Why aren't green lasers solid state?

[windstrings]

Educate me here if someone would....

In the past.. we had Crystal radios that developed resonance of certain frequencies based on "crystal" technology... now we have gone to solid state etc.

Why are lasers still in the crystal era?... why can't we use solid state technology to transmit a certain frequency... ie: 532nm?

Instead we have to deal with the fragility of crystals?

 

[SenKat]

Well, by definition, Green (532nm) lasers are solid state. DPSS. Diode Pumped Solid State is the only way at this time (look at how fast Blue lasers developed into bare diodes) to get green, unfortunately. It has taken years to get us this far in technology, but we are getting there ! I am not certain of the EXACT date when blue lasers first came into being - either HeNe, or Argon, or whatever - but they are finally available in blue diode format. And eventually will be inexpensive enough to have everyone of us with a blue pointer on our key-chains ! Time....that is all we are waiting on !

 

[532nm]

For the same reason that we didn't have anything but red LEDs for a while. There was no known chemical combination that could create anything but a red light emitting diode. Eventuall scientists discovered ways to create IR, amber, green, blue, white, even UV. Right now there's no way to create a completely solid state laser diode that lases green light (or if there is it's way too expensive to produce)

 

[windstrings]

Well, by definition, Green (532nm) lasers are solid state.

the diodes are at least but why can't we just simply make a solid state transmitter... like we do for everything else?.... even the frequencies of regular light seem to be out of limits of such technology.

Nothing wrong with crystals, other than they are fragile in everyway.

 

[SenKat]

I hear ya, bud ! I wish they would come out with them, too - it would open up a whole new market then ! It took SOOOO long for blue to be diodes, I guess I can wait a few more years for green....*sigh*

 

[Ragnarok]

the diodes are at least but why can't we just simply make a solid state transmitter... like we do for everything else?.... even the frequencies of regular light seem to be out of limits of such technology.

Lasers, whether diode or crystal, glass, liquid or gas, ARE oscillator/transmitters, operating at an extremely high frequency. It's just that we are used to seeing lots of physical equipment when we deal with radio and microwaves.

At radio frequencies a transmitter consisting of a resonant capacitor/inductor "tank" circuit oscillator feeds a long (say 1/4 wavelength) resonant wire antenna which radiates the energy in the form of a radio wave. As the wavelengths get shorter the tank circuit gets smaller and the antenna wire gets shorter.

In the microwave region it becomes impractical to use individual components and wire, and more practical to use a resonant cavity type of oscillator feeding antennas that are very large compared to the wavelength (dishes), which also increases the directivity of the emitted radiation by orders of magnitude. It's beginning to sound kind of "laserish" already.

Light waves are far smaller, so the parameters for the equipment have to change - drastically.

At light frequencies the dimensions of a quarter-wavelength cavity resonator are extremely small, so instead it is made very large in one or more directions (compared to the wavelength) so as to be practical. Individual atoms or molecules become the oscillator/transmitters. But we can only get so much power out of one atom. So, we take BILLIONS of them and place them between reflecting mirrors that provide feedback and phase-lock (by stimulating their emission) the otherwise random outputs of our mass of transmitters into a coherent beam of radiation. Think of the atoms between the laser mirrors as a massive phased array of oscillator/transmitters working as one.

Probably a pretty crappy description, but maybe it will help?

Right now there's no way to create a completely solid state laser diode that lases green light (or if there is it's way too expensive to produce)

That's why you don't see green diode lasers. The IR/crystal technology is already firmly established and can produce very high powers, far more than a green diode could, at a reasonable price. But who knows what the future holds?

 

[windstrings]

I thought it was a damn good explanation!!!!

I liked the part about the atoms and molecules being the proper size for a 1/4 wavelength...

my next question is if we can use full wavelengths for radio waves and even multiple wavelengths and run it through a "device" to electronically "perfect" the wavelength... as ham operators will use one wire as the resonator for many "different" frequencies when ran through that "matcher".

I don't know if similiar technology could be used for such high frequencies, but I know they use "LED" technology to get light around the 6000k area or so..... The Cree technology is a small step towards the power we would want... and those types of light are not the same "type" of light in respect to how its polarized... laser light is somewhat linear and very efficient for long distances whereas regular light sprays everywhere, even though its focused.

As I'm showing my ignorance by my questions... there is allot I don't know about this subject.

