808 nm Pen: Interesting Spectrometer Readings

[mwang]

I was doing some spectrometer readings for my research samples and slipped in my laser...

Did a quick test on my 808nm ebay pen (power output 220 mW, multimode bar-shaped output). I took the lens off, and directly allow the laser output into the spectrometer from a few feet away to let the laser diverge and compensate for the power. So there is no effects from other optics, the light is directly traveling from the diode into the spectrometer. I didn't have time to set up an attenuator to lower the output even further, so I couldn't prevent it from maxing out the spectrometer around the peaks.

Here are the preliminary results:

Directly from the spectrometer:


Trimmed Excel graph:



There seems to be 2 peaks: an 808nm one (expected), and a 799nm one.
Is this common for these IR diodes?

 

[Alaskan]

Wish I knew the answer, but I am very interested in knowing what the normal room temperature swings are for the wavelength of a 808nm laser diode which is not temperature controlled, especially the higher power producing diodes which can output several watts.

 

[Cyparagon]

Such is the nature of multimode operation. You essentially have several lasers in one resonator. They don't always have the same parameters.

Also, don't point lasers into the spectrometer! This will either damage it or cause erroneous readings. Use the diffuse reflection from some white object if you need to.

Wish I knew the answer, but I am very interested in knowing what the normal room temperature swings are for the wavelength of a 808nm laser diode which is not temperature controlled

I believe the common quote is about 0.3nm per degree C.

 

[mwang]

Such is the nature of multimode operation. You essentially have several lasers in one resonator. They don't always have the same parameters.

Also, don't point lasers into the spectrometer! This will either damage it or cause erroneous readings. Use the diffuse reflection from some white object if you need to.



I believe the common quote is about 0.3nm per degree C.

Interesting. This would mean that there are a large amount of lasers outputting at 800nm and 808nm, but a relatively small amount in between? I would think that the spectrum should be somewhat continuous like a gaussian distribution, and not with two distinct peaks.

And don't worry, the spot size around the point where the laser was hitting the spectrometer input was around 5-6 ft wide by 2 ft tall, while the total power output is only 220 mW. With an input size of about 1mm x 1mm, the optical density is way too low for it to do any damage to the spectrometer. We do reflection measurements with this spectrometer that can be very bright, with a much higher optical density than what I was inputting. The peaks were off the chart mainly because the current settings I was putting it on were for my transmission measurements, and I didn't want to change the settings around too much. I'll keep your tip in mind next time though.

 

[joeyss]

Such is the nature of multimode operation. You essentially have several lasers in one resonator. They don't always have the same parameters.

Also, don't point lasers into the spectrometer! This will either damage it or cause erroneous readings. Use the diffuse reflection from some white object if you need to.



I believe the common quote is about 0.3nm per degree C.

Still haven't figured out why my 808nm gets dimmben but emits yellow and green light. I have no lens on it it's 1.2-1.5W mltimode from a o like 400mw green. I can see the light in the dark room. It needs to get really hot. normally draws 2 amps but it does it when down to 1.71 thats how hot it gets.

I was able to get the green light focused with a Fresnel lens but it was cheap plastic one. it made line on the wall a few feet away the green looked in between 532 and 561nm


https://i.imgur.com/SmDrRZO.jpg zoom in all the way.


i took a pic of the dioide with a small pinhole lens

wtf is this why is it doing that when it gets really hot?

here's the laser.

https://imgur.com/a/xvWEJ

 

[Cyparagon]

There's a (rather gargantuan) difference between spontaneous emission and stimulated emission, Mr Joe.

Such is the nature of multimode operation... They don't always have the same parameters.

This would mean that there are a large amount of lasers outputting at 800nm and 808nm

That's not what I said. I have no idea how you took "They don't always have the same parameters" and twisted it into "many/most have different parameters"

 

[Benm]

It is possible that one of the emissions is choherent laser light and the other is incoherent (led-like) light.

One way to tell would be to use an attenuator so you do not saturate the spectrometer at all, and then see if the ratio between the peaks varies between the center and the edges of the output light area.

Another option is that they both are lasing lines, which is possible for multimode lasers like these 808 nm pumps. This would raise the question how much pump light is actually lost because the 1064 nm solid state cannot absorb it.

 

[joeyss]

There's a (rather gargantuan) difference between spontaneous emission and stimulated emission, Mr Joe.

That's not what I said. I have no idea how you took "They don't always have the same parameters" and twisted it into "many/most have different parameters"

yeah but diodes shift up in wavelength and not down when they get hot. It must get 120 F on the host. The muiltmode pattern changes when i switch it off for a second and back on once its hot. That pinhole is good enough to see laser diffraction. I wonder if there's any relation between this and the cyan line in my 980.

 

[Cyparagon]

... I'm a little surprised you've been on the forum 8 years and still don't seem to know the difference between spontaneous emission and stimulated emission.

I'll try to put it simply, Joe: The light you're seeing is not laser light.

 

[mwang]

It is possible that one of the emissions is choherent laser light and the other is incoherent (led-like) light.

One way to tell would be to use an attenuator so you do not saturate the spectrometer at all, and then see if the ratio between the peaks varies between the center and the edges of the output light area.

Another option is that they both are lasing lines, which is possible for multimode lasers like these 808 nm pumps. This would raise the question how much pump light is actually lost because the 1064 nm solid state cannot absorb it.

Next time I use the spectrometer I'll be sure to try and take more readings. By the width of the peaks from this data, though, it looks like both are lasing lines. Can't tell for sure though.