# Directly injected 532nm green laser diodes on the horizon!!!



## The_LED_Museum (Apr 9, 2007)

It shouldn't be that long now before *DIRECTLY INJECTED* green laser diodes become available. I just read in Compound Semiconductor magazine that chip maker Rohm in cooperation with Shuji Nakumura (of Nichia blue LED fame) had success with making a non polar blue-violet laser diode, and are now setting their sights on (and will probably be able to make) a green laser diode that emits at 532nm.

This could eventually spell the end of DPSS green lasers, and the IR radiation associated with some of them.


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## dr_lava (Apr 9, 2007)

mmmmm, yeah.
http://www.rohm.com/news/070201.html


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## greenlight (Apr 9, 2007)

Interesting article.


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## LiteTheWay (Apr 9, 2007)

Great stuff - should be cheaper, eventually anyway, too since no crystals etc.


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## luvlasers (Apr 9, 2007)

So when directly injected green laser diodes come out (mass produced) green lasers will be the way red lasers are now. Then all we'll need to wait for then is blue lasers to become cheap and common. 

Bring it on!!!


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## fixorater (Apr 9, 2007)

Imagine affordable 125mW and higher? Drooooool.


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## PhotonWrangler (Apr 9, 2007)

Cool! This should offer many bebefits when they get into mass production - 

Lower cost.
Smaller sized pointers.
Rugged - they'll likely still work after being dropped.
Lower current draw since a pump diode is no longer needed, increasing battery life.

Looking forward to non-DPSS greenies!


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## 2xTrinity (Apr 9, 2007)

PhotonWrangler said:


> So when directly injected green laser diodes come out (mass produced) green lasers will be the way red lasers are now. Then all we'll need to wait for then is blue lasers to become cheap and common.
> 
> Bring it on!!!


I wouldn't be surprised if blue lasers actually come out first in the cheaper category -- as they're being implemented in all the next generation optical disc readers.

However, even the idea of having something like a 1-2mW green laser in a keychain sized form factor would be awesome -- it would be low power, and still relative safe, yet appear about 4 times brighter than a comparable red laser. Soemthing like the equivalent of a 30mW direct laser, in a 1xCR123 size for outdoor pointing would be awesome too -- and with the lower current draw it could have quite long runtime and a very convenient size/packaging.


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## Rubycon (Apr 9, 2007)

There is one very bad aspect of semiconductor lasers - beam quality. Mode and coherence length is inferior to solid state and gas lasers.

Of course for the majority of the enthusiast crowd that lights matches and pops balloons, this will not matter. 

It's possible to at least circularize the beam and get extremely good divergence - at the cost of power attentuation. Obviously for a pointer compact form factor and much reduced current consumption are very strong points. The days of a 5 mW greenie pulling 200 mA at 3VDC will long be gone.


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## Patriot (Apr 9, 2007)

Just how delicate are current green lasers with crystals? Does a single drop from waste level really mean death to a green laser? Is there a big difference in impact resistance between say a $200 pen bodied laser versus an RPL or Hercules? Thanks.


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## The_LED_Museum (Apr 9, 2007)

Current green lasers using crystals (DPSS lasers) are fairly delicate; many times, a drop from waste-height onto a hard surface like concrete or asphalt can kill them. :shakehead:
As far as I'm aware, large DPSS lasers are just as vulnerable to drop damage as pen-style DPSS lasers.


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## COMMANDR (Apr 10, 2007)

The development of cost effective red, green and blue direct injected lasers will be a boon to the HDTV industry. This will make the HDTVs much cheaper and the color saturation and gamut will be incredible. Looking forward to a 3 laser light source HDTV to replace my Samsang xenon lamp DLP. Here are a few links on Laser TV.


http://www.pcmag.com/article2/0,1895,2079229,00.asp

http://www.sed-fernseher.eu/what-means-laser-tv


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## AJ_Dual (Apr 10, 2007)

This will make HD video projectors about the size of a pack of ciggarettes possible.


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## PhotonWrangler (Apr 10, 2007)

COMMANDR said:


> The development of cost effective red, green and blue direct injected lasers will be a boon to the HDTV industry. This will make the HDTVs much cheaper and the color saturation and gamut will be incredible. Looking forward to a 3 laser light source HDTV to replace my Samsang xenon lamp DLP. Here are a few links on Laser TV.
> 
> 
> http://www.pcmag.com/article2/0,1895,2079229,00.asp
> ...



The second article claims that lasers "have a very large color gamut"... HUH? Lasers are _highly_ monochromatic, much more so than even LEDs, with a spread of only a few nm. Just compare Craig's laser spectrographs to those of LEDs and you'll see what I mean. So how do we get a _larger_ color gamut from _narrower _spectral lines?
:thinking:


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## hellokitty[hk] (Apr 10, 2007)

this may sound sort of stupid but why didn't they just do this before? I have seen nice green leds before even if they were not 532nm. im really not that fussed for it to be 532nm if it is alot cheeper when its not.


