrate materials far better than visible light. It all depends on whether the light can interact with (be absorbed by) the substance or not.

As for paper or other things that burn better with shorter visible wavelengths, it is, again, just a function of the material's absorption spectrum. Cellulose probably absorbs UV/near-UV wavelengths better than longer visible wavelengths, maybe because of its organic nature. You can easily affect your paper's visible wavelength absorption by coloring the paper (you know, like sharpieing matches).

It's not 'disinformation' because for our intents and purposeswhen you're dealing with visible wavelengths (or near-visible wavelengths) then the general trend is that shorter wavelengths are more readily absorbed.

I should've been more specific, yes, but as far as I'm aware, we aren't dealing with gamma and/or X-Ray lasers every day.

Bionic-Badger · Jul 12, 2012

Oceansoul said:
It's not 'disinformation' because for our intents and purposeswhen you're dealing with visible wavelengths (or near-visible wavelengths) then the general trend is that shorter wavelengths are more readily absorbed.

I should've been more specific, yes, but as far as I'm aware, we aren't dealing with gamma and/or X-Ray lasers every day.

No, that is still erroneous information, because it is the absorption spectrum that determines how wavelengths are absorbed, not a simple matter of shorter wavelength = better burning. The specific materials you probably burn (like paper or plastic) simply absorb those shorter wavelengths better because those are the properties of those specific materials. However, to assert that shorter visible wavelengths burn better as a rule is not correct, and should not be stated as such because it is patently false.

You need to tie your assertion to the specific materials that have the property you're stating. Otherwise examples, such goggles meant to block longer wavelengths, will contradict your statements.

Oceansoul · Jul 12, 2012

Bionic-Badger said:
No, that is still erroneous information, because it is the absorption spectrum that determines how wavelengths are absorbed, not a simple matter of shorter wavelength = better burning. The specific materials you probably burn (like paper or plastic) simply absorb those shorter wavelengths better because those are the properties of those specific materials. However, to assert that shorter visible wavelengths burn better as a rule is not correct, and should not be stated as such because it is patently false.

You need to tie your assertion to the specific materials that have the property you're stating. Otherwise examples, such goggles meant to block longer wavelengths, will contradict your statements.

Enough about absorption spectra for now, because if you want to go back to these so-called basics, then that's what we'll do.

1. Shorter wavelength = higher energy = greater energy transfer.

If you were to go back to your examples of gamma rays -- they are penetrating, however, when they do interact with an atom, the results can be described as catastrophic.

Regardless of the absorption spectrum theory, a photon with a shorter wavelength will impart more energy to an object than a photon with a longer wavelength.

Oh, wait, I forgot that we were talking about visible wavelengths, even though we'd established that, oh, how many posts ago?

Now that we've got that out of the way --

it's by nature that just about all materials (and not just paper and plastic, which people like burning, we're talking materials including supposedly optically 'flat' reflectors and metals) that all exhibit a trend towards greater absorption at higher frequencies.

If you were to play your argument then it's a rule because there is such a trend, and also because very few exceptions to this trend exist.

I never 'asserted' (I don't even know where you got that crazy notion from) that it was a hard-and-fast rule. I've always maintained that it was a mere trend, that, for our intents and purposes, could be held loosely as a 'rule'.

Heck, in my original statement I even implied that the more-favourable burning properties of higher-frequency beams was due to a material's absorption spectra (see under: if everything was a blackbody, it'd be fine, but everything is not).

Bottom line: the greater energy possessed by a photon alone does not account for 'burning' power but neither does the absorption spectra. It's a combination of the two.

Bionic-Badger · Jul 12, 2012

Oceansoul said:
Enough about absorption spectra for now, because if you want to go back to these so-called basics, then that's what we'll do.

1. Shorter wavelength = higher energy = greater energy transfer.

If you were to go back to your examples of gamma rays -- they are penetrating, however, when they do interact with an atom, the results can be described as catastrophic.

Regardless of the absorption spectrum theory, a photon with a shorter wavelength will impart more energy to an object than a photon with a longer wavelength.

Sure, if a photon with higher energy/shorter wavelength is absorbed it will transfer more energy than one with a longer wavelength. However, that works under the assumption that both wavelengths are being absorbed equally. That, however, is not true. That's why this statement (emphasis mine):

"Shorter wavelengths are more readily absorbed by substances than longer wavelengths. If it were a perfect blackbody, it wouldn't make a difference, but as most objects aren't, the wavelength does play a role in energy transfer insofar as it is the reason why blue and violet lasers are, to use forum terminology, such good burners."

is incorrect.

Oh, wait, I forgot that we were talking about visible wavelengths, even though we'd established that, oh, how many posts ago?

Who cares if they're visible wavelengths? Visible wavelengths are simply a small range of wavelengths your eyes happen to be able to see because the sun produces them. They're nothing special in the greater context, and spectroscopy often extends this range further into the UV and IR ranges that the human eye cannot see. Even so, despite only occupying about 400nm of bandwidth, materials still have all kinds of absorption spectra even across that narrow band that buck the idea that shorter wavelengths--in the visible spectrum--are more readily absorbed than longer ones. Pigments are a good example of this.

it's by nature that just about all materials (and not just paper and plastic, which people like burning, we're talking materials including supposedly optically 'flat' reflectors and metals) that all exhibit a trend towards greater absorption at higher frequencies.

