Diode Wavelengths

[agravlin]

Why exactly is it only possible to make plain old diodes that produce only a few wavelengths?

Why do we have to produce 532nm light with IR flowing through a crystal? Why do we have to produce 488nm light by passing a beam through Argon gas?

These wavelengths are functionally no different from any other visible light. Why can't they be produced by a diode alone?

 

[Kulhu]

Because potatoes.


We will someday... just not now.

 

[ElektroFreak]

Like all technology, laser diodes progress with time. Green laser diodes have been produced recently and should be relatively common before long. Then we will be able to have nearly any color laser emission from diodes.

 

[Morgan]

Why exactly is it only possible to make plain old diodes that produce only a few wavelengths?

Why do we have to produce 532nm light with IR flowing through a crystal? Why do we have to produce 488nm light by passing a beam through Argon gas?

These wavelengths are functionally no different from any other visible light. Why can't they be produced by a diode alone?

Not technically correct there Agravlin. The argon gas is excited by high voltage electricity, much like a fluorescent tube, and emits the 488nm light, (in single line systems). No, "... passing a beam through Argon gas...", to get 488.

M

 

[Kulhu]

What if we mix HeNe(red) with Argon(light blue) would we get a greenish yellow color?

 

[Kulhu]

If red ruby makes red and sapphire makes blue would emerald make green?

 

[qumefox]

What if we mix HeNe(red) with Argon(light blue) would we get a greenish yellow color?

Argon-ion's lase everywhere from UV to IR. 488nm is just the most common because that's the line that has the most gain. 514nm and 458nm are two other relatively common wavelengths for it. What you get depends on what optics you use. Use broadband optics and you get multiple lines at once.

and mixing helium and neon with the argon would likely be a mix that wouldn't lase at all on any power that the tube would survive.

 

[Morgan]

If red ruby makes red and sapphire makes blue would emerald make green?

By that logic, diamond should make white...

... And a banana should make yellow...

... Nice thinking though.

Here's a link that should clear up that thinking -

Ti-sapphire laser - Wikipedia, the free encyclopedia . Not blue, but IR and red!

M

 

[Cyparagon]

According to a quick google search, emerald lasers are IR as well.

 

[ElektroFreak]

Emerald or doped emerald? Rubies contain chromium which is the actual lasing medium, so I'm sure Emeralds also have a "built-in" lasing medium.. I wonder if it's the same?

Seems emerald likes to be pumped with visible red around the 640-660nm range. Could make for some interesting DPSSFD possibilities. I'm also curious as to whether it has the same difficulties running CW that ruby does..

 

[HIMNL9]

Well, i remember i've read, times ago, that in the very start of laser researches (when the only way for have a laser beam was pumping a ruby bar), Soviet scentitst was experimenting with a lot, literally, of different substances, and reached to obtain laser emissions from a bunch of unusual items (including a tube filled with vodka, yes )

So, theorically, a laser can be made with a lot of things, and have a lot of different wavelenghts ..... the only problem is the EFFICENCE of the lasing medium ..... i mean, what worth the effort to have a laser that emits 517nm (or any other "exotic" color you can imagine), if for obtain 1 or 2mW of laser light, you have to pump 50 or 100W in the lasing system, plus other same power in the cooling or heating assembly (when the medium don't lase at ambient temperature) ?

 

[Event_Horizon]

The reason diodes are only available for specific wavelengths is because of the materials they are made out of. The laser diode needs to be made of two semiconductor materials, and those materials need to support stimulated emission. Most semiconductors don't emit light at all! The junction between the two semiconductors will have a voltage drop, and the amount of voltage drop across the junction depends entirely on the materials the junction is made of. The kicker is this: the voltage drop determines the wavelength.

As each electron passes through the junction, it loses energy. In fact, if the junction has a 1V drop across it, the electron loses 1 eV (electron-volt) of energy. The 1eV of energy lost from the electron becomes a photon with 1eV of energy, which corresponds to a wavelength of 1200nm, which is infrared. So to produce red at 660nm, you need materials that provide you a 1.9V drop. To produce violet at 405nm, you need materials that produce a 3.1V drop. The hard part is finding the right materials. It's literally a case of trial and error, and there are tens of thousands of possible material combinations and producing them one at a time is very expensive and time consuming.

You can see the same effect with LEDs, as well. LED materials are easier to make because they only need to produce spontaneous emission and not stimulated emission.

EDIT: And like HIMNL9 said, most of the time when you find a working combination, the amount of energy the electrons lose being converted into laser light is ridiculously low. Most of it ends up as heat, and cooling semiconductors is an art unto itself. And then you also need to consider beam quality as well.