1st build: 445nm 1500ma, low divergence lens

Jubathoph · Aug 10, 2011

DTR When I get my 405g1 lens and figure out a reducer I will let you know and send it out. After the LPM results come in you guys can look forward to a full writeup on the relative benefits of the lens. Right now it is difficult for me to comment without experience of other
lenses. I can tell you that there is some splash but the main beam stays pretty tight. I have been putting in some allnighters at work so haven't had a chance to take more pics or measure beam at aperture.

Thanks everybody for the interest

Helios · Aug 10, 2011

You are going to fit right in here I can already tell. Awesome work. Cant wait to see the lens data.

DTR · Aug 11, 2011

Sounds like a plan.:beer:

LORDJET · Aug 14, 2011

I like what I see so far, it's always nice to have options. This lens could be the new hot ticket.

steve001 · Aug 15, 2011

Jubathoph said:
Hello,

Divergence test:

Beam @ 8' = 6.35mm
Beam @ 24' = 15.875 mm

Divergence mrad~= (width 2 -width1)mm/(Distance 2-distance 2)m

Results in divergence of 1.95 mrad.

Power Transmittance: Unable to test at this time (no LPM).

Beam profile: Beam was actually tighter than I expected.

Check out the pics!

Regards,

-James

You may have done just as well with one of these lenses.
405nm Laser-Line Coated Plano-Convex (PCX) Lenses - Edmund Optics
or
VIS 0° Coated Plano-Convex (PCX) Lenses - Edmund Optics

For lower divergence go with an even longer focal length. And measure the divergence at 10 meters 32.8 feet not 24 feet. Round off to 33 feet

qumefox · Aug 15, 2011

The problem with longer focal lengths is that you need a larger diameter lens to not have extreme losses due to truncation. And you also get a larger diameter beam as well. At some point you get to a size that becomes impractical for use in handhelds.

steve001 · Aug 15, 2011

qumefox said:
The problem with longer focal lengths is that you need a larger diameter lens to not have extreme losses due to truncation. And you also get a larger diameter beam as well. At some point you get to a size that becomes impractical for use in handhelds.

Possibly impractical. An extension tube could be machined to except the new larger lens. Some members have the capability to do that for others.

Jubathoph · Aug 16, 2011

Hello Steve the PCX lens will suffer from spherical abberation at such a high numeric aperture, that is why most collimation lenses are aspheric. Regarding the distances used to measure divergence, what difference does it make to use 33 ft. Vs 24 ft.? Slightly better accuracy in measurement? I simply used the most convenient space available, the distance between my bedroom wall and kitchen!

Hello Qumefox, I avoided truncation losses by choosing a high numeric aperture lens. It is 0.5 ,the G1 is a little better at .6. Regarding the width of the beam, it seems pretty tight and visible but as of now I lack experience to compare.

qumefox · Aug 16, 2011

Jubathoph said:
Hello Qumefox, I avoided truncation losses by choosing a high numeric aperture lens. It is 0.5 ,the G1 is a little better at .6. Regarding the width of the beam, it seems pretty tight and visible but as of now I lack experience to compare.

That's not really what I meant. Your lens specifications don't mean anything in that regard if width of the raw output of the laser diode is wider than your lens when your lens is at it's focal distance. That's why I said longer focal lengths require larger diameter lenses.

Jubathoph · Aug 16, 2011

The lens is pretty wide at 8mm, it is not clipping much if any of the beam.

The numeric aperture is a measure of lens diameter relative to focal length. It is directly related to the "capture angle" of the lens. In fact the NA of a lens is the best way to compare beam capture between lenses with different parameters. You are correct that large focal length lens requires a larger diameter, that would be keeping the same numeric aperture if both are adjusted by the same factor.

The raw 445 diode diverges at a 45 degree angle requiring NA around .5

steve001 · Aug 16, 2011

Jubathoph said:
Hello Steve the PCX lens will suffer from spherical abberation at such a high numeric aperture, that is why most collimation lenses are aspheric.
Hello Qumefox, I avoided truncation losses by choosing a high numeric aperture lens. It is 0.5 ,the G1 is a little better at .6. Regarding the width of the beam, it seems pretty tight and visible but as of now I lack experience to compare.

I've wondered for a long time but could not find either an explanation or an illustration of what spherical aberration would do to the beam profile. Could you explain what it would do ?
I took a quick look. Spherical aberration seems to be an issue when you want to focus a laser beam to a point. Now is it important when the goal is achieving infinite conjugation ?

Generally, when working at or near infinite conjugate (collimated light on one end of the lens), a plano-convex/concave lens or achromatic doublet lens will work best.
Spherical & Aspherical Lens Selection Guide

Jubathoph said:
Regarding the distances used to measure divergence, what difference does it make to use 33 ft. Vs 24 ft.? Slightly better accuracy in measurement? I simply used the most convenient space available, the distance between my bedroom wall and kitchen!

First let me ask you this. Are you familiar with the term Rayleigh length [or distance] ?

Thanks

1st build: 445nm 1500ma, low divergence lens

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