Nichia to Ship Green Diode Laser

seoguy · Aug 7, 2010

RA_pierce said:
Yes, the gamut should be better, but I am not interested in it's use in projectors.

Oh, OK! But I'm thinking a bluish emerald green beam would also look pretty sweet.

I think that the 510nm diode would make a nice, stable, and bright pointer for night use. I plan on getting a telescope soon and I think a cool green guide would be spectacular.

Agreed. I think it would make the perfect star pointer!

It would definitely beat DPSS for stability in outdoor operating temperatures.

That's for sure! Thinking about that, it would also make green a lot more practical for use in hunting & camping - no need to worry about maintaining proper temp range, or shock from recoil damaging delicately aligned crystals!

The thing I like about DPSS is that it looks so "clean" compared to the output of diodes. I don't know how to describe it but it looks "more" monochromatic and the profile is much sharper.

Spectral purity is probably an accurate description - some LD's are worse than others! I recall seeing some spectrum analyzer screenshots of some "less-than-perfect" LD's (@LED Museum, IIRC), and the spectrum was not exactly a thin vertical line!

We also need to remember that a DPSS has at it's heart a crystal solid-state laser (just like a ruby laser), whose wavelength is basically locked in place by the laws of physics!

Many green DPSS modules also have built-in beam expanders, which probably makes the beam sometimes look a bit better than our homemade "extracted diode+Aixiz" creations.

And thanks for the explanation on the scotopic curve.

Your welcome!

I'm ready for these diodes. Are we there yet?... oke:

LOL! Well, they said they were going to start sampling this month - that's why I said Nichia need to send some of those samples over to IgorT for testing!

HaloBlu · Aug 7, 2010

Prototype said:
1. By spectral purity I assume they meant the wavelength shift range is a lot smaller. It's only a few nm for DPSS vs. the +/-10nm diodes can have.

:thinking: I was under the impression that the crystals gave exactly 532.

seoguy said:
We also need to remember that a DPSS has at it's heart a crystal solid-state laser (just like a ruby laser), whose wavelength is basically locked in place by the laws of physics!

Would it be locked to a few nm or exactly 532 then?

jmgallego · Aug 7, 2010

HAHAHAHAHA!!! I meant scotopic, mispelled, HAHAHAHAHA!!! Nuclear vision... :drool:

jmgallego said:
And I, what was the isotopic peak! Great chart!

Thanks!

seoguy said:
Your welcome!

Isotopic? Nuclear vision? :thinking: Is that like Superman?

Searching for what you meant, I did find a blog incorrectly referring to night vision as "isotopic".

If you are talking about night vision, that's scotopic - the curve for that one is the graph I just posted above. It peaks at 505nm - which is one of the reasons I think that the beam of this 510nm LD would look so awesome at night!

ossumguywill · Aug 7, 2010

Do you think they'll keep pushing the wavelength of the diode or stop here? I'm kinda hoping they make it to 520nm...

pullbangdead · Aug 7, 2010

Sumitomo has published results up to 533nm lasing pulsed, and up to around 525 or so CW, but that's on semipolar GaN, and therefore not yet manufacturable at scale.

There's not a lot of commercial incentive to go much past 520nm, but there is definitely a lot of commercial incentive to get to and maybe just a little beyond 520nm. I believe most of the commercial green diodes will eventually be sold around 520nm, like how blue has kind of settled on ~445nm or so nm. Of course there will be variation because they're diodes, but that's about the goal. And if a company can make powerful CW 520nm, then they will probably be capable of pushing a few diodes out to beyond 530nm, but there's no commercial incentive to do so. There are some fundamental limits out there, but we've gotten around each one so far with careful and creative engineering.

ossumguywill · Aug 7, 2010

Pullbangdead, do you work for a semi company or something? You're like the go-to-guy on diode science lol. Anyway, do you think they will make a super high power red any time soon? We have super high power blue, green soon to follow, but what about red? The absolute cap on red (for us) is ~300mW in a 5.6mm package. I understand this is due to different chemistries, but could they ever make a >1watt small die red diode? It seems to be the missing piece in DLP tech...

