Welcome to Laser Pointer Forums - discuss green laser pointers, blue laser pointers, and all types of lasers

Laser Pointer Store

# Narrowing the beam and focusing a laser through additional lenses?

#### haveblue

##### New member
I have this 300mw+ CNI PGL-III-C. It has an initial beam diameter of roughly 2mm. Then of course, it has beam divergence. The upper image shows (exaggerated) the stock focusing lens and the diverging output beam. I want to replace this lens with a more convex one to converge the beam, and then add a second focusable convex lens in front of it that refocuses the beam to neither diverge nor converge, like in the lower image.

Where can I get optics to do this? If I know the angle Θ, I should be able to find the lenses I need, correct? I've converged the beam before with a lens. It seems that at its focus in the picture below, the beam is 0.04mm. Thus it should be very possible to rediverge the beam at the first lens's focal point.

(Each dash mark is a millimeter)

Last edited:

#### ElektroFreak

##### New member
You're describing a beam expander, but it is impossible to have a beam with no divergence at all, with or without a beam expander. You can come close, but there is always some divergence.

#### Moptsp

##### New member
Yeah it is physically impossible to have 0 divergence.

#### haveblue

##### New member
Hmm, so it looks like Θ=(2λ/(pi*r)) with r being beam radius at beam waist. Thus when minimum beam radius decrease, divergence increases, so you can't have both decrease at the same time. Bummer.

#### Moptsp

##### New member
Seems correct.
Not going to be easy to bend physics. :\

#### haveblue

##### New member
I'll have to say though, focusing 300+mw into a circle 0.04mm in diameter results in some serious energy density per area. Cuts through electrical tape and human hair like a hot knife through butter

#### f22warzone

##### New member
meh try 581mw of green : ) plus with the 30x beam expander on my rpl i achieve a divergence of .04mrad's but its a 30mm beam plus side is i shined it at a tower near my friends apartments 1700 feet away and it was only 50mm : )

#### mfo

##### Banned
Unless you can emit a beam of gravity with the laser so it won't expand! =D

#### Hallucynogenyc

##### New member
Unless you can emit a beam of gravity with the laser so it won't expand! =D
what?

#### Moptsp

##### New member
Unless you can emit a beam of gravity with the laser so it won't expand! =D
I'm not sure a beam of gravity is possible. Though your just joking.
Though a tunnel might be (a black hole), but that's only theoretically possible currently.

@Hallucynogenyc --
Hes talking about high gravity forces. Gravity can even bend light.

Last edited: