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Finally, a True Green Laser
dusty writes "Remember those green lasers from Star Wars? Turns out that faking green lasers has been easy for years, but making true green laser diodes has been the stuff of science fiction. Until recently, that is. Now researchers from Japan have created the world's first true green laser diode. Until now, only red and blue laser diodes were available, and now with the addition of green, new TVs and projectors that are more efficient can be produced. And if you were wondering how green lasers pointers are already produced, it is a hack that involved doubling the frequency of an infrared laser. The new true green laser diodes have much higher efficiency than the current 6%, leading many to expect big time laser display breakthroughs in the near future. Ars Technica has a well-written article on this breakthrough."
*head explodes*
"A laser diode is much more robust than (a laser diode and the frequency-doubling package of nonlinear crystals).
Title should read "True green laser diode". 'Green' laser output has been achievable for for more than three decades with Argon ion, Krypton ion, and Copper vapor lasers. This just makes it more 'convenient' to achieve green output.
Sig this!
Nothing is slowed down. Light always goes at the same speed. Guess its name.
What happens in a non-linear crystal is that two infrared photons combine to make one more energetic photon. If you can achieve 100% efficiency, then you start with a beam of power P in the infrared and end up with a beam of the same power in green, but only half the number of photons, each photon having double the energy, at the same speed.
The heating comes from inefficiency (transparency is never 100%) of the crystal, not from slowing down.
This is all, of course, well-documented in the page you have linked to, but not read. A more specific page might be
http://en.wikipedia.org/wiki/Second_harmonic_generation
Let me add to what you have said: Green beams can be obtained from solid-state infrared lasers (e.g., Nd:YAG) by using KTP or KDP crystals, which combine two photons into one (!) with twice the energy/frequency. The resulting beam is collimated and coherent - i.e., the same as the original and any other laser beam. The technique was first demonstrated in 1961, predating this new discovery by almost half a century. Green laser diodes are most definitely interesting and useful, but to suggest that the green lasers from before were "fake" is incorrect. The new part here is having green as the fundamental frequency from a solid-state laser.
Let me c.
Hang on a minute, the article says light travels at the same speed in a vacuum. Stupid intarwebs. I'll fix Wikipedia and you can do all the others, OK?
Confucius say, "Find worm in apple - bad. Find half a worm - worse."
Sweet. Now we just need it to draw on your eyeball. And not blind you.
You mean like this?
That is not fully correct. It is true that the speed of light, in a vacuum, is a constant. But, the speed of light through a transparent medium is something less than c. How much light gets slowed down by a medium is frequency-dependent, as described by snell's law, which is how lenses are able to bend light.
The fact that the speed of light through a medium is less than c also allows for some more exotic phenomena, such as Cherenkov radiation, created when a particle's velocity through a medium exceeds that medium's speed of light (but definitely remains less than c).
From the article it says, "At Sumitomo Electric, they have overcome this problem by developing a GaN crystal which inhibits the efficiency drop, resulting in room temperature pulse operation of a laser diode emitting in the pure-green region at 531nm." Having worked on development of GaN blue lasers, there are a lot of challenges to getting a reliable, continuous wave (CW) diode laser that operates at this wavelength. My guess is they hammered their green diode laser with very short high power pulses just to get it to lase. So it is probably not a very useful laser if it cannot operate in CW mode.
RGB is the additive set of primary colours, CMY is subtractive.
No kidding!!! What do you say at this point?
I know you're joking, but some people won't realize that blu-ray (405nm) can store more data per disc than a green could. It can be focussed more tightly.
I had a sucky sig.
depends on whether you're talking about primary additive colours or primary substractive colours.
As the idea here is to send light in your eyes, and not buckets of paint, I guess additive is what you're looking for
"DRM is like the Ford Pinto: it's a smooth ride, right up the point at which it explodes and ruins your day."-C.Doctorow
From the Slashdot summary: "And if you were wondering how green lasers pointers are already produced, it is a hack that involved doubling the frequency of an infrared laser. The new true green laser diodes..."
The intention is not to say they are fake lasers. The former green solid-state laser devices aren't just laser diodes; they are diodes plus another complicated structure. The new green laser devices are true diode lasers.
Corrections to the Ars article:
"Ever wonder why projector systems and televisions don't use laser illumination?"
More important error, and my guess about the correct information: "For instance, blue laser diodes use a gallium nitride system, and figuring out how to get indium nitride to mix through the gallium nitride evenly turned out to be quite difficult."
Full Text PDF of the Applied Physics Express scientific paper. (Free)
Laser projectors, dude!
Great contrast, tremendous color gamut, and they can project from any off angle since there's no real focusing issue.
Granted, there's more bugs to work out, but the lack of a cheap green laser was the probably the biggest issue holding the technology back.
How can I believe you when you tell me what I don't want to hear?
A prop on Firefly was named Vera.
Not if it's pulsed, as one commenter mentioned before; pulsed lasers aren't quite as fun as CW and they especially aren't useful in laser shows. The low power DPSS lasers have gotten so cheap, it will take ages for production of green diodes to catch up. Several years ago, a 50mW pointer would sell for thousands of dollars, and now you can get reliable ones for as little as $20 now and I've tested some $40 150mW pointers and found them to be accurate. I'm curious to see the maximum energy output for a single die; it might not be high enough to surpass the CW-equivalent power of a DPSS laser (which wouldn't be great for pointers), but it should be possible to create diode bars (lots of dies on one plate, typically water-cooled), likely yielding tens of watts of green light, which is extremely difficult to do with a DPSS system.
Not to go off-toic here or anything, but there are plenty of companies that sell far higher quality lasers (i.e. they actually meet or exceed the power ratings given) than Wicked Lasers... the laser hobbyist community has grown to mistrust this company in the past.
Also, green DPSS lasers typically achieve much higher efficiency than 6%. Higher power laser pointers typically achieve at least 10%, often 15-20%. I've seen some pretty nice setups that can get to 30% with advanced cooling... the trick is to tune the crystals according to their optimal temperatures. YAG crystals like to be hot, KTP crystals like to be as cool as possible.
According to my handy photonic spectrum wall chart, there are green lasers already: Argon ion, Copper vapor, Nd:YAG, Xe, and HeNe, as well as, of course, tunable dye lasers. Just not laser diodes, until now.
...the future crusty old bastards are already drinking the Kool-Aid.