Question about 808nm

[ENX]

I am relatively new to lasers and thanks to my "new found addiction", I have quite a few lasers in my collection.

I am interested in the varying uses of the different wavelenghts and I have a question about 808nm... These scare me due to the invisible danger they pose to your eyes, so I don't think I will buy any in the near future. However, given that these are everywhere on eBay and LPF and the inexpensive $ / mW ratio, I am wondering if there is a specific use for these that I am missing.

I have read some posts where people are using these to enhance night vision scopes, some are using them to disrupt police speed lasers, and some are building DIY green lasers using various lenses and filters. O-Like and Lazerer sells portable ones in all ranges of power. The burning power of these seems good, but it looks like you have to be very close to the object in order to get any real power.

The only valid purpose I can see if to enhance night vision and then would you really need a 2W portable for this?

What are the majority of these 808nm being used for?

 

[Sigurthr]

They're available because they are used as pump diodes for NdYAG and other DPSS systems. That is the sole reason they are inexpensive for the output power.

Hobbyists only use them for the 3 things you said: nightvision, DIY DPSS, and burning.

Also, it isn't truly invisible, at least it isn't for me. I can see 808nm rather well and will be picking up a 5mW module for my wavelength collection. I just got a 780nm (5mW) today and I can use it like a pointer and clearly see the spot across the room. It just appears like a low power 670nm to my eyes, no real color difference. 808nm is the same way but much dimmer, I don't think I'll be able to see 5mW from much farther than a few feet.

 

[ENX]

Thank you for the fast reply.

Is it true that the object needs to be relatively close to the laser for burning opposed to a 445 or 405 of equal power or is that just a focusing issue?

Is it feasible to use the optics from a lower powered green module and replace the diode with a high powered 808 or is there much more to it?

 

[Sigurthr]

Yes it is possible to upgrade the pump diode in a DPSS system, but often it is more trouble than it is worth as you need to realign the diode with the rest of the system and not all setups allow this to be easily facilitated. Lab lasers the the exception, fairly easy to replace the pump diode and realign everything.

Burning all depends on focus, the reason why a 445(450) doesn't burn well at a distance is due to the multimode beam, the axes aren't equal in divergence and you lose power density as distance increases. If you were to use a prism pair to correct the fast axis and a beam expander to set the focal point out at a distance you would be able to burn just as well at 100ft as you can at 10ft or 1ft.

Spectral absorbances do determine the localized heating efficiency and thus burning ability but this is not a wavelength specific case for <500nm. 405nm burns so well because it is VERY rare to see something violet colored. As the frequency increases each photon increases in energy and the photons per mW decrease but the overall total energy deposited is identical. Which weighs more a pound of lead or a pound of aluminum? Same scenario, a mW is a mW. There are an aweful lot of things that do not absorb >600nm very well, and that extends well beyond the visible spectrum. 1064nm isn't absorbed very well by most organic matter either, NdYAG pulse lasers just blow holes in stuff because the huge energy density of qswitched pulse lasers.

IMO: enjoy 370nm-850nm lasers for their visual effects (that is my approximate range of sensitivity, your mileage may vary) and leave burning to CO2 lasers.

 

[Flaminpyro]

Every one knows that a pound of Lead weighs more than a pound of Aluminum :crackup:

@ Sigurthr Correct me if I'm wrong here but I was under the impression that mW for mW
a 405 is a better burner than a 650 because of literally it's beam size.

It's my understanding they developed the 405 to use in BluRay players and recorders because
the beam width is about 1/2 of a 650 beam and that let them put more info on the disc, so if
you have the same power in a smaller area it can burn faster correct.

 

[ENX]

Very clear now! Thank you!!!
I think I am going to stick with the visible range.

PS: I vote for lead too

 

[Sigurthr]

Every one knows that a pound of Lead weighs more than a pound of Aluminum :crackup:

@ Sigurthr Correct me if I'm wrong here but I was under the impression that mW for mW
a 405 is a better burner than a 650 because of literally it's beam size.

It's my understanding they developed the 405 to use in BluRay players and recorders because
the beam width is about 1/2 of a 650 beam and that let them put more info on the disc, so if
you have the same power in a smaller area it can burn faster correct.

Yes, you are correct, however, it really only applies when the application involves optics that focus the beam to the limits of diffraction. However, for popping baloons or lighting matches the level of optics involved doesn't really reach the realm of wavelength based limitation, often by a long shot. A 405G2 lens and a 650G1 lens will focus the spot from a 405 or 650 (respectively) down to basically the same size as neither is designed specifically for microscopic beam waists. The difference in observed beam widths is related to the die size and diode emission angle (spread).

Technically a pound of uranium weighs less than a pound of lead after any appreciable amount of time. The emission of particle radiation lowers the total mass by infinitessimally small amounts. Likewise, a pound of fresh aluminum exposed in atmosphere will weigh more than a pound of lead at first (up until a much later date) due to surface oxidation. Still, a mW is a mW and a mJ is a mJ no matter how you spin it.

 

[Fiddy]

another reason for burning so close is the 808nm diodes have bad beam specs.

see my bad beam spec 808nm here:

 

[ENX]

That is some wide beam you have there Fiddy!
Thanks for sharing that video and thank you all for the clarification.
It's much appreciated.