Cni pgl iii 655

[WRM]

I was about to order a CNI PGL III 655 500mw from the latest group buy; and I looked at the specs and was wondering about something. I noticed that the divergence is <5 mrad and the beam diameter is 6 mm. I was wondering if this is typical for high power hand held reds. The 635's also have the same beam diameter and divergence. This would make the beam fat like most 405's. Does anyone know the reason for this? Thanks, Bill

 

[RA_pierce]

This is because high power red lasers (>300mW) will generally use a multimode diode.
A multimode diode is basically a laser diode that has several dies "stacked" to form one large emitter.
Since multimode diodes have several dies on one emitter, the output is rectangular or shaped like a line. These diodes require special optics (there is information in the forums) to correct the beam profile and divergence to come close to what you get with single mode diodes.
I'm not sure what kind of optics are used in this particular laser, but it probably has FAC and a convex lens at the least.

 

[ElektroFreak]

^Yep. It's definitely multimode. It most likely uses FAC, 2 anamorphic prisms, and a final collimation assembly.

Diode lasers almost always have larger beam diameters than DPSS. Systems like yours are intended for laser show use, during which the beam moves so much that you would never notice the fact that it is multimode. My CNI 650 has a divergence of less than 2mrad, so 5 would be an extreme case.

You won't find any single-mode red lasers at these powers. Laser-wave recently released a line of 640nm diode modules that have round beams with good specs, but they are very new and expensive. You could also use a DPSS 671nm laser, but they are much less visible than what you are already getting.

Here's a picture of the beam from a multimode red laser that has been expanded to show detail:

Thanks to FrothyChimp for the pic

You can clearly see the separate emission regions..

 

[WRM]

Re: CNI PGL III 655

Thanks for the input. I seem to learn something new on LPF every day. Did anyone ever see CNI's 500mw 655 red? It sounds like my dollars would be spent better on something different; and that I would be disappointed if I purchased it. Thanks, Bill

 

[ElektroFreak]

The beam above is from a CNI 650nm red, which is pretty much the same. Yours will look like that as well. Whether or not you're disappointed depends on the application. A multimode diode is the only way to get that much power from a single diode source.