Re: Spreading beam from green laser

Steve wrote:
On 14 Jul 2007 19:16:22 -0400, Sam Goldwasser <sam@xxxxxxxxxxxxxxxxxxx> put
together some random words that came up with:


Steve <nospam@xxxxxxxxxxx> writes:


I have a 120 mw 532nm DPSS laser and I would like to spread the beam at a 30
degree angle in order to illuminate a larger area than would normally be=20
possible (that is, to project a larger spot size).

The beam coming from the laser seems to be about 1.5mm diameter (the
exit= hole from the laser is about 3mm diameter), and the divergence
seems to be = much less than a degree. The exit end surface of the
laser is 22mm in diameter.

What would be the best way of doing this? A plano concave lens
glued on to the end of the laser seems like the way to go, but I
don't know how to = calculate the EFL or what diameter lens to use.

For a simple lens, just figure f1/d1=f2/d2 where f1 is the focal length
and d1 is the beam diameter. Then f2 is the distance to the object or
screen and d2 is the projected beam diameter at the screen.

Try a DVD or CD objective lens.

Didn't you ask this Yesterday?


Yes, but no one bothered to tell me how to calculate a lens. I don't have an
old cd or dvd player that I can cannibalize. I will purchase a lens probably
from Edmund.

From your equations, using a 4' spot at a distance of 7', I get a f1 of 2.62mm.
Would this be a concave or convex lens?

Steve

Either negative or positive lenses will work for beam spreading. Some ideas for free lenses: cannibalizing
cheap plastic cameras, telescope and microscope objectives and eyepieces, etc. Shiny ball-bearings work too.
The (negative) focal length is the radius of the bearing, I think. Toy optics are easy to find and
achromaticity doesn't matter for single wavelength light.

BUT - you will be immediately HORRIFIED by the amount of diffracted crap in the beam that even a tiny amount
of dust & dirt on the lens will show up. You will definitely want to look into "spatial filter" setups if this
is a concern. Another approach, maybe useless depending on why you want a spread beam, is to just run the beam
through a ground glass or opal diffuser. Not the best for holography but even there I've heard that
interesting effects are possible.

regards, Tom
.

Relevant Pages

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  • Re: Spreading beam from green laser
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