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How colours work.

Paul0759

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Why is it that we are pretty much restricted as to what wavelength a laser can produce.
What makes a Red laser Red, what makes a Green laser Green, what makes a Blue laser Blue?

-Paul
 
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LaZeRz

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Re: This may be a very silly question.

Its the die of the laser...

Like how LED's can produce different colours laser diodes can too

Sorry if im not technical enough. :)
 
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Kevlar

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Re: This may be a very silly question.

You have some reading to do my friend. ;)

Diode Lasers
 
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Paul0759

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Re: This may be a very silly question.

Indeed i do, and read i will... i like to try to understand a bit more about the science behind things but in all honestly colour is way more complex than we as infants are taught.

Am i right in assuming it has something to do with the colour of the crystal placed at the front of a diode?... The wavelength of the DPSSFD lasers is 532 nm based on the intracavity frequency doubling of a Nd:YVO4 (vanadate) chip using a Potassium Titanyl Phosphate, KTiOPO4 (KTP) crystal inside the laser cavity... if these are the compounds used to produce green... then why arnt we seeing a mixure of the other compounds used for other colours, Eg: what ever compounds used for blue / whatever compounds used for red = Pink?

Wow, i really do feel like im just standing here waiting to be shot down in flames by you guys.... i have no idea weather my logic is even pointing in the right direction or im just thinking like an idiot.



i guess ill start reading heheh
 
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JBTexas

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Re: This may be a very silly question.

*Basic* answer for a *basic* question;

There are some compounds in nature that *can* produce laser radiation *under the right circumstances*. But not EVERYTHING can produce a laser beam.

Seawater doesn't produce laser beams. Neither does coffee (although I WISH it did, I drink enough of the stuff). Common glass doesn't "lase". But believe it or not, some organic material found in jellyfish apparantly "lases":
http://laserpointerforums.com/f54/laser-light-living-biological-material-64338.html

If you took a ruby laser, but replaced the ruby with a rod of quartz, it wouldn't produce a laser beam, because quartz doesn't "lase", at ANY color. But when ruby "lases", it "lases" red.

Infrared (808 nanometers) laser diodes use aluminium gallium arsenide(GaAlAs). Most of the blue (445nm) lasers and also the violet (405nm) use indium gallium nitride(InGaN). Cheap red laser pointers use Aluminium gallium indium phosphide (AlGalnP). Those compounds all produce lasers at SPECIFIC colors. BUT; replace any of those diode components with, say, a grain of SALT, and then it would NOT make a laser.

So; only specific things "lase". And they all "lase specifically" at "their" color. But there are always new discoveries. They might find a NEW compound for a NEW shade of blue. Or a CHEAPER compound for an already existing color.
 

Paul0759

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Re: This may be a very silly question.

JBTexas... Understood, i guess i was sort of thinking in the right direction then, Thanks for that very informative piece of information :)
 

JBTexas

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Re: This may be a very silly question.

Am i right in assuming it has something to do with the colour of the crystal placed at the front of a diode?... The wavelength of the DPSSFD lasers is 532 nm based on the intracavity frequency doubling of a Nd:YVO4 (vanadate) chip using a Potassium Titanyl Phosphate, KTiOPO4 (KTP) crystal inside the laser cavity... if these are the compounds used to produce green... then why arnt we seeing a mixure of the other compounds used for other colours, Eg: what ever compounds used for blue / whatever compounds used for red = Pink?
It isn't necessarily the color of the cyrstal, or the *gas*, etc. It's a function of chemistry and physics.
 

joeyss

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Re: This may be a very silly question.

Crystals are only used in green true blue(473nm) or yellow lasers.(593.5nm or 589nm) These work similar to flouresence, but with a added effect. 808nm infrared light gets converted to 1064nm by hitting a certain crystal and then after that it gets cut down to 532nm, which is green looking to humans. the nms are diffirent for other colors. There's even a red one at 671 nm. This is called DPSS(diode pumped solid state)
 

JBTexas

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Re: This may be a very silly question.

(technically the 808nm or 1064nm doesn't get "converted"; it pumps or "energizes" the crystals for the final output color).
 

Paul0759

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Re: This may be a very silly question.

(InGaN) mixed with (AlGalnP), would create the means to create a pink laser? if those can even be mixed without some sort of negative reaction, or even if they would still "lase" if mixed... it is pretty obvious to me that if it was as simple as that it would have already been done and every colour in the spectrum would be available, any idea why this seems not to be the case? :)

Edit: Like i said, i have a lot of reading to do, im just shooting into the dark at the moment heheh.
 
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Kevlar

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Re: This may be a very silly question.

*Basic* answer for a *basic* question;

There are some compounds in nature that *can* produce laser radiation *under the right circumstances*. But not EVERYTHING can produce a laser beam.