RA_pierce · Aug 7, 2010

HaloBlu said:
:thinking: I was under the impression that the crystals gave exactly 532.

Would it be locked to a few nm or exactly 532 then?

Yes. Kinda.

Diodes can shift wavelength or output a range of frequencies depending on temperature and other factors.
DPSS lasers are generally more "pure" than diodes.
The doubling process will give you almost exactly 532nm and not much more.
With a temperature shift, the wavelength of the diode may change which reduces the efficiency of the laser. If the pump source deviates from it's optimal wavelength, the pumped crystal will generate less light. This is what causes the instability and warm up we see in many cheap greenies.

As always, Sam's Laser FAQ is a good place to start:

Exact Wavelengths of Neodymium Lasers

The most common YAG and Nd:YVO4 (vanadate) lasers are usually listed as operating at 1,064 nm. However, this is not totally accurate and their wavelengths differ slightly. The wavelength for vanadate is more precisely 1,064.3 nm. There is also a weaker line at 1,342 nm.
(Portions from: Juozas Reksnys (rexnys@uj.pfi.lt).)
This most powerful lasing Nd:YAG line is composed from two lines 1,064.17 nm (strong line) and 1,064.4 (week line). At room temperature, the half-width of lasing line is 6.5 cm-1 which exceeds the distance of 2 cm-1 between two lines. Therefore, they are a joint line.
The wavelength of this line depends on temperature. In the practical range of +/-60 °C, it linearly shifts to longer wavelengths during heating by 5x10-3 nm/deg. At 27 °C (300 °K), the center of the lasing line is at 1,064.15 nm.
In addition to the common 1,064 nm wavelength, Nd:YAG has over a dozen other weaker lasing transitions between 1,052 nm and 1,444 nm.
(From: Sam.)
However, the vanadate and YAG wavelengths are close enough (0.15 nm) that a lamp or diode pumped YAG crystal can be used as an amplifier for the output of a vanadate laser in a (MOPA - Master Oscillator Power Amplifier) configuration since the gain bandwidth of YAG is about 0.5 nm.

The wavelength of DPSS can shift, but not as drastically as diodes.

Edit to add this:

Temperature Dependence of Laser Diodes

In addition to impact on expected lifetime (power degradation and MTBF) (See the section: Laser Diode Life), temperature effects the wavelength of an unstabilized (internal cavity) laser diode due to changes in physical dimensions:

The wavelength shift for 808 nm diodes is generally around 2.5 nm (+/- 0.2 or 0.3 nm) per 10 °C (or just say 0.3 nm/°C)(, with the wavelength shift to the red (longer) with increasing temperature.

For the violet/blue Nichia laser diodes, it's typically 0.04 nm per °C.

Note that diode current also affect wavelength, partially due to temperature. So, as a diode ages and requires more current for the same output, its wavelength will also change.

(From: Lynn Strickland (stricks760@earthlink.net).)

It really depends on the laser (i.e., manufacturer) and temperature range you are talking about. A good rule of thumb is 0.3 nm per °C over the operating temperature range of the device (About 30 GHz per °C). That's the average slope of the curve though - it includes mode hops. If you're operating at a mode hop, you can get a lot more change than 30 GHz with a 1 °C temperature change. If you are between mode hops, it can be much less.

Mode hops can be a moving target too. Optical feedback can cause them (even minute amounts). Or, you can operate at a specific temperature where there are no mode hops today, but next week it might mode hop at that temperature.

Note that you can only go so far if you want to use temperature to reduce the wavelength. Even if you got the electronics to work under frigid conditions, there is a minimum laser wavelength you can get from a particular diode laser chip. I'm not a physicist, but it has to do with the bandgap of the materials used. What you would get, as you cooled the thing, is lower and lower threshold current, lower operating current, and longer lifetime.

(From: Richard Alexander (pooua@aol.com).)

