487 nm. Laser possible ?

[Xtrm2Rick]

combining 445nm + 532 wouldnt look so great eitherway because of beam diameters i think you will just see green with blue around it... correct me if im wrong..

 

[goninanbl00d]

Human's vision is trichromatic yes, but it's not Red Green Blue.

It's actually Red Green Violet , and "blue" is what you get between violet and green. Take powerful 405nm laser and middle-range-power green pointer and point them at the same dot. You can see how they mix into some sort of bluish color.

It's also same situation with yellow. It's between red and green, same as blue is between green and violet.

Hate to correct ya here, but human vision is actually Red-Green-Blue, with peak blue sensitivity at 450-455nm.

http://upload.wikimedia.org/wikipedia/commons/1/1e/Cones_SMJ2_E.svg

Violet at 405nm is still high enough in terms of wavelength to be able to stimulate the cone cells responsible for detecting blue light, however, it is not very effective at doing so. This is why 405nm isn't visible in terms of spot visibility, when compared to other wavelengths.

It's the same principle by which we can see 808nm. We aren't very sensitive to it, but if there's enough of it stimulating red cones we can see it.

If the human eye did have cone cells responsible for detecting violet and not blue, then 445 would appear as a dim spot and 405 very bright.

However, we see yellow differently. Yellow stimulates both the green and red receptors in the human eye equal amounts, hence allowing the brain to register yellow. This is also why red and green combined will appear as yellow.

combining 445nm + 532 wouldnt look so great eitherway because of beam diameters i think you will just see green with blue around it... correct me if im wrong..

You'd see a bright cyan spot, with faint 445nm wings. Depending on the distance, this may change (as the green and blue will have different divergences).

With 445 and 532nm, you need equal ratios. Even though the green may appear to overpower the blue, they will even out once blended.

If you use visually equivalent amounts of green and blue, the blue will 'drown out' the blue as soon as the two are combined.

 

[FrothyChimp]

Here's your solution: A three-level transition of Yb3+ lases at 974 nm. It frequency doubles to 487nm. Three level lasing transitions are not the easiest to work with because the lower lasing level is also ground state. This means that non-stimulated Yb3+ can absorb the photons just emitted. You have to ensure that the entire cavity is stimulated. Also Yb3+ lasers are fiber lasers.

 

[Eudaimonium]

Ahh thanks for the correction, goninan_bl00d. But still, violet is much different from blue to me, and I am not sure how it can be related with blue detecting cells...

But we'll trust the scientific definitions

 

[Jaseth]

I think a weak 447nm would appear to be the same colour as a powerful 405nm laser. Of course the unique features of 405nm, such as a high level of Rayleigh scattering and the ability to make many objects fluoresce (even if a 447nm can fluoresce most of the same objects), would still make you able to tell them apart though.

Basically, I get this idea from two things:
1) Many people have reported their ~1800mW 447nm lasers to be "more blue" than their weaker 447nm lasers.

2) Since 447nm and 405nm only stimulate the blue cone cells, I would think that the colour perception is only down to how much they are stimulated. Therefore, a weak 447nm which stimulates the cells as much as a powerful 405 would both end up looking what we consider to be violet.

This is based on very little and there are probably loads of flaws in my hypothesis (for example, I believe 10W of 405nm would probably still look violet).
I would be delighted if someone could give me educated feedback on this. I am very interested in discovering how it works.

Seb

 

[Eudaimonium]

I can tell you right away that few miliwatts of laser produced by 445nm diode still looks exactly the same color as 1W.

Any power of 405nm is exactly the same in color. At least , to me.

 

[Jaseth]

It may have something to do with me being colour blind (mostly between dark reds and dark greens, and pink/grey tones), but I see my slightly unfocused 174mw 405nm lasers as exactly the same colour as my very unfocused ~950mW 447nm laser. I just tested it again - both looked like a somewhat violet blue to me.

I know I am probably wrong, but I would love to have someone who is very knowledgeable in this area tell me why I am wrong.