Seawater doesn't produce laser beams. Neither does coffee (although I WISH it did, I drink enough of the stuff). Common glass doesn't "lase". But believe it or not, some organic material found in jellyfish apparantly "lases":
http://laserpointerforums.com/f54/laser-light-living-biological-material-64338.html

If you took a ruby laser, but replaced the ruby with a rod of quartz, it wouldn't produce a laser beam, because quartz doesn't "lase", at ANY color. But when ruby "lases", it "lases" red.

Infrared (808 nanometers) laser diodes use aluminium gallium arsenide(GaAlAs). Most of the blue (445nm) lasers and also the violet (405nm) use indium gallium nitride(InGaN). Cheap red laser pointers use Aluminium gallium indium phosphide (AlGalnP). Those compounds all produce lasers at SPECIFIC colors. BUT; replace any of those diode components with, say, a grain of SALT, and then it would NOT make a laser.

So; only specific things "lase". And they all "lase specifically" at "their" color. But there are always new discoveries. They might find a NEW compound for a NEW shade of blue. Or a CHEAPER compound for an already existing color.
Good *basic* answer but don't forget DPSS. I'm in NO WAY any expert but it is quite complex.

These crystals have to be grown in a lab. Many things contribute to why we don't have a diode for every color of the rainbow. But a lot of it comes down to stability of the crystals.

Here is another helpful link for for you Paul: Laser pointer - Wikipedia, the free encyclopedia

Scroll down to the "Green" labeled section for some more info.
 

JBTexas

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Re: This may be a very silly question.

Don't think of lasing materials as "paints" or "pigments". "Mixing" them is the wrong way to think. Lasing occurs at an atomic or molecular level... reactions between energy and chemistry. You need to study more.
 

Paul0759

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Re: This may be a very silly question.

I'm starting to get it now.... just like mixing a cow with a man wouldn't create a ManCow, As just pointed out... "Growing crystals" in a lab makes my thinking a bit better also... not all compounds used for lasers are crystals :) wow you guys know alot, at first i was just like yay lasers are cool, its to easy to overlook the science behind them, i feel like i'm headed to learn a pretty interesting subject now :)


Wow -> Green laser pointers appeared on the market circa 2000, and are the most common type of DPSS lasers (also called DPSSFD for "diode pumped solid state frequency-doubled"). They are more complicated than standard red laser pointers, because laser diodes are not commonly available in this wavelength range. The green light is generated in an indirect process, beginning with a high-power (typically 100–300 mW) infrared AlGaAs laser diode operating at 808 nm. The 808 nm light pumps a crystal of neodymium-doped yttrium aluminum vanadate (Nd:YVO4) (or Nd:YAG or less common Nd:YLF), which lases deeper in the infrared at 1064 nm. The vanadate crystal is coated on the diode side with a dielectric mirror that reflects at 808 nm and transmits at 1064 nm. The crystal is mounted on a copper block, acting as a heat sink; its 1064 nm output is fed into a crystal of potassium titanyl phosphate (KTP), mounted on a heat sink in the laser cavity resonator. The orientation of the crystals must be matched, as they are both anisotropic and the Nd:YVO4 outputs polarized light. This unit acts as a frequency doubler, and halves the wavelength to the desired 532 nm.
 
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Kevlar

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Re: This may be a very silly question.

Yup, I think the basic answer (as basic as can be) has been given.

And to answer your question of why don't they just mix this crystal with that crystal to get this color is they have tried. For a very long time, and to this day, there are VERY smart people doing R&D to get more colors out of one diode.

As I said before, a lot has to do with growing the crystal properly. Getting good quality crystals that are stable to produce a certain nm. Even some of the laser produced today are very finicky. They must be kept at a certain temperature, using TEC's, to get a stable output.
 

LORDJET

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Re: This may be a very silly question.

^^^That's also why you can't just pick a ruby that the earth has made, cut and polish it, and expect it to lase. ANY impurities in the crystal will kill the laser action. They have to be made ( grown ) under strict quality control procedures. It must also have the correct amount of chromium for it to work. Because it is the chromium atoms that do the actual laser action, ( Ruby's just the host ).
 
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DrSid

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Re: This may be a very silly question.

Green DPSS is union of several factors. First is KTP crystal which in simple terms halves the wavelength of the light. That indeed is a mechanism which can be used to achieve many colors. But then there is the vanadate, which lases on wavelength double of green. This is generally 'good luck' for us. That cannot be engineered. It can be predicted to some amount. But then there is question of materials availability and price. Same thing with the pumping diode. They too can't come in any color, but only based on properties of available materials.
So with reds, infrareds, and blues we are very lucky .. it can be done directly for reasonable price. With green, there is long way using 3 wavelengths, but still we must consider our selves lucky that it is possible. With other colors were not so lucky, so far. We must wait till new materials are discovered, or available for reasonable price.
 




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