Its a facinating prospect that I thought should be asked.... its quite ludicrase to not explore and think out of the box.

I know nasa has built tremendous lasers, but they have tons of money and often get caught in a rut of thought building upon what they have been taught in school rather than inventing new ways that would be far less expensive. And they are a far cry from "portable".

To me its fun to explore the options.

 

[Ragnarok]

I liked the part about the atoms and molecules being the proper size for a 1/4 wavelength...

Well, they aren't, I did not mean to infer that, because one atom can emit tens to thousands of wavelengths. I was suggesting that since they emit bursts of electromagnetic energy, they are transmitters. You feed certain electron- or vibrational- or rotational transitions power in various ways, and then they release it as a photon, either at random or when "triggered" by another photon.

There is some frequency broadening in lasers, because the cavity is so large in relation to the wavelength, many frequencies close to the "central" one oscillate at the same time.

... they use "LED" technology to get light around the 6000k area or so..... The Cree technology is a small step towards the power we would want... and those types of light are not the same "type" of light in respect to how its polarized...

The white LEDs achieve their "broadband" emission by color mixing - they use a blue LED coated with a phosphor layer, which glows and adds its yellow-orange contribution to the blue light from the LED. It "looks" like 6000K light, but it's not.

In lasers sometimes you can get more wavelengths by running more than one laser at a time in the same cavity, like the mixing of argon and krypton gas in the same laser tube enables output from both, which can give you a "white" laser when their proportions and other conditions are properly adjusted.

Some lasers naturally like to lase at many frequencies; the helium-selenium laser can emit on 20 or more lines at the same time, from blue to red.

my next question is if we can use full wavelengths for radio waves and even multiple wavelengths and run it through a "device" to electronically "perfect" the wavelength... as ham operators will use one wire as the resonator for many "different" frequencies when ran through that "matcher".

I have heard of true broadband lasers that use doped fibers as the active medium, but I don't know anything about them. That's probably what you're after.

 

[windstrings]

Trippy..... this stuff is over my head......

 

[Aseras]

i was gonna say that they are solid state... i think the question you were looking for was why aren't green laser diodes available. blue/violets are as are some UV laser diodes.. the main problem is making them functional and profitable. they can be made but right now it's far cheaper to pump a ktp crystal with IR to reach another harmonic and frequency double. eventually a process will be found that will make the diode more effiecient and then they will come to common market. blueray for instact is $$$ now

look at this for instance.. http://www.sciencewatch.com/jan-feb2000/sw_jan-feb2000_page3.htm

it's all process and profitability.

 

[FloggedSynapse]

Well, technically green lasers are solid state. You're asking why there aren't any 'direct injection' diodes that can create coherent green light directly. Unfortunately at this point no one has come up with a 'recipe' to make visible laser diodes outside of red and violet. In order to get other colors they typically fire an IR laser diode through a crystal set to get the desired color/frequency (DPSS, like used in the greenies). The drawback to this approach is it's much less efficient at creating the desired frequency than a direct injection diode (for example, in a greenie no more than 1/10 of the pump diodes radiation gets converted to green. The rest ends up as heat) and it's more fragile (more mirrors and xtals that need to be held in alignment).

There certainly would be a market for different colored direct injection laser diodes, just as there's a market for the many different visible LEDs out there.

Basically a laser diode is a P/N junction tuned to fluoresce ("spontaneous emission") at a narrow band of frequencies. By sticking mirrors at either end of the cavity a specific wavelength can be chosen and a standing wave starts to live between the two mirrors feeding off the population inversion (the molecules in the junction before they fluoresce). OK, so I'm simplifying things a lot, but that's the gist of it.

Apparently the concentrated EM fields in the crystalline P/N junction make it hard to create long lasting laser diodes (see [size=-1]catastrophic optical damage - COD - fixing this is where many of the patents and black magic are for making reliable diodes)[/size]. For example, in the 90's Sony had developed a green laser diode, but they were stymied by a very short device life. See this link:
http://www.sony.net/SonyInfo/News/Press_Archive/199601/96D-014E/

They had a green laser diode, but it only lasted ~100 hours before expiring. And this was in 1996, so apparently they were unable to improve upon it.

Now that Nichia has developed violet direct injection laser diodes I fear we may never see other laser diodes in the heart of the visible spectrum as they are very expensive to develop (lots of R&D) and DPSS lasers are already here, even if they are not as efficient.