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Old 06-27-2011, 12:47 PM #81
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Default Re: 808nm laser visibility

Yes I do. Thats quite normal after living so long in a country. Nevertheless i still know where my roots are and am not ashamed like many others do that even change their names to hide their roots.


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Old 06-27-2011, 01:54 PM #82
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Default Re: 808nm laser visibility

Quote:
Originally Posted by honeyx View Post
Yes I do. Thats quite normal after living so long in a country. Nevertheless i still know where my roots are and am not ashamed like many others do that even change their names to hide their roots.
Are you saying that I am ashamed of my roots and that I have
changed my name.....

I have never changed my name (Bauer) and am proud that I was
born in Germany... even though I am a Canadian now...


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Old 06-27-2011, 02:05 PM #83
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Default Re: 808nm laser visibility

No Jerry. And itīs good you didnīt. You also donīt have to be ashamed. I was talking about people living here in germany who came from other countries. Many of them are changing their names to german ones and doing so like they were more german than the germans born here.
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Old 06-27-2011, 02:12 PM #84
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Default Re: 808nm laser visibility

Quote:
Originally Posted by Morgan View Post
I don't like trolling, (as some will be aware!), and hate to side with someone that may be guilty of it but I have to post this...

Visible red light from 940nm led laser

The whole page is sort of interesting, certainly relevant, but it's the last post that is telling.

From Roithner Lasers, unequivocally a respectable name, had a batch of 980nm laser diodes emitting at 670nm as well. I'm not saying the red light seen from 808nm diodes is a spurious emission of a very separate wavelength , which seems to be the argument, but it certainly seems to show it is possible for an IR laser diode to emit a visible line as well.

I hope this doesn't kick the argument into another gear; just food for thought as to how someone may find it easy to believe that 808s emit visible wavelengths too. Other LD do it so why not 808s?

M
Nobody replied to this, it's actually very interesting stuff. Can we (and I mean everybody that went off topic) stop the trolling and just find the answer to the question at hand? Seemed to work last time.

There's more effort here in flaming and trolling than finding the answer and be done with it. We say noobs shouldn't be trolling, apparently some here like to keeps that right to themselves.
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Old 06-27-2011, 02:19 PM #85
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Default Re: 808nm laser visibility

The thing Roithner did not say is whether or not the emission was actually coherent.

We know that everyone who's seen 808nm has seen a faint red dot. Roithner was surprised at their situation, telling us it's rare.

This quote from that link sums up my thoughts:

Quote:
I'm surprised Sam didn't pick up on this.

You're looking directly at the laser emission with your eye, right?

The human eye's response doesn't just stop cold at some wavelength.
You can actually see into the infrared a tiny bit. Some people can
see further than others. The eye will interpret this IR light as
red, but not very dimly.

There is a danger to you looking at this 904nm laser directly. Because
the eye is so insensitive to that frequency it doesn't appear bright,
but in fact there is a lot of laser radiation entering your eye.

I believe you said in your original post that it was 50mw? That is
definately bright enough to have a real danger of causing eye damage.

I recommend reading the following sections from Sam's LaserFAQ:

Laser Visibility and Color
Sam's Laser FAQ - Items of Interest

Laser Safety
Sam's Laser FAQ - Laser Safety

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Old 06-27-2011, 03:38 PM #86
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Default Re: 808nm laser visibility

Everyone agrees now that IR can be seen. So why is it a stretch to believe that you're seeing 808? It is very dim as it should be, and spectrograph and diffraction grating show only one line.

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Old 06-27-2011, 03:59 PM #87
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Default Re: 808nm laser visibility

But how about the wide spectrum of quality of laserdiodes? They are actually in mass production, so canīt it be some of them produced with less quality do emit two different wavelenghts? Maybe they are rare and you didnīt come across such a diode till now?

Just thinking about all the LPCs-815 where one can easily be driven with more than 400mA and anotherone dies while just be driven with a bit more than 300mA.
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Old 06-27-2011, 05:02 PM #88
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Default Re: 808nm laser visibility

Quote:
Originally Posted by honeyx View Post
But how about the wide spectrum of quality of laserdiodes? They are actually in mass production, so canīt it be some of them produced with less quality do emit two different wavelenghts? Maybe they are rare and you didnīt come across such a diode till now?

Just thinking about all the LPCs-815 where one can easily be driven with more than 400mA and anotherone dies while just be driven with a bit more than 300mA.
Perhaps you should define what you mean by emitting different
wavelengths...

632.8001nm and 632.8000 are two different wavelength...
Or do you mean 2 different wavelengths that you can be perceived
by the human eye...

What yardstick are you using to define different wavelengths...


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Old 06-27-2011, 05:24 PM #89
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Default Re: 808nm laser visibility

Iīm refering now to my observation with the nightvision as well as to the blue one with a small peak in IR and to what Morgan posted about Roithner Lasers having a batch IR diodes emitting also a small amount at 670nm. Not two weavelenghts with just 1Hz of difference. At least the guy who analized the blue one got a small peak with a specific weavelenght in the IR range an Roithner also must have meassured the weavelenght of the visible red, else he wouldnīt say 670nm but just red.

Here a translation about the blue http://translate.google.de/translate...d4e7b1c3d0595c

Btw. If you canīt see red, look at me

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Old 06-27-2011, 06:08 PM #90
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Default Re: 808nm laser visibility

In the same thread the measured 890nm IR from a 445nm diode is explained. There is actually no IR, it's a measurement artifact because the second diffraction order of the grating of the spectrometer isn't completely absent.
The case of Roithner lasers is interesting, but it has to be mentioned that 10 microwatts of 670 out of such a diode can't be coherent, so it's certain that there can't be coherent emission from a laser diode significantly away from it's operating wavelength.

Why there is still red emission from such a diode: maybe inside the semiconductor not all the electron-hole recombination occurs inside the active region. Outside of the active region the bandgap of the material is larger because of a different semiconductor material. The electrons and holes will want to recombine at the point of the lowest bandgap (the active region), but there's a finite possibility of recombination outside of the active region. The light generated there won't be confined and impossible to get above the lasing threshold, but there will be light of a shorter wavelength.
This effect would depend on the whole structure of the laser die, things like the semiconductormaterial, doping and type would matter. This is probably why in this rare case of Roithner there can be emission at 670nm

Any feedback on that part is welcome, I'm not very experienced in this semiconductor stuff.
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