Best RGB Laser Combination

[EpicHam]

Hey there folks.
I am currently researching about RGB laser here and I have a question.

What is the best combination to produce a tight coherent white beam?

• 532nm(150mW)+638nm(300mW)+445nm(500mW)

• 532nm(250mW)+635nm(250mW)+450nm(500mW)

• 532nm(200mW)+660nm(500mW)+450nm(500mW)

• 532nm(80mW)+638nm(300mW)+445nm(400mW)

I see lots of different wavelength ,power combination. Each of them claiming to produce a white beam.
However, which one is the most efficient?
Since, a different combination at the same power level can yield a VERY different price .
Kinda confused here :undecided:

 

[LordKaramazov]

I would always recommend more red than green for yellow (which is necessary for the while light). In a ratio of about 1 green to 3 red. As you go to higher powers though, you dont need to keep this ratio so high and you could go to 1:2.

For blue id say somewhere between green and red power. Although for the blue quantity i dont have so much experience.

Id say that in all your combinations you should reduce the blue. Those powers seem more for a 405nm laser rather to a 450nm. But lets see if someone else speaks about it.

Id go like: 150mW 532nm, 300mW 638nm and 250~300mW 450nm

But if you can tune the power with pots, even better, as you can do it by yourself

 

[EpicHam]

I would always recommend more red than green for yellow (which is necessary for the while light). In a ratio of about 1 green to 3 red. As you go to higher powers though, you dont need to keep this ratio so high and you could go to 1:2.

For blue id say somewhere between green and red power. Although for the blue quantity i dont have so much experience.

Id say that in all your combinations you should reduce the blue. Those powers seem more for a 405nm laser rather to a 450nm. But lets see if someone else speaks about it.

Id go like: 150mW 532nm, 300mW 638nm and 250~300mW 450nm

But if you can tune the power with pots, even better, as you can do it by yourself

What about the frequency tho?
Why that combination?
638nm and 660nn goes a long way.
Same with 445 and 450 and 405
Whhhhhhhhhhhhhyyyyyy, do you mind explaining it a bit so I can try to wrap my brain round it lol

 

[LordKaramazov]

the thing is that for our eyes, the difference between 638nm to 660nm is not so noticeable as from 405 to 450, same power. At least from my experience.

it has to do with absorption bands of our cones and also because of the transmisson of the eye lenses. at 405 transmission starts getting very low (although our eyes can pick up wavelengths as low as 380nm, our lenses absorb this light instead of transmitting, and so you cannot see it), while for both 638 and 660, transmission is about the same.

The best combination of the ones you posted, i like the 3rd one the best i guess.

But again, the easiest way is to build the laser, and then adjust the power of each color until you get a nice balance. I assume, for an RGB laser, that the lasers are tuneable

 

[EpicHam]

the thing is that for our eyes, the difference between 638nm to 660nm is not so noticeable as from 405 to 450, same power. At least from my experience.

it has to do with absorption bands of our cones and also because of the transmisson of the eye lenses. at 405 transmission starts getting very low (although our eyes can pick up wavelengths as low as 380nm, our lenses absorb this light instead of transmitting, and so you cannot see it), while for both 638 and 660, transmission is about the same.

The best combination of the ones you posted, i like the 3rd one the best i guess.

But again, the easiest way is to build the laser, and then adjust the power of each color until you get a nice balance. I assume, for an RGB laser, that the lasers are tuneable

sadly no....
Its a TTL module... its either on or off... so no fine tuning for me.
Alright... so the wavelength difference is rather minimum when it comes to our eye's sensitivity but how does that affect the final white beam?
I heard that as for Gaussian beams such as those we often use , the shorter the wavelength the better the divergence (narrower?).

So in the case for white lasers. Its better to get a combination with the shorter wavelength being the dominant composition. Right?

 

[Leodahsan]

This may be of use:
Beam: (400nm 1mw) vs. (507nm 1mw)
credits to member RHD

cheers

 

[chipdouglas]

this has been talked about countless times. you would have had an answer much quicker if you typed your question into google.

http://laserpointerforums.com/f40/rgb-laser-white-57502.html go to post 3

 

[EpicHam]

this has been talked about countless times. you would have had an answer much quicker if you typed your question into google.

http://laserpointerforums.com/f40/rgb-laser-white-57502.html go to post 3

but what they don't say is.

