Wavelength production

[rocketparrotlet]

Does anyone know why some wavelengths of diodes are so easily produced, yet others so rare and expensive (ex:green)? I don't mean DPSS. Does this have to do with the rarity of the materials excited in the laser? If so, since there are such small quantities of these materials in the laser, why would it affect it so much?

-Mark

 

[hydrogenman15]

It is a mix of rarity of materials and probably the biggest problem of "why the hell would I want a green laser diode?" Blu-rays where only built because people needed to store more information on a single disc. They could have used DPSS if they really wanted to, but it works better under some conditions to use diodes because they can be better controlled and more stable then DPSS lasers. There are probably some green diodes out there but they are CRAZY inefficient so DPSS is still the way to go.

--hydro15

 

[Things]

. There are probably some green diodes out there but they are CRAZY inefficient so DPSS is still the way to go.

--hydro15

and EXTREMELY expensive. I'd expect to pay atleast $1500 for a 5mw green diode!

 

[diachi]

try adding another one or two 0's onto that figure .

 

[Ace82]

Laser projectors are not too far away you now... :

 

[diachi]

You might actually find there are a few prototype laser projectors already available,
Flat panel TVs existed over 20 years ago, and I don't mean 15", I mean like 32", they just weren't on the market at that point .

-Adam

 

[pullbangdead]

Green laser diodes DO NOT EXIST, at any price, anywhere.  If a company had made one, they would have patented it and published it immediately.  As soon as you patent something, it becomes public, and everyone would have picked up on it already.  It's no big secret what the "path to green" is, so it's not a big secret that a company would want to keep secret if they made one.  And a patent doesn't have to reveal enough for a reader to be able to make an exact copy, so it doesn't necessarily give away any secrets anyway.  Making a green laser diode would be a great commercial success for your company, and you don't make commercial success by keeping products secret; so if it existed, it would be patented and we would know about it.  I happen to be "in the biz", and it doesn't exist.

The difficulty in making specific colors of laser diodes comes in *making* the material.  You have to make a coherent, extremely-high-quality very thin film of a material with a specific bandgap, and the material you use has to have several other properties:  It has to be a semiconductor (duh), it has to be able to be doped (n-type, p-type, and conducting in both regimes of doping), its optical properties have to align well with the device you want, it has to be direct-bandgap, lots of things.

The current research is for a green laser diode.  The hope is that using the gallium nitride system, a device can be made such that the active layers will have a bandgap low enough to produce green light.  Gallium nitride is a direct bandgap, and it's optical properties are fine, and its bandgap falls into the near-Uv range, just below violet.  And with gallium nitride, you can do some cool things to engineer the bandgap.  Indium and aluminum can both be incorporated into the gallium nitride lattice, a la an alloy, and will substitute for gallium atoms.  Adding aluminum increases the bandgap energy, and adding indium decreases the bandgap energy.  For violet LEDs and laser diodes, you add indium to the gallium nitride, and it lowers teh bandgap to the point where it emits violet light.  Add more indium, and the bandgap gets lower still until you can get to blue light.  The hope is that by adding even more indium, the bandgap will get low enough that green light will be emitted.

But this has problems: basically, indium isn't the same size as a gallium atom, so you can only put so many indium atoms in place of gallium atoms and still have it sit there ok (ie, you want indium gallium nitride, but if you put too much indium, the atoms aren't happy and the whole thing will change into a mixture of indium nitride and gallium nitride, it'll experience phase segregation and form two separate phase regions).  Right now, the limits to how much indium you can add put max wavelength you can get at somewhere around the transition from blue to bluish green, but it is a trade secret how far any individual company can go (not letting the people you're racing know how far ahead or behind you are; but rest assured, when someone wins, they'll announce it).  So it sounds simple: just add more indium, but to actually make a coherent film of a single phase with that much indium in it, and with all the other properties you have to incorporate into the device, it is anything but trivial.

So basically, you can have a materials system that is "at home" at a single bandgap energy, and you can engineer that bandgap only so far from it's "home" value.  With reds and Ir, you notice you can never get as high an energy out of a 635nm diode as you can out of 650nm diodes, because 635nm is a lot further from "home" for THAT materials system, which is a completely different materials system from the nitrides that are using for the low wavelength devices.

Since violet is "closer to home" for gallium nitride, it was MUCH easier to make, and the materials in either color would be the same, just in different amounts or in different places, so there's no rarity issue with green laser diodes. As far as economic forces, there is much less push for green thatn there was for violet, but also violet was MUCH easier to make in the first place. There is still a draw for a green laser and for better/cheaper blue lasers for laser display technology. A diode will also pretty much always be cheaper and more efficient than a DPSS system, and will always be smaller.

 

[FireMyLaser]

http://www.laserpointerforums.com/forums/YaBB.pl?num=1210795895/17#17

 

[Ace82]

Sony actually had to stop making the green LD for their master plan because their competitors were making a laser that was even "sharper"...can you guess what it was?

The laser pointer industry is not currently in demand for these type of applications, since the average Joe/Jane could do fine pointing with 5mW red, and now blue, green, yellow, and violet. The need for LD's to be mass produced is determined from their application, and that's why we still have to harvest the blu-ray and 650 burners because they were, are, and probably never will be, worth all the time and money (which is a life/death investment gamble), the application we use it for. There are limits to what visable lasers are “practically beneficial”, as tools or appliances. But laser pointing is a privilege and a hobby to most of us, to where as in the industry, computers, movies, data storage at the best quality and efficiency is much more practical to the overall population world wide, and even necessary. Not to mention, the IR LD has been absolutely mastered, and the DPSS process for green is much more efficient at the moment compared to what might happen in the future. DPSS lasers are also very unstable for data transfer, and the 405nm has quite the "sharp" point. If anything, they will further progress in data storage, so I can bet they would continue toward the opposite direction of the spectrum, meaning UV laser diodes because then even more storage (until the rays simply pass through the disk) ;D So yeah, they exist, but they don't, and I'd bet that none of us will ever see one, but who knows, many things can change very quickly, and with the talk of laser projectors, they just might come to reality.

http://www.sony.net/SonyInfo/News/Press_Archive/199601/96D-014E/

 

[rocketparrotlet]

Wow, thanks everybody for all of your great explanations! I never knew that "simple" laser diodes could be so complex and hard to design.

What makes a "direct injection" diode different from the diodes we use in our lasers?

-Mark