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## Bimmerboy (Apr 10, 2007)

It's gonna' be a tough wait, but sooner or later... 

If I can sort of answer both PW and HK in one shot... I think the answer lies in that the monochromatic nature of each primary color that a laser system would produce, allows for much higher precision in varying the mix of those colors.

It can likely be said better than that, but I think that's barking up the right tree.


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## comozo (Apr 11, 2007)

hellokitty[hk] said:


> this may sound sort of stupid but why didn't they just do this before? I have seen nice green leds before even if they were not 532nm. im really not that fussed for it to be 532nm if it is alot cheeper when its not.



Because it's much harder to produce a room temperature long life working green laser diode. It's even more difficult than making a directly injected blue laser diode. That's why.


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## COMMANDR (Apr 11, 2007)

Bimmerboy said:


> It's gonna' be a tough wait, but sooner or later...
> 
> If I can sort of answer both PW and HK in one shot... I think the answer lies in that the monochromatic nature of each primary color that a laser system would produce, allows for much higher precision in varying the mix of those colors.
> 
> It can likely be said better than that, but I think that's barking up the right tree.


 
What he said.




I agree with Bimmerboy, it is the color mixing of the three primary colors that will give the super color gamut. The dithering of the DLP mirrors can produce trillions of colors.

The white light generated by the lamp in a DLP® projection system passes through a color wheel as it travels to the surface of the DLP® chip. The color wheel filters the light into red, green, and blue, from which a single-chip DLP® projection system can create at least *16.7 million colors*. And the 3-chip system found in DLP Cinema® projection systems is capable of producing no fewer than *35 trillion colors.* 

http://www.dlp.com/tech/what.aspx?revkey=0&sid=0&gd=42699739-9d7c-4221-9615-b8f268996a71&ct=633118698230728812&frm=/Default

Gary


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## hellokitty[hk] (Apr 11, 2007)

oh well i just got smarter lol


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## Guliver (Apr 11, 2007)

PhotonWrangler said:


> The second article claims that lasers "have a very large color gamut"... HUH? Lasers are _highly_ monochromatic, much more so than even LEDs, with a spread of only a few nm. Just compare Craig's laser spectrographs to those of LEDs and you'll see what I mean. So how do we get a _larger_ color gamut from _narrower _spectral lines?
> :thinking:



Hehe , Yeah.. I read that too.
I am sure they meant the laser projection tv itself as a whole would produce a wider color gamut because of the deeper blue and the deeper red diodes, as compared to CRT or lamp driven units.
I guess they didnt proof read it first.
it'l be interesting how the green also progresses !!


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## Corona (Apr 11, 2007)

It's possible already to reduce the crystal count by 50% using a 1064nm IR laser diode, instead of the 810nm diode and pumped Nd:YVO4. This leaves only the KTP doubler "in the way", efficiency-wise. 

Unfortunately, 1064nm laser diodes don't have a very large market (compared to the 810nm variety), and now that the costs for the (dual-conversion) greenies, as we know them, are so cheap - there ain't much hope for higher power, lower cost/quality 1064nm device development to happen.

It would be "nice" to increase the efficiency by, oh, 50% or so, and reduce the amount of IR needed to generate a given green output.

But it would still need an IR filter, and besides, dropping such an "improved" greenie (or getting it wet, or cold, etc.) would still be bad. Two steps forward, one step back 

I can't wait to see these direct injected greenies come along!


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## ajohnson (Apr 11, 2007)

hellokitty[hk] said:


> this may sound sort of stupid but why didn't they just do this before? I have seen nice green leds before even if they were not 532nm. im really not that fussed for it to be 532nm if it is alot cheeper when its not.


 
The smallest LEDs are still kinda big. You can focus a laser to a much much smaller dot pitch. However, LED displays do exist, see http://www.largescreenvideo.com/


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## hellokitty[hk] (Apr 15, 2007)

still kinda big? wouldn't it be bigger if you had a 200mw ir laser and two crystals?


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## 2xTrinity (Apr 15, 2007)

> still kinda big? wouldn't it be bigger if you had a 200mw ir laser and two crystals?


I think he meant the surface area of the die is bigger, not the overall package. Also, simply producing light from a diode is not the same as true laser light -- which is very strictly monochromatic, and coherent (light exits as one continuous wave, with consistent phase). Simply collimating light doesn't make it a laser (and even that can't really be done with an LED due to the fairly large die size, without a huge lens)


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## Canuke (Apr 16, 2007)

PhotonWrangler said:


> So how do we get a _larger_ color gamut from _narrower _spectral lines?
> :thinking:



The reason why we can get a larger gamut from purer (narrower) sources, is because of saturation.