False. Look at various pigments and their absorption spectra. Look at laser goggles that absorb colors from one region of the spectrum and not the other. Are these "all" trending towards greater absorption at higher frequencies? The very fact that we observe colors at all implies that substances have different absorption spectra. Otherwise everything would be look more reddish because that is the wavelength being reflected. It's not a trend, and you shouldn't rely on it as a trend.

If you were to play your argument then it's a rule because there is such a trend, and also because very few exceptions to this trend exist.

Just because some things you test correlate with your assertion doesn't imply causation or a rule. A blanket statement like "shorter wavelengths are absorbed more than longer wavelengths" is not a rule because many exceptions exist. A more complete model is required, and that model is the absorption spectrum.

I never 'asserted' (I don't even know where you got that crazy notion from) that it was a hard-and-fast rule. I've always maintained that it was a mere trend, that, for our intents and purposes, could be held loosely as a 'rule'.

You made the statement of fact, therefore you asserted that fact. Go read above. Yes, it reads like a hard-and-fast rule. Nor have you limited your "trend" to specific materials where your "trend" may exist. Even above you've made assertions about "all" materials.

Heck, in my original statement I even implied that the more-favourable burning properties of higher-frequency beams was due to a material's absorption spectra (see under: if everything was a blackbody, it'd be fine, but everything is not).

No, you stated that, and I quote again:

"Shorter wavelengths are more readily absorbed by substances than longer wavelengths. If it were a perfect blackbody, it wouldn't make a difference, but as most objects aren't, the wavelength does play a role in energy transfer insofar as it is the reason why blue and violet lasers are, to use forum terminology, such good burners. "

And continue to make such assertions in your subsequent replies.

Bottom line: the greater energy possessed by a photon alone does not account for 'burning' power but neither does the absorption spectra. It's a combination of the two.

So then say that--not false statements involving rules that are not rules.

Stryker295 · Jul 12, 2012

Two things: first, who cares whether it's visible spectrum? the original poster, that's who. the person whose questions we're supposed to be answering, in case you forgot.

Second, and a bit OT, but am I the only one who has a horrendous amount of empty black space past what should be the bottom of the page?? It's like the formatting is all wrong.

Cyparagon · Jul 12, 2012

Oceansoul said:
1. Shorter wavelength = higher energy = greater energy transfer.

higher energy PER PHOTON, yes.

That just means a violet beam will have fewer photons than a red beam of equal power. Therefore, assuming equal power in either color, the absorption spectrum is the sole determination of net energy transfer.

Bionic-Badger · Jul 13, 2012

Stryker295 said:
Two things: first, who cares whether it's visible spectrum? the original poster, that's who. the person whose questions we're supposed to be answering, in case you forgot.

I'm using "who cares" as in "it doesn't make a difference to the property/effect in question," not "who cares" as in "I'm ignoring the conditions that you're operating under to make my point."

For example: "Who cares if your dog has brown spots? He can still bite!" (1st case); "Who cares you're allergic to peanuts? Eat the lunch I made for you!" (2nd case)

In this case, my "who cares" is to state that the fact that the light is in the visible region doesn't change the fact that you cannot rely on a "trend" involving absorption of shorter wavelengths. To drive the point home, I even mentioned how the "visible region" is somewhat arbitrary as it is mostly based on what the sun produces, not because the band is really special.

Second, and a bit OT, but am I the only one who has a horrendous amount of empty black space past what should be the bottom of the page?? It's like the formatting is all wrong.

Those are some terrible ads in a frame that unfortunately are very tall. You probably don't see the ads themselves because of some browser plugin like AdBlock Plus. You can reduce (but not eliminate) the effect of that frame by adding this filter to your AdBlock Plus:

Code:

|http://laserpointerforums.com/1918.htm

(sorry Avery, but they're just so obnoxious!)

Flaminpyro · Jul 13, 2012

Power density is the key to burning, PSI photons per square inch :crackup:

Stryker295 · Jul 13, 2012

Bionic-Badger said:
Those are some terrible ads in a frame that unfortunately are very tall. You probably don't see the ads themselves because of some browser plugin like AdBlock Plus. You can reduce (but not eliminate) the effect of that frame by adding this filter to your AdBlock Plus:

Code:

|http://laserpointerforums.com/1918.htm

(sorry Avery, but they're just so obnoxious!)

I figured some was ads but that's freakishly tall. Like at least 1 and a half what the entire rest of the page is :/ I was blocking the individual ad images before... I'll try that one. Thanks.

Question on combining beams and more!

Jchad20

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Machinist Joe

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chipdouglas

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Stryker295

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Oceansoul

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Stryker295

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Bionic-Badger

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Oceansoul

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Bionic-Badger

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Oceansoul

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Bionic-Badger

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Stryker295

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Cyparagon

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Bionic-Badger

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