 

[mod101]

Blue looks different than violet because as you increase the wavelength on the spectrum, just a few of the green cones are able to be hit by the higher blue wavelength. So while purple only stimulates blue cones, blue stimulates mostly blue but some green cones, the higher you increase the wavelength the more green cones are stimulated and thus the more green things look. Check the picture posted earlier, green extends pretty far into blue

http://upload.wikimedia.org/wikipedia/commons/1/1e/Cones_SMJ2_E.svg

 

[goninanbl00d]

It may have something to do with me being colour blind (mostly between dark reds and dark greens, and pink/grey tones), but I see my slightly unfocused 174mw 405nm lasers as exactly the same colour as my very unfocused ~950mW 447nm laser. I just tested it again - both looked like a somewhat violet blue to me.

I know I am probably wrong, but I would love to have someone who is very knowledgeable in this area tell me why I am wrong.

Well, you're partly correct.

Diodes taken from the A-130s are known to be more 'violet' than the A-140 diodes. There's a pic of an Arctic beamshot vs an A140 beamshot. The difference is extremely noticable.

Also, when the diodes run at a higher current, they get hotter. (duh! ) When they do get hotter, the parts (including the die) expand. This expansion causes a lengthening of the resonant cavity, increasing the wavelength. Temperature can cause a wavelength shift of up to 5nm.

Besides that, there's also inconsistencies in wavelength resulting from manufacturing processes. There's been reports of 405nm diodes coming in at up to 410nm, and at 395nm.

Of course, then there's human perception. For some it'd be similar to how we perceive wavelengths in the IR. 780 and 808nm appear as the exact same hue of red, except they differ in brightness for a given power.

But for me, violet is definitely violet, and 445nm is a deep royal blue with a hint of violet. But they certainly aren't identical.

 

[Xplorer877]

Diodes taken from the A-130s are known to be more 'violet' than the A-140 diodes.

I've never heard of that. I find that hard to believe. Similar projectors wouldn't use two different wavelength light sources. I think that is just a matter of wavelength tolerances between the diodes.

-Tony

 

[goninanbl00d]

I've never heard of that. I find that hard to believe. Similar projectors wouldn't use two different wavelength light sources. I think that is just a matter of wavelength tolerances between the diodes.

-Tony

That's what it is. They aren't different diodes, just different wavelength tolerances.

But there is a noticable difference.

 

[Pontiacg5]

445 looks incredibly violet next to a "real" blue laser, a 473 DPSS or 488 Argon for example. I'd take a picture to show you but my camera is also colorblind.

Plus the 445 diodes have horrendous divergence and beam profiles. The needle thin beam of an argon is about the most sexy laser beam ever. It even makes DPSS lasers look like crap

(Care to guess who's doing a monthly burn today? :shhh

 

[mfo]

no it would be 487

c'mon laser geeks, help me here...

Jesus Christ man.

It's one to think to ask something here for the purpose of learning. But to post something like this is beyond stupid. Especially the laser geeks part.


And screw you, we're not laser geeks.

 

[pullbangdead]

Also, when the diodes run at a higher current, they get hotter. (duh! ) When they do get hotter, the parts (including the die) expand. This expansion causes a lengthening of the resonant cavity, increasing the wavelength. Temperature can cause a wavelength shift of up to 5nm.

Incorrect. For edge-emitting diodes like we use, the physical size change of the cavity with temperature is a negligible effect. The wavelength changes with temperature because the refractive index of the materials change, not the physical size.

Also, you're talking about heat as a result of current: high current and high temperature can competing effects when it comes to wavelength. High temperature causes a refractive index change that favors a red-shift, while high current can cause band-filling that favors a blue-shift. Generally the temperature shift wins, especially with the lasers we see around here like handhelds, but just saying that increased current doesn't cause a red-shift directly, and can actually cause a blue-shift directly.

ETA: Also, as far as making a 487nm laser diode, it is very possible. The III-nitride system can be and has been used to make any color laser diode from some number below 400nm (~350nm I think?) to some number just above 530nm, and every color in between.

 

[Heirophant]

yes there's all that and then there's brain chemistry and state of mind --- what you've had to eat ... drink ... how much sleep or how little sleep you've had ... how much hydro-weed you've vaporized/smoked , so on and so on ...

 

[benmwv]

ETA: Also, as far as making a 487nm laser diode, it is very possible. The III-nitride system can be and has been used to make any color laser diode from below 400nm to above 530nm, and every color in between.

Doesn't that just mean every color?

<400 + >530 + 400-530 = ALL