Need help with lens selection

[Giannis_TDM]

So I am going to build a 445 M140 blue laser and I have the lens for short-range burning but I still want to see the beam and do astronomy with it in my private house at my village (My dad owns a house with 10-15 acres of land far from the city ) stuff. Do you guys know of any decent quality lenses that output a clean beam without much divergence?
Edit: Ok so I checked out some of the amazing lenses DTR has I am in between the G8 and the DTR 3E -B what would you guys recommend?

 

[absolute]

The 3 element will give the lowest divergence and the tightest beam over long distance. The G8 will have slightly higher divergence but also more light throughput, so a brighter beam. It's up to you to choose the one you prefer. Or both.
They are good quality lenses, everyone on the forum will assure you that's a given when you buy from DTR.

Good luck!

 

[Alaskan]

If you want low divergence, don't use those 6 mm lenses, use a larger diameter PCX or plano-convex lens with a 3 to 4 inch focal length. To determine the diameter of the PCX lens you need, you would need to determine how wide the spot from the raw output of the laser diode would be at the focal length you will use, that isn't too difficult to figure out, or just take a laser using the diode you want, remove the collimation lens, and measure yourself on a wall.

Then you would have uber low divergence compared to those tiny 6 mm collimation lenses like the G2, G8, 3 element etc., putting them all to shame! I like to use a 6 inch diameter collimation lens myself, the beam isn't as bright due to a lower power density for the first few hundred feet, but beyond that, far brighter than anything a 6 mm lens can produce for thousands and thousands of feet, miles.

 

[Lifetime17]

Hi,
The M140 diode has already a really good divergent for a MM 5.6mm diode. 3 element will make the beam better but you will loose about 200/300 mW's. As for the G8 great lens with a lower power loss. G2 no power loss and retains the M140 natural divergence.
Rich

 

[paul1598419]

Actually, the G2 does have about a 5% power loss. The G8 has a higher power loss, but it will keep the beam from diverging as fast as it will with the G2. That is because the G2 has a FL of ~2.39 mm while the G8 is 8 mm. This will cause the beam to be expanded with the G8. But, either one is a good choice with an M140 diode because it has a very tight beam for a multi mode diode.

 

[steve001]

So I am going to build a 445 M140 blue laser and I have the lens for short-range burning but I still want to see the beam and do astronomy with it in my private house at my village (My dad owns a house with 10-15 acres of land far from the city ) stuff. Do you guys know of any decent quality lenses that output a clean beam without much divergence?
Edit: Ok so I checked out some of the amazing lenses DTR has I am in between the G8 and the DTR 3E -B what would you guys recommend?

Do what Alaskan said: one single optic of a long focal length. It will also need to be wide so it does not truncate the sides of the beam, about 10 % wider than the beam is. In order to burn it will be necessary to be able to move the lens. That means you'll have to find a way to make that happen.

 

[Lifetime17]

hi,
As Paul said the M140 has a great beam profile to begin with, and with a 5% loss it's not much considering the nature of the M140's divergence,
Rich

 

[Alaskan]

I realize my suggestions for a lens isn't what you are looking for as they can't be purchased off the shelf ready to thread into the end of a common laser pointer, but if you have something made custom for you by one of the members here who can do that, it's something to consider if you don't mind a fat beam. My crazy 6 inch diameter collimation lenses are not commonly used on a laser, or even inside a laser beam expander, the largest most people use is about an inch to inch and a half. That's more than enough for most any diode we have, I just like to go to extremes.

PCX lenses are good, but If you can find an aspheric lens which is AR coated even better, but stay away from cheap Chinese aspheric lenses made for LED's, those are terrible, they get their aspheric shape from a mold and use cheap glass which due to temperature variations within them as they cool, have inconsistencies within the glass which don't show up when used with LED'S, but when used to collimate coherent light produce swirl patterns within the beam spot and god knows what happens to the beam hundreds of feet out. Not that it matters to most of us, we just like seeing the beams going across a room or used for burning etc., not wanting to use them outside.

Manufacturers can make molded aspheric lenses which will work well enough for our needs, but the glass used isn't the cheap stuff commonly used for LED lenses, and the manufacturing process is tightly controlled to keep the index of refraction more consistent throughout the glass.

 

[CDBEAM777]

Hmmmmm ???? Chris...Concerning a diode mount for laser pointers to be used with anything larger than 6.33 mm diameter lenses. Well...This is a challenge !! Well....I will start a separate thread on that topic. Bob