Wavelength selecting red diodes - how orange can it get?

[bulukaki]

There are many diodes in the 635-638nm range, and in the datasheet of some (e.g. Mitsubishi ML501P73) it is mentioned that they can get as low as 632nm. Has anybody tried to select those low wavelength reds (as orange as possible)? How different (in color and apparent brightness) it would be when compared to the typical 635-638nm?

 

[Alaskan]

The lowest red laser diode I am finding advertised right now is 633 nm. There are likely lower, just I haven't seen them yet.

I'm from an RF background, and in my world we usually refer to frequency where low means a longer wavelength, where as in lasers instead of using frequency, they use wavelength, so a lower number means a higher frequency...

You probably understand that, just saying. You can find fairly decent output power red laser diodes at great prices at 638 nm on ebay, but most people think of them as orange-red, when compared next to a 650 nm red laser. Even though 638 nm isn't much different in wavelength to, for example, 650 nm, and both are often considered a red wavelength, the sensitivity of the eye to 638 nm is better than 650 nm.

See:

https://upload.wikimedia.org/wikipedia/commons/c/c0/Eyesensitivity.svg

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IR and red laser diodes usually have fairly high divergence, unless single mode. What I usually do is put a 10 X beam expander on them so the divergence is relatively low. That causes the beam to be ten times thicker, but the beam also spreads ten times slower into the distance.

 

[ZRaffleticket]

633's are the shortest room temperature reds I know of. 628's exist but need to run at 5C. There are some commercial diodes down to 618nm (orange by that point) but need to run at -35C.

Though I think you'd be skirting the line between red and orange in the 620 band. Not sure how useful it would be as a "red" hence why not many options exist in this range.

 

[Giannis_TDM]

633's are the shortest room temperature reds I know of. 628's exist but need to run at 5C. There are some commercial diodes down to 618nm (orange by that point) but need to run at -35C.

Though I think you'd be skirting the line between red and orange in the 620 band. Not sure how useful it would be as a "red" hence why not many options exist in this range.

This exists on CNI's site too 622nm diode: http://www.cnilaser.com/PDF/MDL-H-622.pdf . What do you think? Like are they coolling it down or is it actual room temp 622?

 

[CurtisOliver]

You might want to check out this video. AlGaInP/AlGaAs are far more tolerant to temperature tuning than InGaN/GaN diodes. Blood Orange is the max shift you could expect without a liquid nitrogen setup.

 

[ZRaffleticket]

This exists on CNI's site too 622nm diode: http://www.cnilaser.com/PDF/MDL-H-622.pdf . What do you think? Like are they coolling it down or is it actual room temp 622?

You'd have to check with them to be sure but if I were to make bets yes those are using the diodes that need tons of cooling.

Edit. Looks like newer versions of the diode can run warmer. 5C now for 622nm. Here's what I'm referencing. 618nm no longer seems available

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[bulukaki]

I'm from an RF background, and in my world we usually refer to frequency where low means a longer wavelength, where as in lasers instead of using frequency, they use wavelength, so a lower number means a higher frequency...

Whoops... aside from handling laser pointers and reading about generally-available lasers, my technical knowledge is quite limited... Happy to learn something new though

633's are the shortest room temperature reds I know of. 628's exist but need to run at 5C. There are some commercial diodes down to 618nm (orange by that point) but need to run at -35C.

Though I think you'd be skirting the line between red and orange in the 620 band. Not sure how useful it would be as a "red" hence why not many options exist in this range.

So, no matter how many batches of diodes one selects (bins?), 633nm seems to be the limit for room-temperature diodes?

You'd have to check with them to be sure but if I were to make bets yes those are using the diodes that need tons of cooling.

Edit. Looks like newer versions of the diode can run warmer. 5C now for 622nm. Here's what I'm referencing. 618nm no longer seems available

Wish we can get affordable room temp yellow and orange diodes in the future!

 

[hakzaw1]

Unlikely in our lifetime.
Use by us is less than nothing to the diode makers.


here is a side by side pic from 'Norty303' over at plex.
He has been a lasershow op for many years in the UK.
IIRC the 640 diodes are very very expensive.. might even be cheaper to use 2 or 4 more cheaper diodes joined to achieve that 'brightness'
__________________
'Wish we can get affordable room temp yellow and orange diodes in the future!==''-- me too.

COPYPASTA from Norty.

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400mW 640nm vs 1.1 watt 650nm - Pics and videos! ​

Ok, so I know a couple of you have been waiting to see how these heads compare, so in the interest of fulfilling demand for pics AND vids, here are some pics and vids...

The camera captures the colours poorly, its much more purple than in real life, in fact I was hard pressed to spot the difference in wavelength. However, it does do justice to the brightness perception, again I was hard pressed to tell.

See what you think....


I did take some shots and vids with the greens on as well, however it looks as if my older 532 is somewhat down on power compared to the new one, which I need to investigate. It only has about 30hrs on it and was doing just over 400mW when I got it. The difference in brightness is as noticeable in real life as in the vid, and if you've been paying attention it gives away which is the 650nm out of the 2. So, I've posted those pics/vids over on my RGY build thread so as not to spoil it if you want to have a guess here.''

 

[CurtisOliver]

There are many diodes in the 635-638nm range, and in the datasheet of some (e.g. Mitsubishi ML501P73) it is mentioned that they can get as low as 632nm. Has anybody tried to select those low wavelength reds (as orange as possible)? How different (in color and apparent brightness) it would be when compared to the typical 635-638nm?

The colour difference between a 632 and a 635-638 is barely noticeable. 632.8nm (633nm) is HeNe wavelength and you can notice a difference against a 650nm. But distinguishability is reduced at the red part of the spectrum vs that at yellow and cyan peaks. So 3-5nm difference would only be told apart by side by side tests under favourable conditions.

Laser diodes are given a central wavelength and a range because every one differs slightly. We bin diodes by wavelength and it is not uncommon to see high and low wavelength diodes that are far from the desired central wavelength.

As you know the diode mentioned it is specified as having a central wavelength at 638nm +/- 6nm. A low wavelength diode may very well be close to your target of 632nm. But it should be noted that this is dependant on temperature and driving current. If you got a low wavelength diode you would need to have adequate cooling to prevent the diode temperature rising, and drive it at a lower current. A way of getting around this would be to spectro the diode under your desired test conditions. Exceed these conditions then expect a wavelength shift.

This then would answer your question of apparent brightness. Yes the lower the wavelength (in the red spectrum) the higher the perceived brightness. But a over-driven 638nm compared to a under-driven 632nm is no competition. The only way of artificially lowering the diode whilst maintaining a high output power would be to cool the diode further. Like my video demonstrates above. You can do this via a TEC rather than liquid nitrogen but obviously with less tuning range due to less extreme temperature variations.

 

[kecked]

My favorite red is 660 but I use 642. Hard to tell the difference. I used 632 hene for years as red. Unless you have a reference it looks red. Until you get down to 610 or so it still looks red. 605 is the first line I call orange and you can only get it if your rich via dpss or other non diode sources.

yellow in the 560-590 range exist but it’s really rare and is not room temp diode. I have a batch of 570 and 575 in dpss and they are lovely and low power. They also don’t live long.

 

[18LJ]

Oh there's orange out there in the wild. They're just extremely rare incredibly expensive and can even be a bit dangerous.

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https//www.laserfocusworld.com/lasers-sources/article/16571762/vi-systems-develops-novel-yellow-laser-diode-emitting-at-599-to-605-nm