Back in the old days, about 15 years ago, the only way to get visible light from a laser diode was by using cryogenic cooling. My textbooks from my laser degree program only knows of this type of visible laser diode (they were written in the early '80s). The first room temperature visible laser diode was invented about 1991; I still have a "Radio-Electronics" issue mentioning it.

(From: Flavio Spedalieri (fspedalieri@nightlase.com.au).)

All laser diodes have a tolerance when it comes to wavelength, these tolerances can be as high as +/- 10 nm.

The wavelength tolerances are due to thermal effects, and current. As the diode heats up, the wavelength will change 0.3 nm/°C. and results in mode-hopping.

pullbangdead · Aug 8, 2010

ossumguywill said:
Pullbangdead, do you work for a semi company or something? You're like the go-to-guy on diode science lol. Anyway, do you think they will make a super high power red any time soon? We have super high power blue, green soon to follow, but what about red? The absolute cap on red (for us) is ~300mW in a 5.6mm package. I understand this is due to different chemistries, but could they ever make a >1watt small die red diode? It seems to be the missing piece in DLP tech...

I'm currently working on my Ph.D, with my research focusing on laser diode fabrication.

And reds are tough, the materials are just different. It's a really interesting topic to look really deeply into though. In a lot of ways, red diodes are much simpler. That's largely because they've been around so much longer and alot of the issues have been settled, whereas in the violet/blue/green we're still working on settling the big issues. But yeah, in many ways red is much simpler, but in many ways it's much worse. GaN (the stuff in violet/blue/green) is just amazing stuff, to the point where even though it has existed like half as long as all the red diode technology, in many ways it has already surpassed the reds, even though in several ways it still hasn't really caught up yet. The ceiling for violet/blue/green is much higher than the ceiling for the red diodes, I'll put it that way.

As far as wavelength shift, diodes shift a lot more because the transitions are much more akin to band-to-band, whereas solid state stuff like Nd:YAG or Nd:YVO4 can almost be thought of as more of orbital-to-orbital. An electron in an orbital is locked in at a specific energy, whereas in semiconductors, since you have bands instead of orbitals, electrons have multiple allowed energies within the bands. This leads to broader emission and more wavelength shift. That's not a 100% pure, accurate description, but it's good enough for government work.

ossumguywill · Aug 8, 2010

Lol I was under the impression ALL lasers used electrons dropping orbit, which made me wonder why there could be so many different frequencies with the same or similar semiconductors :thinking: I guess the physics teacher was just sticking with gas lasers or something.... Anyway, I sure hope they can come up with some better red diodes, or maybe even yellow but I can't see many industry uses for that... Looks like we're stuck with violet to green for now

cistercian · Aug 9, 2010

aryntha said:
I really doubt it. At this point, I think there's a possibility that more cheap DPSS greens have been made, than people that want them.

It's amazing though, since I remember how exotic the tech was 10 years ago. 473s were just about to start to follow that trend, and then, bam - 445... I'm not sure how "cheap blue" is going to play out now, since 445 seems to be "blow your eyes out powerful" or nothing at all.

You are probably right.I really like the beam quality possible with a DPSS laser as opposed to what diode lasers produce.Once the diodes are ultra mass produced 4 dollar green pointers will arrive.I can't wait.I would like a 5mw pen with a green diode to carry at work.DPSS lasers are too fragile to carry everyday.One good shock and oops!A 40 or 50mw for cloud height finding would be nice too....but the beam characteristics without an expander might yield poor results.
At any rate, the green diode is here...and it certainly is exciting.

On the blow your eyes out....I really wanted a 405nm for fluorescing work, but I have ruled it out.The blues are just too dangerous.I just ordered a 100mw green...which is instant blindness in it's own right.And I struggled with that.I got some excellent goggles and have secure storage.And the key will not be kept in the laser either.It will be on my person so no one can hurt themselves with it.There are some silly tricks as well as more serious work I need higher power for and I was seriously concerned that if I waited availability might be problematic.
Lower power is more fun most of the time however.
I can't even imagine a 1 watt 445.Imagine the stress on your macula...yikes.

qumefox · Aug 9, 2010

ossumguywill said:
It seems to be the missing piece in DLP tech...