Why??

I mean, yes.
The sensitivity of the human eye is different to different spectrums, but what I am asking now is.
How does that affect our choice of color combination when we need the best beam quality and the highest perceived brightness?
Cos I just see a bunch of people throwing out numbers and stuff :O

 

[chipdouglas]

ignore what is or isn't said. White is just a perceived color. member cyparagon created a perceived white beam with just 2 colors.

just stick to the link I posted.

michael

 

[LordKaramazov]

1- you were wrong. We do not only use gaussian beams. Depending on many factors, either you use gaussian or not. For example 532 and 473 are gaussian, while 450nm (the direct injection one) is not. The diode has a fast diverging axis and slow diverging axis, making it rectangular in the far field. And for the purposes, the equation you showed does not matter. What you should bear in mind is the fact that multimode diodes have a much bigger divergence angle and thus are not useful for shows in a very large space, still doesnt mean that if u have lots of power and you actually point it to the sky, rather than to the people (which either way would be a NO NO as you have lots of power), you wouldnt perceive it as white, because you would.

2-Being TTL or not, before setting everything up u should be able to change its power. Unless ur buying the labby style ones where u cannot change anything and just have an input the signal. In that case, and if you only use it for a single beam and not for a show, then you can modulate the different colors at different rates to obtain the best white light mixture. Or you open the laser and change it for yourself.

3-For a white light laser, at the powers that you described, you wouldnt have much problems in percieving it as white. And no, its not a rule to have more power at short wavelengths. Id rather say the other way around. Because you have to consider other factors like air scattering. Thats what makes it possible to see a beam with no fog (red is much less scattered than blue, thats why with no fog and same power you would see much better a 450nm than a 650nm: http://en.wikipedia.org/wiki/Rayleigh_scattering). Then comes eye sensivity.

Summarizing: its not that linear. Read the above posts. If you want a white light, all the combinations you posted will give you a white light.
What will change from one to the other is only in the case of having 2 different setups side by side. Then you notice that one light is more greenish or bluish than the other...but still, if you had nothing to compare to, you would say "Look, its a white laser!"

Search more around this forum, you will find lots of useful information

 

[chipdouglas]

You will never get a pure white beam, especially if you are expecting a white dot on a wall.

If you want pure white all you have to do is step outside.

michael

 

[EpicHam]

1- you were wrong. We do not only use gaussian beams. Depending on many factors, either you use gaussian or not. For example 532 and 473 are gaussian, while 450nm (the direct injection one) is not. The diode has a fast diverging axis and slow diverging axis, making it rectangular in the far field. And for the purposes, the equation you showed does not matter. What you should bear in mind is the fact that multimode diodes have a much bigger divergence angle and thus are not useful for shows in a very large space, still doesnt mean that if u have lots of power and you actually point it to the sky, rather than to the people (which either way would be a NO NO as you have lots of power), you wouldnt perceive it as white, because you would.

2-Being TTL or not, before setting everything up u should be able to change its power. Unless ur buying the labby style ones where u cannot change anything and just have an input the signal. In that case, and if you only use it for a single beam and not for a show, then you can modulate the different colors at different rates to obtain the best white light mixture. Or you open the laser and change it for yourself.

3-For a white light laser, at the powers that you described, you wouldnt have much problems in percieving it as white. And no, its not a rule to have more power at short wavelengths. Id rather say the other way around. Because you have to consider other factors like air scattering. Thats what makes it possible to see a beam with no fog (red is much less scattered than blue, thats why with no fog and same power you would see much better a 450nm than a 650nm: http://en.wikipedia.org/wiki/Rayleigh_scattering). Then comes eye sensivity.

Summarizing: its not that linear. Read the above posts. If you want a white light, all the combinations you posted will give you a white light.
What will change from one to the other is only in the case of having 2 different setups side by side. Then you notice that one light is more greenish or bluish than the other...but still, if you had nothing to compare to, you would say "Look, its a white laser!"