Check out this diagram. It shows the CIE diagram of the human eye's total gamut, and within it the triangle that is the gamut of an RGB additive system; it is the total set of colors displayable by that system.

The three corners of the triangle represent the R, G and B sources in isolation. The purer they are, the closer to the outer curve they become, enlarging the triangle's area and including more colors in its gamut. If your RGB sources are less pure, the corners are closer to the middle, making the triangle smaller, which means fewer displayable colors = less gamut.

Those of you seeking to construct multi-color laser devices or RGB arrays can use the CIE diagram to predict your available gamut by plotting the three points of your primaries' wavelengths against the outer curve. Here I have constructed a rough approximation of what a three-color laser assembly using 658nm red, 532 green and 405nm violet would give you:







(odd, the code is right, and that site's fine with hotlinking, so why no pic?)

This shows that you could still do a lot of color with the blu-ray diodes, but your deeper greens through pure blues wouldn't be very saturated, with emerald green and teal being the worst hit. If you plot the center of the triangle (I didn't think to do it in the example, sorry), that's the system's "white" point where the sources are at equal power; here it's in the magenta-ish zone.

If you swap in the 473nm diode-pump for the blue-ray, move the lower-left corner of the triangle up the curve to the location nearest 473; you give up some saturation in your deepest blues and violets in return for a richer sky blue and turquoise range. The white point would be pulled up and a bit left towards a yellow-white.

If your sources are not very saturated, as would be the case with regular LED's, the three points would be closer to the triangle center, representing a smaller gamut.

(Source pic drawn from Wikimedia Commons, and is in the public domain, as is my modified pic).


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## 2xTrinity (Apr 17, 2007)

Canuke said:


> The reason why we can get a larger gamut from purer (narrower) sources, is because of saturation.
> 
> Check out this diagram. It shows the CIE diagram of the human eye's total gamut, and within it the triangle that is the gamut of an RGB additive system; it is the total set of colors displayable by that system.
> 
> ...


That gamut doesn't look any better than my own crappy computer monitor...



> (odd, the code is right, and that site's fine with hotlinking, so why no pic?)
> 
> This shows that you could still do a lot of color with the blu-ray diodes, but your deeper greens through pure blues wouldn't be very saturated, with emerald green and teal being the worst hit.
> 
> If you swap in the 473nm diode-pump for the blue-ray, move the lower-left corner of the triangle up the curve to the location nearest 473; you give up some saturation in your deepest blues and violets in return for a richer sky blue and turquoise range.


IMHO that's a better tradeoff -- the sky blue/turquoise generall shows up a lot more in most photos/movies. The violet can be approximated anyway using the deepest blue + a little bit of red.

I know in printing, better photos can be produced by augmenting CMYK (the "subtractive" equivalent to RGB, cyan is lack of red, magenta is lack of green, yellow is lack of blue) with deep blue and deep red inks. I wonder if an optical system could do the same -- use wavelengths with higher efficacy, such as 473nm blue, and 630nm red most of the time, and augment those with a deep red, and deep blue just to achieve those "rare" colors.


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## Canuke (Apr 17, 2007)

2xTrinity said:


> I wonder if an optical system could do the same -- use wavelengths with higher efficacy, such as 473nm blue, and 630nm red most of the time, and augment those with a deep red, and deep blue just to achieve those "rare" colors.



They can, and they have. I've seen demonstration systems with six primaries, where the resulting gamut leaves almost nothing out. I can't recall the company though. Its effect is mainly to display the monochromatic colors more accurately.

The normal RGB system usually is most deficient in getting the rich emeralds and blue-green colors, which is why that's usually the first place that a "fourth primary" is added (Fuji Reala film used a fourth layer of emulsion that reacted to the emerald green/teal range). Ask anybody here how hard it is to get accurate-looking color beamshots of cyan and amber LED's; this is because the more saturated a wavelength is, the more "shoved into a corner" the resulting image gets (that's why beezaur experienced his camera trying to "turn amber into red" in post #13 [url="https://www.candlepowerforums.com/threads/132734]here[/url]).

Here is a photo I took with my Canon5D of the full spectrum coming off the surface of a CD. Notice how the pure colors get pushed into the three primaries, resulting in an image that is not very representative of a spectrum at all, but looks like three RGB bands: 




That was in reality a full spectrum, but because of its saturation it gets shoved into red, green and blue. The cyan and the amber are squeezed out. Where excessive dynamic range results in luma clipping in images (blown highlights, solid blacks etc.), this "squeezing" effect is the result of too much *chromatic* range for the gamut.

This doesn't happen very often in the real world; the vast majority of colors are not so saturated, fall within the gamut and are reproduced accurately. However, as megapixels reach their limits, sooner or later I expect the camera manufacturers to start moving in the direction of greater luminance range (so-called high dynamic range or HDR photography) and greater chromatic range (more primaries to increase color sampling and display accuracy).


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