Seems like i've discussed this in another thread. You will never see RGB lasers in a DLP tv or projector. There is no point. The only reason we find 445's in the casio's, is because they were cost effective. By using a bank of 445's, they were able to eliminate a light source (green) by replacing it with a phosphor disc. That eliminates DLP's from ever having green diodes right there. No point in replacing a cheap phosphor disc with an expensive array of LD's.
Red is the same deal. A high powered red LED is a lot cheaper than a LD array, and DLP has no need for coherent light other than to drive the phosphor wheel.

So you can thank casio for cutting costs, as it's the only reason there is a DLP projector at all with lasers in it.

Projectors with high powered RGB diodes won't ever hit the market as DLP's, But they will eventually show up as scanning beam projectors like the current pico projectors once high power red and green appear on the scene. But these projectors won't have hundreds of diodes in them. They'll most likely only have one of each.

ossumguywill · Aug 9, 2010

Qumefox-who says it won't become cost effective to use red laser diodes over LEDs? It's appears that it was cheaper to use LDs than LEDs, as you easily could have gotten some blue LEDs to drive the phosphor wheel and illuminate if it was cheaper. Also, you're forgetting that there is a market for far-focus projectors. We have MEMS that will take a straight beam from a laser and darken or lighten regions, giving you an image with a long projection range. And those pico-projectors will be cheap eventually too, even if they only have 1 red, green, and blue diode.

qumefox · Aug 9, 2010

I'm not saying you won't have projectors with RGB LD's. I'm saying you won't have DLP projectors with lots of LD's other than 445nm. You also miss the point. An array of red LD's won't be as cheap as a single high power red LED... However, an array of 445 LD's ARE cheaper than a high power blue and green LED combined... Which is why casio did it.

And scanning beam projectors (ala the current pico projectors) will be a lot more suited for your long throw projectors than DLP will. With normal image projection, you start hitting size limits pretty quickly in regards to your lensing before you start having to make the projectors HUGE.

I'm saying the light source for DLP in no way needs or benefits from lasers. Actually it looks better WITHOUT them. Since the speckle from the interference patterns in coherent light definitely doesn't help image quality in the least.

I happen to fix TV's for a living. I have training from various manufacturers in the operation, servicing, and alignment of various display technologies.. including DLP.. I'm not talking out of my ass on this subject.

I know everybody that wants high powered LD's has wet dreams of some manufacture releasing something with dozens of various color high powered in them and we can get them for $10 each... but that's a pipe dream. Such a device may eventually appear on the market, but it certainly WON'T be a projector that uses DLP technology. It'd be a crappy idea just from a thermal standpoint. Anyone who's dealt with the casio's will attest to that, plus with the phosphor wheel, they'll never have green diodes anyway.

The truth is, the 445's in the casio's are a fluke, as far as DLP is concerned. Ask anyone who deals with the technology. And apparently cheap high powered diodes have a lot of us spoiled now.

What are you going to do when LED manufacturers make green's and blue's cheaper and casio drops their complicated 'hybrid light engine'? It will happen eventually. And the price of blue will go back up.

The image quality on these casio's isn't the greatest in the world. And it wouldn't surprise me if they weren't selling more to people disassembling them than they were to people actually using them as projectors.

ossumguywill · Aug 9, 2010

Now hold on-casio easily could have used a blue LED to both make blue light AND illuminate the phosphor wheel if LEDs were cheaper. Phosphors don't need lasers to work properly, do they?

qumefox · Aug 9, 2010

The phosphor fluoresces much more brightly with coherent light I believe. But that's relatively easy to test too if someone has a phosphor wheel, a 445, and a blue phatlight.

ossumguywill · Aug 9, 2010

I've never heard that before-plus, don't they put the blue laser light through a diffusion grating BEFORE they fluoresce the wheel? That should ruin any coherence...

Nichia to Ship Green Diode Laser

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