Search more around this forum, you will find lots of useful information

Hmm... interesting...
I am currently reading into another thread on Photolexicon

It appears that for the brightest white laser for beam oriented people such as myself.
Ill want a white laser dominant by a 498nm source.
As under the scotopic vision which this laser will be used, the human eye is at its most sensitive to such frequency ....
As for the divergence.. it appears that Rayleigh scattering is insignificant when compared to the mie scattering which isnt wavelength dependent ....
Hmmmmm

How come my job isnt as interesting as this lol

 

[EpicHam]

You will never get a pure white beam, especially if you are expecting a white dot on a wall.

If you want pure white all you have to do is step outside.

michael

I know , I know.
Besides, with how big the divergence difference is for red and green.
Ill probably be looking at a colorwheel anyway.
Im more of a beam kinda guy than dot.
If I wanted a nice dot, I would have went for a laser projector now wouldnt I

 

[chipdouglas]

If I wanted a nice dot, I would have went for a laser projector now wouldnt I

No you wouldn't lol. A projector doesn't change beam characteristics. If you have shitty beams hitting the galvo mirrors, they you will have shitty beams coming out.

 

[LordKaramazov]

You will never get a pure white beam, especially if you are expecting a white dot on a wall.

If you want pure white all you have to do is step outside.

michael

Well...you can...I'm working with one right now....
but :shhh: dont tell anyone (best part is when we separare it chromatically and you see a perfect laser rainbow! :drool: )


To EpicHam:
If you want a beam and not a projector, then TTL modulate the 3 different lasers until you get the "perfect" white.
Secondly scattering and divergence are different things, so they dont mix.
And, if what you said is true (i dont recall now) where Mie scattering is not wavelength dependent then you have a term that is dependent and one that isnt:
I_scattered(lambda)=Mie+Rayleigh(lambda)

So you see that you then dont care about mie, but care about rayleigh. Believe me, it is important!

If you are so focused on good beam specs (aka divergence) then go for a totally Solid state lasers setup (473nm, 532nm and the red i cant remember now the wavelngth, u need to search it). But a person that wants good beam specs is a person that wants a nice round dot, and does not care about the beam. The difference of the beam itself isnt noticeable unless you are quite far from the source for good and bad divergences


*EDIT*
One more thing. With the posted powers, i can guarantee you that you wont be working in the scotopic vision. As you turn on that laser, if you are in a room, you will just illuminate the whole room like with a flashlight. Plus, the beam is percieved normally by the cones, not the rods (because the powers from scattering particles is much more intense than the one from low light conditions), which will make it normal vision and not scotopic

 

[Bionic-Badger]

With laser projectors your "white" is going to be whatever combination of RGB-ish light sources you use and their perceived differences to other colors. So long as your "white" isn't too far unbalanced, it's not going to make a big difference if you have a "perfect" D65 illuminant white, or some sort of off-mix. Your audience's eyes will adapt and their brains will register your white as "white."

If you want "tight" beams, you need to have the lasers themselves have higher quality beams. Those 638nm lasers will probably have poor beam specs, as they usually produce bar-shaped beams. The 445/450 lasers also have poor quality beam shapes -- a rectangle -- but not so bad as the 638nm.

Why choose those lasers with bad beam shapes? They have high output power level, and will produce far more light than something like a 405nm or 660nm laser would, despite the latter having nice round beams.

So you're going to have to make some choices: do you want a nice looking dot? A lot of power? Or pay a whole lot for both for specialized optics, or more expensive lasers?

What mix? Most of the color mixing models assume photopic (daylight) vision, including the models used in that Chroma program on PL and online mixing tools. That's nice, but you're rarely watching laser shows during the day; a photopic vision model isn't all that appropriate. There are also night-time (scotopic) color vision models; however, you're not watching laser shows in true scotopic conditions either. That's more like dark moon-light, not night-time with dazzling laser lights. Your laser shows are somewhere in between (mesopic vision) which isn't all that well studied because it relies on your eyes adapting to conditions constantly (like during driving).

I'd look at a mix (RGB) of around 4:1:2 or 5:1:3 for "white" using (638nm, 532nm, 445nm). Again, a specific mix probably won't make a difference as your audience's eyes will adapt to "your" white, and it's really more about how you use colors rather than having some "perfect" chromatic representation.